@article{ScheffczykEngbertKrampeetal.1996, author = {Scheffczyk, Christian and Engbert, Ralf and Krampe, Ralf-Thomas and Kurths, J{\"u}rgen and Rosenblum, Michael and Zaikin, Alexei A.}, title = {Nonlinear Modelling of Polyrhythmic Hand Movements}, year = {1996}, language = {en} } @article{ScheffczykKrampeEngbertetal.1997, author = {Scheffczyk, Christian and Krampe, Ralf-Thomas and Engbert, Ralf and Rosenblum, Michael and Kurths, J{\"u}rgen and Kliegl, Reinhold}, title = {Tempo-induced transitions in polyrhythmic hand movements}, year = {1997}, abstract = {We investigate the cognitive control in polyrhythmic hand movements as a model paradigm for bimanual coordination. Using a symbolic coding of the recorded time series, we demonstrate the existence of qualitative transitions induced by experimental manipulation of the tempo. A nonlinear model with delayed feedback control is proposed, which accounts for these dynamical transitions in terms of bifurcations resulting from variation of the external control parameter. Furthermore, it is shown that transitions can also be observed due to fluctuations in the timing control level. We conclude that the complexity of coordinated bimanual movements results from interactions between nonlinear control mechanisms with delayed feedback and stochastic timing components.}, language = {en} } @article{ZaikinRosenblumScheffczyketal.1997, author = {Zaikin, Alexei A. and Rosenblum, Michael and Scheffczyk, Christian and Engbert, Ralf and Krampe, Ralf-Thomas and Kurths, J{\"u}rgen}, title = {Modeling qualitative changes in bimanual movements}, year = {1997}, language = {en} } @article{EngbertKrampeKliegl2002, author = {Engbert, Ralf and Krampe, Ralf-Thomas and Kliegl, Reinhold}, title = {Synchronizing movements with the metronome : nonlinear error corrections and unstable periodic orbits}, year = {2002}, language = {en} } @article{KrampeEngbertKliegl2002, author = {Krampe, Ralf-Thomas and Engbert, Ralf and Kliegl, Reinhold}, title = {Representational models and nonlinear dynamics : irreconcilable approaches to human movement timing and coordination or two sides of the same coin? : Introduction to the special issue on movement timing and coordination}, year = {2002}, language = {en} } @article{EngbertScheffczykKrampeetal.2002, author = {Engbert, Ralf and Scheffczyk, Christian and Krampe, Ralf-Thomas and Kurths, J{\"u}rgen and Kliegl, Reinhold}, title = {Symbolic dynamics of bimanual production of polyrhythms}, isbn = {3-540- 63481-9}, year = {2002}, abstract = {We analyse time series from a study on bimanual rhythmic movements in which the speed of performance (the external control parameter) was experimentally manipulated. Using symbolic transformations as a visualization technique we observe qualitative changes in the dynamics of the timing patterns. Such phase transitions are quantitatively described by measures of complexity. Using these results we develop an advanced symbolic coding which enables us to detect important dynamical structures. Furthermore, our analysis raises new questions concerning the modelling of the underlying human cognitive-motor system.}, language = {en} } @article{KrampeKlieglMayretal.2000, author = {Krampe, Ralf-Thomas and Kliegl, Reinhold and Mayr, Ulrich and Engbert, Ralf and Vorberg, D.}, title = {The fast and the slow of skilled bimanual rhythm production : parallel versus integrated timing}, year = {2000}, language = {en} } @unpublished{EngbertScheffczykKrampeetal.1997, author = {Engbert, Ralf and Scheffczyk, Christian and Krampe, Ralf-Thomas and Rosenblum, Mikhael and Kurths, J{\"u}rgen and Kliegl, Reinhold}, title = {Tempo-induced transitions in polyrhythmic hand movements}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-14380}, year = {1997}, abstract = {We investigate the cognitive control in polyrhythmic hand movements as a model paradigm for bimanual coordination. Using a symbolic coding of the recorded time series, we demonstrate the existence of qualitative transitions induced by experimental manipulation of the tempo. A nonlinear model with delayed feedback control is proposed, which accounts for these dynamical transitions in terms of bifurcations resulting from variation of the external control parameter. Furthermore, it is shown that transitions can also be observed due to fluctuations in the timing control level. We conclude that the complexity of coordinated bimanual movements results from interactions between nonlinear control mechanisms with delayed feedback and stochastic timing components.}, language = {en} } @unpublished{GuastiEngbertKrampeetal.2000, author = {Guasti, Giovanna and Engbert, Ralf and Krampe, Ralf T. and Kurths, J{\"u}rgen}, title = {Phase transitions, complexity, and stationarity in the production of polyrhythms}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-14933}, year = {2000}, abstract = {Contents: 1 Introduction 2 Experiment 3 Data 4 Symbolic dynamics 4.1 Symbolic dynamics as a tool for data analysis 4.2 2-symbols coding 4.3 3-symbols coding 5 Measures of complexity 5.1 Word statistics 5.2 Shannon entropy 6 Testing for stationarity 6.1 Stationarity 6.2 Time series of cycle durations 6.3 Chi-square test 7 Control parameters in the production of rhythms 8 Analysis of relative phases 9 Discussion 10 Outlook}, language = {en} } @article{SchiekScheffczykEngbertetal.1997, author = {Schiek, Michael and Scheffczyk, Christian and Engbert, Ralf and Kurths, J{\"u}rgen and Krampe, Ralf-Thomas and Kliegl, Reinhold and Drepper, Friedhelm R.}, title = {Symbolic dynamics of physiological synchronisation : examples from bimanual movements and cardiorespiratory interaction}, year = {1997}, abstract = {Key words: Nonlinear time series analysis, symbolic dynamics, phase transitions, physiological data, biological synchronization, production of polyrhythms, cardiorespiratory interaction, variation of control parameter}, language = {en} } @article{KrampeEngbertKliegletal.2000, author = {Krampe, Ralf-Thomas and Engbert, Ralf and Kliegl, Reinhold and Kurths, J{\"u}rgen}, title = {Koordination und Synchronisation der H{\"a}nde beim rhythmischen Timing}, year = {2000}, language = {de} } @article{KrampeEngbertKliegl2002, author = {Krampe, Ralf-Thomas and Engbert, Ralf and Kliegl, Reinhold}, title = {The effects of expertise and age on rhythm production : adaptations to timing and sequencing constraints}, year = {2002}, language = {en} } @article{KrampeEngbertKliegl2001, author = {Krampe, Ralf-Thomas and Engbert, Ralf and Kliegl, Reinhold}, title = {Age-specific problems in rhythmic timing}, year = {2001}, language = {en} } @article{ScheffczykEngbertKurthsetal.1995, author = {Scheffczyk, Christian and Engbert, Ralf and Kurths, J{\"u}rgen and Krampe, Ralf-Thomas and Kliegl, Reinhold}, title = {Nonlinear Phenomena in Polyrhythmic Hand Movements}, isbn = {981-02-2689-6}, year = {1995}, abstract = {In this paper we apply symbolic transformations as a visualisation technique for analysing rhythm production. It is shown that qualitative information can be extracted from the experimental data. This approach may provide new insights into the organisation of temporal order by the brain on different levels of description. A simple phenomenological model for the explanation of the observed phenomena is proposed.}, language = {en} } @article{HerrmannMetzlerEngbert2017, author = {Herrmann, Carl J. J. and Metzler, Ralf and Engbert, Ralf}, title = {A self-avoiding walk with neural delays as a model of fixational eye movements}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-13489-8}, pages = {17}, year = {2017}, abstract = {Fixational eye movements show scaling behaviour of the positional mean-squared displacement with a characteristic transition from persistence to antipersistence for increasing time-lag. These statistical patterns were found to be mainly shaped by microsaccades (fast, small-amplitude movements). However, our re-analysis of fixational eye-movement data provides evidence that the slow component (physiological drift) of the eyes exhibits scaling behaviour of the mean-squared displacement that varies across human participants. These results suggest that drift is a correlated movement that interacts with microsaccades. Moreover, on the long time scale, the mean-squared displacement of the drift shows oscillations, which is also present in the displacement auto-correlation function. This finding lends support to the presence of time-delayed feedback in the control of drift movements. Based on an earlier non-linear delayed feedback model of fixational eye movements, we propose and discuss different versions of a new model that combines a self-avoiding walk with time delay. As a result, we identify a model that reproduces oscillatory correlation functions, the transition from persistence to antipersistence, and microsaccades.}, language = {en} } @article{KlieglEngbert2005, author = {Kliegl, Reinhold and Engbert, Ralf}, title = {Fixation durations before word skipping in reading}, issn = {1069-9384}, year = {2005}, abstract = {We resolve a controversy about reading fixations before word-skipping saccades which were reported as longer or shorter than control fixations in earlier studies. Our statistics are based on resampling of matched sets of fixations before skipped and nonskipped words, drawn from a database of 121,321 single fixations contributed by 230 readers of the Potsdam sentence corpus. Matched fixations originated from single-fixation forward-reading patterns and were equated for their positions within words. Fixations before skipped words were shorter before short or high-frequency words and longer before long or low-frequency words in comparison with control fixations. Reasons for inconsistencies in past research and implications for computational models are discussed}, language = {en} } @article{RolfsEngbertKliegl2005, author = {Rolfs, Martin and Engbert, Ralf and Kliegl, Reinhold}, title = {Crossmodal coupling of oculomotor control and spatial attention in vision and audition}, issn = {0014-4819}, year = {2005}, abstract = {Fixational eye movements occur involuntarily during visual fixation of stationary scenes. The fastest components of these miniature eye movements are microsaccades, which can be observed about once per second. Recent studies demonstrated that microsaccades are linked to covert shifts of visual attention. Here, we generalized this finding in two ways. First, we used peripheral cues, rather than the centrally presented cues of earlier studies. Second, we spatially cued attention in vision and audition to visual and auditory targets. An analysis of microsaccade responses revealed an equivalent impact of visual and auditory cues on microsaccade-rate signature (i.e. an initial inhibition followed by an overshoot and a final return to the pre-cue baseline rate). With visual cues or visual targets, microsaccades were briefly aligned with cue direction and then opposite to cue direction during the overshoot epoch, probably as a result of an inhibition of an automatic saccade to the peripheral cue. With left auditory cues and auditory targets microsaccades oriented in cue direction. We argue that microsaccades can be used to study crossmodal integration of sensory information and to map the time course of saccade preparation during covert shifts of visual and auditory attention}, language = {en} } @article{EngbertMergenthaler2005, author = {Engbert, Ralf and Mergenthaler, Konstantin}, title = {Statistics of fixational eye movements and oculomotor control}, issn = {0301-0066}, year = {2005}, language = {en} } @article{LiangMoshelZivotofskyetal.2005, author = {Liang, Jin-Rong and Moshel, Shay and Zivotofsky, Ari Z. and Caspi, Avi and Engbert, Ralf and Kliegl, Reinhold and Havlin, Shlomo}, title = {Scaling of horizontal and vertical fixational eye movements}, issn = {1063-651X}, year = {2005}, abstract = {Eye movements during fixation of a stationary target prevent the adaptation of the visual system to continuous illumination and inhibit fading of the image. These random, involuntary, small movements are restricted at long time scales so as to keep the target at the center of the field of view. Here we use detrended fluctuation analysis in order to study the properties of fixational eye movements at different time scales. Results show different scaling behavior between horizontal and vertical movements. When the small ballistic movements, i.e., microsaccades, are removed, the scaling exponents in both planes become similar. Our findings suggest that microsaccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. This difference may be due to the need for continuously moving the eyes in the horizontal plane, in order to match the stereoscopic image for different viewing distances}, language = {en} } @article{LaubrockEngbertKliegl2005, author = {Laubrock, Jochen and Engbert, Ralf and Kliegl, Reinhold}, title = {Microsaccade dynamics during covert attention}, issn = {0042-6989}, year = {2005}, abstract = {We compared effects of covert spatial-attention shifts induced with exogenous or endogenous cues on microsaccade rate and direction. Separate and dissociated effects were obtained in rate and direction measures. Display changes caused microsaccade rate inhibition, followed by sustained rate enhancement. Effects on microsaccade direction were differentially tied to cue class (exogenous vs. endogenous) and type (neutral vs. directional). For endogenous cues, direction effects were weak and occurred late. Exogenous cues caused a fast direction bias towards the cue (i.e., early automatic triggering of saccade programs), followed by a shift in the opposite direction (i.e, controlled inhibition of cue-directed saccades, leading to a 'leakage' of microsaccades in the opposite direction). (C) 2004 Elsevier Ltd. All rights reserved}, language = {en} } @article{KlieglGrabnerRolfsetal.2004, author = {Kliegl, Reinhold and Grabner, Ellen and Rolfs, Martin and Engbert, Ralf}, title = {Length, frequency, and predictability effects of words on eye movements in reading}, year = {2004}, language = {en} } @article{EngbertKlieglLongtin2004, author = {Engbert, Ralf and Kliegl, Reinhold and Longtin, Andre}, title = {Complexity of eye movements in reading}, year = {2004}, abstract = {During reading, our eyes perform complicated sequences of fixations on words. Stochastic models of eye movement control suggest that this seemingly erratic behaviour can be attributed to noise in the oculomotor system and random fluctuations in lexical processing. Here, we present a qualitative analysis of a recently published dynamical model [Engbert et al., 2002] and propose that deterministic nonlinear control accounts for much of the observed complexity of eye movement patterns during reading. Based on a symbolic coding technique we analyze robust statistical features of simulated fixation sequences}, language = {en} } @article{EngbertKliegl2003, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {Microsaccades uncover the orientation of covert attention}, year = {2003}, language = {en} } @article{EngbertKliegl2003, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {Noise-enhanced performance in reading}, year = {2003}, language = {en} } @article{KlieglEngbert2003, author = {Kliegl, Reinhold and Engbert, Ralf}, title = {SWIFT explorations}, year = {2003}, language = {en} } @article{EngbertKliegl2003, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {The game of word skipping : who are the competitors?}, year = {2003}, abstract = {Computational models such as E-Z Reader and SWIFT are ideal theoretical tools to test quantitatively our current understanding of eye-movement control in reading. Here we present a mathematical analysis of word skipping in the E-Z Reader model by semianalytic methods, to highlight the differences in current modeling approaches. In E-Z Reader, the word identification system must outperform the oculomotor system to induce word skipping. In SWIFT, there is competition among words to be selected as a saccade target. We conclude that it is the question of competitors in the "game" of word skipping that must be solved in eye movement research}, language = {en} } @article{KruegelEngbert2010, author = {Kr{\"u}gel, Andr{\´e} and Engbert, Ralf}, title = {On the launch-site effect for skipped words during reading}, issn = {0042-6989}, doi = {10.1016/j.visres.2010.05.009}, year = {2010}, abstract = {The launch-site effect, a systematic variation of within-word landing position as a function of launch-site distance, is among the most important oculomotor phenomena in reading. Here we show that the launch-site effect is strongly modulated in word skipping, a finding which is inconsistent with the view that the launch-site effect is caused by a saccadic-range error. We observe that distributions of landing positions in skipping saccades show an increased leftward shift compared to non-skipping saccades at equal launch-site distances. Using an improved algorithm for the estimation of mislocated fixations, we demonstrate the reliability of our results.}, language = {en} } @article{RisseEngbertKliegl2008, author = {Risse, Sarah and Engbert, Ralf and Kliegl, Reinhold}, title = {Eye-movement control in reading : experimental and corpus-analysis challenges for a computational model}, isbn = {978-7-201-06107-8}, year = {2008}, language = {en} } @article{KleinKruegelRisseetal.2015, author = {Klein, Angela Ines and Kruegel, Andre and Risse, Sarah and Esser, G{\"u}nter and Engbert, Ralf and Pereira, Vera Wannmacher}, title = {The processing of pronominal anaphora by children that have attention deficit hyperactivity disorder or dyslexia: a study through the analysis of eye movements}, series = {Letras de hoje}, volume = {50}, journal = {Letras de hoje}, number = {1}, publisher = {PUCRS}, address = {Porto Alegre}, issn = {0101-3335}, pages = {40 -- 48}, year = {2015}, abstract = {The aim of this work was to verify the processing of pronominal anaphora by children that have attention deficit hyperactivity disorder or dyslexia. The sample studied consisted of 75 children that speak German, which read two texts of 80 words containing pronominal anaphora. The eye movements of all participants were recorded and, to make sure they were reading with attention, two activities that tested reading comprehension were proposed. Through the analysis of eye movements, specifically the fixations, the data indicate that children with disorders have difficulty to process the pronominal anaphora, especially dyslexic children.}, language = {it} } @article{NuthmannEngbertKliegl2007, author = {Nuthmann, Antje and Engbert, Ralf and Kliegl, Reinhold}, title = {The IOVP-effect in mindless reading : Experiment and modeling}, doi = {10.1016/j.visres.2006.11.005}, year = {2007}, abstract = {Fixation durations in reading are longer for within-word fixation positions close to word center than for positions near word boundaries. This counterintuitive result was termed the Inverted-Optimal Viewing Position (IOVP) effect. We proposed an explanation of the effect based on error-correction of mislocated fixations [Nuthmann, A., Engbert, R., \& Kliegl, R. (2005). Mislocated fixations during reading and the inverted optimal viewing position effect. Vision Research, 45, 2201-2217], that suggests that the IOVP effect is not related to word processing. Here we demonstrate the existence of an IOVP effect in "mindless reading", a G-string scanning task. We compare the results from experimental data with results obtained from computer simulations of a simple model of the IOVP effect and discuss alternative accounts. We conclude that oculornotor errors, which often induce mislocalized fixations, represent the most important source of the IOVP effect. (c) 2006 Elsevier Ltd. All rights reserved.}, language = {en} } @article{LaubrockKlieglRolfsetal.2010, author = {Laubrock, Jochen and Kliegl, Reinhold and Rolfs, Martin and Engbert, Ralf}, title = {When do microsaccades follow spatial attention?}, issn = {1943-3921}, doi = {10.3758/APP.72.3.683}, year = {2010}, abstract = {Following up on an exchange about the relation between microsaccades and spatial attention (Horowitz, Fencsik, Fine, Yurgenson, \& Wolfe, 2007; Horowitz, Fine, Fencsik, Yurgenson, \& Wolfe, 2007; Laubrock, Engbert, Rolfs, \& Kliegl, 2007), we examine the effects of selection criteria and response modality. We show that for Posner cuing with saccadic responses, microsaccades go with attention in at least 75\% of cases (almost 90\% if probability matching is assumed) when they are first (or only) microsaccades in the cue target interval and when they occur between 200 and 400 msec after the cue. The relation between spatial attention and the direction of microsaccades drops to chance level for unselected microsaccades collected during manual-response conditions. Analyses of data from four cross-modal cuing experiments demonstrate an above-chance, intermediate link for visual cues, but no systematic relation for auditory cues. Thus, the link between spatial attention and direction of microsaccades depends on the experimental condition and time of occurrence, but it can be very strong.}, language = {en} } @article{BarthelmeTrukenbrodEngbertetal.2013, author = {Barthelme, Simon and Trukenbrod, Hans Arne and Engbert, Ralf and Wichmann, Felix A.}, title = {Modeling fixation locations using spatial point processes}, series = {Journal of vision}, volume = {13}, journal = {Journal of vision}, number = {12}, publisher = {Association for Research in Vision and Opthalmology}, address = {Rockville}, issn = {1534-7362}, doi = {10.1167/13.12.1}, pages = {34}, year = {2013}, abstract = {Whenever eye movements are measured, a central part of the analysis has to do with where subjects fixate and why they fixated where they fixated. To a first approximation, a set of fixations can be viewed as a set of points in space; this implies that fixations are spatial data and that the analysis of fixation locations can be beneficially thought of as a spatial statistics problem. We argue that thinking of fixation locations as arising from point processes is a very fruitful framework for eye-movement data, helping turn qualitative questions into quantitative ones. We provide a tutorial introduction to some of the main ideas of the field of spatial statistics, focusing especially on spatial Poisson processes. We show how point processes help relate image properties to fixation locations. In particular we show how point processes naturally express the idea that image features' predictability for fixations may vary from one image to another. We review other methods of analysis used in the literature, show how they relate to point process theory, and argue that thinking in terms of point processes substantially extends the range of analyses that can be performed and clarify their interpretation.}, language = {en} } @article{SchiekDrepperEngbertetal.1998, author = {Schiek, Michael and Drepper, Friedhelm R. and Engbert, Ralf and Suder, Katrin and Abel, Hans-Henning}, title = {Cardiorespiratory Synchronization}, isbn = {3-540-63481-9}, year = {1998}, abstract = {The complex behaviour of cardiorespiratory dynamics is shown to be related to the interaction between several physiological oscillators. This study is based on electrocardiogram and respiratory flow data obtained from 3 different subjects during paced breathing at 10 different pacing cycle lengths ranging from 5 s to 12 s. Two different methods ideally suited for the analysis of synchronization pattern of coupled oscillators are applied: 1. Symbolic dynamics based on symbol coding adapted for the detection of respiratory modulation of cardiac parasympathetic activity discloses two regimes of different synchronization behaviour within the frequency area corresponding to the Arnold tongue of 1:1 frequency-locking between respiratory flow and respiratory heartbeat variation (respiratory sinus arrhythmia). 2. The analysis of the phase shift between respiratory flow and respiratory sinus arrhythmia indicates that synchronization is not a static but a dynamic phenomenon. The observed dependence of the phase shift on respiratory cycle length shows large inter-individual variation. These findings turn out to be further hints for the existence of an additional central oscillator in the frequency range of respiration interacting with the central respiratory oscillator driving mechanical respiration.}, language = {en} } @article{EngbertHainzlZoelleretal.1998, author = {Engbert, Ralf and Hainzl, Sebastian and Z{\"o}ller, Gert and Kurths, J{\"u}rgen}, title = {Testing for unstable periodic orbits to characterize spatiotemporal dynamics}, year = {1998}, language = {en} } @article{MergenthalerEngbert2010, author = {Mergenthaler, Konstantin and Engbert, Ralf}, title = {Microsaccades are different from saccades in scene perception}, year = {2010}, abstract = {Eye-fixation durations are among the best and most widely used measures of ongoing cognition in visual tasks, e.g., reading, visual search or scene perception. However, fixations are characterized by ongoing motor activity (or fixational eye movements) with microsaccades as their most pronounced components. Recent work demonstrated the similarities of microsaccades and inspection saccades. Here, we show that distinct properties of microsaccades and inspection saccades can be found in a scene perception task, based on descriptive measures (e.g., a bimodal amplitude distribution) as well as functional characteristics (e.g., inter saccadic-event intervals and generating processes). Besides these specific differences, microsaccade rates produced by individual participants in a fixation paradigm are correlated with microsaccade rates extracted from fixations in scene perception, indicating a common neurophysiological basis. Finally, we observed that slow fixational eye movements, called drift, are significantly reduced during long fixations in scene viewing, which informs about the control of eye movements in scene viewing.}, language = {en} } @article{EngbertKruegel2010, author = {Engbert, Ralf and Kruegel, Andr{\´e}}, title = {Readers use Bayesian estimation for eye movement control}, issn = {0956-7976}, doi = {10.1177/0956797610362060}, year = {2010}, abstract = {During reading, saccadic landing positions within words show a pronounced peak close to the word center, with an additional systematic error that is modulated by the distance from the launch site and the length of the target word. Here we show that the systematic variation of fixation positions within words, the saccadic range error, can be derived from Bayesian decision theory. We present the first mathematical model for the saccadic range error; this model makes explicit assumptions regarding underlying visual and oculomotor processes. Analyzing a corpus of eye movement recordings, we obtained results that are consistent with the view that readers use Bayesian estimation for saccade planning. Furthermore, we show that alternative models fail to reproduce the experimental data.}, language = {en} } @article{KlieglRolfsLaubrocketal.2009, author = {Kliegl, Reinhold and Rolfs, Martin and Laubrock, Jochen and Engbert, Ralf}, title = {Microsaccadic modulation of response times in spatial attention tasks}, issn = {0340-0727}, doi = {10.1007/s00426-008-0202-2}, year = {2009}, language = {en} } @article{StarzynskiEngbert2009, author = {Starzynski, Christian and Engbert, Ralf}, title = {Noise-enhanced target discrimination under the influence of fixational eye movements and external noise}, issn = {1054-1500}, doi = {10.1063/1.3098950}, year = {2009}, abstract = {Active motor processes are present in many sensory systems to enhance perception. In the human visual system, miniature eye movements are produced involuntarily and unconsciously when we fixate a stationary target. These fixational eye movements represent self-generated noise which serves important perceptual functions. Here we investigate fixational eye movements under the influence of external noise. In a two-choice discrimination task, the target stimulus performed a random walk with varying noise intensity. We observe noise-enhanced discrimination of the target stimulus characterized by a U-shaped curve of manual response times as a function of the diffusion constant of the stimulus. Based on the experiments, we develop a stochastic information-accumulator model for stimulus discrimination in a noisy environment. Our results provide a new explanation for the constructive role of fixational eye movements in visual perception.}, language = {en} } @article{LaubrockEngbertKliegl2008, author = {Laubrock, Jochen and Engbert, Ralf and Kliegl, Reinhold}, title = {Fixational eye movements predict the perceived direction of ambiguous apparent motion}, issn = {1534-7362}, doi = {10.1167/8.14.13}, year = {2008}, abstract = {Neuronal activity in area LIP is correlated with the perceived direction of ambiguous apparent motion (Z. M. Williams, J. C. Elfar, E. N. Eskandar, L. J. Toth, \& J. A. Assad, 2003). Here we show that a similar correlation exists for small eye movements made during fixation. A moving dot grid with superimposed fixation point was presented through an aperture. In a motion discrimination task, unambiguous motion was compared with ambiguous motion obtained by shifting the grid by half of the dot distance. In three experiments we show that (a) microsaccadic inhibition, i.e., a drop in microsaccade frequency precedes reports of perceptual flips, (b) microsaccadic inhibition does not accompany simple response changes, and (c) the direction of microsaccades occurring before motion onset biases the subsequent perception of ambiguous motion. We conclude that microsaccades provide a signal on which perceptual judgments rely in the absence of objective disambiguating stimulus information.}, language = {en} } @article{MoshelZivotofskyLiangetal.2008, author = {Moshel, Shay and Zivotofsky, Ari Z. and Liang, Jin-Rong and Engbert, Ralf and Kurths, J{\"u}rgen and Kliegl, Reinhold and Havlin, Shlomo}, title = {Persistence and phase synchronization properties of fixational eye movement}, issn = {1951-6355}, year = {2008}, abstract = {When we fixate our gaze on a stable object, our eyes move continuously with extremely small involuntary and autonomic movements, that even we are unaware of during their occurrence. One of the roles of these fixational eye movements is to prevent the adaptation of the visual system to continuous illumination and inhibit fading of the image. These random, small movements are restricted at long time scales so as to keep the target at the centre of the field of view. In addition, the synchronisation properties between both eyes are related to binocular coordination in order to provide stereopsis. We investigated the roles of different time scale behaviours, especially how they are expressed in the different spatial directions (vertical versus horizontal). We also tested the synchronisation between both eyes. Results show different scaling behaviour between horizontal and vertical movements. When the small ballistic movements, i.e., microsaccades, are removed, the scaling behaviour in both axes becomes similar. Our findings suggest that microsaccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. We also applied the phase synchronisation decay method to study the synchronisation between six combinations of binocular fixational eye movement components. We found that the vertical-vertical components of right and left eyes are significantly more synchronised than the horizontal-horizontal components. These differences may be due to the need for continuously moving the eyes in the horizontal plane in order to match the stereoscopic image for different viewing distances.}, language = {en} } @article{BaptistaBohnKliegletal.2008, author = {Baptista, Murilo da Silva and Bohn, Christiane and Kliegl, Reinhold and Engbert, Ralf and Kurths, J{\"u}rgen}, title = {Reconstruction of eye movements during blinks}, issn = {1054-1500}, doi = {10.1063/1.2890843}, year = {2008}, language = {en} } @article{RomanoThielKurthsetal.2009, author = {Romano, Maria Carmen and Thiel, Marco and Kurths, J{\"u}rgen and Mergenthaler, Konstantin and Engbert, Ralf}, title = {Hypothesis test for synchronization : twin surrogates revisited}, issn = {1054-1500}, doi = {10.1063/1.3072784}, year = {2009}, abstract = {The method of twin surrogates has been introduced to test for phase synchronization of complex systems in the case of passive experiments. In this paper we derive new analytical expressions for the number of twins depending on the size of the neighborhood, as well as on the length of the trajectory. This allows us to determine the optimal parameters for the generation of twin surrogates. Furthermore, we determine the quality of the twin surrogates with respect to several linear and nonlinear statistics depending on the parameters of the method. In the second part of the paper we perform a hypothesis test for phase synchronization in the case of experimental data from fixational eye movements. These miniature eye movements have been shown to play a central role in neural information processing underlying the perception of static visual scenes. The high number of data sets (21 subjects and 30 trials per person) allows us to compare the generated twin surrogates with the "natural" surrogates that correspond to the different trials. We show that the generated twin surrogates reproduce very well all linear and nonlinear characteristics of the underlying experimental system. The synchronization analysis of fixational eye movements by means of twin surrogates reveals that the synchronization between the left and right eye is significant, indicating that either the centers in the brain stem generating fixational eye movements are closely linked, or, alternatively that there is only one center controlling both eyes.}, language = {en} } @article{LaubrockEngbertRolfsetal.2007, author = {Laubrock, Jochen and Engbert, Ralf and Rolfs, Martin and Kliegl, Reinhold}, title = {Microsaccades are an index of covert attention : commentary on Horowitz, Fine, Fencsik, Yurgenson and Wolfe}, issn = {0956-7976}, doi = {10.1111/j.1467-9280.2007.01904.x}, year = {2007}, language = {en} } @article{HeissEngbertGroepeletal.2010, author = {Heiss, Christian and Engbert, Kai and Groepel, Peter and Ziegler, Matthias and Brand, Ralf}, title = {Self-leadership and volition : distinct and potentially supplemental constructs?}, issn = {0033-2941}, doi = {10.2466/01.03.07.14.Pr0.107.5.447-462}, year = {2010}, abstract = {Self-leadership and volition are conceptually similar concepts. Both propose self-influence strategies that aim to improve the motivation and self-direction necessary to perform well. The present study assesses whether self- leadership strategies maintain construct-specific variance when compared with the similar strategies of volition. Results from a questionnaire study (N=320) indicate that self-leadership and volitional strategies are distinguishable and only moderately (r=.33) correlated. Self-leadership, therefore, supplements volition during goal attainment. Findings are discussed in light of the Rubicon model of action phases.}, language = {en} } @article{SinnEngbert2011, author = {Sinn, Petra and Engbert, Ralf}, title = {Saccadic facilitation by modulation of microsaccades in natural backgrounds}, series = {Attention, perception, \& psychophysics : AP\&P ; a journal of the Psychonomic Society, Inc.}, volume = {73}, journal = {Attention, perception, \& psychophysics : AP\&P ; a journal of the Psychonomic Society, Inc.}, number = {4}, publisher = {Springer}, address = {New York}, issn = {1943-3921}, doi = {10.3758/s13414-011-0107-9}, pages = {1029 -- 1033}, year = {2011}, abstract = {Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner (Current Biology, 18, 124-128, 2008) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that microsaccades contribute to the saccadic facilitation effect, due to a modulation of microsaccade rates by properties of the background.}, language = {en} } @article{LangeStarzynskiEngbert2012, author = {Lange, Elke B. and Starzynski, Christian and Engbert, Ralf}, title = {Capture of the gaze does not capture the mind}, series = {Attention, perception, \& psychophysics : AP\&P ; a journal of the Psychonomic Society, Inc.}, volume = {74}, journal = {Attention, perception, \& psychophysics : AP\&P ; a journal of the Psychonomic Society, Inc.}, number = {6}, publisher = {Springer}, address = {New York}, issn = {1943-3921}, doi = {10.3758/s13414-012-0318-8}, pages = {1168 -- 1182}, year = {2012}, abstract = {Sudden visual changes attract our gaze, and related eye movement control requires attentional resources. Attention is a limited resource that is also involved in working memory-for instance, memory encoding. As a consequence, theory suggests that gaze capture could impair the buildup of memory respresentations due to an attentional resource bottleneck. Here we developed an experimental design combining a serial memory task (verbal or spatial) and concurrent gaze capture by a distractor (of high or low similarity to the relevant item). The results cannot be explained by a general resource bottleneck. Specifically, we observed that capture by the low-similar distractor resulted in delayed and reduced saccade rates to relevant items in both memory tasks. However, while spatial memory performance decreased, verbal memory remained unaffected. In contrast, the high-similar distractor led to capture and memory loss for both tasks. Our results lend support to the view that gaze capture leads to activation of irrelevant representations in working memory that compete for selection at recall. Activation of irrelevant spatial representations distracts spatial recall, whereas activation of irrelevant verbal features impairs verbal memory performance.}, language = {en} } @article{KruegelEngbert2014, author = {Kruegel, Andre and Engbert, Ralf}, title = {A model of saccadic landing positions in reading under the influence of sensory noise}, series = {Visual cognition}, volume = {22}, journal = {Visual cognition}, number = {3-4}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {1350-6285}, doi = {10.1080/13506285.2014.894166}, pages = {334 -- 353}, year = {2014}, language = {en} } @article{KrausEngbertDollingeretal.2012, author = {Kraus, Uta and Engbert, Kai and Dollinger, Anika and Heiss, Christian and Brand, Ralf}, title = {Evaluation of a mitial interview guide for sport psychology counseling}, series = {Zeitschrift f{\"u}r Sportpsychologie}, volume = {19}, journal = {Zeitschrift f{\"u}r Sportpsychologie}, number = {4}, publisher = {Hogrefe}, address = {G{\"o}ttingen}, issn = {1612-5010}, doi = {10.1026/1612-5010/a000080}, pages = {145 -- 162}, year = {2012}, abstract = {The initial interview is important for psychological counseling regarding the acquisition of diagnostic information and in terms of establishing a professional counseling relationship. In applied sports psychology there so far exist no clear guidelines to structure this process. To improve the quality of sports psychological consultations, the present study introduces and evaluates a semi-structured guideline for an initial interview in which the content and form of the consultation are determined, the concerns of the client are systematically explored, and the objectives of the collaboration and the further process are defined. Eleven sport psychology trainees participated in our study and conducted initial interviews with actors. One interview was conducted by using the initial interview guide and the other interview was created individually by each sport psychology trainee based on his own expertise. The results showed that the quality of the interview process (i.e., formal requirements, use of open questions) as well as the satisfaction of the consultant with the interview was significantly higher when following the guideline. No differences were found regarding the quality of the consultation findings and the satisfaction of the athletes with the interview. The results are discussed with respect to their theoretical and practical implications.}, language = {de} } @article{Engbert2012, author = {Engbert, Ralf}, title = {Computational modeling of collicular integration of perceptual responses and attention in microsaccades}, series = {The journal of neuroscience}, volume = {32}, journal = {The journal of neuroscience}, number = {23}, publisher = {Society for Neuroscience}, address = {Washington}, issn = {0270-6474}, doi = {10.1523/JNEUROSCI.0808-12.2012}, pages = {8035 -- 8039}, year = {2012}, abstract = {During visual fixation on a target object, our eyes are not motionless but generate slow fixational eye movements and microsaccades. Effects of visual attention have been observed in both microsaccade rates and spatial directions. Experimental results, however, range from early (<200 ms) to late (>600 ms) effects combined with cue-congruent as well as cue-incongruent microsaccade directions. On the basis of well characterized neural circuitry in superior colliculus, we construct a dynamical model of neural activation that is modulated by perceptual input and visual attention. Our results show that additive integration of low-level perceptual responses and visual attention can explain microsaccade rate and direction effects across a range of visual cueing tasks. These findings suggest that the patterns of microsaccade direction observed in experiments are compatible with a single dynamical mechanism. The basic principles of the model are highly relevant to the general problem of integration of low-level perception and top-down selective attention.}, language = {en} } @article{TrukenbrodEngbert2012, author = {Trukenbrod, Hans Arne and Engbert, Ralf}, title = {Eye movements in a sequential scanning task - evidence for distributed processing}, series = {Journal of vision}, volume = {12}, journal = {Journal of vision}, number = {1}, publisher = {Association for Research in Vision and Opthalmology}, address = {Rockville}, issn = {1534-7362}, doi = {10.1167/12.1.5}, pages = {12}, year = {2012}, abstract = {Current models of eye movement control are derived from theories assuming serial processing of single items or from theories based on parallel processing of multiple items at a time. This issue has persisted because most investigated paradigms generated data compatible with both serial and parallel models. Here, we study eye movements in a sequential scanning task, where stimulus n indicates the position of the next stimulus n + 1. We investigate whether eye movements are controlled by sequential attention shifts when the task requires serial order of processing. Our measures of distributed processing in the form of parafoveal-on-foveal effects, long-range modulations of target selection, and skipping saccades provide evidence against models strictly based on serial attention shifts. We conclude that our results lend support to parallel processing as a strategy for eye movement control.}, language = {en} } @inproceedings{Engbert2012, author = {Engbert, Ralf}, title = {A computational model of microsaccadic responses to shifts of covert attention}, series = {Perception}, volume = {41}, booktitle = {Perception}, publisher = {Sage Publ.}, address = {London}, issn = {0301-0066}, pages = {55 -- 55}, year = {2012}, language = {en} } @inproceedings{TrukenbrodBarthelmeWichmannetal.2012, author = {Trukenbrod, Hans Arne and Barthelme, S. and Wichmann, Felix A. and Engbert, Ralf}, title = {Color does not guide eye movements: Evidence from a gaze-contingent experiment}, series = {PERCEPTION}, volume = {41}, booktitle = {PERCEPTION}, publisher = {PION LTD}, address = {LONDON}, issn = {0301-0066}, pages = {88 -- 88}, year = {2012}, language = {en} } @inproceedings{LaubrockCajarEngbert2012, author = {Laubrock, Jochen and Cajar, Anke and Engbert, Ralf}, title = {Peripheral spatial frequency processing affects timing and metrics of saccades}, series = {Perception}, volume = {41}, booktitle = {Perception}, publisher = {Sage Publ.}, address = {London}, issn = {0301-0066}, pages = {170 -- 170}, year = {2012}, language = {en} } @article{WidmannEngbertSchroeger2014, author = {Widmann, Andreas and Engbert, Ralf and Schroeger, Erich}, title = {Microsaccadic responses indicate fast categorization of sounds: A novel approach to study auditory cognition}, series = {The journal of neuroscience}, volume = {34}, journal = {The journal of neuroscience}, number = {33}, publisher = {Society for Neuroscience}, address = {Washington}, issn = {0270-6474}, doi = {10.1523/JNEUROSCI.1568-14.2014}, pages = {11152 -- 11158}, year = {2014}, abstract = {The mental chronometry of the human brain's processing of sounds to be categorized as targets has intensively been studied in cognitive neuroscience. According to current theories, a series of successive stages consisting of the registration, identification, and categorization of the sound has to be completed before participants are able to report the sound as a target by button press after similar to 300-500 ms. Here we use miniature eye movements as a tool to study the categorization of a sound as a target or nontarget, indicating that an initial categorization is present already after 80-100 ms. During visual fixation, the rate of microsaccades, the fastest components of miniature eye movements, is transiently modulated after auditory stimulation. In two experiments, we measured microsaccade rates in human participants in an auditory three-tone oddball paradigm (including rare nontarget sounds) and observed a difference in the microsaccade rates between targets and nontargets as early as 142 ms after sound onset. This finding was replicated in a third experiment with directed saccades measured in a paradigm in which tones had to be matched to score-like visual symbols. Considering the delays introduced by (motor) signal transmission and data analysis constraints, the brain must have differentiated target from nontarget sounds as fast as 80-100 ms after sound onset in both paradigms. We suggest that predictive information processing for expected input makes higher cognitive attributes, such as a sound's identity and category, available already during early sensory processing. The measurement of eye movements is thus a promising approach to investigate hearing.}, language = {en} } @article{CajarSchneeweissEngbertetal.2016, author = {Cajar, Anke and Schneeweiß, Paul and Engbert, Ralf and Laubrock, Jochen}, title = {Coupling of attention and saccades when viewing scenes with central and peripheral degradation}, series = {Journal of Vision}, volume = {16}, journal = {Journal of Vision}, number = {2}, publisher = {ARVO}, address = {Rockville, Md.}, issn = {1534-7362}, doi = {10.1167/16.2.8}, pages = {1 -- 19}, year = {2016}, abstract = {Degrading real-world scenes in the central or the peripheral visual field yields a characteristic pattern: Mean saccade amplitudes increase with central and decrease with peripheral degradation. Does this pattern reflect corresponding modulations of selective attention? If so, the observed saccade amplitude pattern should reflect more focused attention in the central region with peripheral degradation and an attentional bias toward the periphery with central degradation. To investigate this hypothesis, we measured the detectability of peripheral (Experiment 1) or central targets (Experiment 2) during scene viewing when low or high spatial frequencies were gaze-contingently filtered in the central or the peripheral visual field. Relative to an unfiltered control condition, peripheral filtering induced a decrease of the detection probability for peripheral but not for central targets (tunnel vision). Central filtering decreased the detectability of central but not of peripheral targets. Additional post hoc analyses are compatible with the interpretation that saccade amplitudes and direction are computed in partial independence. Our experimental results indicate that task-induced modulations of saccade amplitudes reflect attentional modulations.}, language = {en} } @article{EngbertLongtinKliegl2002, author = {Engbert, Ralf and Longtin, Andre and Kliegl, Reinhold}, title = {A dynamical model of saccade generation in reading based on spatially distributed lexical processing}, year = {2002}, language = {en} } @misc{KlieglRolfsLaubrocketal.2009, author = {Kliegl, Reinhold and Rolfs, Martin and Laubrock, Jochen and Engbert, Ralf}, title = {Microsaccadic Modulation of Response Times in Spatial Attention Tasks}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57098}, year = {2009}, abstract = {Covert shifts of attention are usually reflected in RT differences between responses to valid and invalid cues in the Posner spatial attention task. Such inferences about covert shifts of attention do not control for microsaccades in the cue target interval. We analyzed the effects of microsaccade orientation on RTs in four conditions, crossing peripheral visual and auditory cues with peripheral visual and auditory discrimination targets. Reaction time was generally faster on trials without microsaccades in the cue-target interval. If microsaccades occurred, the target-location congruency of the last microsaccade in the cuetarget interval interacted in a complex way with cue validity. For valid visual cues, irrespective of whether the discrimination target was visual or auditory, target-congruent microsaccades delayed RT. For invalid cues, target-incongruent microsaccades facilitated RTs for visual target discrimination, but delayed RT for auditory target discrimination. No reliable effects on RT were associated with auditory cues or with the first microsaccade in the cue-target interval. We discuss theoretical implications on the relation about spatial attention and oculomotor processes.}, language = {en} } @misc{CajarEngbertLaubrock2022, author = {Cajar, Anke and Engbert, Ralf and Laubrock, Jochen}, title = {Potsdam Eye-Movement Corpus for Scene Memorization and Search With Color and Spatial-Frequency Filtering}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Humanwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Humanwissenschaftliche Reihe}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {1866-8364}, doi = {10.25932/publishup-56318}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-563184}, pages = {1 -- 7}, year = {2022}, language = {en} } @book{Engbert1997, author = {Engbert, Ralf}, title = {Tempo-induced transitions in polyrhythmic hand movements}, series = {Preprint NLD}, volume = {41}, journal = {Preprint NLD}, publisher = {Univ. Potsdam}, address = {Potsdam}, issn = {1432-2935}, pages = {12 S. : graph. Darst.}, year = {1997}, language = {en} } @misc{WarschburgerCalvanoRichteretal.2015, author = {Warschburger, Petra and Calvano, Claudia and Richter, Eike M. and Engbert, Ralf}, title = {Analysis of Attentional Bias towards Attractive and Unattractive Body Regions among Overweight Males and Females}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-86570}, year = {2015}, abstract = {Background Body image distortion is highly prevalent among overweight individuals. Whilst there is evidence that body-dissatisfied women and those suffering from disordered eating show a negative attentional bias towards their own unattractive body parts and others' attractive body parts, little is known about visual attention patterns in the area of obesity and with respect to males. Since eating disorders and obesity share common features in terms of distorted body image and body dissatisfaction, the aim of this study was to examine whether overweight men and women show a similar attentional bias. Methods/Design We analyzed eye movements in 30 overweight individuals (18 females) and 28 normalweight individuals (16 females) with respect to the participants' own pictures as well as gender- and BMI-matched control pictures (front and back view). Additionally, we assessed body image and disordered eating using validated questionnaires. Discussion The overweight sample rated their own body as less attractive and showed a more disturbed body image. Contrary to our assumptions, they focused significantly longer on attractive compared to unattractive regions of both their own and the control body. For one's own body, this was more pronounced for women. A higher weight status and more frequent body checking predicted attentional bias towards attractive body parts. We found that overweight adults exhibit an unexpected and stable pattern of selective attention, with a distinctive focus on their own attractive body regions despite higher levels of body dissatisfaction. This positive attentional bias may either be an indicator of a more pronounced pattern of attentional avoidance or a self-enhancing strategy. Further research is warranted to clarify these results.}, language = {en} } @article{WarschburgerCalvanoRichteretal.2015, author = {Warschburger, Petra and Calvano, Claudia and Richter, Eike M. and Engbert, Ralf}, title = {Analysis of Attentional Bias towards Attractive and Unattractive Body Regions among Overweight Males and Females}, series = {PLoS one}, journal = {PLoS one}, number = {10}, publisher = {Public Library of Science}, address = {Lawrence, Kan.}, issn = {1932-6203}, doi = {10.1371/journal.pone.0140813}, pages = {17}, year = {2015}, abstract = {Background Body image distortion is highly prevalent among overweight individuals. Whilst there is evidence that body-dissatisfied women and those suffering from disordered eating show a negative attentional bias towards their own unattractive body parts and others' attractive body parts, little is known about visual attention patterns in the area of obesity and with respect to males. Since eating disorders and obesity share common features in terms of distorted body image and body dissatisfaction, the aim of this study was to examine whether overweight men and women show a similar attentional bias. Methods/Design We analyzed eye movements in 30 overweight individuals (18 females) and 28 normalweight individuals (16 females) with respect to the participants' own pictures as well as gender- and BMI-matched control pictures (front and back view). Additionally, we assessed body image and disordered eating using validated questionnaires. Discussion The overweight sample rated their own body as less attractive and showed a more disturbed body image. Contrary to our assumptions, they focused significantly longer on attractive compared to unattractive regions of both their own and the control body. For one's own body, this was more pronounced for women. A higher weight status and more frequent body checking predicted attentional bias towards attractive body parts. We found that overweight adults exhibit an unexpected and stable pattern of selective attention, with a distinctive focus on their own attractive body regions despite higher levels of body dissatisfaction. This positive attentional bias may either be an indicator of a more pronounced pattern of attentional avoidance or a self-enhancing strategy. Further research is warranted to clarify these results.}, language = {en} } @article{EngbertMergenthaler2006, author = {Engbert, Ralf and Mergenthaler, Konstantin}, title = {Microsaccades are triggered by low retinal image slip}, issn = {0027-8424}, doi = {10.1073/pnas.0509557103}, year = {2006}, abstract = {Even during visual fixation of a stationary target, our eyes perform rather erratic miniature movements, which represent a random walk. These "fixational" eye movements counteract perceptual fading, a consequence of fast adaptation of the retinal receptor systems to constant input. The most important contribution to fixational eye movements is produced by microsaccades; however, a specific function of microsaccades only recently has been found. Here we show that the occurrence of microsaccades is correlated with low retinal image slip approximate to 200 ms before microsaccade onset. This result suggests that microsaccades are triggered dynamically, in contrast to the current view that microsaccades are randomly distributed in time characterized by their rate-of-occurrence of 1 to 2 per second. As a result of the dynamic triggering mechanism, individual microsaccade rate can be predicted by the fractal dimension of trajectories. Finally, we propose a minimal computational model for the dynamic triggering of microsaccades}, language = {en} } @article{KlieglNuthmannEngbert2006, author = {Kliegl, Reinhold and Nuthmann, Antje and Engbert, Ralf}, title = {Tracking the mind during reading : the influence of past, present, and future words on fixation durations}, issn = {0096-3445}, doi = {10.1037/0096-3445.135.1.12}, year = {2006}, abstract = {Reading requires the orchestration of visual, attentional, language-related, and oculomotor processing constraints. This study replicates previous effects of frequency, predictability, and length of fixated words on fixation durations in natural reading and demonstrates new effects of these variables related to previous and next words. Results are based on fixation durations recorded from 222 persons, each reading 144 sentences. Such evidence for distributed processing of words across fixation durations challenges psycholinguistic immediacy-of-processing and eye- mind assumptions. Most of the time the mind processes several words in parallel at different perceptual and cognitive levels. Eye movements can help to unravel these processes}, language = {en} } @article{Engbert2006, author = {Engbert, Ralf}, title = {Flick-induced flips in perception}, issn = {0896-6273}, doi = {10.1016/j.neuron.2006.01.005}, year = {2006}, abstract = {Microsaccades are miniature eye movements produced involuntarily during visual fixation of stationary objects. Since their first description more than 40 years ago, the role of microsaccades in vision has been controversial. In this issue, Martinez-Conde and colleagues present a solution to the long-standing research problem connecting this basic oculomotor function to visual perception, by showing that microsaccades may control peripheral vision during visual fixation by inducing flips in bistable peripheral percepts in head-unrestrained viewing. Their study provides new insight into the functional connectivity between oculomotor function and visual perception}, language = {en} } @article{TrukenbrodEngbert2007, author = {Trukenbrod, Hans Arne and Engbert, Ralf}, title = {Oculomotor control in a sequential search task}, doi = {10.1016/j.visres.2007.05.010}, year = {2007}, abstract = {Using a serial search paradigm, we observed several effects of within-object fixation position on spatial and temporal control of eye movements: the preferred viewing location, launch site effect, the optimal viewing position, and the inverted optimal viewing position of fixation duration. While these effects were first identified by eye-movement studies in reading, our approach permits an analysis of the functional relationships between the effects in a different paradigm. Our results demonstrate that the fixation position is an important predictor of the subsequent saccade by influencing both fixation duration and the selection of the next saccade target.}, language = {en} } @article{RolfsKlieglEngbert2008, author = {Rolfs, Martin and Kliegl, Reinhold and Engbert, Ralf}, title = {Toward a model of microsaccade generation : the case of microsaccadic inhibition}, issn = {1534-7362}, doi = {10.1167/8.11.5}, year = {2008}, language = {en} } @article{SchwetlickRothkegelTrukenbrodetal.2020, author = {Schwetlick, Lisa and Rothkegel, Lars Oliver Martin and Trukenbrod, Hans Arne and Engbert, Ralf}, title = {Modeling the effects of perisaccadic attention on gaze statistics during scene viewing}, series = {Communications biology}, volume = {3}, journal = {Communications biology}, number = {1}, publisher = {Springer Nature}, address = {London}, issn = {2399-3642}, doi = {10.1038/s42003-020-01429-8}, pages = {11}, year = {2020}, abstract = {Lisa Schwetlick et al. present a computational model linking visual scan path generation in scene viewing to physiological and experimental work on perisaccadic covert attention, the act of attending to an object visually without obviously moving the eyes toward it. They find that integrating covert attention into predictive models of visual scan paths greatly improves the model's agreement with experimental data.
How we perceive a visual scene depends critically on the selection of gaze positions. For this selection process, visual attention is known to play a key role in two ways. First, image-features attract visual attention, a fact that is captured well by time-independent fixation models. Second, millisecond-level attentional dynamics around the time of saccade drives our gaze from one position to the next. These two related research areas on attention are typically perceived as separate, both theoretically and experimentally. Here we link the two research areas by demonstrating that perisaccadic attentional dynamics improve predictions on scan path statistics. In a mathematical model, we integrated perisaccadic covert attention with dynamic scan path generation. Our model reproduces saccade amplitude distributions, angular statistics, intersaccadic turning angles, and their impact on fixation durations as well as inter-individual differences using Bayesian inference. Therefore, our result lend support to the relevance of perisaccadic attention to gaze statistics.}, language = {en} } @article{RichterEngbertKliegl2006, author = {Richter, Eike M. and Engbert, Ralf and Kliegl, Reinhold}, title = {Current advances in SWIFT}, issn = {1389-0417}, doi = {10.1016/j.cogsys.2005.07.003}, year = {2006}, abstract = {Models of eye movement control are very useful for gaining insights into the intricate connections of different cognitive and oculomotor subsystems involved in reading. The SWIFT model (Engbert, Longtin, \& Kliegl (2002). Vision Research, 42, 621 - 636) proposed a unified mechanism to account for all types of eye movement patterns that might be observed in reading behavior. The model is based on the notion of spatially distributed, or parallel, processing of words in a sentence. We present a refined version of SWIFT introducing a letter-based approach that proposes a processing gradient in the shape of a smooth function. We show that SWIFT extents its capabilities by accounting for distributions of landing positions.}, language = {en} } @article{EngbertKliegl2001, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {Mathematical models of eye movements in reading : a possible role for autonomous saccades}, year = {2001}, language = {en} } @misc{SinnEngbert2011, author = {Sinn, Petra and Engbert, Ralf}, title = {Saccadic facilitation by modulation of microsaccades in natural backgrounds}, series = {Postprints der Universit{\"a}t Potsdam : Humanwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Humanwissenschaftliche Reihe}, number = {595}, issn = {1866-8364}, doi = {10.25932/publishup-43181}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-431817}, pages = {7}, year = {2011}, abstract = {Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner (Current Biology, 18, 124-128, 2008) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that microsaccades contribute to the saccadic facilitation effect, due to a modulation of microsaccade rates by properties of the background.}, language = {en} } @misc{LaubrockEngbertCajar2017, author = {Laubrock, Jochen and Engbert, Ralf and Cajar, Anke}, title = {Gaze-contingent manipulation of the FVF demonstrates the importance of fixation duration for explaining search behavior}, series = {Behavioral and brain sciences : an international journal of current research and theory with open peer commentary}, volume = {40}, journal = {Behavioral and brain sciences : an international journal of current research and theory with open peer commentary}, publisher = {Cambridge Univ. Press}, address = {New York}, issn = {0140-525X}, doi = {10.1017/S0140525X16000145}, pages = {31 -- 32}, year = {2017}, abstract = {Hulleman \& Olivers' (H\&O's) model introduces variation of the functional visual field (FVF) for explaining visual search behavior. Our research shows how the FVF can be studied using gaze-contingent displays and how FVF variation can be implemented in models of gaze control. Contrary to H\&O, we believe that fixation duration is an important factor when modeling visual search behavior.}, language = {en} } @phdthesis{Engbert1997, author = {Engbert, Ralf}, title = {Nichtlineare Dynamik kognitiv-motorischer Prozesse}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000157}, school = {Universit{\"a}t Potsdam}, year = {1997}, abstract = {Die Produktion von Polyrhythmen ist ein wichtiger experimenteller Zugang f{\"u}r die Untersuchung der menschlichen Motorik. Durch Variation des Tempos (externer Kontrollparameter) bei rhythmischen Bewegungsabl{\"a}ufen k{\"o}nnen qualitative {\"U}berg{\"a}nge in der Koordinationsdynamik induziert werden. Diese {\"U}berg{\"a}nge lassen sich mit der Methode der symbolischen Dynamik in experimentellen Zeitreihen nachweisen und sind ein wichtiger Hinweis darauf, dass die untersuchten Bewegungsabl{\"a}ufe nichtlinearen Kontrollprozessen unterliegen. Die theoretische Beschreibung bimanueller Rhythmusproduktion mit gekoppelten Differenzengleichungen f{\"u}hrt auf ein Modell mit nichtlinearer Fehlerkontrolle. Es ist eine wichtige Eigenschaft der Kontrollprozesse, dass sie mit zeitverz{\"o}gerter R{\"u}ckkopplung arbeiten. Neben deterministischen Steuerungsmechanismen ist die Motorik des Menschen ausserdem von Fluktuationen auf zwei Ebenen gekennzeichnet, der kognitiven Kontrollebene und der Ebene der motorischen Systeme. Daher ist die Koordination von Bewegungen das Ergebnis von Wechselwirkungen zwischen nichtlinearen, zeitverz{\"o}gerten Kontrollprozessen und stochastischen Fluktuationen.}, language = {de} } @misc{EngbertNuthmannRichteretal.2005, author = {Engbert, Ralf and Nuthmann, Antje and Richter, Eike M. and Kliegl, Reinhold}, title = {SWIFT: A Dynamical Model of Saccade Generation during Reading}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57145}, year = {2005}, abstract = {Mathematical models have become an important tool for understanding the control of eye movements during reading. Main goals of the development of the SWIFT model (Engbert, Longtin, \& Kliegl, 2002)were to investigate the possibility of spatially distributed processing and to implement a general mechanism for all types of eye movements we observe in reading experiments. Here, we present an advanced version of SWIFT which integrates properties of the oculomotor system and effects of word recognition to explain many of the experimental phenomena faced in reading research. We propose new procedures for the estimation of model parameters and for the test of the model's performance. A mathematical analysis of the dynamics of the SWIFT model is presented. Finally, within this framework, we present an analysis of the transition from parallel to serial processing.}, language = {en} } @misc{RolfsEngbertKliegl2005, author = {Rolfs, Martin and Engbert, Ralf and Kliegl, Reinhold}, title = {Crossmodal coupling of oculomotor controland spatial attention in vision and audition}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-56804}, year = {2005}, abstract = {Fixational eye movements occur involuntarily during visual fixation of stationary scenes. The fastest components of these miniature eye movements are microsaccades, which can be observed about once per second. Recent studies demonstrated that microsaccades are linked to covert shifts of visual attention [e.g., Engbert \& Kliegl (2003), Vision Res 43:1035-1045]. Here,we generalized this finding in two ways. First, we used peripheral cues, rather than the centrally presented cues of earlier studies. Second, we spatially cued attention in vision and audition to visual and auditory targets. An analysis of microsaccade responses revealed an equivalent impact of visual and auditory cues on microsaccade-rate signature (i.e., an initial inhibition followed by an overshoot and a final return to the pre-cue baseline rate). With visual cues or visual targets,microsaccades were briefly aligned with cue direction and then opposite to cue direction during the overshoot epoch, probably as a result of an inhibition of an automatic saccade to the peripheral cue. With left auditory cues and auditory targets microsaccades oriented in cue direction. Thus, microsaccades can be used to study crossmodal integration of sensory information and to map the time course of saccade preparation during covert shifts of visual and auditory attention.}, language = {en} } @misc{RolfsKlieglEngbert2004, author = {Rolfs, Martin and Kliegl, Reinhold and Engbert, Ralf}, title = {Microsaccade orientation supports attentional enhancement opposite to a peripheral cue: Commentary on Tse, Sheinberg, and Logothetis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57081}, year = {2004}, language = {en} } @article{NuthmannEngbertKliegl2005, author = {Nuthmann, Antje and Engbert, Ralf and Kliegl, Reinhold}, title = {Mislocated fixations during reading and the inverted optimal viewing position effect}, year = {2005}, abstract = {Refixation probability during reading is lowest near the word center, suggestive of an optimal viewing position (OVP). Counter-intuitively, fixation durations are largest at the OVP, a result called the inverted optimal viewing position (IOVP) effect [Vitu, McConkie, Kerr, \& O'Regan, (2001). Vision Research 41, 3513-3533]. Current models of eye-movement control in reading fail to reproduce the IOVP effect. We propose a simple mechanism for generating this effect based on error-correction of mislocated fixations due to saccadic errors, First, we propose an algorithm for estimating proportions of mislocated fixations from experimental data yielding a higher probability for mislocated fixations near word boundaries. Second, we assume that mislocated fixations trigger an immediate start of a new saccade program causing a decrease of associated durations. Thus, the IOVP effect could emerge as a result of a coupling between cognitive and oculomotor processes. (c) 2005 Elsevier Ltd. All rights reserved}, language = {en} } @article{EngbertNuthmannRichteretal.2005, author = {Engbert, Ralf and Nuthmann, Antje and Richter, Eike M. and Kliegl, Reinhold}, title = {SWIFT : A dynamical model of saccade generation during reading}, issn = {0033-295X}, year = {2005}, abstract = {Mathematical, models,have become an important tool for understanding the control of eye movements during reading. Main goals of the development of the SWIFT model (R. Engbert, A. Longtin, \& R. Kliegl, 2002) were to investigate the possibility of spatially distributed processing and to implement a general mechanism for all types of eye movements observed in reading experiments. The authors present an advanced version of SWIFT that integrates properties of the oculomotor system and effects of word recognition to explain many of the experimental phenomena faced in reading research. They propose new procedures for the estimation of model parameters and for the test of the model's performance. They also present a mathematical analysis of the dynamics of the SWIFT model. Finally, within this framework, they present an analysis of the transition from parallel to serial processing}, language = {en} } @article{MoshelLiangCaspietal.2005, author = {Moshel, Shay and Liang, Jin-Rong and Caspi, Avi and Engbert, Ralf and Kliegl, Reinhold and Havlin, Shlomo and Zivotofsky, Ari Z.}, title = {Phase-synchronization decay of fixational eye movements}, year = {2005}, language = {en} } @article{LaubrockEngbertKliegl2005, author = {Laubrock, Jochen and Engbert, Ralf and Kliegl, Reinhold}, title = {Microsaccade rate during (un)ambiguous apparent motion}, issn = {0301-0066}, year = {2005}, language = {en} } @article{RichterEngbert2005, author = {Richter, Eike M. and Engbert, Ralf}, title = {Impossible gap paradigm : Experimental evidence for autonomous saccade timing}, issn = {0301-0066}, year = {2005}, language = {en} } @article{RolfsEngbertKliegl2004, author = {Rolfs, Martin and Engbert, Ralf and Kliegl, Reinhold}, title = {Microsaccade orientation supports attentional enhancement opposite to a peripheral cue}, year = {2004}, language = {en} } @article{Engbert2004, author = {Engbert, Ralf}, title = {Microsaccades keep the eyes' balance during fixation}, year = {2004}, abstract = {During fixation of a stationary target, small involuntary eye movements exhibit an erratic trajectory-a random walk. Two types of these fixational eye movements are drift and microsaccades (small-amplitude saccades). We investigated fixational eye movements and binocular coordination using a statistical analysis that had previously been applied to human posture control. This random-walk analysis uncovered two different time scales in fixational eye movements and identified specific functions for microsaccades. On a short time scale, microsaccades enhanced perception by increasing fixation errors. On a long time scale, microsaccades reduced fixation errors and binocular disparity (relative to pure drift movements). Thus, our findings clarify the role of oculomotor processes during fixation}, language = {en} } @article{KlieglEngbert2003, author = {Kliegl, Reinhold and Engbert, Ralf}, title = {How tight is the link between lexical processing and saccade programs?}, year = {2003}, abstract = {We question the assumption of serial attention shifts and the assumption that saccade programs are initiated or canceled only after stage one of word identification. Evidence: (1) Fixation durations prior to skipped words are not consistently higher compared to those prior to non-skipped words. (2) Attentional modulation of microsaccade rate might occur after early visual processing. Saccades are probably triggered by attentional selection}, language = {en} } @article{LaubrockKlieglEngbert2006, author = {Laubrock, Jochen and Kliegl, Reinhold and Engbert, Ralf}, title = {SWIFT explorations of age differences in eye movements during reading}, issn = {0149-7634}, doi = {10.1016/j.neubiorev.2006.06.013}, year = {2006}, language = {en} } @article{NuthmannEngbertKliegl2006, author = {Nuthmann, Antje and Engbert, Ralf and Kliegl, Reinhold}, title = {Messung von Blickbewegungen}, isbn = {978-3-8017-1846-6}, year = {2006}, language = {de} } @article{EngbertKliegl2003, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {Binocular coordination in microsaccades}, year = {2003}, language = {en} } @article{RichterEngbert2004, author = {Richter, Eike M. and Engbert, Ralf}, title = {Parafoveal processing during reading}, issn = {0301-0066}, year = {2004}, language = {en} } @article{NuthmannSmithEngbertetal.2010, author = {Nuthmann, Antje and Smith, Tim J. and Engbert, Ralf and Henderson, John M.}, title = {CRISP: a computational model of fixation duration in scene viewing}, year = {2010}, abstract = {Eye-movement control during scene viewing can be represented as a series of individual decisions about where and when to move the eyes. While substantial behavioral and computational research has been devoted to investigating the placement of fixations in scenes, relatively little is known about the mechanisms that control fixation durations. Here, we propose a computational model (CRISP) that accounts for saccade timing and programming and thus for variations in fixation durations in scene viewing. First, timing signals are modeled as continuous-time random walks. Second, difficulties at the level of visual and cognitive processing can inhibit and thus modulate saccade timing. Inhibition generates moment-by-moment changes in the random walk's transition rate and processing-related saccade cancellation. Third, saccade programming is completed in 2 stages: an initial, labile stage that is subject to cancellation and a subsequent, nonlabile stage. Several simulation studies tested the model's adequacy and generality. An initial simulation study explored the role of cognitive factors in scene viewing by examining how fixation durations differed under different viewing task instructions. Additional simulations investigated the degree to which fixation durations were under direct moment-to-moment control of the current visual scene. The present work further supports the conclusion that fixation durations, to a certain degree, reflect perceptual and cognitive activity in scene viewing. Computational model simulations contribute to an understanding of the underlying processes of gaze control.}, language = {en} } @article{NuthmannEngbert2009, author = {Nuthmann, Antje and Engbert, Ralf}, title = {Mindless reading revisited : an analysis based on the SWIFT model of eye-movement control}, issn = {0042-6989}, doi = {10.1016/j.visres.2008.10.022}, year = {2009}, abstract = {In this article, we revisit the mindless reading paradigm from the perspective of computational modeling. In the standard version of the paradigm, participants read sentences in both their normal version as well as the transformed (or mindless) version where each letter is replaced with a z. z-String scanning shares the oculomotor requirements with reading but none of the higher-level lexical and semantic processes. Here we use the z-string scanning task to validate the SWIFT model of saccade generation [Engbert, R., Nuthmann, A., Richter, E., \& Kliegl, R. (2005). SWIFT: A dynamical model of saccade generation during reading. Psychological Review, 112(4), 777-813] as an example for an advanced theory of eye-movement control in reading. We test the central assumption of spatially distributed processing across an attentional gradient proposed by the SWIFT model. Key experimental results like prolonged average fixation durations in z-string scanning compared to normal reading and the existence of a string-length effect on fixation durations and probabilities were reproduced by the model, which lends support to the model's assumptions on visual processing. Moreover, simulation results for patterns of regressive saccades in z-string scanning confirm SWIFT's concept of activation field dynamics for the selection of saccade targets.}, language = {en} } @misc{EngbertKliegl2003, author = {Engbert, Ralf and Kliegl, Reinhold}, title = {The game of word skipping: Who are the competitors?}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-56899}, year = {2003}, abstract = {Computational models such as E-Z Reader and SWIFT are ideal theoretical tools to test quantitatively our current understanding of eye-movement control in reading. Here we present a mathematical analysis of word skipping in the E-Z Reader model by semianalytic methods, to highlight the differences in current modeling approaches. In E-Z Reader, the word identification system must outperform the oculomotor system to induce word skipping. In SWIFT, there is competition among words to be selected as a saccade target. We conclude that it is the question of competitors in the "game" of word skipping that must be solved in eye movement research.}, language = {en} } @article{RothkegelTrukenbrodSchuettetal.2017, author = {Rothkegel, Lars Oliver Martin and Trukenbrod, Hans Arne and Sch{\"u}tt, Heiko Herbert and Wichmann, Felix A. and Engbert, Ralf}, title = {Temporal evolution of the central fixation bias in scene viewing}, series = {Journal of vision}, volume = {17}, journal = {Journal of vision}, publisher = {Association for Research in Vision and Opthalmology}, address = {Rockville}, issn = {1534-7362}, doi = {10.1167/17.13.3}, pages = {1626 -- 1638}, year = {2017}, abstract = {When watching the image of a natural scene on a computer screen, observers initially move their eyes toward the center of the image—a reliable experimental finding termed central fixation bias. This systematic tendency in eye guidance likely masks attentional selection driven by image properties and top-down cognitive processes. Here, we show that the central fixation bias can be reduced by delaying the initial saccade relative to image onset. In four scene-viewing experiments we manipulated observers' initial gaze position and delayed their first saccade by a specific time interval relative to the onset of an image. We analyzed the distance to image center over time and show that the central fixation bias of initial fixations was significantly reduced after delayed saccade onsets. We additionally show that selection of the initial saccade target strongly depended on the first saccade latency. A previously published model of saccade generation was extended with a central activation map on the initial fixation whose influence declined with increasing saccade latency. This extension was sufficient to replicate the central fixation bias from our experiments. Our results suggest that the central fixation bias is generated by default activation as a response to the sudden image onset and that this default activation pattern decreases over time. Thus, it may often be preferable to use a modified version of the scene viewing paradigm that decouples image onset from the start signal for scene exploration to explicitly reduce the central fixation bias.}, language = {en} } @article{RothkegelTrukenbrodSchuettetal.2016, author = {Rothkegel, Lars Oliver Martin and Trukenbrod, Hans Arne and Sch{\"u}tt, Heiko Herbert and Wichmann, Felix A. and Engbert, Ralf}, title = {Influence of initial fixation position in scene viewing}, series = {Vision research : an international journal for functional aspects of vision.}, volume = {129}, journal = {Vision research : an international journal for functional aspects of vision.}, publisher = {Elsevier}, address = {Oxford}, issn = {0042-6989}, doi = {10.1016/j.visres.2016.09.012}, pages = {33 -- 49}, year = {2016}, language = {en} } @article{CajarEngbertLaubrock2022, author = {Cajar, Anke and Engbert, Ralf and Laubrock, Jochen}, title = {Potsdam Eye-Movement Corpus for Scene Memorization and Search With Color and Spatial-Frequency Filtering}, series = {Frontiers in psychology / Frontiers Research Foundation}, volume = {13}, journal = {Frontiers in psychology / Frontiers Research Foundation}, publisher = {Frontiers Research Foundation}, address = {Lausanne, Schweiz}, issn = {1664-1078}, doi = {10.3389/fpsyg.2022.850482}, pages = {1 -- 7}, year = {2022}, language = {en} } @article{RomanoThielKurthsetal.2006, author = {Romano, Maria Carmen and Thiel, Marco and Kurths, J{\"u}rgen and Rolfs, Martin and Engbert, Ralf and Kliegl, Reinhold}, title = {Synchronization Analysis and Recurrence in Complex Systems}, isbn = {978-3-527-40623-4}, year = {2006}, language = {en} } @article{EngbertNuthmannKliegl2007, author = {Engbert, Ralf and Nuthmann, Antje and Kliegl, Reinhold}, title = {An lterative algorithm for the estimation of the distribution of mislocated fixations during reading}, isbn = {978-0-08-044980-7}, year = {2007}, language = {en} } @misc{KlieglEngbert2003, author = {Kliegl, Reinhold and Engbert, Ralf}, title = {How tight is the link between lexical processing and saccade programs?}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-56919}, year = {2003}, abstract = {We question the assumption of serial attention shifts and the assumption that saccade programs are initiated or canceled only after stage one of word identification. Evidence: (1) Fixation durations prior to skipped words are not consistently higher compared to those prior to nonskipped words. (2) Attentional modulation of microsaccade rate might occur after early visual processing. Saccades are probably triggered by attentional selection.}, language = {en} } @misc{TrukenbrodEngbert2014, author = {Trukenbrod, Hans Arne and Engbert, Ralf}, title = {ICAT: a computational model for the adaptive control of fixation durations}, series = {Psychonomic bulletin \& review : a journal of the Psychonomic Society}, volume = {21}, journal = {Psychonomic bulletin \& review : a journal of the Psychonomic Society}, number = {4}, publisher = {Springer}, address = {New York}, issn = {1069-9384}, doi = {10.3758/s13423-013-0575-0}, pages = {907 -- 934}, year = {2014}, abstract = {Eye movements depend on cognitive processes related to visual information processing. Much has been learned about the spatial selection of fixation locations, while the principles governing the temporal control (fixation durations) are less clear. Here, we review current theories for the control of fixation durations in tasks like visual search, scanning, scene perception, and reading and propose a new model for the control of fixation durations. We distinguish two local principles from one global principle of control. First, an autonomous saccade timer initiates saccades after random time intervals (local-I). Second, foveal inhibition permits immediate prolongation of fixation durations by ongoing processing (local-II). Third, saccade timing is adaptive, so that the mean timer value depends on task requirements and fixation history (Global). We demonstrate by numerical simulations that our model qualitatively reproduces patterns of mean fixation durations and fixation duration distributions observed in typical experiments. When combined with assumptions of saccade target selection and oculomotor control, the model accounts for both temporal and spatial aspects of eye movement control in two versions of a visual search task. We conclude that the model provides a promising framework for the control of fixation durations in saccadic tasks.}, language = {en} } @article{RisseHohensteinKliegletal.2014, author = {Risse, Sarah and Hohenstein, Sven and Kliegl, Reinhold and Engbert, Ralf}, title = {A theoretical analysis of the perceptual span based on SWIFT simulations of the n+2 boundary paradigm}, series = {Visual cognition}, volume = {22}, journal = {Visual cognition}, number = {3-4}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {1350-6285}, doi = {10.1080/13506285.2014.881444}, pages = {283 -- 308}, year = {2014}, abstract = {Eye-movement experiments suggest that the perceptual span during reading is larger than the fixated word, asymmetric around the fixation position, and shrinks in size contingent on the foveal processing load. We used the SWIFT model of eye-movement control during reading to test these hypotheses and their implications under the assumption of graded parallel processing of all words inside the perceptual span. Specifically, we simulated reading in the boundary paradigm and analysed the effects of denying the model to have valid preview of a parafoveal word n + 2 two words to the right of fixation. Optimizing the model parameters for the valid preview condition only, we obtained span parameters with remarkably realistic estimates conforming to the empirical findings on the size of the perceptual span. More importantly, the SWIFT model generated parafoveal processing up to word n + 2 without fitting the model to such preview effects. Our results suggest that asymmetry and dynamic modulation are plausible properties of the perceptual span in a parallel word-processing model such as SWIFT. Moreover, they seem to guide the flexible distribution of processing resources during reading between foveal and parafoveal words.}, language = {en} } @article{LangeEngbert2013, author = {Lange, Elke B. and Engbert, Ralf}, title = {Differentiating between verbal and spatial encoding using eye-movement recordings}, series = {The quarterly journal of experimental psychology}, volume = {66}, journal = {The quarterly journal of experimental psychology}, number = {9}, publisher = {Wiley}, address = {Hove}, issn = {1747-0218}, doi = {10.1080/17470218.2013.772214}, pages = {1840 -- 1857}, year = {2013}, abstract = {Visual information processing is guided by an active mechanism generating saccadic eye movements to salient stimuli. Here we investigate the specific contribution of saccades to memory encoding of verbal and spatial properties in a serial recall task. In the first experiment, participants moved their eyes freely without specific instruction. We demonstrate the existence of qualitative differences in eye-movement strategies during verbal and spatial memory encoding. While verbal memory encoding was characterized by shifting the gaze to the to-be-encoded stimuli, saccadic activity was suppressed during spatial encoding. In the second experiment, participants were required to suppress saccades by fixating centrally during encoding or to make precise saccades onto the memory items. Active suppression of saccades had no effect on memory performance, but tracking the upcoming stimuli decreased memory performance dramatically in both tasks, indicating a resource bottleneck between display-controlled saccadic control and memory encoding. We conclude that optimized encoding strategies for verbal and spatial features are underlying memory performance in serial recall, but such strategies work on an involuntary level only and do not support memory encoding when they are explicitly required by the task.}, language = {en} } @article{BettenbuehlRusconiEngbertetal.2012, author = {Bettenb{\"u}hl, Mario and Rusconi, Marco and Engbert, Ralf and Holschneider, Matthias}, title = {Bayesian selection of Markov Models for symbol sequences application to microsaccadic eye movements}, series = {PLoS one}, volume = {7}, journal = {PLoS one}, number = {9}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0043388}, pages = {10}, year = {2012}, abstract = {Complex biological dynamics often generate sequences of discrete events which can be described as a Markov process. The order of the underlying Markovian stochastic process is fundamental for characterizing statistical dependencies within sequences. As an example for this class of biological systems, we investigate the Markov order of sequences of microsaccadic eye movements from human observers. We calculate the integrated likelihood of a given sequence for various orders of the Markov process and use this in a Bayesian framework for statistical inference on the Markov order. Our analysis shows that data from most participants are best explained by a first-order Markov process. This is compatible with recent findings of a statistical coupling of subsequent microsaccade orientations. Our method might prove to be useful for a broad class of biological systems.}, language = {en} }