Jochen Laubrock

Preview benefit and parafoveal-on-foveal effects from word n + 2.

Using the gaze-contingent boundary paradigm with the boundary placed after word n, the experiment manipulated preview of word n + 2 for fixations on word n. There was no preview benefit for 1st-pass reading on word n + 2, replicating the results of K. Rayner, B. J. Juhasz, and S. J. Brown (2007), but there was a preview benefit on the 3-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.

SWIFT explorations of age differences in eye movements during reading

Research on eye movements in reading has made significant advances during the past few years, due to both experimental and computational research. Age effects have not been extensively studied, but the overall pattern suggests more quantitative than qualitative differences in fixation durations and fixation probabilities. Here we focus on age-differential effects of word frequency on reading time and on probabilities of skipping a word or regressing to previous ones. We present an overview of SWIFT [Engbert, R., Nuthmann, A., Richter, E.M., Kliegl, R., 2005. SWIFT: a dynamical model of saccade generation during reading. Psychological Review 112, 777-813], a fully implemented computational model of saccade generation and lexical processing during reading, based on spatially distributed processing over several words. Preliminary simulations of age differences recovered most, but not all experimental effects. Age differences in parameter estimates point towards an important role of visual acuity for oculomotor as well as lexical processing.

Semantic Preview Benefit in Eye Movements during Reading: A Parafoveal Fast-Priming Study.

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 pretarget 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 were 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.

Fixational eye movements predict the perceived direction of ambiguous apparent motion

Neuronal activity in area LIP is correlated with the perceived direction of ambiguous apparent motion (Z. M. Williams, J. C. Elfar, E. N. Eskandar, L. J. Toth, & J. A. Assad, 2003). Here we show that a similar correlation exists for small eye movements made during fixation. A moving dot grid with superimposed fixation point was presented through an aperture. In a motion discrimination task, unambiguous motion was compared with ambiguous motion obtained by shifting the grid by half of the dot distance. In three experiments we show that (a) microsaccadic inhibition, i.e., a drop in microsaccade frequency precedes reports of perceptual flips, (b) microsaccadic inhibition does not accompany simple response changes, and (c) the direction of microsaccades occurring before motion onset biases the subsequent perception of ambiguous motion. We conclude that microsaccades provide a signal on which perceptual judgments rely in the absence of objective disambiguating stimulus information.

Microsaccades are an index of covert attention: commentary on Horowitz, Fine, Fencsik, Yurgenson, and Wolfe (2007).

Horowitz, Fine, Fencsik, Yurgenson, and Wolfe (2007, this issue) investigated the relation between microsaccade congruency (MC, the congruency between the direction of the microsaccade and the location of the target) and reaction time (RT) in a spatial cuing paradigm and concluded that ‘‘fixational eye movements are not an index of covert attention.’’ We show that microsaccade direction is a reliable on-line measure of attention that potentially indexes effects beyond those reflected in RT. In Posner’s (1980) task, the spatial cue is the only objective marker of attention. Therefore, a cue-validity effect is a necessary property of any index of attention. Such an effect has been established for both RT (i.e., the RT cue-validity effect) and microsaccades (i.e., the MC effect; Engbert & Kliegl, 2003; Galfano, Betta, & Turatto, 2004; Hafed & Clark, 2002; Rolfs, Engbert, & Kliegl, 2004, 2005). Directional biases in microsaccades are not just an oculomotor reflex: If a task requires shifts in spatial attention, directional biases are elicited by circular color cues; if the task does not require attentional shifts, directional biases are not elicited even by arrow cues (Engbert & Kliegl, 2003; Laubrock, Engbert, & Kliegl, 2005). Horowitz et al. compared (a) RTs from validly cued trials with microsaccades oriented away from the target and (b) RTs from invalidly cued trials with target-congruent microsaccades, arguing that if microsaccades are useful as measures of attention, then RTs in the latter trials should be faster than RTs in the former trials. Here we show that this result can be obtained even if microsaccades and attention are substantially correlated. Let us assume that microsaccade direction is a valid but imperfect measure of attention and that the probability of a microsaccade being oriented toward the location where attention is deployed, p(microsaccade directionjattention), is .75. Pitting MC against cue validity assumes that attention does not always follow the cue (e.g., because subjects match probabilities; Brunswik, 1939). Let us therefore further assume that the probability that attention does follow the cue, p(attentionjcue), is .8. Given these assumptions, attention and microsaccades will both be directed opposite the target on 15% of the valid-cue trials (.2 .75 of all valid-cue trials), but attention will follow the cue toward the target despite a target-incongruent microsaccade on 20% of the valid-cue trials (.8 .25). Similarly, invalidly cued trials with target-congruent microsaccades will be a mixture containing ‘‘attentional error’’ trials on which microsaccades follow attention toward the target (.2 .75 5 .15 of all invalid-cue trials) and trials on which microsaccades are directed toward the target but attention is not (.8 .25 5 .20). Hence, the cue-validity effect on RT (i.e., benefits and costs of valid and invalid cues, respectively) will dominate theMC effect in the conditions that Horowitz et al. compared. Even if microsaccades are well correlated with attention, this selection of conditions imposes prior odds of 4:1 against finding a benefit of MC in RT. Therefore, showing that RT is slower for trials with valid cues and target-incongruent microsaccades than for trials with invalid cues and target-congruent microsaccades is not evidence against the direction of the microsaccade reflecting covert attention, but a consequence of the cue controlling attention.

Microsaccadic modulation of response times in spatial attention tasks.

Covert shifts of attention are usually reflected in RT differences between responses to valid and invalid cues in the Posner spatial attention task. Such inferences about covert shifts of attention do not control for microsaccades in the cue-target interval. We analyzed the effects of microsaccade orientation on RTs in four conditions, crossing peripheral visual and auditory cues with peripheral visual and auditory discrimination targets. Reaction time was generally faster on trials without microsaccades in the cue-target interval. If microsaccades occurred, the target-location congruency of the last microsaccade in the cue-target interval interacted in a complex way with cue validity. For valid visual cues, irrespective of whether the discrimination target was visual or auditory, target-congruent microsaccades delayed RT. For invalid cues, target-incongruent microsaccades facilitated RTs for visual target discrimination but delayed RT for auditory target discrimination. No reliable effects on RT were associated with auditory cues or with the first microsaccade in the cue-target interval. We discuss theoretical implications on the relation about spatial attention and oculomotor processes.

Eye-voice span during rapid automatized naming of digits and dice in Chinese normal and dyslexic children.

We measured Chinese dyslexic and control childrens eye movements during rapid automatized naming (RAN) with alphanumeric (digits) and symbolic (dice surfaces) stimuli. Both types of stimuli required identical oral responses, controlling for effects associated with speech production. Results showed that naming dice was much slower than naming digits for both groups, but group differences in eye-movement measures and in the eye-voice span (i.e. the distance between the currently fixated item and the voiced item) were generally larger in digit-RAN than in dice-RAN. In addition, dyslexics were less efficient in parafoveal processing in these RAN tasks. Since the two RAN tasks required the same phonological output and on the assumption that naming dice is less practiced than naming digits in general, the results suggest that the translation of alphanumeric visual symbols into phonological codes is less efficient in dyslexic children. The dissociation of the print-to-sound conversion and phonological representation suggests that the degree of automaticity in translation from visual symbols to phonological codes in addition to phonological processing per se is also critical to understanding dyslexia.

Interoceptive focus shapes the experience of time

The perception of time is a fundamental part of human experience. Recent research suggests that the experience of time emerges from emotional and interoceptive (bodily) states as processed in the insular cortex. Whether there is an interaction between the conscious awareness of interoceptive states and time distortions induced by emotions has rarely been investigated so far. We aimed to address this question by the use of a retrospective time estimation task comparing two groups of participants. One group had a focus on interoceptive states and one had a focus on exteroceptive information while watching film clips depicting fear, amusement and neutral content. Main results were that attention to interoceptive processes significantly affected subjective time experience. Fear was accompanied with subjective time dilation that was more pronounced in the group with interoceptive focus, while amusement led to a quicker passage of time which was also increased by interoceptive focus. We conclude that retrospective temporal distortions are directly influenced by attention to bodily responses. These effects might crucially interact with arousal levels. Sympathetic nervous system activation affecting memory build-up might be the decisive factor influencing retrospective time judgments. Our data substantially extend former research findings underscoring the relevance of interoception for the effects of emotional states on subjective time experience.

The eye-voice span during reading aloud

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.

Registering eye movements during reading in Alzheimer’s disease: Difficulties in predicting upcoming words

Reading requires the fine integration of attention, ocular movements, word identification, and language comprehension, among other cognitive parameters. Several of the associated cognitive processes such as working memory and semantic memory are known to be impaired by Alzheimer’s disease (AD). This study analyzes eye movement behavior of 18 patients with probable AD and 40 age-matched controls during Spanish sentence reading. Controls focused mainly on word properties and considered syntactic and semantic structures. At the same time, controls’ knowledge and prediction about sentence meaning and grammatical structure are quite evident when we consider some aspects of visual exploration, such as word skipping, and forward saccades. By contrast, in the AD group, the predictability effect of the upcoming word was absent, visual exploration was less focused, fixations were much longer, and outgoing saccade amplitudes were smaller than those in controls. The altered visual exploration and the absence of a contextual predictability effect might be related to impairments in working memory and long-term memory retrieval functions. These eye movement measures demonstrate considerable sensitivity with respect to evaluating cognitive processes in Alzheimer’s disease. They could provide a user-friendly marker of early disease symptoms and of its posterior progression.