The effect of cognitive load on saccadic eye movements

EM-COGLOAD: An investigation into age and cognitive load detection using eye tracking and deep learning

Alzheimer's Disease is the most prevalent neurodegenerative disease, and is a leading cause of disability among the elderly. Eye movement behaviour demonstrates potential as a non-invasive biomarker for Alzheimer's Disease, with changes detectable at an early stage after initial onset. This paper introduces a new publicly available dataset: EM-COGLOAD (available at https://osf.io/zjtdq/, DOI: 10.17605/OSF.IO/ZJTDQ). A dual-task paradigm was used to create effects of declined cognitive performance in 75 healthy adults as they carried out visual tracking tasks. Their eye movement was recorded, and time series classification of the extracted eye movement traces was explored using a range of deep learning techniques. The results of this showed that convolutional neural networks were able to achieve an accuracy of 87.5% when distinguishing between eye movement under low and high cognitive load, and 76% when distinguishing between the oldest and youngest age groups.

A Comparison of Head Movement Classification Methods

To understand human behavior, it is essential to study it in the context of natural movement in immersive, three-dimensional environments. Virtual reality (VR), with head-mounted displays, offers an unprecedented compromise between ecological validity and experimental control. However, such technological advancements mean that new data streams will become more widely available, and therefore, a need arises to standardize methodologies by which these streams are analyzed. One such data stream is that of head position and rotation tracking, now made easily available from head-mounted systems. The current study presents five candidate algorithms of varying complexity for classifying head movements. Each algorithm is compared against human rater classifications and graded based on the overall agreement as well as biases in metrics such as movement onset/offset time and movement amplitude. Finally, we conclude this article by offering recommendations for the best practices and considerations for VR researchers looking to incorporate head movement analysis in their future studies.

Microsaccade rate activity during the preparation of pro- and antisaccades

Microsaccades belong to the category of fixational micromovements and may be crucial for image stability on the retina. Eye movement paradigms typically require fixational control, but this does not eliminate all oculomotor activity. The antisaccade task requires a planned eye movement in the direction opposite of an onset, allowing separation of planning and execution. We build on previous studies of microsaccades in the antisaccade task using a combination of fixed and mixed pro- and antisaccade blocks. We hypothesized that microsaccade rates may be reduced prior to the execution of antisaccades as compared with regular saccades (prosaccades). In two experiments, we measured microsaccades in four conditions across three trial blocks: one block each of fixed prosaccade and antisaccade trials, and a mixed block where both saccade types were randomized. We anticipated that microsaccade rates would be higher prior to antisaccades than prosaccades due to the need to preemptively suppress reflexive saccades during antisaccade generation. In Experiment 1, with monocular eye tracking, there was an interaction between the effects of saccade and block type on microsaccade rates, suggesting lower rates on antisaccade trials, but only within mixed blocks. In Experiment 2, eye tracking was binocular, revealing suppressed microsaccade rates on antisaccade trials. A cluster permutation analysis of the microsaccade rate over the course of a trial did not reveal any particular critical time for this difference in microsaccade rates. Our findings suggest that microsaccade rates reflect the degree of suppression of the oculomotor system during the antisaccade task.

Choosing optimal means of knowledge visualization based on eye tracking for online education

In online education, the appropriate choice of means of knowledge visualization can reduce cognitive load and improve cognitive efficiency. However, no universal basis for selection can cause confusion in the pedagogical context. This study used the revised Bloom's taxonomy to combine the types of knowledge with cognitive goals. We used a course on marketing research as an example to summarize the choices for visualizing factual knowledge (FK), conceptual knowledge (CK), procedural knowledge (PK), and metacognitive knowledge (MK) through four experiments. Visualized cognitive stages were used to determine the cognitive efficiencies of visualization for different knowledge types. In this stage, eye tracking is used for collecting eye movement indicators to measure cognitive load. The cognitive goals stage is used to get cognitive goals of the means of knowledge visualization. Combining the two stages, we get the conclusions as follows: Teachers and students can mostly benefit from presenting FK and CK points via mind maps. Using mind maps to teach FK online could be indirectly beneficial for improving students' creativity. Concept maps may be chosen for this point if the linked knowledge points are PK and the achievement of the analytical objective is emphasized in the student's knowledge points. The flowchart can be used to display PK, while timelines could be utilized if the PK point is to be presented in a temporal dimension. Teachers should choose the curve area chart to display MK. A pie chart might be chosen and added more instructions. The findings suggest that mind maps are very effective as a means of knowledge visualization in online education. In the meantime, it suggests that overly simplistic graphs increase cognitive load, while it also raises the possibility that redundant information in the text may increase cognitive load.

Estimating Phosphene Locations Using Eye Movements of Suprachoroidal Retinal Prosthesis Users

Purpose

Accurate mapping of phosphene locations from visual prostheses is vital to encode spatial information. This process may involve the subject pointing to evoked phosphene locations with their finger. Here, we demonstrate phosphene mapping for a retinal implant using eye movements and compare it with retinotopic electrode positions and previous results using conventional finger-based mapping.

Methods

Three suprachoroidal retinal implant recipients (NCT03406416) indicated the spatial position of phosphenes. Electrodes were stimulated individually, and the subjects moved their finger (finger based) or their eyes (gaze based) to the perceived phosphene location. The distortion of the measured phosphene locations from the expected locations (retinotopic electrode locations) was characterized with Procrustes analysis.

Results

The finger-based phosphene locations were compressed spatially relative to the expected locations all three subjects, but preserved the general retinotopic arrangement (scale factors ranged from 0.37 to 0.83). In two subjects, the gaze-based phosphene locations were similar to the expected locations (scale factors of 0.72 and 0.99). For the third subject, there was no apparent relationship between gaze-based phosphene locations and electrode locations (scale factor of 0.07).

Conclusions

Gaze-based phosphene mapping was achievable in two of three tested retinal prosthesis subjects and their derived phosphene maps correlated well with the retinotopic electrode layout. A third subject could not produce a coherent gaze-based phosphene map, but this may have revealed that their phosphenes were indistinct spatially.

Translational Relevance

Gaze-based phosphene mapping is a viable alternative to conventional finger-based mapping, but may not be suitable for all subjects.

Effect of Cognitive Mental Load on Attended and Nonattended Visual Stimuli

SIGNIFICANCE

In the real word, visual tasks may be concurrent with other activity that imposes mental load. Although the brain's capacity to process information is limited, attention can improve visual performance by selectively allocating processing resources. Therefore, measuring visual performance under such circumstances can reflect patients' vision more accurately.

PURPOSE

The aim of this study was to evaluate the effect of nonvisual task-induced mental load on visual performance at both attended and unattended locations in stimulus-driven captured attention.

METHODS

Visual function was measured with an orientation discrimination task for Gabor patches with contrasts of 10, 15, 30, 50, and 80%. Three attentional conditions (valid-cue, invalid-cue, and neutral-cue) were randomly interleaved within runs. To modulate mental load, the visual task was performed either with or without a simultaneous auditory n-back task (two-back for maximum mental load and zero-back to control for the effect of having to perform a simultaneous task).

RESULTS

Our result showed that the effect of mental load on correct responses was significant ( P = .02). Correct responses decreased significantly during the two-back task when compared with the baseline condition ( P = .03), but there was no significant difference between baseline and zero-back conditions ( P = .06). The effect of attention and spatial frequencies on the percentage of correct responses was significant ( P < .001). There was no significant interaction between mental load and spatial frequency, contrast level, or attention ( P > .05).

CONCLUSIONS

Mental load had a similar decreasing effect on attended and unattended visual stimuli. This may be due to a generalized effect on processing resources upstream to where spatial attention is allocated.

Cognitive load influences oculomotor behavior in natural scenes

Cognitive neuroscience researchers have identified relationships between cognitive load and eye movement behavior that are consistent with oculomotor biomarkers for neurological disorders. We develop an adaptive visual search paradigm that manipulates task difficulty and examine the effect of cognitive load on oculomotor behavior in healthy young adults. Participants (N = 30) free-viewed a sequence of 100 natural scenes for 10 s each, while their eye movements were recorded. After each image, participants completed a 4 alternative forced choice task in which they selected a target object from one of the previously viewed scenes, among 3 distracters of the same object type but from alternate scenes. Following two correct responses, the target object was selected from an image increasingly farther back (N-back) in the image stream; following an incorrect response, N decreased by 1. N-back thus quantifies and individualizes cognitive load. The results show that response latencies increased as N-back increased, and pupil diameter increased with N-back, before decreasing at very high N-back. These findings are consistent with previous studies and confirm that this paradigm was successful in actively engaging working memory, and successfully adapts task difficulty to individual subject's skill levels. We hypothesized that oculomotor behavior would covary with cognitive load. We found that as cognitive load increased, there was a significant decrease in the number of fixations and saccades. Furthermore, the total duration of saccades decreased with the number of events, while the total duration of fixations remained constant, suggesting that as cognitive load increased, subjects made fewer, longer fixations. These results suggest that cognitive load can be tracked with an adaptive visual search task, and that oculomotor strategies are affected as a result of greater cognitive demand in healthy adults.

Eye movements in anorexia nervosa: State or trait markers?

OBJECTIVE

Differences in saccadic eye movements are widely reported in mental illnesses, and can indirectly inform our understanding of neurobiological and cognitive underpinnings of psychiatric conditions, including anorexia nervosa (AN). Preliminary research has suggested that individuals with AN may show specific eye movement abnormalities; whether these deficits are representative of state or trait effects is, however, unclear. The aim of this study was to identify whether there are demonstrable differences in performance on saccadic eye movement tasks in individuals with current AN (c-AN), those who are weight-restored from AN (wr-AN), biological sisters of individuals with AN (AN-sis), and healthy controls (HC).

METHODS

Eighty participants took part in the study (n = 20/group). A set of saccadic eye movement tasks was administered, including prosaccade, antisaccade, memory-guided saccade, and visual scanpath tasks.

RESULTS

The c-AN group showed an increased rate of inhibitory errors to 10° targets on the memory-guided saccade task.

DISCUSSION

The results are discussed in terms of the potential role of the superior colliculus in AN, and that the findings may reflect a state measure of AN.

Pupil diameter as a biomarker of effort in goal-directed gait

Subjects' eye movement behavior related to cognitive effort during gait was measured as subjects walked to perform low and high cognitive load tasks. We found that all pupil diameter measures, fixation durations, and the proportion of blink duration changed significantly during gait as a function of task load. In contrast, the number of fixations, saccade durations and travel time did not change significantly as a function of task load. Findings showed that pupil diameter was the best predictor of task load during one's gait preceding the performance of the task. While other studies have demonstrated the importance of eye fixation characteristics during gait, our findings showed that eye measures related to pupil diameter were better at detecting cognitive load while walking to perform a task compared to eye fixation data. We also found that cognitive effort was not limited to just the performance of the task, but that it was also exerted during one's gait preceding the performance of the task. Therefore, the additional attention demand caused by an increase in task complexity may result in less attentional resources being available to adequately handle distractions (such as obstacle avoidance) while walking to perform the task. Consequently, this may increase the likelihood of falls in those individuals with lower attentional capacity.

Saccades under Mental Load in Infantile Nystagmus Syndrome and Controls

SIGNIFICANCE

This study compares saccades and visual task performance in patients with infantile nystagmus syndrome (INS) with that in normally sighted individuals under mental load. The results highlighted that to more completely evaluate INS therapies recognition time should also be measured with mental load, resembling real-world conditions.

PURPOSE

Patients with INS may complain of "being slow to see." Stress is reported to worsen nystagmus and to prolong visual recognition time. We hypothesized that the effects of mental load on timing indices of visual recognition, for example, saccade latency, target acquisition time, target viewing time, and subjects' reaction time, differ between the INS and control groups.

METHODS

Eye movements were recorded when participants (INS group, n = 15; controls, n = 25) reported the direction of tumbling-E targets presented randomly across ±25°. The task was repeated with both mental arithmetic and time restriction to impose high mental load, confirmed through subjective ratings and heart rate measurement.

RESULTS

Mental load increased saccade latency (mean, 32.69 milliseconds; 95% confidence interval [CI], 21.17 to 44.20 milliseconds; P < .001) and target acquisition time (57.00 milliseconds; 95% CI, 34 to 81 milliseconds; P < .001). Patients with INS showed longer saccade latency (39.79 milliseconds; 95% CI, 23.98 to 55.62 milliseconds; P < .001) and target acquisition time (134.00 milliseconds; 95% CI, 96 to 172 milliseconds; P < .001) compared with controls. The interaction between task and group was significant for saccade gain (0.11; 95% CI, 0.02 to 0.19; P = .015), target acquisition time (37.93 milliseconds; 95% CI, 36.91 to 38.96 milliseconds; P = .011), and subjects' reaction time (95.37 milliseconds; 95% CI, 65.91 to 124.84 milliseconds; P = .043). There was an inverse correlation between the changes in subjects' response errors and target viewing time with mental load only for controls (r = -0.484, P = .014). Total foveation exposure time and target viewing time remained unchanged.

CONCLUSIONS

Mental load worsens "being slow to see" in INS because of delayed target acquisition and possibly because efficiency of visual processing decreases more in patients with INS compared with controls. To investigate outcomes of INS therapies, visual recognition time should be also measured with mental load.

Inhibitory attentional control in anxiety: Manipulating cognitive load in an antisaccade task

Theorists have proposed that heightened anxiety vulnerability is characterised by reduced attentional control performance and have made the prediction in turn that elevating cognitive load will adversely impact attentional control performance for high anxious individuals to a greater degree than low anxious individuals. Critically however, existing attempts to test this prediction have been limited in their methodology and have presented inconsistent findings. Using a methodology capable of overcoming the limitations of previous research, the present study sought to investigate the effect of manipulating cognitive load on inhibitory attentional control performance of high anxious and low anxious individuals. High and low trait anxious participants completed an antisaccade task, requiring the execution of prosaccades towards, or antisaccades away from, emotionally toned stimuli while eye movements were recorded. Participants completed the antisaccade task under conditions that concurrently imposed a lesser cognitive load, or greater cognitive load. Analysis of participants' saccade latencies revealed high trait anxious participants demonstrated generally poorer inhibitory attentional control performance as compared to low trait anxious participants. Furthermore, conditions imposing greater cognitive load, as compared to lesser cognitive load, resulted in enhanced inhibitory attentional control performance across participants generally. Crucially however, analyses did not reveal an effect of cognitive load condition on anxiety-linked differences in inhibitory attentional control performance, indicating that elevating cognitive load did not adversely impact attentional control performance for high anxious individuals to a greater degree than low anxious individuals. Hence, the present findings are inconsistent with predictions made by some theorists and are in contrast to the findings of earlier investigations. These findings further highlight the need for research into the relationship between anxiety, attentional control, and cognitive load.

Saccadic impairment in chronic traumatic brain injury: examining the influence of cognitive load and injury severity

OBJECTIVE

Previous research suggests that saccadic eye movements can be uniquely sensitive to impairment in chronic traumatic brain injury (TBI). This study was conducted to examine saccadic eye movements across varying levels of cognitive load and TBI history/severity. We hypothesized that saccadic impairment in chronic mild and moderate-severe TBI would be most pronounced under conditions of high cognitive load.

METHODS

In total, 61 participants (including n = 20 with chronic mild TBI, n = 15 with chronic moderate-severe TBI, and 26 uninjured controls) completed a battery of conventional neuropsychological tests and the Fusion n-Back Test, which measures manual and saccadic response time (RT) across varying cognitive load and cueing conditions.

RESULTS

Consistent with our hypotheses, chronic mild and moderate-severe TBI were associated with substantial saccadic impairment under conditions of high cognitive load. Participants with moderate-severe TBI also demonstrated saccadic impairment at low levels of cognitive load. TBI groups and uninjured controls did not differ significantly on manual metrics or conventional neuropsychological measures.

CONCLUSIONS

This study provides additional support for the value of eye tracking for enhanced assessment of TBI. Additionally, findings suggest that TBI is associated with greatest susceptibility to oculomotor interference under high levels of cognitive load.

Detection-Response Task-Uses and Limitations

The Detection-Response Task is a method for assessing the attentional effects of cognitive load in a driving environment. Drivers are presented with a sensory stimulus every 3–5 s, and are asked to respond to it by pressing a button attached to their finger. Response times and hit rates are interpreted as indicators of the attentional effect of cognitive load. The stimuli can be visual, tactile and auditory, and are chosen based on the type of in-vehicle system or device that is being evaluated. Its biggest disadvantage is that the method itself also affects the driver’s performance and secondary task completion times. Nevertheless, this is an easy to use and implement method, which allows relevant assessment and evaluation of in-vehicle systems. By following the recommendations and taking into account its limitations, researchers can obtain reliable and valuable results on the attentional effects of cognitive load on drivers.

Back to basics: The effects of block vs. interleaved trial administration on pro- and anti-saccade performance

The pro and anti-saccade task (PAT) is a widely used tool in the study of overt and covert attention with promising potential role in neurocognitive and psychiatric assessment. However, specific PAT protocols can vary significantly between labs, potentially resulting in large variations in findings across studies. In light of recent calls towards a standardization of PAT the current study's objective was to systematically and purposely evaluate the effects of block vs. interleaved administration—a fundamental consideration—on PAT measures in a within subject design. Additionally, this study evaluated whether measures of a Posner-type cueing paradigm parallels measures of the PAT paradigm. As hypothesized, results indicate that PAT performance is highly susceptible to administration mode. Interleaved mode resulted in larger error rates not only for anti (blocks: M = 22%; interleaved: M = 42%) but also for pro-saccades (blocks: M = 5%; interleaved: M = 12%). This difference between block and interleaved administration was significantly larger in anti-saccades compared to pro-saccades and cannot be attributed to a 'speed/accuracy tradeoff'. Interleaved mode produced larger pro and anti-saccade differences in error rates while block administration produced larger latency differences. Results question the reflexive nature of pro-saccades, suggesting they are not purely reflexive. These results were further discussed and compared to previous studies that included within subject data of blocks and interleaved trials.

Influence of Coactors on Saccadic and Manual Responses

Two experiments were conducted to investigate the effects of coaction on saccadic and manual responses. Participants performed the experiments either in a solitary condition or in a group of coactors who performed the same tasks at the same time. In Experiment 1, participants completed a pro- and antisaccade task where they were required to make saccades towards (prosaccades) or away (antisaccades) from a peripheral visual stimulus. In Experiment 2, participants performed a visual discrimination task that required both making a saccade towards a peripheral stimulus and making a manual response in reaction to the stimulus’s orientation. The results showed that performance of stimulus-driven responses was independent of the social context, while volitionally controlled responses were delayed by the presence of coactors. These findings are in line with studies assessing the effect of attentional load on saccadic control during dual-task paradigms. In particular, antisaccades – but not prosaccades – were influenced by the type of social context. Additionally, the number of coactors present in the group had a moderating effect on both saccadic and manual responses. The results support an attentional view of social influences.

Effects of preparation time and trial type probability on performance of anti- and pro-saccades

Cognitive control optimizes responses to relevant task conditions by balancing bottom-up stimulus processing with top-down goal pursuit. It can be investigated using the ocular motor system by contrasting basic prosaccades (look toward a stimulus) with complex antisaccades (look away from a stimulus). Furthermore, the amount of time allotted between trials, the need to switch task sets, and the time allowed to prepare for an upcoming saccade all impact performance. In this study the relative probabilities of anti- and pro-saccades were manipulated across five blocks of interleaved trials, while the inter-trial interval and trial type cue duration were varied across subjects. Results indicated that inter-trial interval had no significant effect on error rates or reaction times (RTs), while a shorter trial type cue led to more antisaccade errors and faster overall RTs. Responses following a shorter cue duration also showed a stronger effect of trial type probability, with more antisaccade errors in blocks with a low antisaccade probability and slower RTs for each saccade task when its trial type was unlikely. A longer cue duration yielded fewer errors and slower RTs, with a larger switch cost for errors compared to a short cue duration. Findings demonstrated that when the trial type cue duration was shorter, visual motor responsiveness was faster and subjects relied upon the implicit trial probability context to improve performance. When the cue duration was longer, increased fixation-related activity may have delayed saccade motor preparation and slowed responses, guiding subjects to respond in a controlled manner regardless of trial type probability.

Modulation of cognitive control levels via manipulation of saccade trial-type probability assessed with event-related BOLD fMRI

Cognitive control supports flexible behavior adapted to meet current goals and can be modeled through investigation of saccade tasks with varying cognitive demands. Basic prosaccades (rapid glances toward a newly appearing stimulus) are supported by neural circuitry, including occipital and posterior parietal cortex, frontal and supplementary eye fields, and basal ganglia. These trials can be contrasted with complex antisaccades (glances toward the mirror image location of a stimulus), which are characterized by greater functional magnetic resonance imaging (MRI) blood oxygenation level-dependent (BOLD) signal in the aforementioned regions and recruitment of additional regions such as dorsolateral prefrontal cortex. The current study manipulated the cognitive demands of these saccade tasks by presenting three rapid event-related runs of mixed saccades with a varying probability of antisaccade vs. prosaccade trials (25, 50, or 75%). Behavioral results showed an effect of trial-type probability on reaction time, with slower responses in runs with a high antisaccade probability. Imaging results exhibited an effect of probability in bilateral pre- and postcentral gyrus, bilateral superior temporal gyrus, and medial frontal gyrus. Additionally, the interaction between saccade trial type and probability revealed a strong probability effect for prosaccade trials, showing a linear increase in activation parallel to antisaccade probability in bilateral temporal/occipital, posterior parietal, medial frontal, and lateral prefrontal cortex. In contrast, antisaccade trials showed elevated activation across all runs. Overall, this study demonstrated that improbable performance of a typically simple prosaccade task led to augmented BOLD signal to support changing cognitive control demands, resulting in activation levels similar to the more complex antisaccade task.

Ocular motor signatures of cognitive dysfunction in multiple sclerosis

The anatomical and functional overlap between ocular motor command circuitry and the higher-order networks that form the scaffolding for cognition makes for a compelling hypothesis that measures of ocular motility could provide a means to sensitively interrogate cognitive dysfunction in people with multiple sclerosis (MS). Such an approach may ultimately provide objective and reproducible measures of cognitive dysfunction that offer an innovative capability to refine diagnosis, improve prognostication, and more accurately codify disease burden. A further dividend may be the validation and application of biomarkers that can be used in studies aimed at identifying and monitoring preventative, protective and even restorative properties of novel neurotherapeutics in MS. This Review discusses the utility of ocular motor measures in patients with MS to characterize disruption to wide-ranging networks that support cognitive function.

Stable Task Representations under Attentional Load Revealed with Multivariate Pattern Analysis of Human Brain Activity

Performing multiple tasks concurrently places a load on limited attentional resources and results in disrupted task performance. Although human neuroimaging studies have investigated the neural correlates of attentional load, how attentional load affects task processing is poorly understood. Here, task-related neural activity was investigated using fMRI with conventional univariate analysis and multivariate pattern analysis (MVPA) while participants performed blocks of prosaccades and antisaccades, either with or without a rapid serial visual presentation (RSVP) task. Performing prosaccades and antisaccades with RSVP increased error rates and RTs, decreased mean activation in frontoparietal brain areas associated with oculomotor control, and eliminated differences in activation between prosaccades and antisaccades. However, task identity could be decoded from spatial patterns of activation both in the absence and presence of an attentional load. Furthermore, in the FEFs and intraparietal sulcus, these spatial representations were found to be similar using cross-trial-type MVPA, which suggests stability under attentional load. These results demonstrate that attentional load may disrupt the strength of task-related neural activity, rather than the identity of task representations.

Ocular motor measures of cognitive dysfunction in multiple sclerosis II: working memory

Our companion paper documents pervasive inhibitory deficits in multiple sclerosis (MS) using ocular motor (OM) measures. Here we investigated the utility of an OM working memory (WMem) task in characterising WMem deficits in these patients as a function of disease status and disease duration. 22 patients with CIS, 22 early clinically definite MS patients (CDMS: <7 years of diagnosis), 22 late CDMS patients (>7 years from diagnosis), and 22 healthy controls participated. All participants completed the ocular motor WMem task, the paced auditory serial addition test (PASAT), and the symbol digit modalities test (SDMT). Clinical disability was characterised in CDMS patients using the Expanded Disability Severity Scale (EDSS). WMem performance was measured as proportion of errors (WMem errors), saccade latency, and relative sensitivity to WMem loading (WMem effect), an indicator of WMem capacity. All patient groups performed more WMem errors than controls with proportion of WMem errors, and degree of WMem effect increasing with increasing disease duration. A larger WMem effect, reflecting poorer WMem capacity, corresponded to poorer performance on neuropsychological measures, and a higher disability score for CDMS patients with the longest disease duration; an observation that suggests wider implication of WMem executive processes with advancing disease. Conspicuously, performance decrements on standard neuropsychological testing did not similarly increase commensurate with disease duration. The ocular motor WMem task appears to meaningfully dissociate WMem deficit from healthy individuals as well as a function of increasing disease duration. Potentially, this task represents a highly informative and objective method by which to ascertain progressive WMem changes from the earliest inception of MS.

Trial-type probability and task-switching effects on behavioral response characteristics in a mixed saccade task

Eye movement circuitry involved in saccade production offers a model for studying cognitive control: visually guided prosaccades are stimulus-directed responses, while goal-driven antisaccades rely upon more complex control processes to inhibit the prepotent tendency to look toward a cue, transform its spatial location, and generate a volitional saccade in the opposite direction. By manipulating the relative probability of these saccade types, we measured participants' behavioral responses to different levels of implicit trial-type probability and task-switching demands in conditions with relatively long inter-trial fixation and trial-type cue lengths. Results indicated that when prosaccades were less probable in a run, more prosaccade errors were generated; however, for antisaccades, trial-type probability had no effect on the percent of correct responses. For reaction times, specifically in runs with a larger probability of antisaccade trials, latencies increased for both anti- and pro-saccades. Furthermore, task switching resulted in a lower percentage of correct responses on switched trials, but a prior antisaccade trial led to slower reaction times for both trial types (i.e., a task switch cost for prosaccades and switch benefit for antisaccades). These findings indicate that cognitive control demands and residual inhibition from antisaccades alter performance relative to trial-type probability and task switching within a run, with the prosaccade task showing greater susceptibility to the influence of a large probability of cognitively complex antisaccades.

Oculomotor inhibitory control in express saccade makers

Express saccade makers (ESMs) produce high proportions (>30 %) of low-latency (80-130 ms) express saccades in tasks in which such responses are usually suppressed. In addition, high directional error rates on the antisaccade (AS) task suggest a failure of oculomotor inhibitory mechanisms in ESMs. However, the AS task is complex and does not provide a measure of inhibitory processes in isolation. We therefore examined inhibitory control in 25 ESM and 28 non-ESM ('Norm') participants, using a minimally delayed oculomotor response (MDOR) task. After a randomised fixation period, a pro-saccade target appeared for 200 or 1,000 ms. Participants were instructed to maintain fixation and saccade to the target position upon target offset. In a control task, they saccaded on target onset. Overall, saccade latency was considerably increased in the MDOR task compared to the control task (354 vs. 170 ms; p < 0.001), and we also observed a latency modulation with display time (200: 399, 1,000: 302 ms; p < 0.001). However, there was no evidence of a difference between groups (p = 0.29). Errors consisted primarily of responses to target onsets and error rates were comparable between the groups (p = 0.33). The overproduction of fast, reflexive responses was still observed in ESMs who generated a higher proportion of their errors within the express latency range (p < 0.001). We confirmed that in the AS task, the ESMs exhibited a higher directional error rate (p = 0.03). These results suggest that the performance 'deficit' observed on the AS task in ESMs cannot be attributed to generally weaker inhibitory control.

Symbiosis of executive and selective attention in working memory

The notion of working memory (WM) was introduced to account for the usage of short-term memory resources by other cognitive tasks such as reasoning, mental arithmetic, language comprehension, and many others. This collaboration between memory and other cognitive tasks can only be achieved by a dedicated WM system that controls task coordination. To that end, WM models include executive control. Nevertheless, other attention control systems may be involved in coordination of memory and cognitive tasks calling on memory resources. The present paper briefly reviews the evidence concerning the role of selective attention in WM activities. A model is proposed in which selective attention control is directly linked to the executive control part of the WM system. The model assumes that apart from storage of declarative information, the system also includes an executive WM module that represents the current task set. Control processes are automatically triggered when particular conditions in these modules are met. As each task set represents the parameter settings and the actions needed to achieve the task goal, it will depend on the specific settings and actions whether selective attention control will have to be shared among the active tasks. Only when such sharing is required, task performance will be affected by the capacity limits of the control system involved.

Modulation of antisaccade costs through manipulation of target-location probability: only under decisional uncertainty

Latencies of antisaccades made in the direction opposite to a peripheral target are typically slower longer than of prosaccades towards such a target by 50-100 ms. Antisaccades have proved to be an important tool for diagnostic purposes in neurology, psychology and psychiatry, providing invaluable insights into attentional function, decision making and the functionality of eye movement control. Recent findings have suggested, however, that latency differences between pro- and antisaccades can be eliminated by manipulating target-location probabilities. Pro- and antisaccades were equally fast to locations where a target rarely appeared, a finding that may be of promise for more elaborate diagnoses of neurological and psychiatric illness and further understanding of the eye movement system. Here, we tested probability manipulations for a number of different pro- and antisaccade tasks of varied difficulty. Probability only modulated antisaccade costs in a difficult antisaccade task involving decisional uncertainty with low target saliency. For other tasks including standard ones from the literature, target-location probability asymmetries had minimal effects. Probability modulation of antisaccade costs may therefore reflect effects upon decision making rather than saccade generation. This may limit the usefulness of probability manipulations of antisaccades for diagnostic purposes in neurology, psychology and related disciplines.

Attentional resource allocation during a cued saccade task

Attentional selection of sensory information and motor output is critical for successful interaction with one's surroundings. However, organization of attentional processes involved in selection of salient visual information, decision making, and movement planning has not yet been fully elucidated. We hypothesized that attentional processes involved in these tasks can function independently and draw from separate resources. If true, challenging the capacity limit of one attentional process would not affect performance of others. Healthy participants performed a cued saccade task in which target cues were embedded in a central stream of letters in a Rapid Serial Visual Presentation (RSVP). Participants performed saccades as quickly and as accurately as possible to a peripheral target location based on cue presentation within the central letter stream. To challenge visual attention, we parametrically varied the duration at which each letter of the RSVP was presented (50-200ms). In a separate experiment we challenged motor attention by increasing the number of possible saccade trajectories (1-6 peripheral targets). As expected, increasing attentional load in one domain of the task negatively affected performance in that domain, while performance in other domains was unaffected. We interpret our results as support for the independent allocation of attentional resources, at least in the early stages of processing, required across components of a cued saccade task. Deciphering the contributions of attention during visuomotor tasks is a critical step to understanding how humans process information necessary to successfully interact with the environment.

Focusing on attention: the effects of working memory capacity and load on selective attention

Background

Working memory (WM) is imperative for effective selective attention. Distractibility is greater under conditions of high (vs. low) concurrent working memory load (WML), and in individuals with low (vs. high) working memory capacity (WMC). In the current experiments, we recorded the flanker task performance of individuals with high and low WMC during low and high WML, to investigate the combined effect of WML and WMC on selective attention.

Methodology/Principal Findings

In Experiment 1, distractibility from a distractor at a fixed distance from the target was greater when either WML was high or WMC was low, but surprisingly smaller when both WML was high and WMC low. Thus we observed an inverted-U relationship between reductions in WM resources and distractibility. In Experiment 2, we mapped the distribution of spatial attention as a function of WMC and WML, by recording distractibility across several target-to-distractor distances. The pattern of distractor effects across the target-to-distractor distances demonstrated that the distribution of the attentional window becomes dispersed as WM resources are limited. The attentional window was more spread out under high compared to low WML, and for low compared to high WMC individuals, and even more so when the two factors co-occurred (i.e., under high WML in low WMC individuals). The inverted-U pattern of distractibility effects in Experiment 1, replicated in Experiment 2, can thus be explained by differences in the spread of the attentional window as a function of WM resource availability.

Conclusions/Significance

The current findings show that limitations in WM resources, due to either WML or individual differences in WMC, affect the spatial distribution of attention. The difference in attentional constraining between high and low WMC individuals demonstrated in the current experiments helps characterise the nature of previously established associations between WMC and controlled attention.

Capture of the gaze does not capture the mind

Sudden visual changes attract our gaze, and related eye movement control requires attentional resources. Attention is a limited resource that is also involved in working memory--for instance, memory encoding. As a consequence, theory suggests that gaze capture could impair the buildup of memory respresentations due to an attentional resource bottleneck. Here we developed an experimental design combining a serial memory task (verbal or spatial) and concurrent gaze capture by a distractor (of high or low similarity to the relevant item). The results cannot be explained by a general resource bottleneck. Specifically, we observed that capture by the low-similar distractor resulted in delayed and reduced saccade rates to relevant items in both memory tasks. However, while spatial memory performance decreased, verbal memory remained unaffected. In contrast, the high-similar distractor led to capture and memory loss for both tasks. Our results lend support to the view that gaze capture leads to activation of irrelevant representations in working memory that compete for selection at recall. Activation of irrelevant spatial representations distracts spatial recall, whereas activation of irrelevant verbal features impairs verbal memory performance.

The effects of self-report cognitive failures and cognitive load on antisaccade performance

Individuals reporting high levels of distractibility in everyday life show impaired performance in standard laboratory tasks measuring selective attention and inhibitory processes. Similarly, increasing cognitive load leads to more errors/distraction in a variety of cognitive tasks. How these two factors interact is currently unclear; highly distractible individuals may be affected more when their cognitive resources are taxed, or load may linearly affect performance for all individuals. We investigated the relationship between self-reported levels of cognitive failures (CF) in daily life and performance in the antisaccade task, a widely used tool examining attentional control. Levels of concurrent cognitive demand were manipulated using a secondary auditory discrimination task. We found that both levels of self-reported CF and task load increased antisaccade latencies while having no effect on prosaccade eye-movements. However individuals rating themselves as suffering few daily life distractions showed a comparable load cost to those who experience many. These findings suggest that the likelihood of distraction is governed by the addition of both internal susceptibility and the external current load placed on working memory.

Influence of response prepotency strength, general working memory resources, and specific working memory load on the ability to inhibit predominant responses: a comparison of young and elderly participants

One conception of inhibitory functioning suggests that the ability to successfully inhibit a predominant response depends mainly on the strength of that response, the general functioning of working memory processes, and the working memory demand of the task (Roberts, Hager, & Heron, 1994). The proposal that inhibition and functional working memory capacity interact was assessed in the present study using two motor inhibition tasks (Go/No-Go and response incompatibility) in young and older participants. The strength of prepotency was assessed with a short or long training phase for the response to be inhibited. The influence of working memory resources was evaluated by administering the tasks in full vs. divided attention conditions. The effect of working memory load was manipulated by increasing the number of target and distracter items in each task. Results showed no effect of prepotency strength, whereas dividing attentional resources and increasing working memory load were associated with greater inhibitory effects in both groups and for both tasks. This deleterious effect was higher for older participants, except in the working memory load condition of the Go/No-Go task. These results suggest an interactive link between working memory and response inhibition by showing that taxing working memory resources increases the difficulty of inhibiting prepotent responses in younger and older subjects. The additional detrimental effect of these factors on healthy elderly subjects was related to their decreased cognitive resources and to their shorter span size.

Attention control and the antisaccade task: a response time distribution analysis

In three experiments response time (RT) differences between correct prosaccade and antisaccade trials were examined via distribution analyses by fitting an ex-Gaussian function to individual RT distributions. Experiment 1 demonstrated that antisaccades are slower than prosaccades and this difference is due to both a shift in the overall distribution as well as a lengthening of the tail of the distribution. Experiment 2 demonstrated that manipulating foreperiod duration led to changes in both accuracy and RT for antisaccades but not prosaccades. Furthermore, the change in RT for antisaccades resulted in a lengthening in the tail of the distribution but not a shift in the distribution. Finally, Experiment 3 demonstrated that with sufficient practice performance on antisaccades was equated with performance on prosaccades in terms of both accuracy and RT. An examination of the RT distributions suggested that practice led to parallel changes in both the mean of the distribution and the tail of the antisaccade distribution. These results are interpreted within a two-factor theory of attention control that suggests that performance on antisaccades is driven by both competition resolution and goal-maintenance abilities.

Cognitive correlates of anti-saccade task performance

The anti-saccade task (AST) is widely used in experimental, clinical, and neuroscience research as a pronounced test of executive functions. AST research includes to some extent also the investigation into its cognitive correlates. In the present study, we have examined cognitive correlates of the AST in the short-term/working memory, executive functions, and intelligence domains in healthy adults. We have obtained the following results. In line with previous research, the global percentage of direction errors PDE comprised of two only negligibly correlated components, direction errors with express or regular latencies. Substantial correlations with the other cognitive measures were obtained only for regular direction errors and, less so, for the global PDE. Results add to the evidence that distinguishes express and regular direction errors and underline that the complex requirements of the AST are reflected in a comparatively rich set of non-redundant parameters.

[Saccade: a potential diagnostic tool and drug efficacy test criterion for mental disorders]

Saccades may play an important role in mental disorders research and diagnosis. Not only can saccade be used to help researchers to acquire the early and specific neuropathological changes, but also be a criterion of new drug development and drug efficacy tests. Abnormalities of saccadic eye movement appear in Parkinson's disease, Alzheimer's disease and major depressive disorder patients, but difficulties for its applications arise from unclear processes of neuropathological development and individual differences in patients. Establishing nonhuman primates' model of mental disorders and monitoring saccadic parameters during the model construction will help us to overcome such difficulties.

Executive working memory load does not compromise perceptual processing during visual search: evidence from additive factors analysis

Executive working memory (WM) load reduces the efficiency of visual search, but the mechanisms by which this occurs are not fully known. In the present study, we assessed the effect of executive load on perceptual processing during search. Participants performed a serial oculomotor search task, looking for a circle target among gapped-circle distractors. The participants performed the task under high and low executive WM load, and the visual quality (Experiment 1) or discriminability of targets and distractors (Experiment 2) was manipulated across trials. By the logic of the additive factors method (Sternberg, 1969, 1998), if WM load compromises the quality of perceptual processing during visual search, manipulations of WM load and perceptual processing difficulty should produce nonadditive effects. Contrary to this prediction, the effects of WM load and perceptual difficulty were additive. The results imply that executive WM load does not degrade perceptual analysis during visual search.

Need threat can motivate performance after ostracism

Ostracism threatens fundamental needs of belonging, self-esteem, control, and meaningful existence, which should motivate participants to respond to this threat. However, research has yet to examine the role of need threat in producing motivation after ostracism. In the current work, participants completed a "cognitive ability" (antisaccade) task following Cyberball-induced ostracism or inclusion. In two experiments, it was found that when ostracized, participants do not see antisaccade performance as a means of responding to the concerns produced by need threat; they respond only to the social threat, leading to worse performance than included participants (Experiments 1 and 2). However, when participants see an avenue of response (the Cyberball players can compare antisaccade performances), ostracized participants outperform included participants (Experiment 2). Moreover, this effect was mediated by the need for belonging, suggesting that ostracized participants were motivated to elevate their inclusionary status by demonstrating their worth on the cognitive ability task.

Saccade suppression by electrical microstimulation in monkey caudate nucleus

It has been suggested that the caudate nucleus, the input stage of the basal ganglia, facilitates and suppresses saccade initiation based on its anatomical characteristics. Although the involvement of the caudate nucleus in saccade facilitation has been shown previously, it is still unclear whether the caudate nucleus is also involved in saccade suppression. Here, we revealed the direct involvement of the caudate nucleus in saccade suppression by electrical microstimulation in behaving monkeys. We delivered microstimulation to the caudate nucleus while monkeys performed the prosaccade (look toward a peripheral visual stimulus) and antisaccade (look away from the stimulus) paradigm. The reaction times of contralateral saccades were prolonged on both prosaccade and antisaccade trials. The suppression effects on reaction times were stronger on prosaccade trials compared with antisaccade trials. The analysis of reaction time distributions using the linear approach to threshold with ergodic rate model (LATER model) revealed that microstimulation prolonged reaction times by reducing the rate of rise to the threshold for saccade initiation. Microstimulation also worsened correct performance rates for contralateral saccades. The same microstimulation prolonged and/or shortened the reaction times of ipsilateral saccades, although the effects were not as consistent as those on contralateral saccades. We conclude that caudate signals are sufficient to suppress contralateral saccades and influence saccadic decision by controlling contralateral and ipsilateral saccade commands at the same time.

The Effect of Cognitive Distraction on Saccadic Latency

Saccadic initiation is increasingly being studied as a surrogate for more general neural mechanisms of decision-making. Visual ‘decision-making’ is thought to be controlled by higher cortical functions. Lower areas such as the superior colliculus are thought to be involved with more primitive optomotor reflexes that can generate short-latency saccades. It is now well established that imposition of fronto-executive load on subjects performing a saccadic task which, in particular, involves suppression of saccades (the no-go saccadic task), increases the number of errors made. It is theorised that a weakening of cortical control of the superior colliculus is responsible for the increase in error rate. One way to test this theory is to measure the latency of incorrect saccades made in a no-go saccadic task in relation to error rate under different conditions of fronto-executive load. A high error rate combined with an increased number of short-latency saccades in the range of express or early saccades would indicate that subjects have an inability to inhibit these short-latency more reflexive saccades, which seem to originate in the superior colliculus. Hence the normal cortical control of the superior colliculus is weakened. We used a saccadic go/no-go task under fronto-executive load and found that the proportion of short-latency saccades increased with audio-verbal interference, in conjunction with an increase in error rate. These findings provide strong empirical evidence to support the theory that maintenance of cortical functions is key to the control of saccadic responses. Under conditions of fronto-executive loading such cortical control is weakened, leaving subjects with a reduced ability to inhibit short-latency more reflexive saccades.

The Search for Oculomotor Inhibition

When a saccadic target is presented simultaneously with a distractor, the distractor has to be inhibited in order to successfully perform an eye movement to the target. Insufficient inhibition results in an erroneous eye movement to the distractor. This study investigated whether the influence of a distractor on eye movements is mediated by working memory. A working memory task was added to a saccadic paradigm in which an irrelevant element had to be inhibited. Results show that participants made more erroneous saccades to the distractor when working memory was occupied. This suggests that working memory is involved in the oculomotor inhibition of saccadic distractors.

Antisaccade cost is modulated by contextual experience of location probability

It is well known that pro- and antisaccades may deploy different cognitive processes. However, the specific reason why antisaccades have longer latencies than prosaccades is still under debate. In three experiments, we studied the factors contributing to the antisaccade cost by taking attentional orienting and target location probabilities into account. In experiment 1, using a new antisaccade paradigm, we directly tested Olk and Kingstone's hypothesis, which attributes longer antisaccade latency to the time it takes to reorient from the visual target to the opposite saccadic target. By eliminating the reorienting component in our paradigm, we found no significant difference between the latencies of the two saccade types. In experiment 2, we varied the proportion of prosaccades made to certain locations and found that latencies in the high location-probability (75%) condition were faster than those in the low location-probability condition. Moreover, antisaccade latencies were significantly longer when location probability was high. This pattern can be explained by the notion of competing pathways for pro- and antisaccades in findings of others. In experiment 3, we further explored the degrees of modulation of location probability by decreasing the magnitude of high probability from 75 to 65%. We again observed a pattern similar to that seen in experiment 2 but with smaller modulation effects. Together, these experiments indicate that the reorienting process is a critical factor in producing the antisaccade cost. Furthermore, the antisaccade cost can be modulated by probabilistic contextual information such as location probabilities.

Using the antisaccade task to investigate the relationship between the development of inhibition and the development of intelligence

A number of authors have proposed models of cognitive development that explain improvements in intelligence over the course of childhood via changes in the efficiency of inhibitory processes (Anderson, 2001; Bjorklund & Harnishfeger, 1990; Dempster, 1991, 1992; Dempster & Corkill, 1999a; Harnishfeger, 1995; Harnishfeger & Bjorklund, 1993). A review of the literature reveals little empirical support for the thesis. This is largely due to a failure to distinguish between age-related and non-age-related changes in both inhibitory ability and intelligence. Empirical evidence is presented from a developmental study employing the antisaccade task to provide support for the role of inhibitory processes in the development of intelligence. Additionally, a case is made for a functional difference underlying antisaccade errors that are subsequently corrected and those that remain uncorrected.