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Olaf Dimigen

Humboldt Universität zu Berlin, Psychology, Post-Doc

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Phone: +49-30-2093-4849
Address: Biologische Psychologie
Institut für Psychologie
Humboldt-Universität zu Berlin
Zum Grossen Windkanal 6
12489 Berlin

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Reinhold Kliegl

Universitaet Potsdam

Charles Clifton

University of Massachusetts Amherst

University of Salzburg

Michael Dambacher

University of Leicester

Hinnerk Eißfeldt

University of Salzburg

Lorenzo Vignali

University of Salzburg

Freie Universität Berlin

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Papers by Olaf Dimigen

Long-Range Reading Regressions Are Accompanied By A P600-Like Brain Potential: Evidence From The Co-Registration Of Erps And Eye Movements

About 15% of reading saccades move the eyes backwards in the text. To study the neurophysiologica... more About 15% of reading saccades move the eyes backwards in the text. To study the neurophysiological correlates of such regressions, we co-registered gaze position and ERPs of 54 subjects during natural, left-to-right reading. Sentences were grammatically diverse but contained no syntactic violations or local ambiguities. Accompanying the onset of long-range regressions, we observed a late centroparietal positivity, closely resembling the P600 component commonly observed for syntactic violations and garden-path sentences in traditional ERP experiments. This suggests that the P600 indexes individual comprehension difficulty or parsing problems even in the absence of syntactic ambiguity. Co-registration of eye movements and ERPs may help to differentiate between regressions caused by oculomotor overshoot, word identification failures, and syntactic parsing problems.

Regression-based analysis of combined EEG and eye-tracking data: Theory and applications

Journal of Vision, 2021

Unfold: An integrated toolbox for overlap correction, non-linear modeling, and regression-based EEG analysis

ABSTRACTElectrophysiological research with event-related brain potentials (ERPs) is increasingly ... more ABSTRACTElectrophysiological research with event-related brain potentials (ERPs) is increasingly moving from simple, strictly orthogonal stimulation paradigms towards more complex, quasi-experimental designs and naturalistic situations that involve fast, multisensory stimulation and complex motor behavior. As a result, electrophysiological responses from subsequent events often overlap with each other. In addition, the recorded neural activity is typically modulated by numerous covariates, which influence the measured responses in a linear or nonlinear fashion. Examples of paradigms where systematic temporal overlap variations and low-level confounds between conditions cannot be avoided include combined EEG/eye-tracking experiments during natural vision, fast multisensory stimulation experiments, and mobile brain/body imaging studies. However, even “traditional”, highly controlled ERP datasets often contain a hidden mix of overlapping activity (e.g. from stimulus onsets, involuntary...

Fixation-related brain activity during semantic integration of object-scene information

Objects are the building blocks of scenes, and for this reason, the time-course of object recogni... more Objects are the building blocks of scenes, and for this reason, the time-course of object recognition has been a key topic of investigation in the vision sciences. It is well known that object meaning is extracted within the first few fixations after scene onset. However, there is conflicting evidence on whether this can occur in extra-foveal vision, or whether foveal vision is required instead. In this study, we addressed this question by co-registering eye-movement and EEG responses of participants performing a change-detection task. Within images of natural scenes, an embedded target object was either consistent or inconsistent with the scene context (e.g., toothpaste vs. flashlight in a bathroom). In the eye-movement behaviour, we analysed the very first saccade during scene exploration, the latency to first fixation on the target object, as well as the duration of the first fixation on it. In the fixation-related brain potentials (FRP), we compared the activity elicited by sema...

Optimized ICA-based removal of ocular EEG artifacts from free viewing experiments

Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vis... more Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vision, but the resulting recordings are also heavily contaminated by activity of the eye balls, eye lids, and extraocular muscles. While Independent Component Analysis (ICA) is commonly used to suppress these ocular artifacts, its performance under free viewing conditions has not been systematically evaluated and many published findings display residual artifacts. Here I evaluated and optimized ICA-based correction for two tasks with unconstrained eye movements: visual search in images and sentence reading. In a first step, four parameters of the ICA pipeline were systematically varied: the (1) high-pass and (2) low-pass filter applied to the training data, (3) the proportion of training data containing myogenic saccadic spike potentials (SP), and (4) the threshold for eye tracker-based component rejection. In a second step, the eye-tracker was used to objectively quantify correction quali...

Lateralization of posterior alpha EEG reflects the distribution of spatial attention during saccadic reading

Psychophysiology, Jun 27, 2017

Visuospatial attention is an important mechanism in reading that governs the uptake of informatio... more Visuospatial attention is an important mechanism in reading that governs the uptake of information from foveal and parafoveal regions of the visual field. However, the spatiotemporal dynamics of how attention is allocated during eye fixations are not completely understood. The current study explored the use of EEG alpha-band oscillations to investigate the spatial distribution of attention during reading. We reanalyzed two data sets, focusing on the lateralization of alpha activity at posterior scalp sites. In each experiment, participants read short lists of German nouns in two paradigms: either by freely moving their eyes (saccadic reading) or by fixating the screen center while the text moved passively from right to left at the same average speed (RSVP paradigm). In both paradigms, upcoming words were either visible or masked, and foveal processing load was manipulated by varying the words' lexical frequencies. Posterior alpha lateralization revealed a sustained rightward bia...

Neural Correlates of Word Recognition: A Systematic Comparison of Natural Reading and Rapid Serial Visual Presentation

Journal of cognitive neuroscience, 2016

Neural correlates of word recognition are commonly studied with (rapid) serial visual presentatio... more Neural correlates of word recognition are commonly studied with (rapid) serial visual presentation (RSVP), a condition that eliminates three fundamental properties of natural reading: parafoveal preprocessing, saccade execution, and the fast changes in attentional processing load occurring from fixation to fixation. We combined eye-tracking and EEG to systematically investigate the impact of all three factors on brain-electric activity during reading. Participants read lists of words either actively with eye movements (eliciting fixation-related potentials) or maintained fixation while the text moved passively through foveal vision at a matched pace (RSVP-with-flankers paradigm, eliciting ERPs). The preview of the upcoming word was manipulated by changing the number of parafoveally visible letters. Processing load was varied by presenting words of varying lexical frequency. We found that all three factors have strong interactive effects on the brain's responses to words: Once a ...

Reading training by means of disappearing text: effects on reading performance and eye movements

Reading and Writing, 2016

Abstract The Reading Acceleration Program (RAP), which uses adaptively increasing text erasure ra... more Abstract The Reading Acceleration Program (RAP), which uses adaptively increasing text erasure rates to enforce reading rate improvements, has been positively evaluated in various languages, reader and age groups. The current study compared the established incremental increase of text erasure rate with a training using fixed erasure rates in two groups of young, non-impaired German adults. Eye-tracking measures prior and post training examined training-related changes of eye-movement patterns. Equal gains in reading performance in both training groups led to the conclusion that not the adaptive increase but already text erasure at fixed rates provides an economically efficient tool for the enhancement of reading rates. Furthermore, eye-tracking results suggest that text erasure training affects word processing not only at one specific level, but simultaneously at pre-lexical, lexical, and post-lexical stages. Although these outcomes are promising, further research is necessary to determine the optimal individual erasure rates that preserve good comprehension at varying levels of text difficulty and in different orthographies.

Parafoveal processing in reading Chinese sentences: Evidence from event-related brain potentials

Psychophysiology, Jan 20, 2015

Natural reading involves the preprocessing of upcoming words, resulting in shorter fixations on w... more Natural reading involves the preprocessing of upcoming words, resulting in shorter fixations on words visible in the parafovea during preceding fixations. While this preview benefit is established in behavior, its brain-electric correlates have only recently been investigated. Using fixation-related potentials, an attenuation of the occipitotemporal N1 component for words that were parafoveally visible during preceding fixations has been demonstrated. In contrast, another study, using an RSVP paradigm with parafoveal flanker words, observed no such general preview benefit in ERPs, but instead reported N400 effects triggered by semantically incongruous parafoveal words. To follow up on these discrepant findings and to extend them to a nonalphabetic writing system, we conducted two ERP experiments with Chinese readers using the RSVP-with-flankers paradigm and rigorous fixation control via eye tracking. We replicate robust parafoveal N400 semantic congruency effects in Chinese particip...

Are individual differences in reading speed related to extrafoveal visual acuity and crowding?

PloS one, 2015

Readers differ considerably in their speed of self-paced reading. One factor known to influence f... more Readers differ considerably in their speed of self-paced reading. One factor known to influence fixation durations in reading is the preprocessing of words in parafoveal vision. Here we investigated whether individual differences in reading speed or the amount of information extracted from upcoming words (the preview benefit) can be explained by basic differences in extrafoveal vision-i.e., the ability to recognize peripheral letters with or without the presence of flanking letters. Forty participants were given an adaptive test to determine their eccentricity thresholds for the identification of letters presented either in isolation (extrafoveal acuity) or flanked by other letters (crowded letter recognition). In a separate eye-tracking experiment, the same participants read lists of words from left to right, while the preview of the upcoming words was manipulated with the gaze-contingent moving window technique. Relationships between dependent measures were analyzed on the observa...

Microsaccade-related brain potentials signal the focus of visuospatial attention

NeuroImage, 2015

Covert shifts of visuospatial attention are traditionally assumed to occur in the absence of ocul... more Covert shifts of visuospatial attention are traditionally assumed to occur in the absence of oculomotor behavior. In contrast, recent behavioral studies have linked attentional cueing effects to the occurrence of microsaccades, small eye movements executed involuntarily during attempted fixation. Here we used a new type of electrophysiological marker to explore the attention-microsaccade relationship, the visual brain activity evoked by the microsaccade itself. By shifting the retinal image, microsaccades frequently elicit neural responses throughout the visual pathway, scalp-recordable in the human EEG as a microsaccade-related potential (mSRP). Although mSRPs contain similar signal components (P1/N1) as traditional visually-evoked potentials (VEPs), it is unknown whether they are also influenced by cognition. Based on established findings that VEPs are amplified for visual inputs at currently attended locations, we expected a selective gain-modulation also for mSRPs. Eye movements...

Stimulus onset asynchrony and the timeline of word recognition: Event-related potentials during sentence reading

Neuropsychologia, 2012

Please note that this unproofed preprint may be subject to minor changes.

Trans-saccadic parafoveal preview benefits in fluent reading: A study with fixation-related brain potentials

NeuroImage, 2012

Order Patterns Networks (ORPAN)—a method to estimate time-evolving functional connectivity from multivariate time series

Frontiers in Computational Neuroscience, 2012

Complex networks provide an excellent framework for studying the function of the human brain acti... more Complex networks provide an excellent framework for studying the function of the human brain activity. Yet estimating functional networks from measured signals is not trivial, especially if the data is non-stationary and noisy as it is often the case with physiological recordings. In this article we propose a method that uses the local rank structure of the data to define functional links in terms of identical rank structures. The method yields temporal sequences of networks which permits to trace the evolution of the functional connectivity during the time course of the observation. We demonstrate the potentials of this approach with model data as well as with experimental data from an electrophysiological study on language processing.

Oculomotor control, brain potentials, and timelines of word recognition during natural reading

Current Trends in Eye Tracking Research, 2014

312 semantically associated pairs of German nouns with equal word length

This document describes the word materials used in: Dimigen, O., Kliegl, R., Sommer, W. (2012). T... more This document describes the word materials used in: Dimigen, O., Kliegl, R., Sommer, W. (2012). Trans-saccadic parafoveal preview ben-efits in fluent reading: A study with fixation-related brain potentials. Neuroimage. DOI:10.1016/j.neuroimage.2012.04.006 Materials are provided as a.csv text file (comma separated values) which contains the set of 312 German noun pairs together with full word statistics and rating data. The organization of the.csv file is described further below. The materials may be freely used for research purposes, provided that the original publication is cited. 1 Construction of word pairs Preview-targets pairs The basis for the construction of target nouns and their preview nouns was a set of 312 pairs of semantically associated German nouns (e.g. Frau Dame, woman lady; or Wald Baum, forest tree). Pairs were selected from a larger set of pairs after a semantic rating (see below). The nouns of each pair had the same length (between 4-7 letters, M = 5.4) and were...

Is there magnocellular facilitation of early neural processes underlying visual word recognition? Evidence from masked repetition priming with ERPs

An influential theory in the field of visual object recognition proposes that fast magnocellular ... more An influential theory in the field of visual object recognition proposes that fast magnocellular (M) information facilitates neural processing of spatially more fine-grained but slower parvocellular (P) information. While written words can be considered as a special type of visual objects, it is unknown whether magnocellular facilitation also plays a role in reading. We used a masked priming paradigm that has been shown to result in neural facilitation in visual word processing and tested whether these facilitating effects are mediated by the magnocellular system. In two experiments, we manipulated the influence of magnocellular and parvocellular systems on visual processing of a contextually predictable target character by contrasting high versus low spatial frequency and luminance versus color contrast, respectively. In addition, unchanged (normal) primes were included in both experiments as a manipulation check. As expected, unchanged primes elicited typical repetition effects in...

Optimizing the ICA-based removal of ocular EEG artifacts from free viewing experiments

NeuroImage

Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vis... more Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vision, but the resulting recordings are also heavily contaminated by activity of the eye balls, eye lids, and extraocular muscles. While Independent Component Analysis (ICA) is commonly used to suppress these ocular artifacts, its performance under free viewing conditions has not been systematically evaluated and many published reports contain residual artifacts. Here I evaluated and optimized ICA-based correction for two tasks with unconstrained eye movements: visual search in images and sentence reading. In a first step, four parameters of the ICA pipeline were varied orthogonally: the (1) high-pass and (2) low-pass filter applied to the training data, (3) the proportion of training data containing myogenic saccadic spike potentials (SP), and (4) the threshold for eye tracker-based component rejection. In a second step, the eye-tracker was used to objectively quantify correction quality of each ICA solution, both in terms of undercorrection (residual artifacts) and overcorrection (removal of neurogenic activity). As a benchmark, results were compared to those obtained with an alternative spatial filter, Multiple Source Eye Correction (MSEC). With commonly used settings, Infomax ICA not only left artifacts in the data, but also distorted neurogenic activity during eye movement-free intervals. However, correction could be strongly improved by training the ICA on optimally filtered data in which SPs were massively overweighted. With optimized procedures, ICA removed virtually all artifacts, including the SP and its associated spectral broadband artifact from both viewing paradigms, with little distortion of neural activity. It also outperformed MSEC in terms of SP correction. Matlab code is provided.

Analyzing combined eye-tracking/EEG experiments with (non)linear deconvolution models

Fixation-related potentials (FRPs), neural responses aligned to saccade offsets, are a promising ... more Fixation-related potentials (FRPs), neural responses aligned to saccade offsets, are a promising tool to study the dynamics of attention and cognition under natural viewing conditions. In the past, four methodological problems have complicated the analysis of combined eye-tracking and EEG experiments: (i) the synchronization of data streams, (ii) the removal of ocular artifacts, (iii) the condition-specific temporal overlap between the brain responses evoked by consecutive fixations, (iv) and the fact that numerous low-level stimulus and saccade properties also influence the post-saccadic neural responses. While effective solutions exist for the first two problems, the latter ones are only beginning to be addressed. In the current paper, we present and review a unified framework to deconvolve overlapping potentials and control for linear and nonlinear confounds on the FRPs. An open software implementation is provided for all suggested procedures. We then demonstrate the advantages o...

1 Manuscript accepted for publication in The Journal of Neuroscience (unedited proof) Behavioral/Systems/Cognitive Human Microsaccade-Related Visual Brain Responses

Microsaccades are very small, involuntary flicks in eye position that occur on average once or tw... more Microsaccades are very small, involuntary flicks in eye position that occur on average once or twice per second during attempted visual fixation. Microsaccades give rise to EMG eye muscle spikes that can distort the spectrum of the scalp EEG and mimic increases in gamma band power. Here we demonstrate that microsaccades are also accompanied by genuine and sizeable cortical activity, manifested in the EEG. In three experiments, highresolution eye movements were co-recorded with the EEG; during sustained fixation of checkerboard and face stimuli, and in a standard visual oddball task that required the counting of target stimuli. Results show that microsaccades as small as 0.15° generate a field potential over occipital cortex and midcentral scalp sites 100-140 ms after movement onset, which resembles the visual lambda response evoked by larger voluntary saccades. This challenges the standard assumption of human brain imaging studies that saccade-related brain activity is precluded by fixation, even when fully complied with. Instead, additional cortical potentials from microsaccades were present in 86% of the oddball task trials and of similar amplitude as the visual response to stimulus onset. Furthermore, microsaccade probability varied systematically according to the proportion of target stimuli in the oddball task, causing modulations of late stimulus-locked ERP components. Microsaccades present an unrecognized source of visual brain signal that is of interest for vision research and may have influenced the data of many ERP and neuroimaging studies.

Long-Range Reading Regressions Are Accompanied By A P600-Like Brain Potential: Evidence From The Co-Registration Of Erps And Eye Movements

About 15% of reading saccades move the eyes backwards in the text. To study the neurophysiologica... more About 15% of reading saccades move the eyes backwards in the text. To study the neurophysiological correlates of such regressions, we co-registered gaze position and ERPs of 54 subjects during natural, left-to-right reading. Sentences were grammatically diverse but contained no syntactic violations or local ambiguities. Accompanying the onset of long-range regressions, we observed a late centroparietal positivity, closely resembling the P600 component commonly observed for syntactic violations and garden-path sentences in traditional ERP experiments. This suggests that the P600 indexes individual comprehension difficulty or parsing problems even in the absence of syntactic ambiguity. Co-registration of eye movements and ERPs may help to differentiate between regressions caused by oculomotor overshoot, word identification failures, and syntactic parsing problems.

Regression-based analysis of combined EEG and eye-tracking data: Theory and applications

Journal of Vision, 2021

Unfold: An integrated toolbox for overlap correction, non-linear modeling, and regression-based EEG analysis

ABSTRACTElectrophysiological research with event-related brain potentials (ERPs) is increasingly ... more ABSTRACTElectrophysiological research with event-related brain potentials (ERPs) is increasingly moving from simple, strictly orthogonal stimulation paradigms towards more complex, quasi-experimental designs and naturalistic situations that involve fast, multisensory stimulation and complex motor behavior. As a result, electrophysiological responses from subsequent events often overlap with each other. In addition, the recorded neural activity is typically modulated by numerous covariates, which influence the measured responses in a linear or nonlinear fashion. Examples of paradigms where systematic temporal overlap variations and low-level confounds between conditions cannot be avoided include combined EEG/eye-tracking experiments during natural vision, fast multisensory stimulation experiments, and mobile brain/body imaging studies. However, even “traditional”, highly controlled ERP datasets often contain a hidden mix of overlapping activity (e.g. from stimulus onsets, involuntary...

Fixation-related brain activity during semantic integration of object-scene information

Objects are the building blocks of scenes, and for this reason, the time-course of object recogni... more Objects are the building blocks of scenes, and for this reason, the time-course of object recognition has been a key topic of investigation in the vision sciences. It is well known that object meaning is extracted within the first few fixations after scene onset. However, there is conflicting evidence on whether this can occur in extra-foveal vision, or whether foveal vision is required instead. In this study, we addressed this question by co-registering eye-movement and EEG responses of participants performing a change-detection task. Within images of natural scenes, an embedded target object was either consistent or inconsistent with the scene context (e.g., toothpaste vs. flashlight in a bathroom). In the eye-movement behaviour, we analysed the very first saccade during scene exploration, the latency to first fixation on the target object, as well as the duration of the first fixation on it. In the fixation-related brain potentials (FRP), we compared the activity elicited by sema...

Optimized ICA-based removal of ocular EEG artifacts from free viewing experiments

Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vis... more Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vision, but the resulting recordings are also heavily contaminated by activity of the eye balls, eye lids, and extraocular muscles. While Independent Component Analysis (ICA) is commonly used to suppress these ocular artifacts, its performance under free viewing conditions has not been systematically evaluated and many published findings display residual artifacts. Here I evaluated and optimized ICA-based correction for two tasks with unconstrained eye movements: visual search in images and sentence reading. In a first step, four parameters of the ICA pipeline were systematically varied: the (1) high-pass and (2) low-pass filter applied to the training data, (3) the proportion of training data containing myogenic saccadic spike potentials (SP), and (4) the threshold for eye tracker-based component rejection. In a second step, the eye-tracker was used to objectively quantify correction quali...

Lateralization of posterior alpha EEG reflects the distribution of spatial attention during saccadic reading

Psychophysiology, Jun 27, 2017

Visuospatial attention is an important mechanism in reading that governs the uptake of informatio... more Visuospatial attention is an important mechanism in reading that governs the uptake of information from foveal and parafoveal regions of the visual field. However, the spatiotemporal dynamics of how attention is allocated during eye fixations are not completely understood. The current study explored the use of EEG alpha-band oscillations to investigate the spatial distribution of attention during reading. We reanalyzed two data sets, focusing on the lateralization of alpha activity at posterior scalp sites. In each experiment, participants read short lists of German nouns in two paradigms: either by freely moving their eyes (saccadic reading) or by fixating the screen center while the text moved passively from right to left at the same average speed (RSVP paradigm). In both paradigms, upcoming words were either visible or masked, and foveal processing load was manipulated by varying the words' lexical frequencies. Posterior alpha lateralization revealed a sustained rightward bia...

Neural Correlates of Word Recognition: A Systematic Comparison of Natural Reading and Rapid Serial Visual Presentation

Journal of cognitive neuroscience, 2016

Neural correlates of word recognition are commonly studied with (rapid) serial visual presentatio... more Neural correlates of word recognition are commonly studied with (rapid) serial visual presentation (RSVP), a condition that eliminates three fundamental properties of natural reading: parafoveal preprocessing, saccade execution, and the fast changes in attentional processing load occurring from fixation to fixation. We combined eye-tracking and EEG to systematically investigate the impact of all three factors on brain-electric activity during reading. Participants read lists of words either actively with eye movements (eliciting fixation-related potentials) or maintained fixation while the text moved passively through foveal vision at a matched pace (RSVP-with-flankers paradigm, eliciting ERPs). The preview of the upcoming word was manipulated by changing the number of parafoveally visible letters. Processing load was varied by presenting words of varying lexical frequency. We found that all three factors have strong interactive effects on the brain's responses to words: Once a ...

Reading training by means of disappearing text: effects on reading performance and eye movements

Reading and Writing, 2016

Abstract The Reading Acceleration Program (RAP), which uses adaptively increasing text erasure ra... more Abstract The Reading Acceleration Program (RAP), which uses adaptively increasing text erasure rates to enforce reading rate improvements, has been positively evaluated in various languages, reader and age groups. The current study compared the established incremental increase of text erasure rate with a training using fixed erasure rates in two groups of young, non-impaired German adults. Eye-tracking measures prior and post training examined training-related changes of eye-movement patterns. Equal gains in reading performance in both training groups led to the conclusion that not the adaptive increase but already text erasure at fixed rates provides an economically efficient tool for the enhancement of reading rates. Furthermore, eye-tracking results suggest that text erasure training affects word processing not only at one specific level, but simultaneously at pre-lexical, lexical, and post-lexical stages. Although these outcomes are promising, further research is necessary to determine the optimal individual erasure rates that preserve good comprehension at varying levels of text difficulty and in different orthographies.

Parafoveal processing in reading Chinese sentences: Evidence from event-related brain potentials

Psychophysiology, Jan 20, 2015

Natural reading involves the preprocessing of upcoming words, resulting in shorter fixations on w... more Natural reading involves the preprocessing of upcoming words, resulting in shorter fixations on words visible in the parafovea during preceding fixations. While this preview benefit is established in behavior, its brain-electric correlates have only recently been investigated. Using fixation-related potentials, an attenuation of the occipitotemporal N1 component for words that were parafoveally visible during preceding fixations has been demonstrated. In contrast, another study, using an RSVP paradigm with parafoveal flanker words, observed no such general preview benefit in ERPs, but instead reported N400 effects triggered by semantically incongruous parafoveal words. To follow up on these discrepant findings and to extend them to a nonalphabetic writing system, we conducted two ERP experiments with Chinese readers using the RSVP-with-flankers paradigm and rigorous fixation control via eye tracking. We replicate robust parafoveal N400 semantic congruency effects in Chinese particip...

Are individual differences in reading speed related to extrafoveal visual acuity and crowding?

PloS one, 2015

Readers differ considerably in their speed of self-paced reading. One factor known to influence f... more Readers differ considerably in their speed of self-paced reading. One factor known to influence fixation durations in reading is the preprocessing of words in parafoveal vision. Here we investigated whether individual differences in reading speed or the amount of information extracted from upcoming words (the preview benefit) can be explained by basic differences in extrafoveal vision-i.e., the ability to recognize peripheral letters with or without the presence of flanking letters. Forty participants were given an adaptive test to determine their eccentricity thresholds for the identification of letters presented either in isolation (extrafoveal acuity) or flanked by other letters (crowded letter recognition). In a separate eye-tracking experiment, the same participants read lists of words from left to right, while the preview of the upcoming words was manipulated with the gaze-contingent moving window technique. Relationships between dependent measures were analyzed on the observa...

Microsaccade-related brain potentials signal the focus of visuospatial attention

NeuroImage, 2015

Covert shifts of visuospatial attention are traditionally assumed to occur in the absence of ocul... more Covert shifts of visuospatial attention are traditionally assumed to occur in the absence of oculomotor behavior. In contrast, recent behavioral studies have linked attentional cueing effects to the occurrence of microsaccades, small eye movements executed involuntarily during attempted fixation. Here we used a new type of electrophysiological marker to explore the attention-microsaccade relationship, the visual brain activity evoked by the microsaccade itself. By shifting the retinal image, microsaccades frequently elicit neural responses throughout the visual pathway, scalp-recordable in the human EEG as a microsaccade-related potential (mSRP). Although mSRPs contain similar signal components (P1/N1) as traditional visually-evoked potentials (VEPs), it is unknown whether they are also influenced by cognition. Based on established findings that VEPs are amplified for visual inputs at currently attended locations, we expected a selective gain-modulation also for mSRPs. Eye movements...

Stimulus onset asynchrony and the timeline of word recognition: Event-related potentials during sentence reading

Neuropsychologia, 2012

Please note that this unproofed preprint may be subject to minor changes.

Trans-saccadic parafoveal preview benefits in fluent reading: A study with fixation-related brain potentials

NeuroImage, 2012

Order Patterns Networks (ORPAN)—a method to estimate time-evolving functional connectivity from multivariate time series

Frontiers in Computational Neuroscience, 2012

Complex networks provide an excellent framework for studying the function of the human brain acti... more Complex networks provide an excellent framework for studying the function of the human brain activity. Yet estimating functional networks from measured signals is not trivial, especially if the data is non-stationary and noisy as it is often the case with physiological recordings. In this article we propose a method that uses the local rank structure of the data to define functional links in terms of identical rank structures. The method yields temporal sequences of networks which permits to trace the evolution of the functional connectivity during the time course of the observation. We demonstrate the potentials of this approach with model data as well as with experimental data from an electrophysiological study on language processing.

Oculomotor control, brain potentials, and timelines of word recognition during natural reading

Current Trends in Eye Tracking Research, 2014

312 semantically associated pairs of German nouns with equal word length

This document describes the word materials used in: Dimigen, O., Kliegl, R., Sommer, W. (2012). T... more This document describes the word materials used in: Dimigen, O., Kliegl, R., Sommer, W. (2012). Trans-saccadic parafoveal preview ben-efits in fluent reading: A study with fixation-related brain potentials. Neuroimage. DOI:10.1016/j.neuroimage.2012.04.006 Materials are provided as a.csv text file (comma separated values) which contains the set of 312 German noun pairs together with full word statistics and rating data. The organization of the.csv file is described further below. The materials may be freely used for research purposes, provided that the original publication is cited. 1 Construction of word pairs Preview-targets pairs The basis for the construction of target nouns and their preview nouns was a set of 312 pairs of semantically associated German nouns (e.g. Frau Dame, woman lady; or Wald Baum, forest tree). Pairs were selected from a larger set of pairs after a semantic rating (see below). The nouns of each pair had the same length (between 4-7 letters, M = 5.4) and were...

Is there magnocellular facilitation of early neural processes underlying visual word recognition? Evidence from masked repetition priming with ERPs

An influential theory in the field of visual object recognition proposes that fast magnocellular ... more An influential theory in the field of visual object recognition proposes that fast magnocellular (M) information facilitates neural processing of spatially more fine-grained but slower parvocellular (P) information. While written words can be considered as a special type of visual objects, it is unknown whether magnocellular facilitation also plays a role in reading. We used a masked priming paradigm that has been shown to result in neural facilitation in visual word processing and tested whether these facilitating effects are mediated by the magnocellular system. In two experiments, we manipulated the influence of magnocellular and parvocellular systems on visual processing of a contextually predictable target character by contrasting high versus low spatial frequency and luminance versus color contrast, respectively. In addition, unchanged (normal) primes were included in both experiments as a manipulation check. As expected, unchanged primes elicited typical repetition effects in...

Optimizing the ICA-based removal of ocular EEG artifacts from free viewing experiments

NeuroImage

Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vis... more Combining EEG with eye-tracking is a promising approach to study neural correlates of natural vision, but the resulting recordings are also heavily contaminated by activity of the eye balls, eye lids, and extraocular muscles. While Independent Component Analysis (ICA) is commonly used to suppress these ocular artifacts, its performance under free viewing conditions has not been systematically evaluated and many published reports contain residual artifacts. Here I evaluated and optimized ICA-based correction for two tasks with unconstrained eye movements: visual search in images and sentence reading. In a first step, four parameters of the ICA pipeline were varied orthogonally: the (1) high-pass and (2) low-pass filter applied to the training data, (3) the proportion of training data containing myogenic saccadic spike potentials (SP), and (4) the threshold for eye tracker-based component rejection. In a second step, the eye-tracker was used to objectively quantify correction quality of each ICA solution, both in terms of undercorrection (residual artifacts) and overcorrection (removal of neurogenic activity). As a benchmark, results were compared to those obtained with an alternative spatial filter, Multiple Source Eye Correction (MSEC). With commonly used settings, Infomax ICA not only left artifacts in the data, but also distorted neurogenic activity during eye movement-free intervals. However, correction could be strongly improved by training the ICA on optimally filtered data in which SPs were massively overweighted. With optimized procedures, ICA removed virtually all artifacts, including the SP and its associated spectral broadband artifact from both viewing paradigms, with little distortion of neural activity. It also outperformed MSEC in terms of SP correction. Matlab code is provided.

Analyzing combined eye-tracking/EEG experiments with (non)linear deconvolution models

Fixation-related potentials (FRPs), neural responses aligned to saccade offsets, are a promising ... more Fixation-related potentials (FRPs), neural responses aligned to saccade offsets, are a promising tool to study the dynamics of attention and cognition under natural viewing conditions. In the past, four methodological problems have complicated the analysis of combined eye-tracking and EEG experiments: (i) the synchronization of data streams, (ii) the removal of ocular artifacts, (iii) the condition-specific temporal overlap between the brain responses evoked by consecutive fixations, (iv) and the fact that numerous low-level stimulus and saccade properties also influence the post-saccadic neural responses. While effective solutions exist for the first two problems, the latter ones are only beginning to be addressed. In the current paper, we present and review a unified framework to deconvolve overlapping potentials and control for linear and nonlinear confounds on the FRPs. An open software implementation is provided for all suggested procedures. We then demonstrate the advantages o...

1 Manuscript accepted for publication in The Journal of Neuroscience (unedited proof) Behavioral/Systems/Cognitive Human Microsaccade-Related Visual Brain Responses

Microsaccades are very small, involuntary flicks in eye position that occur on average once or tw... more Microsaccades are very small, involuntary flicks in eye position that occur on average once or twice per second during attempted visual fixation. Microsaccades give rise to EMG eye muscle spikes that can distort the spectrum of the scalp EEG and mimic increases in gamma band power. Here we demonstrate that microsaccades are also accompanied by genuine and sizeable cortical activity, manifested in the EEG. In three experiments, highresolution eye movements were co-recorded with the EEG; during sustained fixation of checkerboard and face stimuli, and in a standard visual oddball task that required the counting of target stimuli. Results show that microsaccades as small as 0.15° generate a field potential over occipital cortex and midcentral scalp sites 100-140 ms after movement onset, which resembles the visual lambda response evoked by larger voluntary saccades. This challenges the standard assumption of human brain imaging studies that saccade-related brain activity is precluded by fixation, even when fully complied with. Instead, additional cortical potentials from microsaccades were present in 86% of the oddball task trials and of similar amplitude as the visual response to stimulus onset. Furthermore, microsaccade probability varied systematically according to the proportion of target stimuli in the oddball task, causing modulations of late stimulus-locked ERP components. Microsaccades present an unrecognized source of visual brain signal that is of interest for vision research and may have influenced the data of many ERP and neuroimaging studies.

Klieg.etal.Chapter.312849_1_En_10_Chapter_ProofPDF.pdf

Reading requires the orchestration of vision, attention, and language processes, usually along wi... more Reading requires the orchestration of vision, attention, and language processes, usually along with the programming of eye movements. The co-registration of eye movements and electroencephalography (EEG) during natural reading promises to deliver two complementary sets of information. Fixation durations reflect the difficulty of sublexical, lexical, and sentence-level properties, such as the frequency and predictability of the fixated word and (at least) its left and right neighbors; they reveal space-related constraints of distributed processing in the perceptual span. Co-registered fixationrelated potentials (FRPs) yield time-related constraints of word recognition within fixation durations. Effects of word frequency and predictability in FRPs are shown to be qualitatively similar to those in event-related potentials (ERPs) measured during serial visual presentation of sentence words. However, FRPs and ERPs differ with respect to the timelines associated with frequency and predictability effects. It is anticipated that space-related and timerelated constraints of word recognition during reading will guide the further development of computational models of eye-movement control during reading as well as their integration with computational models of (isolated) word recognition. R. Kliegl et al. Fig. 1 Illustration of top-down and bottom-up processing in reading: word predictability indexes top-down and word frequency for bottom-up processes Oculomotor Control, Brain Potentials, and Timelines … Fig. 2 Frequency and predictability effects on single fixation durations (FDs) during reading of German sentences. (Kliegl et al. 2006) Fig. 3 Frequency and predictability effects on N400-ERP amplitudes during reading German sentences. (Dambacher et al. 2006)