Initial Saccade Research Articles

Secondary capture: Salience information persistently drives attentional selection.

It is well known that attention is captured by salient objects or events. The notion that attention is attracted by salience information present in the visual field is also at the heart of many influential models of attention. These models typically posit a hierarchy of saliency, suggesting that attention progresses from the most to the least salient item in the visual field. However, despite the significance of this claim in various models, research on eye movements challenges the idea that search strictly follows this saliency hierarchy. Instead, eye-tracking studies have suggested that saliency information has a transient impact, only influencing the initial saccade toward the most salient object, and only if executed swiftly after display onset. While these findings on overt eye movements are important, they do not address covert attentional processes occurring before a saccade is initiated. In the current series of experiments, we explored whether there was evidence for secondary capture-whether attention could be captured by another salient item after the initial capture episode. To explore this, we utilized displays with multiple distractors of varying levels of saliency. Our primary question was whether two distractors with different saliency levels would disrupt search more than a single, highly salient distractor. Across three experiments, clear evidence emerged indicating that two distractors interfered more with search than a single salient distractor. This observation suggests that following initial capture, secondary capture by the next most salient distractor occurred. These findings collectively support the idea that covert attention traverses the saliency hierarchy. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Causal inference during closed-loop navigation: parsing of self- and object-motion.

A key computation in building adaptive internal models of the external world is to ascribe sensory signals to their likely cause(s), a process of causal inference (CI). CI is well studied within the framework of two-alternative forced-choice tasks, but less well understood within the cadre of naturalistic action-perception loops. Here, we examine the process of disambiguating retinal motion caused by self- and/or object-motion during closed-loop navigation. First, we derive a normative account specifying how observers ought to intercept hidden and moving targets given their belief about (i) whether retinal motion was caused by the target moving, and (ii) if so, with what velocity. Next, in line with the modelling results, we show that humans report targets as stationary and steer towards their initial rather than final position more often when they are themselves moving, suggesting a putative misattribution of object-motion to the self. Further, we predict that observers should misattribute retinal motion more often: (i) during passive rather than active self-motion (given the lack of an efference copy informing self-motion estimates in the former), and (ii) when targets are presented eccentrically rather than centrally (given that lateral self-motion flow vectors are larger at eccentric locations during forward self-motion). Results support both of these predictions. Lastly, analysis of eye movements show that, while initial saccades toward targets were largely accurate regardless of the self-motion condition, subsequent gaze pursuit was modulated by target velocity during object-only motion, but not during concurrent object- and self-motion. These results demonstrate CI within action-perception loops, and suggest a protracted temporal unfolding of the computations characterizing CI. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Target-Distractor Competition Modulates Saccade Trajectories in Space and Object Space.

Saccade planning and execution can be affected by a multitude of factors present in a target selection task. Recent studies have shown that the similarity between a target and nearby distractors affects the curvature of saccade trajectories, because of target-distractor competition. To further understand the nature of this competition, we varied the distance between and the similarity of complex target and distractor objects in a delayed match-to-sample task to examine their effects on human saccade trajectories and better understand the underlying neural circuitry. For trials with short saccadic reaction times (SRTs) when target-distractor competition is still active, the distractor is attractive and saccade trajectories are deviated toward the distractor. We found a robust effect of distance consistent with saccade vector averaging, whereas the effect of similarity suggested the existence of an object-based suppressive surround. At longer SRTs, there was sufficient time for competition between the objects to complete and the distractor to be repulsive, which resulted in saccade trajectory deviations away from the distractor exhibiting the effects of a spatial suppressive surround. In terms of similarity, as the target-distractor similarity decreased, the initial saccade angle shifted toward the target, reflecting stronger distractor inhibition. There were no interactions between distance and similarity at any point in the time course of target-distractor competition. Together, saccade trajectories reflect target-distractor competition that is affected independently by both spatial and object space suppressive surrounds. The differences in saccade trajectories at short and long SRTs distinguish between active and completed decision-making processes.

Neural correlates of value-driven spatial orienting.

Reward learning has been shown to habitually guide overt spatial attention to specific regions of a scene. However, the neural mechanisms that support this bias are unknown. In the present study, participants learned to orient themselves to a particular quadrant of a scene (a high-value quadrant) to maximize monetary gains. This learning was scene-specific, with the high-value quadrant varying across different scenes. During a subsequent test phase, participants were faster at identifying a target if it appeared in the high-value quadrant (valid), and initial saccades were more likely to be made to the high-value quadrant. fMRI analyses during the test phase revealed learning-dependent priority signals in the caudate tail, superior colliculus, frontal eye field, anterior cingulate cortex, and insula, paralleling findings concerning feature-based, value-driven attention. In addition, ventral regions typically associated with scene selection and spatial information processing, including the hippocampus, parahippocampal gyrus, and temporo-occipital cortex, were also implicated. Taken together, our findings offer new insights into the neural architecture subserving value-driven attention, both extending our understanding of nodes in the attention network previously implicated in feature-based, value-driven attention and identifying a ventral network of brain regions implicated in reward's influence on scene-dependent spatial orienting.

Do categorically distinct stressors alter the attention to visual food cues?

Stressor exposure affects food intake as well as the preference for high or low palatability foods, but little is known about how stressor types impact the visual attention to food images. We used eye tracking methodology in humans to determine if activation of the hypothalamus–pituitary-adrenal (HPA) axis and sympathetic nervous system is associated with changes in attention to food images as determined by measuring changes in oculomotor activity. Specifically, we tested two questions: 1) Do categorically distinct stressors alter aspects of visual attention to food images as determined by oculomotor activity (i.e., saccade latency, gaze duration, and saccade bouts)? 2) Do categorically distinct stressors differentially affect visual attention to food images of high or low palatability? A total of sixty participants were randomly divided into one of three test groups: controls, an anticipatory stressor group, or a reactive stressor group. We measured salivary cortisol and salivary alpha-amylase (sAA) before and after stressor exposure to confirm activation of the HPA axis and sympathetic nervous system, respectively. Following stressor exposure participants performed an eye-tracking test using a standardized food picture database (Food-pics). We analyzed saccade latency, gaze duration, and saccade bouts in balanced pairs of food and non-food images. Salivary cortisol was elevated by both stressors, although the elevation in salivary cortisol to the reactive stressor was driven by women only. sAA was elevated only by the anticipatory stressor. There were main effects of image type for all three eye-tracking variables, with initial saccades of shorter latency to food images and longer gaze duration and more saccade bouts with food images. Participants exposed to the reactive stressor reduced gaze duration on food images relative to controls, and this affect was not linked to palatability or salivary cortisol levels. We conclude that the reactive stressor decreased time spent looking at food, but not non-food, images. These data are partly consistent with the idea that reactive stressors reduce attention to non-critical visual signals.

Implicit angry faces interfere with response inhibition and response adjustment

ABSTRACT Cognitive control enables people to adjust their thoughts and actions according to the current task demands. Response inhibition and response adjustment are two key aspects of cognitive control. Here, we examined how the implicit processing of emotional information influences these two functions with the help of the double-step saccade task. Each trial had either a single target or two sequential targets. Upon a single target onset, participants were required to make a quick saccade, but upon two target onsets, participants were instructed to inhibit their initial saccades and redirect their gaze to the second target. In three experiments, we manipulated the emotional information of the first and second targets. We found that irrelevant emotional information of the first target impaired response inhibition compared to non-emotional information (geometric shapes) of the first target. When non-emotional information (geometric shape) came as the first target, irrelevant angry emotional faces as the second target interfered with both response inhibition and response adjustment compared to irrelevant happy and neutral faces. We explain these results with previous findings that processing faces with irrelevant angry facial expressions take up many attentional resources, leaving fewer resources available for ongoing activities such as response inhibition and response adjustment.

A cross-linguistic study of spatial parameters of eye-movement control during reading.

Current theories of oculomotor control in reading differ in their accounts of saccadic targeting. Some argue that targets for saccades are solely selected on the basis of the rapidly changing sensory input, whereas others additionally allow for the reader's experiential biases to modulate saccade lengths. We investigated this debate using cross-linguistic data on text reading in 12 alphabetic languages from the Multilingual Eye-Movement Corpus (MECO) database. These languages vary widely in their word length distributions, suggesting that expected word lengths and corresponding biases toward optimal saccade lengths may also vary across readers of these languages. Regression analyses confirmed that readers of languages with longer words (e.g., Finnish) rather than shorter words (e.g., Hebrew) landed further into the word, even when sensory aspects relevant for saccade planning (e.g., word lengths) were controlled for. In the prevalent saccade type, a one-letter difference in mean word length between languages came with one-quarter-letter of a difference in initial landing position and saccade length, and a decrease in 1.5% in refixation probability. Interpreted in the Bayesian framework, the findings highlight the relevance of global language-wide settings for accounts of spatial oculomotor control and lead to testable predictions for further cross-linguistic research. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Searching for meaning: Local scene semantics guide attention during natural visual search in scenes.

Models of visual search in scenes include image salience as a source of attentional guidance. However, because scene meaning is correlated with image salience, it could be that the salience predictor in these models is driven by meaning. To test this proposal, we generated meaning maps that represented the spatial distribution of semantic informativeness in scenes, and salience maps which represented the spatial distribution of conspicuous image features and tested their influence on fixation densities from two object search tasks in real-world scenes. The results showed that meaning accounted for significantly greater variance in fixation densities than image salience, both overall and in early attention across both studies. Here, meaning explained 58% and 63% of the theoretical ceiling of variance in attention across both studies, respectively. Furthermore, both studies demonstrated that fast initial saccades were not more likely to be directed to higher salience regions than slower initial saccades, and initial saccades of all latencies were directed to regions containing higher meaning than salience. Together, these results demonstrated that even though meaning was task-neutral, the visual system still selected meaningful over salient scene regions for attention during search.

Properties of rapid eye movements.

This chapter describes the metrics and kinematics of saccades and quick phases of nystagmus, including microsaccades and large eye-head saccades. Small saccades often display dynamic overshoot, predominantly in the abducting eye. Although the function of these overshoots is unclear, the return movement is saccadic in nature. The saccade kinematics can be quantified by stereotyped relations between amplitude, duration, peak eye velocity, and peak acceleration, which vary somewhat with the initial eye position and saccade direction (centripetal vs centrifugal), possibly due to ocular plant characteristics. Saccades in a structured light environment are considerably faster than when executed in total darkness, although the origin for this facilitation is not known. The horizontal and vertical components of slant saccades are coupled, approximately matching their durations, for which possible underlying neural mechanisms are discussed. The chapter closes with a cross-species comparison of saccade characteristics.

Superior colliculus drives stimulus-evoked directionally biased saccades and attempted head movements in head-fixed mice

Animals investigate their environments by directing their gaze towards salient stimuli. In the prevailing view, mouse gaze shifts entail head rotations followed by brainstem-mediated eye movements, including saccades to reset the eyes. These 'recentering' saccades are attributed to head movement-related vestibular cues. However, microstimulating mouse superior colliculus (SC) elicits directed head and eye movements resembling SC-dependent sensory-guided gaze shifts in other species, suggesting that mouse gaze shifts may be more flexible than has been recognized. We investigated this possibility by tracking eye and attempted head movements in a head-fixed preparation that eliminates head movement-related sensory cues. We found tactile stimuli evoke directionally biased saccades coincident with attempted head rotations. Differences in saccade endpoints across stimuli are associated with distinct stimulus-dependent relationships between initial eye position and saccade direction and amplitude. Optogenetic perturbations revealed SC drives these gaze shifts. Thus, head-fixed mice make sensory-guided, SC-dependent gaze shifts involving coincident, directionally biased saccades and attempted head movements. Our findings uncover flexibility in mouse gaze shifts and provide a foundation for studying head-eye coupling.

Alterations in oculomotor behavior in healthy aging and mild cognitive impairment

Age-related changes in saccade behavior on short timescales (a few seconds) is often ascribed to changes in sensorimotor processing, working memory, or executive functioning. Visual exploration is additionally guided, at long timescales (minutes to hours), by memory representations supported by the hippocampal and broader medial temporal lobe system. Here, we examined whether age-related and neurodegenerative changes to the memory system impact more immediate saccade behavior by comparing the performance of younger adults (YA), healthy older adults (HOA), and older adults diagnosed with amnestic mild cognitive impairment (aMCI). 27 YA (18-35 years), 34 HOA (60-86 years) and 9 aMCI (46-84 years) performed a set of saccade tasks that systematically manipulated memory demands and the complexity of saccadic behaviour. A subset of tasks involved single saccades directed to a target 1) immediately (visually-guided task), 2) after a variable delay 500-1500 ms (gap), and 3) to a remembered location after a variable delay 300-3000 ms (memory-guided task). In another set of memory-guided tasks, participants directed saccades to two remembered targets in sequential and reverse order after a variable delay (double-step forward and backward). Using a multivariate partial least squares analysis, HOA and MCI groups were shown to have longer initial saccade latencies than YA in all but the visually-guided task. HOA and MCI initial saccade latencies did not differ significantly. Second saccade latencies in the double-step forward task were shorter for HOA than YA but longer for MCI as compared to the other two groups. Spatial errors did not differ across groups, suggesting that the differences in latencies were not due to differences in speed-accuracy tradeoffs across groups. Our results confirm previous findings of the impact of age-related changes in sensorimotor processing on saccade behavior. Our findings suggest that functional changes in the medial temporal lobe may affect oculomotor guidance on short timescales.

Oculomotor inhibition and location priming in schizophrenia.

Schizophrenia is widely thought to involve elevated distractibility, which may reflect a general impairment in top-down inhibitory processes. Schizophrenia also appears to involve increased priming of previously performed actions. Here, we used a highly refined eye-tracking paradigm that makes it possible to concurrently assess distractibility, inhibition, and priming. In both healthy control subjects (HCS, N = 41) and people with schizophrenia (PSZ, N = 46), we found that initial saccades were actually less likely to be directed toward a salient "singleton" distractor than toward less salient distractors, reflecting top-down suppression of the singleton. Remarkably, this oculomotor suppression effect was as strong or stronger in PSZ than in HCS, indicating intact inhibitory control. In addition, saccades were frequently directed to the location of the previous-trial target in both groups, but this priming effect was much stronger in PSZ than in HCS. Indeed, PSZ directed gaze toward the location of the previous-trial target as often as they directed gaze to the location of the current-trial target. These results demonstrate that-at least in the context of visual search-PSZ are no more distractable than HCS and are fully capable of inhibiting salient-but-irrelevant stimuli. However, PSZ do exhibit exaggerated priming, focusing on recently attended locations even when this is not beneficial for goal attainment. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Attention neglects a stare-in-the-crowd: Unanticipated consequences of prediction-error coding

Direct gaze — someone looking at you — is an important and subjectively-salient stimulus. Its processing is thought to be enhanced by the brain's internalised predictions — priors — that effectively specify it as the most likely gaze direction. Current consensus holds that, befitting its presumed importance, direct gaze attracts attention more powerfully than other gazes. Conversely, some Predictive Coding (PC) models, in which exogenous attention is drawn to stimuli that violate predictions, may be construed as making the opposite claim — i.e., exogenous attention should be biased away from direct gaze (which conforms to internal predictions), toward averted gaze (which does not). Here, searching displays with salient, ‘odd-one-out’ gazes, we observed attentional bias (in rapid, initial saccades) toward averted gaze, as would be expected by PC models. However, this pattern obtained only when conditions highlighted gaze-uniqueness. We speculate that, in our experiments, task requirements determined how prediction influenced perception.

A novel attention bias modification single session training improves eye gaze behaviour in social anxiety disorder: a pilot study

Background Attention bias modification (ABM) can reduce anxiety and attentional bias towards threatening stimuli, but evidence of its usefulness as a potential intervention for socially anxious individuals has been mixed. Eye contact avoidance, a maladaptive attentional strategy in social anxiety disorder (SAD), has yet to be targeted by ABM research. Aims This study sought to establish whether a new ABM training paradigm could increase attentional deployment towards eyes and what effect this would have on social and gaze-related anxiety. Method Participants (n = 23) recruited through adverts calling for people who felt anxious in social situations completed either a novel ABM training task designed to induce attentional bias towards images of eyes over images of noses, or control training. Data on response times (RTs), accuracy of responses, gaze behaviour (using an eye tracker) and scores on clinical measures of social and gaze-related anxiety were collected before and after both training tasks. Results ABM training produced a greater number of initial saccades towards eye images than did the control task, indicating an induced shift in early attentional deployment. ABM training was also associated with a marginal increase in fixation durations on eye images. No effect was observed on RTs or social and gaze-related anxiety. Conclusions Our results indicate that ABM can alter the gaze behaviour of socially anxious individuals. They also highlight the importance of eye tracking to ABM research, because it was more sensitive than analyses of RTs to changes in early attentional deployment.

Stronger saccadic suppression of displacement and blanking effect in children.

Humans do not notice small displacements to objects that occur during saccades, termed saccadic suppression of displacement (SSD), and this effect is reduced when a blank is introduced between the pre- and postsaccadic stimulus (Bridgeman, Hendry, & Stark, 1975; Deubel, Schneider, & Bridgeman, 1996). While these effects have been studied extensively in adults, it is unclear how these phenomena are characterized in children. A potentially related mechanism, saccadic suppression of contrast sensitivity—a prerequisite to achieve a stable percept—is stronger for children (Bruno, Brambati, Perani, & Morrone, 2006). However, the evidence for how transsaccadic stimulus displacements may be suppressed or integrated is mixed. While they can integrate basic visual feature information from an early age, they cannot integrate multisensory information (Gori, Viva, Sandini, & Burr, 2008; Nardini, Jones, Bedford, & Braddick, 2008), suggesting a failure in the ability to integrate more complex sensory information. We tested children 7 to 12 years old and adults 19 to 23 years old on their ability to perceive intrasaccadic stimulus displacements, with and without a postsaccadic blank. Results showed that children had stronger SSD than adults and a larger blanking effect. Children also had larger undershoots and more variability in their initial saccade endpoints, indicating greater intrinsic uncertainty, and they were faster in executing corrective saccades to account for these errors. Together, these results suggest that children may have a greater internal expectation or prediction of saccade error than adults; thus, the stronger SSD in children may be due to higher intrinsic uncertainty in target localization or saccade execution.

Using aversive conditioning with near-real-time feedback to shape eye movements during naturalistic viewing.

Strategically shaping patterns of eye movements through training has manifold promising applications, with the potential to improve the speed and efficiency of visual search, improve the ability of humans to extract information from complex displays, and help correct disordered eye movement patterns. However, training how a person moves their eyes when viewing an image or scene is notoriously difficult, with typical approaches relying on explicit instruction and strategy, which have notable limitations. The present study introduces a novel approach to eye movement training using aversive conditioning with near-real-time feedback. Participants viewed indoor scenes (eight scenes presented over 48 trials) with the goal of remembering those scenes for a later memory test. During viewing, saccades meeting specific amplitude and direction criteria probabilistically triggered an aversive electric shock, which was felt within 50 ms after the eliciting eye movement, allowing for a close temporal coupling between an oculomotor behavior and the feedback intended to shape it. Results demonstrate a bias against performing an initial saccade in the direction paired with shock (Experiment 1) or generally of the amplitude paired with shock (Experiment 2), an effect that operates without apparent awareness of the relationship between shocks and saccades, persists into extinction, and generalizes to the viewing of novel images. The present study serves as a proof of concept concerning the implementation of near-real-time feedback in eye movement training.

A Novel Attention Bias Modification Single Session Training Improves Eye Gaze Behaviour in Social Anxiety Disorder: A Pilot Study

Abstract Background Attention bias modification (ABM) can reduce anxiety and attentional bias towards threatening stimuli, but evidence of its usefulness as a potential intervention for socially anxious individuals has been mixed. Eye contact avoidance, a maladaptive attentional strategy in social anxiety disorder (SAD), has yet to be targeted by ABM research. Aims This study sought to establish whether a new ABM training paradigm could increase attentional deployment towards eyes and what effect this would have on social and gaze-related anxiety. Method Participants (n = 23) recruited through adverts calling for people who felt anxious in social situations completed either a novel ABM training task designed to induce attentional bias towards images of eyes over images of noses, or control training. Data on response times (RTs), accuracy of responses, gaze behaviour (using an eye tracker) and scores on clinical measures of social and gaze-related anxiety were collected before and after both training tasks. Results ABM training produced a greater number of initial saccades towards eye images than did the control task, indicating an induced shift in early attentional deployment. ABM training was also associated with a marginal increase in fixation durations on eye images. No effect was observed on RTs or social and gaze-related anxiety. Conclusions Our results indicate that ABM can alter the gaze behaviour of socially anxious individuals. They also highlight the importance of eye tracking to ABM research, because it was more sensitive than analyses of RTs to changes in early attentional deployment.

Effects of prior knowledge on active vision and memory in younger and older adults.

In our daily lives we rely on prior knowledge to make predictions about the world around us such as where to search for and locate common objects. Yet, equally important in visual search is the ability to inhibit such processes when those predictions fail. Mounting evidence suggests that relative to younger adults, older adults have difficulty retrieving episodic memories and inhibiting prior knowledge, even when that knowledge is detrimental to the task at hand. However, the consequences of these age-related changes for visual search remain unclear. In the present study, we used eye movement monitoring to investigate whether overreliance on prior knowledge alters the gaze patterns and performance of older adults during visual search. Younger and older adults searched for target objects in congruent or incongruent locations in real-world scenes. As predicted, targets in congruent locations were detected faster than targets in incongruent locations, and this effect was enhanced in older adults. Analysis of viewing behavior revealed that prior knowledge effects emerged early in search, as evidenced by initial saccades, and continued throughout search, with greater viewing of congruent regions by older relative to younger adults, suggesting that schema biasing of online processing increases with age. Finally, both younger and older adults showed enhanced memory for the location of congruent targets and the identity of incongruent targets, with schema-guided viewing during search predicting poor memory for schema-incongruent targets in younger adults on both tasks. Our results provide novel evidence that older adults' overreliance on prior knowledge has consequences for both active vision and memory. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Reward learning biases the direction of saccades

The role of associative reward learning in guiding feature-based attention and spatial attention is well established. However, no studies have looked at the extent to which reward learning can modulate the direction of saccades during visual search. Here, we introduced a novel reward learning paradigm to examine whether reward-associated directions of eye movements can modulate performance in different visual search tasks. Participants had to fixate a peripheral target before fixating one of four disks that subsequently appeared in each cardinal position. This was followed by reward feedback contingent upon the direction chosen, where one direction consistently yielded a high reward. Thus, reward was tied to the direction of saccades rather than the absolute location of the stimulus fixated. Participants selected the target in the high-value direction on the majority of trials, demonstrating robust learning of the task contingencies. In an untimed visual foraging task that followed, which was performed in extinction, initial saccades were reliably biased in the previously rewarded-associated direction. In a second experiment, following the same training procedure, eye movements in the previously high-value direction were facilitated in a saccade-to-target task. Our findings suggest that rewarding directional eye movements biases oculomotor search patterns in a manner that is robust to extinction and generalizes across stimuli and task.

The temporal and spatial constraints of saccade planning to double-step target displacements

The double-step paradigm investigates the characteristics of planning and execution when the motor system must rapidly adjust for a new goal location. Studies have provided detailed temporal information based on the duration available for the motor system to prepare a new movement trajectory (here referred to as re-preparation time). However, previous work has largely examined single displacement sizes, limiting the spatiotemporal understanding of movement planning and execution. The lack of a description of this behavioral timecourse across increasing displacement sizes is true for saccades, rapid eye movements that redirect the fovea. Furthermore, during the double-step paradigm, the primary saccade often fails to accurately foveate the final target location and a secondary saccade brings the target onto the fovea. However, it is also unknown how this compensation is concurrently modified with the exposure duration and displacement of the movement goal. Here, we examined the amount of time required to change the initial saccade direction to a new target location for relatively small (20°, 30°, and 40°) and large (60° and 90°) target spatial separations. Interestingly, we found a clear relationship between the saccade direction and the amount of time allowed to redirect the movement; across separations, intermediate saccades occurred when approximately 60–140 ms was available to readjust the movement plan. Additionally, there was a consistent relationship between the timing of the secondary saccade and the re-preparation time across jump sizes, suggesting that concurrent movement correction planning was dependent on the amount of exposure to the final movement goal.