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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.
The perceptual span describes the size of the visual field from which information is obtained during a fixation in reading. Its size depends on characteristics of writing system and reader, but-according to the foveal load hypothesis-it is also adjusted dynamically as a function of lexical processing difficulty. Using the moving window paradigm to manipulate the amount of preview, here we directly test whether the perceptual span shrinks as foveal word difficulty increases. We computed the momentary size of the span from word-based eye-movement measures as a function of foveal word frequency, allowing us to separately describe the perceptual span for information affecting spatial saccade targeting and temporal saccade execution. First fixation duration and gaze duration on the upcoming (parafoveal) word N + 1 were significantly shorter when the current (foveal) word N was more frequent. We show that the word frequency effect is modulated by window size. Fixation durations on word N + 1 decreased with high-frequency words N, but only for large windows, that is, when sufficient parafoveal preview was available. This provides strong support for the foveal load hypothesis. To investigate the development of the foveal load effect, we analyzed data from three waves of a longitudinal study on the perceptual span with German children in Grades 1 to 6. Perceptual span adjustment emerged early in development at around second grade and remained stable in later grades. We conclude that the local modulation of the perceptual span indicates a general cognitive process, perhaps an attentional gradient with rapid readjustment.
When infants observe a human grasping action, experience-based accounts predict that all infants familiar with grasping actions should be able to predict the goal regardless of additional agency cues such as an action effect. Cue-based accounts, however, suggest that infants use agency cues to identify and predict action goals when the action or the agent is not familiar. From these accounts, we hypothesized that younger infants would need additional agency cues such as a salient action effect to predict the goal of a human grasping action, whereas older infants should be able to predict the goal regardless of agency cues. In three experiments, we presented 6-, 7-, and 11-month-olds with videos of a manual grasping action presented either with or without an additional salient action effect (Exp. 1 and 2), or we presented 7-month-olds with videos of a mechanical claw performing a grasping action presented with a salient action effect (Exp. 3). The 6-month-olds showed tracking gaze behavior, and the 11-month-olds showed predictive gaze behavior, regardless of the action effect. However, the 7-month-olds showed predictive gaze behavior in the action-effect condition, but tracking gaze behavior in the no-action-effect condition and in the action-effect condition with a mechanical claw. The results therefore support the idea that salient action effects are especially important for infants' goal predictions from 7 months on, and that this facilitating influence of action effects is selective for the observation of human hands.
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.
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.
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.
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.
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.
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.
Small eye movements during fixation : the case of postsaccadic fixation and preparatory influences
(2013)
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.
Eye movements in reading are sensitive to foveal and parafoveal word features. Whereas the influence of orthographic or phonological parafoveal information on gaze control is undisputed, there has been no reliable evidence for early parafoveal extraction of semantic information in alphabetic script. Using a novel combination of the gaze-contingent fast-priming and boundary paradigms, we demonstrate semantic preview benefit when a semantically related parafoveal word was available during the initial 125 ms of a fixation on the pre-target word (Experiments 1 and 2). When the target location was made more salient, significant parafoveal semantic priming occurred only at 80 ms (Experiment 3). Finally, with short primes only (20, 40, 60 ms) effects were not significant but numerically in the expected direction for 40 and 60 ms (Experiment 4). In all experiments, fixation durations on the target word increased with prime durations under all conditions. The evidence for extraction of semantic information from the parafoveal word favors an explanation in terms of parallel word processing in reading.
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.
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.
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.
Using the gaze-contingent boundary paradigm with the boundary placed after word n, we manipulated preview of word n+2 for fixations on word n. There was no preview benefit for first-pass reading on word n+2, replicating the results of Rayner, Juhasz, and Brown (2007), but there was a preview benefit on the three-letter word n+1, that is, after the boundary, but before word n+2. Additionally, both word n+1 and word n+2 exhibited parafoveal-on-foveal effects on word n. Thus, during a fixation on word n and given a short word n+1, some information is extracted from word n+2, supporting the hypothesis of distributed processing in the perceptual span.
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.
Moving arms
(2018)
Embodied cognition postulates a bi-directional link between the human body and its cognitive functions. Whether this holds for higher cognitive functions such as problem solving is unknown. We predicted that arm movement manipulations performed by the participants could affect the problem-solving solutions. We tested this prediction in quantitative reasoning tasks that allowed two solutions to each problem (addition or subtraction). In two studies with healthy adults (N=53 and N=50), we found an effect of problem-congruent movements on problem solutions. Consistent with embodied cognition, sensorimotor information gained via right or left arm movements affects the solution in different types of problem-solving tasks.
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.
It sometimes happens that we finish reading a passage of text just to realize that we have no idea what we just read. During these episodes of mindless reading our mind is elsewhere yet the eyes still move across the text. The phenomenon of mindless reading is common and seems to be widely recognized in lay psychology. However, the scientific investigation of mindless reading has long been underdeveloped. Recent progress in research on mindless reading has been based on self-report measures and on treating it as an all-or-none phenomenon (dichotomy-hypothesis). Here, we introduce the levels-of-inattention hypothesis proposing that mindless reading is graded and occurs at different levels of cognitive processing. Moreover, we introduce two new behavioral paradigms to study mindless reading at different levels in the eye-tracking laboratory. First (Chapter 2), we introduce shuffled text reading as a paradigm to approximate states of weak mindless reading experimentally and compare it to reading of normal text. Results from statistical analyses of eye movements that subjects perform in this task qualitatively support the ‘mindless’ hypothesis that cognitive influences on eye movements are reduced and the ‘foveal load’ hypothesis that the response of the zoom lens of attention to local text difficulty is enhanced when reading shuffled text. We introduce and validate an advanced version of the SWIFT model (SWIFT 3) incorporating the zoom lens of attention (Chapter 3) and use it to explain eye movements during shuffled text reading. Simulations of the SWIFT 3 model provide fully quantitative support for the ‘mindless’ and the ‘foveal load’ hypothesis. They moreover demonstrate that the zoom lens is an important concept to explain eye movements across reading and mindless reading tasks. Second (Chapter 4), we introduce the sustained attention to stimulus task (SAST) to catch episodes when external attention spontaneously lapses (i.e., attentional decoupling or mind wandering) via the overlooking of errors in the text and via signal detection analyses of error detection. Analyses of eye movements in the SAST revealed reduced influences from cognitive text processing during mindless reading. Based on these findings, we demonstrate that it is possible to predict states of mindless reading from eye movement recordings online. That cognition is not always needed to move the eyes supports autonomous mechanisms for saccade initiation. Results from analyses of error detection and eye movements provide support to our levels-of-inattention hypothesis that errors at different levels of the text assess different levels of decoupling. Analyses of pupil size in the SAST (Chapter 5) provide further support to the levels of inattention hypothesis and to the decoupling hypothesis that off-line thought is a distinct mode of cognitive functioning that demands cognitive resources and is associated with deep levels of decoupling. The present work demonstrates that the elusive phenomenon of mindless reading can be vigorously investigated in the cognitive laboratory and further incorporated in the theoretical framework of cognitive science.
Dynamical models of cognition play an increasingly important role in driving theoretical and experimental research in psychology. Therefore, parameter estimation, model analysis and comparison of dynamical models are of essential importance. In this article, we propose a maximum likelihood approach for model analysis in a fully dynamical framework that includes time-ordered experimental data. Our methods can be applied to dynamical models for the prediction of discrete behavior (e.g., movement onsets); in particular, we use a dynamical model of saccade generation in scene viewing as a case study for our approach. For this model, the likelihood function can be computed directly by numerical simulation, which enables more efficient parameter estimation including Bayesian inference to obtain reliable estimates and corresponding credible intervals. Using hierarchical models inference is even possible for individual observers. Furthermore, our likelihood approach can be used to compare different models. In our example, the dynamical framework is shown to outperform nondynamical statistical models. Additionally, the likelihood based evaluation differentiates model variants, which produced indistinguishable predictions on hitherto used statistics. Our results indicate that the likelihood approach is a promising framework for dynamical cognitive models.