Presaccadic processes in the generation of pro and anti saccades in human subjects--a reaction-time study

Inhibition failures and late errors in the antisaccade task: influence of cue delay

In the antisaccade task participants are required to saccade in the opposite direction of a peripheral visual cue (PVC). This paradigm is often used to investigate inhibition of reflexive responses as well as voluntary response generation. However, it is not clear to what extent different versions of this task probe the same underlying processes. Here, we explored with the Stochastic Early Reaction, Inhibition, and late Action (SERIA) model how the delay between task cue and PVC affects reaction time (RT) and error rate (ER) when pro- and antisaccade trials are randomly interleaved. Specifically, we contrasted a condition in which the task cue was presented before the PVC with a condition in which the PVC served also as task cue. Summary statistics indicate that ERs and RTs are reduced and contextual effects largely removed when the task is signaled before the PVC appears. The SERIA model accounts for RT and ER in both conditions and better so than other candidate models. Modeling demonstrates that voluntary pro- and antisaccades are frequent in both conditions. Moreover, early task cue presentation results in better control of reflexive saccades, leading to fewer fast antisaccade errors and more rapid correct prosaccades. Finally, high-latency errors are shown to be prevalent in both conditions. In summary, SERIA provides an explanation for the differences in the delayed and nondelayed antisaccade task. NEW & NOTEWORTHY In this article, we use a computational model to study the mixed antisaccade task. We contrast two conditions in which the task cue is presented either before or concurrently with the saccadic target. Modeling provides a highly accurate account of participants' behavior and demonstrates that a significant number of prosaccades are voluntary actions. Moreover, we provide a detailed quantitative analysis of the types of error that occur in pro- and antisaccade trials.

Cerebral blood flow modulations during preparatory attention and proactive inhibition

This study investigated cerebral blood flow modulations during task preparation in a precued saccade paradigm. Bilateral blood flow velocities in the middle cerebral arteries were recorded in 48 subjects using functional transcranial Doppler sonography. Video-based eye-tracking was applied for ocular recording. Antisaccade and prosaccade trials were presented in both block-wise and interleaved order. A right dominant flow response arose during task preparation. While the response was stronger during antisaccade than prosaccade trials, the degree of lateralisation did not differ between the two trial types. Direction error rates were higher and latencies were longer for antisaccades than prosaccades. There were no differences between block-wise and interleaved trials in blood flow or performance. The stronger blood flow increases during antisaccade than prosaccade preparation reflects the complexity of the upcoming task demands as well as proactive inhibition. The right hemispheric lateralisation may be attributed to preparatory attention independent of demands on inhibitory control.

Consider the context: blocked versus interleaved presentation of antisaccade trials

Conclusions about the cognitive and neural requirements of saccade control may differ as a result of stimulus presentation method. This issue was examined in the current study by evaluating behavioral differences in pro- and antisaccade responses among 12 healthy young adults as a function of task presentation method, length of cue-to-target interval, and previous trial type. A 1-s cue-to-target interval fostered goal neglect, indicated by an increase in uncorrected errors and reaction times for "error" saccades. There was also a strong relationship between speed of visual orienting (prosaccade latencies) and failed inhibition (antisaccade errors) for the simultaneous condition. Interestingly, only the simultaneous condition produced task switch costs (on saccade latencies and error response percentages). The saccadic task presentation method, therefore, can influence conclusions about the cognitive operations supporting successful performance.

An effect of context on saccade-related behavior and brain activity

The present study evaluated the effect of context on behavior and brain activity during saccade tasks. FMRI and eye movement data were collected while 36 participants completed three runs in a block design: (1) fixation alternating with pro-saccades, (2) fixation alternating with anti-saccades, and (3) pro- alternating with anti-saccades. Two task-related data-driven regressors, identified using independent component analysis, were used in GLM analyses. Brain activity associated with anti- and pro-saccades were compared under both single (runs 1 and 2) and mixed saccade (run 3) conditions. Brain areas consistently associated with anti-saccades in previous studies, including striatum, thalamus, cuneus, precuneus, lateral and medial frontal eye fields (FEF), supplementary eye fields (SEF), and prefrontal cortex (PFC) showed significantly greater percent signal change during the fixation/anti- compared with the fixation/pro-saccade run. During the pro/anti run, however, only precuneus, SEF and FEF showed greater activation during the anti-saccade trials. This is a clear demonstration that the saccade-related neural circuitry is affected by context. Behavioral results suggest that performance on saccade tasks is also affected by context. Participants made more direction errors on pro-trials that followed anti-trials than on pro-trials that followed fixation. Results from this study indicate that precuneus, SEF and FEF, which showed anti-saccade-related activity during both comparisons, may be more important for supporting this complex behavioral response. Other brain regions, such as PFC, however, which showed anti-saccade-related activity during only the single task comparison, may be more involved in response selection and/or context updating.

Task-switching in schizophrenia: active switching costs and passive carry-over effects in an antisaccade paradigm

It has been hypothesized that impaired task-switching underlies some of the behavioural deficits in schizophrenia. However, task-switching involves many cognitive operations. In this study our goal was to isolate the effects on latency and accuracy that can be attributed to specific task-switch processes, by studying the inter-trial effects in blocks of randomly mixed prosaccades and antisaccades. By varying the preparatory interval between an instructional cue and the target, we assessed the costs of both (1) an active reconfiguration process that was triggered by the cue, and (2) passive carry-over effects persisting from the prior trial. We tested 15 schizophrenic subjects and 14 matched controls. A very short preparatory interval increased error rates and saccadic latencies in both groups, but more so in schizophrenia, suggesting difficulty in rapidly activating saccadic goals. However, the contrast between repeated and switched trials showed that the costs of task switching in schizophrenia were not significantly different from the controls, at either short or long preparatory intervals, for both antisaccades and prosaccades. These results confirm prior observations that passive carry-over effects are normal in schizophrenia, and show that active reconfiguration is also normal in this disorder. Thus problems with executive control in schizophrenia may not affect specific task-switching operations.

Task Switching as a Two-Stage Decision Process

Saccades represent decisions, and the study of their latency has led to a neurally plausible model of the underlying mechanisms, LATER (Linear Approach to Threshold with Ergodic Rate), that can successfully predict reaction time behavior in simple decision tasks, with fixed instructions. However, if the instructions abruptly change, we have a more complex situation, known as task switching. Psychologists' explanations of the phenomena of task switching have so far tended to be qualitative rather than quantitative, and not intended to relate particularly clearly to existing models of decision making or to likely neural implementations. Here, we investigated task switching using a novel saccadic task: we presented the instructions by stimulus elements identical to those of the task itself, allowing us to compare decisions about instructions with decisions in the actual task. Our results support a relatively simple model consisting of two distinct LATER processes in series: the first detects the instruction, the second implements it.

Eye Movements during Task Switching: Reflexive, Symbolic, and Affective Contributions to Response Selection

Active vision is a dynamic process involving the flexible coordination of different gaze strategies to achieve behavioral goals. Although many complex behaviors rely on an ability to efficiently switch between gaze-control strategies, few studies to date have examined mechanisms of task level oculomotor control in detail. Here, we report five experiments in which subjects alternated between conflicting stimulus-saccade mappings within a block of trials. The first experiment showed that there is no performance cost associated with switching between pro and anti saccades. However, follow-up experiments demonstrate that whenever subjects alternate between arbitrary stimulus-saccade mappings, latency costs are apparent on the first trial after a task change. More detailed analysis of switch costs showed that latencies were particularly elevated for saccades directed toward the same location that had been the target for a saccade on the preceeding trial. This saccade “inhibition of return” effect was most marked when unexpected error feedbacks cued task switches, suggesting that saccade selection processes are modulated by reward. We conclude that there are two systems for saccade control that differ in their characteristics following a task switch. The “reflexive” control system can be enabled/disabled in advance of saccade execution without incurring any performance cost. Switch costs are only observed when two or more arbitrary stimulus-saccade mappings have to be coordinated by a “symbolic” control system.

Age Equivalence in Switch Costs for Prosaccade and Antisaccade Tasks

This study examined age differences in task switching using prosaccade and antisaccade tasks. Significant specific and general switch costs were found for both young and old adults, suggesting the existence of 2 types of processes: those responsible for activation of the currently relevant task set and deactivation of the previously relevant task set and those responsible for maintaining more than 1 task active in working memory. Contrary to the findings of previous research, which used manual response tasks with arbitrary stimulus-response mappings to study task-switching performance, no age-related deficits in either type of switch costs were found. These data suggest age-related sparing of task-switching processes in situations in which memory load is low and stimulus-response mappings are well learned.

Are better eye movements an advantage in ball games? A study of prosaccadic and antisaccadic eye movements

The aim of this study was to compare prosaccadic and antisaccadic eye movements of experts in ball sports and controls. In the prosaccadic and antisaccadic task, subjects made saccades respectively towards and away from a suddenly appearing stimulus. By means of infrared-oculography, we compared horizontal eye movements of experts (n=18) and controls (n=20). Experts had shorter overall saccadic latencies, but significantly shorter latencies occurred only on the antisaccade task, not on the prosaccade task. Our findings seem to support the concept that prosaccades and antisaccades have different underlying mechanisms and that expertise in ball games mainly improves antisaccadic performance in terms of latency and variability.

On the production and correction of involuntary prosaccades in a gap antisaccade task

In an antisaccade task, where saccades in the direction opposite of a suddenly presented stimulus are required, certain numbers of prosaccades can occur. The hypothesis is put forward that poor fixation and poor voluntary saccade control constitute two independent sources for the errors. This possibility is investigated by including the corrections of the errors in the analysis. First, the eye movements of 346 normal subjects (group N) performing a gap antisaccade and an overlap prosaccade task were measured. For each subject the proportion of express saccades in the overlap prosaccade task and the proportion of prosaccades in the gap antisaccade task were determined. The data of 150 subjects with more than 20% proerrors were divided into two groups: group A with relatively many, group B with relatively few express saccades in the overlap prosaccade task. Group A subjects produced their errors after significantly shorter reaction times and they corrected their errors significantly faster and more often than group B subjects. Second, we analysed the data of three groups of subjects: the complete normal group N, a group D of dyslexic subjects (n=343), and a group T containing all subjects irrespective of their cognitive achievements (n=780). A highly significant negative correlation exists between the correction rates and the error rates. A factor analysis of the variables performed for each group separately results in only two factors, one describing prosaccade the other antisaccade control. Only the error rate contributes significantly to both factors indicating that high errors may have two independent reasons.

Primate antisaccades. I. Behavioral characteristics

The antisaccade task requires a subject to make a saccade to an unmarked location opposite to a flashed stimulus. This task was originally designed to study saccades made to a goal specified by instructions. Interest for this paradigm surged after the discovery that frontal lobe lesions specifically and severely affect human performance of antisaccades while prosaccades (i.e., saccades directed to the visual stimulus) are facilitated. Training monkeys to perform antisaccades was rarely attempted in the past, and this study is the first one that describes in detail the properties of such antisaccades compared with randomly intermingled prosaccades of varying amplitude in all directions. Such randomization was found essential to force the monkeys to use the instruction cue (pro- or anti-) and the location cue (peripheral stimulus) provided within a trial rather than to direct their saccades to the location of past rewards. Each trial began with the onset of a central fixation target that conveyed by its shape the instruction to make a pro- or an antisaccade to a subsequent peripheral stimulus. In one version of the task, the monkey was allowed to make an immediate saccade to the goal; in a second version, the saccade had to wait for a go signal. Analyses of the accuracy, velocity, and latency of antisaccades compared with prosaccades were performed on a sample of 7,430 pro-/antisaccades in the "immediate saccade" task (delayed saccades suffering from known distortions). Error rates fluctuated approximately 25%. Results were the same for the two monkeys with respect to accuracy and velocity, but they differed in terms of reaction time. Both monkeys generated antisaccades to stimuli in all directions, at various eccentricities, but antisaccades were significantly less accurate and slower than prosaccades elicited by the same stimuli. Interestingly, saccades to the stimulus could be followed by appropriate antisaccades with no intersaccadic interval. Such instances are here referred to as "turnaround saccades." Because they occurred sometimes with a long latency, turnaround saccades did not simply reflect the cancellation of an early foveation reflex. Consistent with human data, latencies of one monkey were longer for antisaccades than for prosaccades, but the reverse was true for the other monkey who was trained differently. In summary, this study demonstrates the feasibility of providing a subhuman primate model of antisaccade performance, but at the same time it suggests some irreducible differences between human and monkey performance.

The antisaccade: a review of basic research and clinical studies

The ability to suppress reflexive responses in favor of voluntary motor acts is crucial for everyday life. Both abilities can be tested with an oculomotor task, the antisaccade task. This task requires subjects to suppress a reflexive prosaccade to a flashed visual stimulus and instead to generate a voluntary saccade to the opposite side. This article reviews what is currently known about the neural structures and processes which are involved in the performance of this task. Current data show that a variety of brain lesions, neurological diseases and psychiatric disorders result in errors, i.e. prosaccades towards the stimulus, in this task. Brain imaging studies have shown that a widely distributed cortical and subcortical network is active during the generation of antisaccades. These findings are discussed and the potential of the antisaccade task for diagnostic purposes is evaluated.

Antisaccade performance predicted by neuronal activity in the supplementary eye field

The voluntary control of gaze implies the ability to make saccadic eye movements specified by abstract instructions, as well as the ability to repress unwanted orientating to sudden stimuli. Both of these abilities are challenged in the antisaccade task, because it requires subjects to look at an unmarked location opposite to a flashed stimulus, without glancing at it. Performance on this task depends on the frontal/prefrontal cortex and related structures, but the neuronal operations underlying antisaccades are not understood. It is not known, for example, how excited visual neurons that normally trigger a saccade to a target (a prosaccade) can activate oculomotor neurons directing gaze in the opposite direction. Visual neurons might, perhaps, alter their receptive fields depending on whether they receive a pro- or antisaccade instruction. If the receptive field is not altered, the antisaccade goal must be computed and imposed from the top down to the appropriate oculomotor neurons. Here we show, using recordings from the supplementary eye field (a frontal cortex oculomotor centre) in monkeys, that visual and movement neurons retain the same spatial selectivity across randomly mixed pro- and antisaccade trials. However, these neurons consistently fire more before antisaccades than prosaccades with the same trajectories, suggesting a mechanism through which voluntary antisaccade commands can override reflexive glances.