Temporal oculomotor inhibition of return and spatial facilitation of return in a visual encoding task

Motor "laziness" constrains fixation selection in real-world tasks

Humans coordinate their eye, head, and body movements to gather information from a dynamic environment while maximizing reward and minimizing biomechanical and energetic costs. However, such natural behavior is not possible in traditional experiments employing head/body restraints and artificial, static stimuli. Therefore, it is unclear to what extent mechanisms of fixation selection discovered in lab studies, such as inhibition-of-return (IOR), influence everyday behavior. To address this gap, participants performed nine real-world tasks, including driving, visually searching for an item, and building a Lego set, while wearing a mobile eye tracker (169 recordings; 26.6 h). Surprisingly, in all tasks, participants most often returned to what they just viewed and saccade latencies were shorter preceding return than forward saccades, i.e., consistent with facilitation, rather than inhibition, of return. We hypothesize that conservation of eye and head motor effort ("laziness") contributes. Correspondingly, we observed center biases in fixation position and duration relative to the head's orientation. A model that generates scanpaths by randomly sampling these distributions reproduced all return phenomena we observed, including distinct 3-fixation sequences for forward versus return saccades. After controlling for orbital eccentricity, one task (building a Lego set) showed evidence for IOR. This, along with small discrepancies between model and data, indicates that the brain balances minimization of motor costs with maximization of rewards (e.g., accomplished by IOR and other mechanisms) and that the optimal balance varies according to task demands. Supporting this account, the orbital range of motion used in each task traded off lawfully with fixation duration.

Influence of initial fixation position in scene viewing

During scene perception our eyes generate complex sequences of fixations. Predictors of fixation locations are bottom-up factors such as luminance contrast, top-down factors like viewing instruction, and systematic biases, e.g., the tendency to place fixations near the center of an image. However, comparatively little is known about the dynamics of scanpaths after experimental manipulation of specific fixation locations. Here we investigate the influence of initial fixation position on subsequent eye-movement behavior on an image. We presented 64 colored photographs to participants who started their scanpaths from one of two experimentally controlled positions in the right or left part of an image. Additionally, we used computational models to predict the images' fixation locations and classified them as balanced images or images with high conspicuity on either the left or right side of a picture. The manipulation of the starting position influenced viewing behavior for several seconds and produced a tendency to overshoot to the image side opposite to the starting position. Possible mechanisms for the generation of this overshoot were investigated using numerical simulations of statistical and dynamical models. Our model comparisons show that inhibitory tagging is a viable mechanism for dynamical planning of scanpaths.

Scanpaths of Complex Image Viewing: Insights From Experimental and Modeling Studies

From the first works of Buswell, Yarbus, and Noton and Stark, the scan path for viewing complex images has been considered as a possible key to objective estimation of cognitive processes and their dynamics. However, evidences both pro and con were revealed in the modern research. In this article, the results supporting the Yarbus-Stark concept are presented. In psychophysical tests, two types of images (three paintings from Yarbus` works and four textures) were used with two instructions, namely, “free viewing” and “search for modified image regions.” The focus of the analysis of experimental results and modeling has been given to local elements of the scan path. It was shown that each parameter used (square of viewing area, S; distance between center of mass of viewing area and image center, R; parameter Xi, based on duration of the current fixation and angle between preceding and following saccades), reflects the specificity of both visual task and image properties. Additionally, the return gaze fixations which have a set of specific properties and mainly address to the areas of interest on image were revealed. Evidently these facts can be formalized in an advanced mathematical model as additional instrument to study the mechanisms of complex image viewing.

Effects of task and task-switching on temporal inhibition of return, facilitation of return, and saccadic momentum during scene viewing

During scene viewing, saccades directed toward a recently fixated location tend to be delayed relative to saccades in other directions ("delay effect"), an effect attributable to inhibition of return (IOR) and/or saccadic momentum (SM). Previous work indicates this effect may be task-specific, suggesting that gaze control parameters are task-relevant and potentially affected by task-switching. Accordingly, the present study investigated task-set control of gaze behavior using the delay effect as a measure of task performance. The delay effect was measured as the effect of relative saccade direction on preceding fixation duration. Participants were cued on each trial to perform either a search, memory, or rating task. Tasks were performed either in pure-task or mixed-task blocks. This design allowed separation of switch-cost and mixing-cost. The critical result was that expression of the delay effect at 2-back locations was reversed on switch versus repeat trials such that return was delayed in repeat trials but speeded in switch trials. This difference between repeat and switch trials suggests that gaze-relevant parameters may be represented and switched as part of a task-set. Existing and new tests for dissociating IOR and SM accounts of the delay effect converged on the conclusion that the delay at 2-back locations was due to SM, and that task-switching affects SM. Additionally, the new test simultaneously replicated noncorroborating results in the literature regarding facilitation-of-return (FOR), which confirmed its existence and showed that FOR is "reversed" SM that occurs when preceding and current saccades are both directed toward the 2-back location.

The role of memory for visual search in scenes

Many daily activities involve looking for something. The ease with which these searches are performed often allows one to forget that searching represents complex interactions between visual attention and memory. Although a clear understanding exists of how search efficiency will be influenced by visual features of targets and their surrounding distractors or by the number of items in the display, the role of memory in search is less well understood. Contextual cueing studies have shown that implicit memory for repeated item configurations can facilitate search in artificial displays. When searching more naturalistic environments, other forms of memory come into play. For instance, semantic memory provides useful information about which objects are typically found where within a scene, and episodic scene memory provides information about where a particular object was seen the last time a particular scene was viewed. In this paper, we will review work on these topics, with special emphasis on the role of memory in guiding search in organized, real-world scenes.

Morphology of Primary Visual Cortex Predicts Individual Differences in Fixation Duration during Text Reading

In skilled reading, fixations are brief periods of time in which the eyes settle on words. E-Z Reader, a computational model of dynamic reading, posits that fixation durations are under real-time control of lexical processing. Lexical processing, in turn, requires efficient visual encoding. Here we tested the hypothesis that individual differences in fixation durations are related to individual differences in the efficiency of early visual encoding. To test this hypothesis, we recorded participants' eye movements during reading. We then examined individual differences in fixation duration distributions as a function of individual differences in the morphology of primary visual cortex measured from MRI scans. The results showed that greater gray matter surface area and volume in visual cortex predicted shorter and less variable fixation durations in reading. These results suggest that individual differences in eye movements during skilled reading are related to initial visual encoding, consistent with models such as E-Z Reader that emphasize lexical control over fixation time.