@phdthesis{Rothkegel2018, author = {Rothkegel, Lars Oliver Martin}, title = {Human scanpaths in natural scene viewing and natural scene search}, doi = {10.25932/publishup-42000}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-420005}, school = {Universit{\"a}t Potsdam}, pages = {xv, 131}, year = {2018}, abstract = {Understanding how humans move their eyes is an important part for understanding the functioning of the visual system. Analyzing eye movements from observations of natural scenes on a computer screen is a step to understand human visual behavior in the real world. When analyzing eye-movement data from scene-viewing experiments, the impor- tant questions are where (fixation locations), how long (fixation durations) and when (ordering of fixations) participants fixate on an image. By answering these questions, computational models can be developed which predict human scanpaths. Models serve as a tool to understand the underlying cognitive processes while observing an image, especially the allocation of visual attention. The goal of this thesis is to provide new contributions to characterize and model human scanpaths on natural scenes. The results from this thesis will help to understand and describe certain systematic eye-movement tendencies, which are mostly independent of the image. One eye-movement tendency I focus on throughout this thesis is the tendency to fixate more in the center of an image than on the outer parts, called the central fixation bias. Another tendency, which I will investigate thoroughly, is the characteristic distribution of angles between successive eye movements. The results serve to evaluate and improve a previously published model of scanpath generation from our laboratory, the SceneWalk model. Overall, six experiments were conducted for this thesis which led to the following five core results: i) A spatial inhibition of return can be found in scene-viewing data. This means that locations which have already been fixated are afterwards avoided for a certain time interval (Chapter 2). ii) The initial fixation position when observing an image has a long-lasting influence of up to five seconds on further scanpath progression (Chapter 2 \& 3). iii) The often described central fixation bias on images depends strongly on the duration of the initial fixation. Long-lasting initial fixations lead to a weaker central fixation bias than short fixations (Chapter 2 \& 3). iv) Human observers adjust their basic eye-movement parameters, like fixation dura- tions and saccade amplitudes, to the visual properties of a target they look for in visual search (Chapter 4). v) The angle between two adjacent saccades is an indicator for the selectivity of the upcoming saccade target (Chapter 4). All results emphasize the importance of systematic behavioral eye-movement tenden- cies and dynamic aspects of human scanpaths in scene viewing.}, language = {en} } @phdthesis{Cajar2016, author = {Cajar, Anke}, title = {Eye-movement control during scene viewing}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395536}, school = {Universit{\"a}t Potsdam}, pages = {vii, 133}, year = {2016}, abstract = {Eye movements serve as a window into ongoing visual-cognitive processes and can thus be used to investigate how people perceive real-world scenes. A key issue for understanding eye-movement control during scene viewing is the roles of central and peripheral vision, which process information differently and are therefore specialized for different tasks (object identification and peripheral target selection respectively). Yet, rather little is known about the contributions of central and peripheral processing to gaze control and how they are coordinated within a fixation during scene viewing. Additionally, the factors determining fixation durations have long been neglected, as scene perception research has mainly been focused on the factors determining fixation locations. The present thesis aimed at increasing the knowledge on how central and peripheral vision contribute to spatial and, in particular, to temporal aspects of eye-movement control during scene viewing. In a series of five experiments, we varied processing difficulty in the central or the peripheral visual field by attenuating selective parts of the spatial-frequency spectrum within these regions. Furthermore, we developed a computational model on how foveal and peripheral processing might be coordinated for the control of fixation duration. The thesis provides three main findings. First, the experiments indicate that increasing processing demands in central or peripheral vision do not necessarily prolong fixation durations; instead, stimulus-independent timing is adapted when processing becomes too difficult. Second, peripheral vision seems to play a prominent role in the control of fixation durations, a notion also implemented in the computational model. The model assumes that foveal and peripheral processing proceed largely in parallel and independently during fixation, but can interact to modulate fixation duration. Thus, we propose that the variation in fixation durations can in part be accounted for by the interaction between central and peripheral processing. Third, the experiments indicate that saccadic behavior largely adapts to processing demands, with a bias of avoiding spatial-frequency filtered scene regions as saccade targets. We demonstrate that the observed saccade amplitude patterns reflect corresponding modulations of visual attention. The present work highlights the individual contributions and the interplay of central and peripheral vision for gaze control during scene viewing, particularly for the control of fixation duration. Our results entail new implications for computational models and for experimental research on scene perception.}, language = {en} } @article{YanZhouShuetal.2015, author = {Yan, Ming and Zhou, Wei and Shu, Hua and Kliegl, Reinhold}, title = {Perceptual span depends on font size during the reading of chinese sentences}, series = {Journal of experimental psychology : Learning, memory, and cognition}, volume = {41}, journal = {Journal of experimental psychology : Learning, memory, and cognition}, number = {1}, publisher = {American Psychological Association}, address = {Washington}, issn = {0278-7393}, doi = {10.1037/a0038097}, pages = {209 -- 219}, year = {2015}, abstract = {The present study explored the perceptual span (i.e., the physical extent of an area from which useful visual information is extracted during a single fixation) during the reading of Chinese sentences in 2 experiments. In Experiment 1, we tested whether the rightward span can go beyond 3 characters when visually similar masks were used. Results showed that Chinese readers needed at least 4 characters to the right of fixation to maintain a normal reading behavior when visually similar masks were used and when characters were displayed in small fonts, indicating that the span is dynamically influenced by masking materials. In Experiments 2 and 3, we asked whether the perceptual span varies as a function of font size in spaced (German) and unspaced (Chinese) scripts. Results clearly suggest perceptual span depends on font size in Chinese, but we failed to find such evidence for German. We propose that the perceptual span in Chinese is flexible; it is strongly constrained by its language-specific properties such as high information density and lack of word spacing. Implications for saccade-target selection during the reading of Chinese sentences are discussed.}, language = {en} } @article{EngbertTrukenbrodBarthelmeetal.2015, author = {Engbert, Ralf and Trukenbrod, Hans Arne and Barthelme, Simon and Wichmann, Felix A.}, title = {Spatial statistics and attentional dynamics in scene viewing}, series = {Journal of vision}, volume = {15}, journal = {Journal of vision}, number = {1}, publisher = {Association for Research in Vision and Opthalmology}, address = {Rockville}, issn = {1534-7362}, doi = {10.1167/15.1.14}, pages = {17}, year = {2015}, abstract = {In humans and in foveated animals visual acuity is highly concentrated at the center of gaze, so that choosing where to look next is an important example of online, rapid decision-making. Computational neuroscientists have developed biologically-inspired models of visual attention, termed saliency maps, which successfully predict where people fixate on average. Using point process theory for spatial statistics, we show that scanpaths contain, however, important statistical structure, such as spatial clustering on top of distributions of gaze positions. Here, we develop a dynamical model of saccadic selection that accurately predicts the distribution of gaze positions as well as spatial clustering along individual scanpaths. Our model relies on activation dynamics via spatially-limited (foveated) access to saliency information, and, second, a leaky memory process controlling the re-inspection of target regions. This theoretical framework models a form of context-dependent decision-making, linking neural dynamics of attention to behavioral gaze data.}, language = {en} } @article{HartmannMastFischer2015, author = {Hartmann, Matthias and Mast, Fred W. and Fischer, Martin H.}, title = {Spatial biases during mental arithmetic: evidence from eye movements on a blank screen}, series = {Frontiers in psychology}, volume = {6}, journal = {Frontiers in psychology}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-1078}, doi = {10.3389/fpsyg.2015.00012}, pages = {8}, year = {2015}, abstract = {While the influence of spatial-numerical associations in number categorization tasks has been well established, their role in mental arithmetic is less clear. It has been hypothesized that mental addition leads to rightward and upward shifts of spatial attention (along the "mental number line"), whereas subtraction leads to leftward and downward shifts. We addressed this hypothesis by analyzing spontaneous eye movements during mental arithmetic. Participants solved verbally presented arithmetic problems (e.g., 2 + 7, 8-3) aloud while looking at a blank screen. We found that eye movements reflected spatial biases in the ongoing mental operation: Gaze position shifted more upward when participants solved addition compared to subtraction problems, and the horizontal gaze position was partly determined by the magnitude of the operands. Interestingly, the difference between addition and subtraction trials was driven by the operator (plus vs. minus) but was not influenced by the computational process. Thus, our results do not support the idea of a mental movement toward the solution during arithmetic but indicate a semantic association between operation and space.}, language = {en} } @article{LaubrockKliegl2015, author = {Laubrock, Jochen and Kliegl, Reinhold}, title = {The eye-voice span during reading aloud}, series = {Frontiers in psychology}, volume = {6}, journal = {Frontiers in psychology}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-1078}, doi = {10.3389/fpsyg.2015.01437}, pages = {19}, year = {2015}, abstract = {Although eye movements during reading are modulated by cognitive processing demands, they also reflect visual sampling of the input, and possibly preparation of output for speech or the inner voice. By simultaneously recording eye movements and the voice during reading aloud, we obtained an output measure that constrains the length of time spent on cognitive processing. Here we investigate the dynamics of the eye-voice span (EVS), the distance between eye and voice. We show that the EVS is regulated immediately during fixation of a word by either increasing fixation duration or programming a regressive eye movement against the reading direction. EVS size at the beginning of a fixation was positively correlated with the likelihood of regressions and refixations. Regression probability was further increased if the EVS was still large at the end of a fixation: if adjustment of fixation duration did not sufficiently reduce the EVS during a fixation, then a regression rather than a refixation followed with high probability. We further show that the EVS can help understand cognitive influences on fixation duration during reading: in mixed model analyses, the EVS was a stronger predictor of fixation durations than either word frequency or word length. The EVS modulated the influence of several other predictors on single fixation durations (SFDs). For example, word-N frequency effects were larger with a large EVS, especially when word N-1 frequency was low. Finally, a comparison of SFDs during oral and silent reading showed that reading is governed by similar principles in both reading modes, although EVS maintenance and articulatory processing also cause some differences. In summary, the EVS is regulated by adjusting fixation duration and/or by programming a regressive eye movement when the EVS gets too large. Overall, the EVS appears to be directly related to updating of the working memory buffer during reading.}, language = {en} } @article{HohensteinKliegl2014, author = {Hohenstein, Sven and Kliegl, Reinhold}, title = {Semantic preview benefit during reading}, series = {Journal of experimental psychology : Learning, memory, and cognition}, volume = {40}, journal = {Journal of experimental psychology : Learning, memory, and cognition}, number = {1}, publisher = {American Psychological Association}, address = {Washington}, issn = {0278-7393}, doi = {10.1037/a0033670}, pages = {166 -- 190}, year = {2014}, abstract = {Word features in parafoveal vision influence eye movements during reading. The question of whether readers extract semantic information from parafoveal words was studied in 3 experiments by using a gaze-contingent display change technique. Subjects read German sentences containing 1 of several preview words that were replaced by a target word during the saccade to the preview (boundary paradigm). In the 1st experiment the preview word was semantically related or unrelated to the target. Fixation durations on the target were shorter for semantically related than unrelated previews, consistent with a semantic preview benefit. In the 2nd experiment, half the sentences were presented following the rules of German spelling (i.e., previews and targets were printed with an initial capital letter), and the other half were presented completely in lowercase. A semantic preview benefit was obtained under both conditions. In the 3rd experiment, we introduced 2 further preview conditions, an identical word and a pronounceable nonword, while also manipulating the text contrast. Whereas the contrast had negligible effects, fixation durations on the target were reliably different for all 4 types of preview. Semantic preview benefits were greater for pretarget fixations closer to the boundary (large preview space) and, although not as consistently, for long pretarget fixation durations (long preview time). The results constrain theoretical proposals about eye movement control in reading.}, language = {en} } @article{FernandezShalomKliegletal.2014, author = {Fernandez, Gerardo and Shalom, Diego E. and Kliegl, Reinhold and Sigman, Mariano}, title = {Eye movements during reading proverbs and regular sentences: the incoming word predictability effect}, series = {Language, cognition and neuroscience}, volume = {29}, journal = {Language, cognition and neuroscience}, number = {3}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {2327-3798}, doi = {10.1080/01690965.2012.760745}, pages = {260 -- 273}, year = {2014}, language = {en} } @article{RisseKliegl2014, author = {Risse, Sarah and Kliegl, Reinhold}, title = {Dissociating preview validity and preview difficulty in parafoveal processing of word n+1 during reading}, series = {Journal of experimental psychology : Human perception and performance}, volume = {40}, journal = {Journal of experimental psychology : Human perception and performance}, number = {2}, publisher = {American Psychological Association}, address = {Washington}, issn = {0096-1523}, doi = {10.1037/a0034997}, pages = {653 -- 668}, year = {2014}, abstract = {Many studies have shown that previewing the next word n + 1 during reading leads to substantial processing benefit (e.g., shorter word viewing times) when this word is eventually fixated. However, evidence of such preprocessing in fixations on the preceding word n when in fact the information about the preview is acquired is far less consistent. A recent study suggested that such effects may be delayed into fixations on the next word n + 1 (Risse \& Kliegl, 2012). To investigate the time course of parafoveal information-acquisition on the control of eye movements during reading, we conducted 2 gaze-contingent display-change experiments and orthogonally manipulated the processing difficulty (i.e., word frequency) of an n + 1 preview word and its validity relative to the target word. Preview difficulty did not affect fixation durations on the pretarget word n but on the target word n + 1. In fact, the delayed preview-difficulty effect was almost of the same size as the preview benefit associated with the n + 1 preview validity. Based on additional results from quantile-regression analyses on the time course of the 2 preview effects, we discuss consequences as to the integration of foveal and parafoveal information and potential implications for computational models of eye guidance in reading.}, language = {en} } @article{RisseKliegl2012, author = {Risse, Sarah and Kliegl, Reinhold}, title = {Evidence for delayed Parafoveal-on-Foveal effects from word n+2 in reading}, series = {Journal of experimental psychology : Human perception and performance}, volume = {38}, journal = {Journal of experimental psychology : Human perception and performance}, number = {4}, publisher = {American Psychological Association}, address = {Washington}, issn = {0096-1523}, doi = {10.1037/a0027735}, pages = {1026 -- 1042}, year = {2012}, abstract = {During reading information is acquired from word(s) beyond the word that is currently looked at. It is still an open question whether such parafoveal information can influence the current viewing of a word, and if so, whether such parafoveal-on-foveal effects are attributable to distributed processing or to mislocated fixations which occur when the eyes are directed at a parafoveal word but land on another word instead. In two display-change experiments, we orthogonally manipulated the preview and target difficulty of word n+2 to investigate the role of mislocated fixations on the previous word n+1. When the eyes left word n, an easy or difficult word n+2 preview was replaced by an easy or difficult n+2 target word. In Experiment 1, n+2 processing difficulty was manipulated by means of word frequency (i.e., easy high-frequency vs. difficult low-frequency word n+2). In Experiment 2, we varied the visual familiarity of word n+2 (i.e., easy lower-case vs. difficult alternating-case writing). Fixations on the short word n+1, which were likely to be mislocated, were nevertheless not influenced by the difficulty of the adjacent word n+2, the hypothesized target of the mislocated fixation. Instead word n+1 was influenced by the preview difficulty of word n+2, representing a delayed parafoveal-on-foveal effect. The results challenge the mislocated-fixation hypothesis as an explanation of parafoveal-on-foveal effects and provide new insight into the complex spatial and temporal effect structure of processing inside the perceptual span during reading.}, 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{LuoYanZhou2013, author = {Luo, Yingyi and Yan, Ming and Zhou, Xiaolin}, title = {Prosodic boundaries delay the processing of upcoming lexical information during silent sentence reading}, series = {Journal of experimental psychology : Learning, memory, and cognition}, volume = {39}, journal = {Journal of experimental psychology : Learning, memory, and cognition}, number = {3}, publisher = {American Psychological Association}, address = {Washington}, issn = {0278-7393}, doi = {10.1037/a0029182}, pages = {915 -- 930}, year = {2013}, abstract = {Prosodic boundaries can be used to guide syntactic parsing in both spoken and written sentence comprehension, but it is unknown whether the processing of prosodic boundaries affects the processing of upcoming lexical information. In 3 eye-tracking experiments, participants read silently sentences that allow for 2 possible syntactic interpretations when there is no comma or other cue specifying which interpretation should be taken. In Experiments 1 and 2, participants heard a low-pass filtered auditory version of the sentence, which provided a prosodic boundary cue prior to each sentence. In Experiment 1, we found that the boundary cue helped syntactic disambiguation after the cue and led to longer fixation durations on regions right before the cue than on identical regions without prosodic boundary information. In Experiments 2 and 3, we used a gaze-contingent display-change paradigm to manipulate the parafoveal visibility of the first constituent character of the target word after the disambiguating position. Results of Experiment 2 showed that previewing the first character significantly reduced the reading time of the target word, but this preview benefit was greatly reduced when the prosodic boundary cue was introduced at this position. In Experiment 3, instead of the acoustic cues, a visually presented comma was inserted at the disambiguating position in each sentence. Results showed that the comma effect on lexical processing was essentially the same as the effect of prosodic boundary cue. These findings demonstrate that processing a prosodic boundary could impair the processing of parafoveal information during sentence reading.}, language = {en} } @misc{LaubrockKliegl2015, author = {Laubrock, Jochen and Kliegl, Reinhold}, title = {The eye-voice span during reading aloud}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-86904}, year = {2015}, abstract = {Although eye movements during reading are modulated by cognitive processing demands, they also reflect visual sampling of the input, and possibly preparation of output for speech or the inner voice. By simultaneously recording eye movements and the voice during reading aloud, we obtained an output measure that constrains the length of time spent on cognitive processing. Here we investigate the dynamics of the eye-voice span (EVS), the distance between eye and voice. We show that the EVS is regulated immediately during fixation of a word by either increasing fixation duration or programming a regressive eye movement against the reading direction. EVS size at the beginning of a fixation was positively correlated with the likelihood of regressions and refixations. Regression probability was further increased if the EVS was still large at the end of a fixation: if adjustment of fixation duration did not sufficiently reduce the EVS during a fixation, then a regression rather than a refixation followed with high probability. We further show that the EVS can help understand cognitive influences on fixation duration during reading: in mixed model analyses, the EVS was a stronger predictor of fixation durations than either word frequency or word length. The EVS modulated the influence of several other predictors on single fixation durations (SFDs). For example, word-N frequency effects were larger with a large EVS, especially when word N-1 frequency was low. Finally, a comparison of SFDs during oral and silent reading showed that reading is governed by similar principles in both reading modes, although EVS maintenance and articulatory processing also cause some differences. In summary, the EVS is regulated by adjusting fixation duration and/or by programming a regressive eye movement when the EVS gets too large. Overall, the EVS appears to be directly related to updating of the working memory buffer during reading.}, language = {en} } @article{LaubrockKliegl2015, author = {Laubrock, Jochen and Kliegl, Reinhold}, title = {The eye-voice span during reading aloud}, series = {Frontiers in psychology}, volume = {6}, journal = {Frontiers in psychology}, number = {1432}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-1078}, doi = {10.3389/fpsyg.2015.01432}, year = {2015}, abstract = {Although eye movements during reading are modulated by cognitive processing demands, they also reflect visual sampling of the input, and possibly preparation of output for speech or the inner voice. By simultaneously recording eye movements and the voice during reading aloud, we obtained an output measure that constrains the length of time spent on cognitive processing. Here we investigate the dynamics of the eye-voice span (EVS), the distance between eye and voice. We show that the EVS is regulated immediately during fixation of a word by either increasing fixation duration or programming a regressive eye movement against the reading direction. EVS size at the beginning of a fixation was positively correlated with the likelihood of regressions and refixations. Regression probability was further increased if the EVS was still large at the end of a fixation: if adjustment of fixation duration did not sufficiently reduce the EVS during a fixation, then a regression rather than a refixation followed with high probability. We further show that the EVS can help understand cognitive influences on fixation duration during reading: in mixed model analyses, the EVS was a stronger predictor of fixation durations than either word frequency or word length. The EVS modulated the influence of several other predictors on single fixation durations (SFDs). For example, word-N frequency effects were larger with a large EVS, especially when word N-1 frequency was low. Finally, a comparison of SFDs during oral and silent reading showed that reading is governed by similar principles in both reading modes, although EVS maintenance and articulatory processing also cause some differences. In summary, the EVS is regulated by adjusting fixation duration and/or by programming a regressive eye movement when the EVS gets too large. Overall, the EVS appears to be directly related to updating of the working memory buffer during reading.}, language = {en} } @phdthesis{Hohenstein2013, author = {Hohenstein, Sven}, title = {Eye movements and processing of semantic information in the parafovea during reading}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70363}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {When we read a text, we obtain information at different levels of representation from abstract symbols. A reader's ultimate aim is the extraction of the meaning of the words and the text. The reserach of eye movements in reading covers a broad range of psychological systems, ranging from low-level perceptual and motor processes to high-level cognition. Reading of skilled readers proceeds highly automatic, but is a complex phenomenon of interacting subprocesses at the same time. The study of eye movements during reading offers the possibility to investigate cognition via behavioral measures during the excercise of an everyday task. The process of reading is not limited to the directly fixated (or foveal) word but also extends to surrounding (or parafoveal) words, particularly the word to the right of the gaze position. This process may be unconscious, but parafoveal information is necessary for efficient reading. There is an ongoing debate on whether processing of the upcoming word encompasses word meaning (or semantics) or only superficial features. To increase the knowledge about how the meaning of one word helps processing another word, seven experiments were conducted. In these studies, words were exachanged during reading. The degree of relatedness between the word to the right of the currently fixated one and the word subsequently fixated was experimentally manipulated. Furthermore, the time course of the parafoveal extraction of meaning was investigated with two different approaches, an experimental one and a statistical one. As a major finding, fixation times were consistently lower if a semantically related word was presented compared to the presence of an unrelated word. Introducing an experimental technique that allows controlling the duration for which words are available, the time course of processing and integrating meaning was evaluated. Results indicated both facilitation and inhibition due to relatedness between the meanings of words. In a more natural reading situation, the effectiveness of the processing of parafoveal words was sometimes time-dependent and substantially increased with shorter distances between the gaze position and the word. Findings are discussed with respect to theories of eye-movement control. In summary, the results are more compatible with models of distributed word processing. The discussions moreover extend to language differences and technical issues of reading research.}, language = {en} } @phdthesis{Ohl2013, author = {Ohl, Sven}, title = {Small eye movements during fixation : the case of postsaccadic fixation and preparatory influences}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69862}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Describing human eye movement behavior as an alternating sequence of saccades and fixations turns out to be an oversimplification because the eyes continue to move during fixation. Small-amplitude saccades (e.g., microsaccades) are typically observed 1-2 times per second during fixation. Research on microsaccades came in two waves. Early studies on microsaccades were dominated by the question whether microsaccades affect visual perception, and by studies on the role of microsaccades in the process of fixation control. The lack of evidence for a unique role of microsaccades led to a very critical view on the importance of microsaccades. Over the last years, microsaccades moved into focus again, revealing many interactions with perception, oculomotor control and cognition, as well as intriguing new insights into the neurophysiological implementation of microsaccades. In contrast to early studies on microsaccades, recent findings on microsaccades were accompanied by the development of models of microsaccade generation. While the exact generating mechanisms vary between the models, they still share the assumption that microsaccades are generated in a topographically organized saccade motor map that includes a representation for small-amplitude saccades in the center of the map (with its neurophysiological implementation in the rostral pole of the superior colliculus). In the present thesis I criticize that models of microsaccade generation are exclusively based on results obtained during prolonged presaccadic fixation. I argue that microsaccades should also be studied in a more natural situation, namely the fixation following large saccadic eye movements. Studying postsaccadic fixation offers a new window to falsify models that aim to account for the generation of small eye movements. I demonstrate that error signals (visual and extra-retinal), as well as non-error signals like target eccentricity influence the characteristics of small-amplitude eye movements. These findings require a modification of a model introduced by Rolfs, Kliegl and Engbert (2008) in order to account for the generation of small-amplitude saccades during postsaccadic fixation. Moreover, I present a promising type of survival analysis that allowed me to examine time-dependent influences on postsaccadic eye movements. In addition, I examined the interplay of postsaccadic eye movements and postsaccadic location judgments, highlighting the need to include postsaccadic eye movements as covariate in the analyses of location judgments in the presented paradigm. In a second goal, I tested model predictions concerning preparatory influences on microsaccade generation during presaccadic fixation. The observation, that the preparatory set significantly influenced microsaccade rate, supports the critical model assumption that increased fixation-related activity results in a larger number of microsaccades. In the present thesis I present important influences on the generation of small-amplitude saccades during fixation. These eye movements constitute a rich oculomotor behavior which still poses many research questions. Certainly, small-amplitude saccades represent an interesting source of information and will continue to influence future studies on perception and cognition.}, language = {en} } @phdthesis{Risse2011, author = {Risse, Sarah}, title = {Processing in the perceptual span : investigations with the n+2-boundary paradigm}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60414}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Cognitive psychology is traditionally interested in the interaction of perception, cognition, and behavioral control. Investigating eye movements in reading constitutes a field of research in which the processes and interactions of these subsystems can be studied in a well-defined environment. Thereby, the following questions are pursued: How much information is visually perceived during a fixation, how is processing achieved and temporally coordinated from visual letter encoding to final sentence comprehension, and how do such processes reflect on behavior such as the control of the eyes' movements during reading. Various theoretical models have been proposed to account for the specific eye-movement behavior in reading (for a review see Reichle, Rayner, \& Pollatsek, 2003). Some models are based on the idea of shifting attention serially from one word to the next within the sentence whereas others propose distributed attention allocating processing resources to more than one word at a time. As attention is assumed to drive word recognition processes one major difference between these models is that word processing must either occur in strict serial order, or that word processing is achieved in parallel. In spite of this crucial difference in the time course of word processing, both model classes perform well on explaining many of the benchmark effects in reading. In fact, there seems to be not much empirical evidence that challenges the models to a point at which their basic assumptions could be falsified. One issue often perceived as being decisive in the debate on serial and parallel word processing is how not-yet-fixated words to the right of fixation affect eye movements. Specifically, evidence is discussed as to what spatial extent such parafoveal words are previewed and how this influences current and subsequent word processing. Four experiments investigated parafoveal processing close to the spatial limits of the perceptual span. The present work aims to go beyond mere existence proofs of previewing words at such spatial distances. Introducing a manipulation that dissociates the sources of long-range preview effects, benefits and costs of parafoveal processing can be investigated in a single analysis and the differing impact is tracked across a three-word target region. In addition, the same manipulation evaluates the role of oculomotor error as the cause of non-local distributed effects. In this respect, the results contribute to a better understanding of the time course of word processing inside the perceptual span and attention allocation during reading.}, language = {en} } @phdthesis{Nuthmann2005, author = {Nuthmann, Antje}, title = {The "where" and "when" of eye fixations in reading}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7931}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {To investigate eye-movement control in reading, the present thesis examined three phenomena related to the eyes' landing position within words, (1) the optimal viewing position (OVP), (2) the preferred viewing location (PVL), and (3) the Fixation-Duration Inverted-Optimal Viewing Position (IOVP) Effect. Based on a corpus-analytical approach (Exp. 1), the influence of variables word length, launch site distance, and word frequency was systematically explored. In addition, five experimental manipulations were conducted. First, word center was identified as the OVP, that is the position within a word where refixation probability is minimal. With increasing launch site distance, however, the OVP was found to move towards the word beginning. Several possible causes of refixations were discussed. The issue of refixation saccade programming was extensively investigated, suggesting that pre-planned and directly controlled refixation saccades coexist. Second, PVL curves, that is landing position distributions, show that the eyes are systematically deviated from the OVP, due to visuomotor constraints. By far the largest influence on mean and standard deviation of the Gaussian PVL curve was exhibited by launch site distance. Third, it was investigated how fixation durations vary as a function of landing position. The IOVP effect was replicated: Fixations located at word center are longer than those falling near the edges of a word. The effect of word frequency and/or launch site distance on the IOVP function mainly consisted in a vertical displacement of the curve. The Fixation-Duration IOVP effect is intriguing because word center (the OVP) would appear to be the best place to fixate and process a word. A critical part of the current work was devoted to investigate the origin of the effect. It was suggested that the IOVP effect arises as a consequence of mislocated fixations, i.e. fixations on unintended words, which are caused by saccadic errors. An algorithm for estimating the proportion of mislocated fixations from empirical data was developed, based on extrapolations of landing position distributions beyond word boundaries. As a new central theoretical claim it was suggested that a new saccade program is started immediately if the intended target word is missed. On average, this will lead to decreased durations for mislocated fixations. Because mislocated fixations were shown to be most prevalent at the beginning and end of words, the proposed mechanism generated the inverted U-shape for fixation durations when computed as a function of landing position. The proposed mechanism for generating the effect is generally compatible with both oculomotor and cognitive models of eye-movement control in reading.}, subject = {Allgemeine Psychologie}, language = {en} }