Christof Körner

Finding a new target in an old display: evidence for a memory recency effect in visual search.

Visual search often involves searching the same environment, consecutively, for a number of different targets. Here we investigate the extent to which search benefits from such previous exposure. In the experiment participants searched the same display consecutively for two different targets. Manual responses were faster in the second search than the first search regardless of whether a target was present or absent in the second search. Eye movement recordings demonstrated that the time necessary to find a target letter in the second search depended on when that letter was last fixated in the previous search. This fixation recency effect lasted for about four fixations. In addition, when a target was absent during the second search, participants were less likely to refixate a distractor if it had been recently fixated in the previous search and refixations tended to also occur later on in the search. These results provide evidence for a limited capacity short-term memory store in this kind of visual search.

Speed of comprehension of visualized ordered sets

The authors investigated the effects of visual properties of hierarchical graphs on speed of comprehension: planarity (crossing of lines), slopes (orientation of lines), and levels (adjustment of dots). In each of 4 experiments, 30 participants responded to interpretive questions that required comparisons among the elements of the graph. Knowledge provided to participants differed across Experiments 1a, 1b, and 1c; question demands varied in Experiment 2. Analysis of response latencies showed that crossing of lines is the most influential variable independent of orientation, dot adjustment, and question demands. Speed of comprehension decreased with increasing question demands. When question demands were high, orientation of lines also had an effect on speed of comprehension. Preliminary conclusions for the presentation of hierarchical graphs are drawn.

Visual search in the real world: evidence for the formation of distractor representations.

Visual search in the real world often requires that we search the same environment a number of times for different targets. What is the fate of information about fixated distractor objects during these searches? Here, participants searched the same array of real objects on a tabletop twice for two different targets successively whilst wearing a head-mounted eye-tracker. We found that fixating an object when it was a distractor in the first search facilitated search for that same object when it became the target in the second search. The results suggest that the location and identity of fixated distractor objects are represented to a level that guides subsequent searches, even when this information is not required at the time of fixation.

Eye movements reflect and shape strategies in fraction comparison

The comparison of fractions is a difficult task that can often be facilitated by separately comparing components (numerators and denominators) of the fractions—that is, by applying so-called component-based strategies. The usefulness of such strategies depends on the type of fraction pair to be compared. We investigated the temporal organization and the flexibility of strategy deployment in fraction comparison by evaluating sequences of eye movements in 20 young adults. We found that component-based strategies could account for the response times and the overall number of fixations observed for the different fraction pairs. The analysis of eye movement sequences showed that the initial eye movements in a trial were characterized by stereotypical scanning patterns indicative of an exploratory phase that served to establish the kind of fraction pair presented. Eye movements that followed this phase adapted to the particular type of fraction pair and indicated the deployment of specific comparison strategies. These results demonstrate that participants employ eye movements systematically to support strategy use in fraction comparison. Participants showed a remarkable flexibility to adapt to the most efficient strategy on a trial-by-trial basis. Our results confirm the value of eye movement measurements in the exploration of strategic adaptation in complex tasks.

Looking for ideas: Eye behavior during goal-directed internally focused cognition

Humans have a highly developed visual system, yet we spend a high proportion of our time awake ignoring the visual world and attending to our own thoughts. The present study examined eye movement characteristics of goal-directed internally focused cognition. Deliberate internally focused cognition was induced by an idea generation task. A letter-by-letter reading task served as external task. Idea generation (vs. reading) was associated with more and longer blinks and fewer microsaccades indicating an attenuation of visual input. Idea generation was further associated with more and shorter fixations, more saccades and saccades with higher amplitudes as well as heightened stimulus-independent variation of eye vergence. The latter results suggest a coupling of eye behavior to internally generated information and associated cognitive processes, i.e. searching for ideas. Our results support eye behavior patterns as indicators of goal-directed internally focused cognition through mechanisms of attenuation of visual input and coupling of eye behavior to internally generated information.

Sequential effects in continued visual search: Using fixation‐related potentials to compare distractor processing before and after target detection

To search for a target in a complex environment is an everyday behavior that ends with finding the target. When we search for two identical targets, however, we must continue the search after finding the first target and memorize its location. We used fixation-related potentials to investigate the neural correlates of different stages of the search, that is, before and after finding the first target. Having found the first target influenced subsequent distractor processing. Compared to distractor fixations before the first target fixation, a negative shift was observed for three subsequent distractor fixations. These results suggest that processing a target in continued search modulates the brains response, either transiently by reflecting temporary working memory processes or permanently by reflecting working memory retention.

Eye Behavior Associated with Internally versus Externally Directed Cognition

What do our eyes do when we are focused on internal representations such as during imagination or planning? Evidence from mind wandering research suggests that spontaneous shifts from externally directed cognition (EDC) to internally directed cognition (IDC) involves oculomotor changes indicative of visual disengagement. In the present study, we investigated potential differences in eye behavior between goal-directed forms of IDC and EDC. To this end, we manipulated the focus of attention (internal versus external) in two demanding cognitive tasks (anagram and sentence generation). IDC was associated with fewer and longer fixations and higher variability in pupil diameter and eye vergence compared to EDC, suggesting reduced visual scanning and higher spontaneous eye activity. IDC was further related to longer blinks, lower microsaccade frequency, and a lower angle of eye vergence. These latter changes appear conducive to attenuate visual input and thereby shield ongoing internal processes from external distraction. Together, these findings suggest that IDC is accompanied by characteristic eye behavior that reflects a decoupling of attention from external events and serves gating out visual input.

The Relation between Reading Skills and Eye Movement Patterns in Adolescent Readers : Evidence from a Regular Orthography

Over the past decades, the relation between reading skills and eye movement behavior has been well documented in English-speaking cohorts. As English and German differ substantially with regard to orthographic complexity (i.e. grapheme-phoneme correspondence), we aimed to delineate specific characteristics of how reading speed and reading comprehension interact with eye movements in typically developing German-speaking (Austrian) adolescents. Eye movements of 22 participants (14 females; mean age = 13;6 years;months) were tracked while they were performing three tasks, namely silently reading words, texts, and pseudowords. Their reading skills were determined by means of a standardized German reading speed and reading comprehension assessment (Lesegeschwindigkeits- und -verständnistest für Klassen 6−12). We found that (a) reading skills were associated with various eye movement parameters in each of the three reading tasks; (b) better reading skills were associated with an increased efficiency of eye movements, but were primarily linked to spatial reading parameters, such as the number of fixations per word, the total number of saccades and saccadic amplitudes; (c) reading speed was a more reliable predictor for eye movement parameters than reading comprehension; (d) eye movements were highly correlated across reading tasks, which indicates consistent reading performances. Contrary to findings in English-speaking cohorts, the reading skills neither consistently correlated with temporal eye movement parameters nor with the number or percentage of regressions made while performing any of the three reading tasks. These results indicate that, although reading skills are associated with eye movement patterns irrespective of language, the temporal and spatial characteristics of this association may vary with orthographic consistency.

Testing the effects of a disgust placebo with eye tracking.

Previous neuroimaging research showed that a disgust placebo (inert pill presented with the verbal suggestion of disgust relief) reduced visual cortex activation during the viewing of disgust-inducing images. In order to investigate whether this effect of automatic emotion regulation was associated with changed visual scanning patterns of the pictures, we conducted two eye tracking experiments. In the first study, 23 women underwent a retest design during which they passively viewed images depicting disgusting, fear-eliciting, neutral items and fractals both with, and without a placebo. The placebo provoked a substantial decrease in experienced disgust. Although none of the recorded eye movement parameters (number of fixations, fixation duration, saccade amplitude, blinking rate) showed placebo-related changes, placebo effects were suggested by an analysis of spatial fixation patterns. In the second study, which focused on attentional (dis)engagement, 46 women looked at two pictures which were presented side-by-side on the screen. These picture pairs (disgust-neutral, neutral-neutral) were once viewed with and once without a placebo. The placebo again provoked a marked decrease of experienced disgust and enhanced the number of fixations for disgusting images. This change might reflect a greater willingness of the participants to view these stimuli while on the placebo.

Eye movements in a simple spatial reasoning task

We report two experiments in which participants read a question about the spatial relationship between two letters, then viewed a visual display containing the letters and were required to respond to the question. The format of the question influenced the nature of the eye movements generated to the visual display. Participants also had a tendency to make additional eye movements in order to generate a fixation sequence that corresponded to the order of the letters in the question. This demonstrates an influence of stored information on eye movement generation, and suggests that the scanpath plays a role in structuring the visual information to facilitate reasoning.