@article{SinnEngbert2016, author = {Sinn, Petra and Engbert, Ralf}, title = {Small saccades versus microsaccades: Experimental distinction and model-based unification}, series = {Vision research : an international journal for functional aspects of vision.}, volume = {118}, journal = {Vision research : an international journal for functional aspects of vision.}, publisher = {Elsevier}, address = {Oxford}, issn = {0042-6989}, doi = {10.1016/j.visres.2015.05.012}, pages = {132 -- 143}, year = {2016}, abstract = {Natural vision is characterized by alternating sequences of rapid gaze shifts (saccades) and fixations. During fixations, microsaccades and slower drift movements occur spontaneously, so that the eye is never motionless. Theoretical models of fixational eye movements predict that microsaccades are dynamically coupled to slower drift movements generated immediately before microsaccades, which might be used as a criterion to distinguish microsaccades from small voluntary saccades. Here we investigate a sequential scanning task, where participants generate goal-directed saccades and microsaccades with overlapping amplitude distributions. We show that properties of microsaccades are correlated with precursory drift motion, while amplitudes of goal-directed saccades do not dependent on previous drift epochs. We develop and test a mathematical model that integrates goal-directed and fixational eye movements, including microsaccades. Using model simulations, we reproduce the experimental finding of correlations within fixational eye movement components (i.e., between physiological drift and microsaccades) but not between goal-directed saccades and fixational drift motion. These results lend support to a functional difference between microsaccades and goal-directed saccades, while, at the same time, both types of behavior may be part of an oculomotor continuum that is quantitatively described by our mathematical model. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{CajarEngbertLaubrock2016, author = {Cajar, Anke and Engbert, Ralf and Laubrock, Jochen}, title = {Spatial frequency processing in the central and peripheral visual field during scene viewing}, series = {Vision research : an international journal for functional aspects of vision.}, volume = {127}, journal = {Vision research : an international journal for functional aspects of vision.}, publisher = {Elsevier}, address = {Oxford}, issn = {0042-6989}, doi = {10.1016/j.visres.2016.05.008}, pages = {186 -- 197}, year = {2016}, abstract = {Visuospatial attention and gaze control depend on the interaction of foveal and peripheral processing. The foveal and peripheral regions of the visual field are differentially sensitive to parts of the spatial frequency spectrum. In two experiments, we investigated how the selective attenuation of spatial frequencies in the central or the peripheral visual field affects eye-movement behavior during real-world scene viewing. Gaze-contingent low-pass or high-pass filters with varying filter levels (i.e., cutoff frequencies; Experiment 1) or filter sizes (Experiment 2) were applied. Compared to unfiltered control conditions, mean fixation durations increased most with central high-pass and peripheral low-pass filtering. Increasing filter size prolonged fixation durations with peripheral filtering, but not with central filtering. Increasing filter level prolonged fixation durations with low-pass filtering, but not with high-pass filtering. These effects indicate that fixation durations are not always longer under conditions of increased processing difficulty. Saccade amplitudes largely adapted to processing difficulty: amplitudes increased with central filtering and decreased with peripheral filtering; the effects strengthened with increasing filter size and filter level. In addition, we observed a trade-off between saccade timing and saccadic selection, since saccade amplitudes were modulated when fixation durations were unaffected by the experimental manipulations. We conclude that interactions of perception and gaze control are highly sensitive to experimental manipulations of input images as long as the residual information can still be accessed for gaze control. (C) 2016 Elsevier Ltd. All rights reserved.}, 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{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{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} } @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{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{SchadEngbert2012, author = {Schad, Daniel and Engbert, Ralf}, title = {The zoom lens of attention simulating shuffled versus normal text reading using the SWIFT model}, series = {Visual cognition}, volume = {20}, journal = {Visual cognition}, number = {4-5}, publisher = {Wiley}, address = {Hove}, issn = {1350-6285}, doi = {10.1080/13506285.2012.670143}, pages = {391 -- 421}, year = {2012}, abstract = {Assumptions on the allocation of attention during reading are crucial for theoretical models of eye guidance. The zoom lens model of attention postulates that attentional deployment can vary from a sharp focus to a broad window. The model is closely related to the foveal load hypothesis, i.e., the assumption that the perceptual span is modulated by the difficulty of the fixated word. However, these important theoretical concepts for cognitive research have not been tested quantitatively in eye movement models. Here we show that the zoom lens model, implemented in the SWIFT model of saccade generation, captures many important patterns of eye movements. We compared the model's performance to experimental data from normal and shuffled text reading. Our results demonstrate that the zoom lens of attention might be an important concept for eye movement control in reading.}, language = {en} } @article{SchadNuthmannEngbert2012, author = {Schad, Daniel and Nuthmann, Antje and Engbert, Ralf}, title = {Your mind wanders weakly, your mind wanders deeply - objective measures reveal mindless reading at different levels}, series = {Cognition : international journal of cognitive science}, volume = {125}, journal = {Cognition : international journal of cognitive science}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0010-0277}, doi = {10.1016/j.cognition.2012.07.004}, pages = {179 -- 194}, year = {2012}, abstract = {When the mind wanders, attention turns away from the external environment and cognitive processing is decoupled from perceptual information. Mind wandering is usually treated as a dichotomy (dichotomy-hypothesis), and is often measured using self-reports. Here, we propose the levels of inattention hypothesis, which postulates attentional decoupling to graded degrees at different hierarchical levels of cognitive processing. To measure graded levels of attentional decoupling during reading we introduce the sustained attention to stimulus task (SAST), which is based on psychophysics of error detection. Under experimental conditions likely to induce mind wandering, we found that subjects were less likely to notice errors that required high-level processing for their detection as opposed to errors that only required low-level processing. Eye tracking revealed that before errors were overlooked influences of high- and low-level linguistic variables on eye fixations were reduced in a graded fashion, indicating episodes of mindless reading at weak and deep levels. Individual fixation durations predicted overlooking of lexical errors 5 s before they occurred. Our findings support the levels of inattention hypothesis and suggest that different levels of mindless reading can be measured behaviorally in the SAST. Using eye tracking to detect mind wandering online represents a promising approach for the development of new techniques to study mind wandering and to ameliorate its negative consequences.}, language = {en} } @article{KruegelVituEngbert2012, author = {Kr{\"u}gel, Andre and Vitu, Francoise and Engbert, Ralf}, title = {Fixation positions after skipping saccades - a single space makes a large difference}, 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 = {8}, publisher = {Springer}, address = {New York}, issn = {1943-3921}, doi = {10.3758/s13414-012-0365-1}, pages = {1556 -- 1561}, year = {2012}, abstract = {During reading, saccadic eye movements are generated to shift words into the center of the visual field for lexical processing. Recently, Krugel and Engbert (Vision Research 50:1532-1539, 2010) demonstrated that within-word fixation positions are largely shifted to the left after skipped words. However, explanations of the origin of this effect cannot be drawn from normal reading data alone. Here we show that the large effect of skipped words on the distribution of within-word fixation positions is primarily based on rather subtle differences in the low-level visual information acquired before saccades. Using arrangements of "x" letter strings, we reproduced the effect of skipped character strings in a highly controlled single-saccade task. Our results demonstrate that the effect of skipped words in reading is the signature of a general visuomotor phenomenon. Moreover, our findings extend beyond the scope of the widely accepted range-error model, which posits that within-word fixation positions in reading depend solely on the distances of target words. We expect that our results will provide critical boundary conditions for the development of visuomotor models of saccade planning during reading.}, language = {en} }