Under time pressure, the exogenous modulation of saccade plans is ubiquitous, intricate, and lawful

Location- and feature-based selection histories make independent, qualitatively distinct contributions to urgent visuomotor performance

Attention mechanisms that guide visuomotor behaviors are classified into three broad types according to their reliance on stimulus salience, current goals, and selection histories (i.e., recent experience with events of many sorts). These forms of attentional control are clearly distinct and multifaceted, but what is largely unresolved is how they interact dynamically to determine impending visuomotor choices. To investigate this, we trained two macaque monkeys to perform an urgent version of an oddball search task in which a red target appears among three green distracters, or vice versa. By imposing urgency, performance can be tracked continuously as it transitions from uninformed guesses to informed choices, and this, in turn, permits assessment of attentional control as a function of time. We found that the probability of making a correct choice was strongly modulated by the histories of preceding target colors and target locations. Crucially, although both effects were gated by success (or reward), the two variables played dynamically distinct roles: whereas location history promoted an early motor bias, color history modulated the later perceptual evaluation. Furthermore, target color and location influenced performance independently of each other. The results show that, when combined, selection histories can give rise to enormous swings in visuomotor performance even in simple tasks with highly discriminable stimuli.

The reduction of saccadic inhibition by distractor repetition

When visual distractors are presented far from the goal of an impending voluntary saccadic eye movement, saccade execution will occur less frequently about 90 ms after distractor appearance, a phenomenon known as saccadic inhibition. However, it is also known that neural responses in visual and visuomotor areas of the brain will be attenuated if a visual stimulus appears several times in the same location in rapid succession. In particular, such visual adaptation can affect neurons in the mammalian superior colliculus (SC). As the SC is known to be intimately involved in the production of saccadic eye movements, and thus perhaps in saccadic inhibition, we used a memory-guided saccade task to test whether saccadic inhibition in humans would diminish if a distractor appeared several times in quick succession. We found that distractor repetition reduced saccadic inhibition considerably when distractors appeared opposite in space to the goal of the impending saccade. In addition, when three distractors appeared in quick succession but in different, spatially disparate locations, with only the final distractor appearing opposite the saccade goal, saccadic inhibition was reduced by an intermediate level, suggesting that its reduction due to distractor inhibition spatially generalizes. This suggests that distractor suppression can help reduce the impact that suddenly appearing visual stimuli have on purposive eye movement behavior.NEW & NOTEWORTHY This work combines approaches studying saccadic inhibition and visual adaptation to demonstrate that saccadic inhibition is largely eliminated with stimulus repetition. This is likely to be the largest demonstrated effect of visual stimulus context on saccadic inhibition. It also provides evidence for the existence of a mechanism that acts to suppress the effect of frequently appearing visual stimuli on purposive eye movement behavior in dynamic visual environments.

Stimulus salience conflicts and colludes with endogenous goals during urgent choices

Selecting where to look next depends on both the salience of objects and current goals (what we are looking for), but discerning their relative contributions over the time frame of typical visuomotor decisions (200-250 ms) has been difficult. Here we investigate this problem using an urgent choice task with which the two contributions can be dissociated and tracked moment by moment. Behavioral data from three monkeys corresponded with model-based predictions: when salience favored the target, perceptual performance evolved rapidly and steadily toward an asymptotic level; when salience favored the distracter, many rapid errors were produced and the rise in performance took more time-effects analogous to oculomotor and attentional capture. The results show that salience has a brief (∼50 ms) but inexorable impact that leads to exogenous, involuntary capture, and this can either help or hinder performance, depending on the alignment between salience and ongoing internal goals.

A conflict between spatial selection and evidence accumulation in area LIP

The lateral intraparietal area (LIP) contains spatially selective neurons that help guide eye movements and, according to numerous studies, do so by accumulating sensory evidence in favor of one choice (e.g., look left) or another (look right). To examine this functional link, we trained two monkeys on an urgent motion discrimination task, a task with which the evolution of both the recorded neuronal activity and the subject's choice can be tracked millisecond by millisecond. We found that while choice accuracy increased steeply with increasing sensory evidence, at the same time, the LIP selection signal became progressively weaker, as if it hindered performance. This effect was consistent with the transient deployment of spatial attention to disparate locations away from the relevant sensory cue. The results demonstrate that spatial selection in LIP is dissociable from, and may even conflict with, evidence accumulation during informed saccadic choices.

Exogenous capture accounts for fundamental differences between pro- and antisaccade performance

To generate the next eye movement, oculomotor circuits take into consideration the physical salience of objects in view and current behavioral goals, exogenous and endogenous influences, respectively. However, the interactions between exogenous and endogenous mechanisms and their dynamic contributions to target selection have been difficult to resolve because they evolve extremely rapidly. In a recent study (Salinas et al., 2019), we achieved the necessary temporal precision using an urgent variant of the antisaccade task wherein motor plans are initiated early and choice accuracy depends sharply on when exactly the visual cue information becomes available. Empirical and modeling results indicated that the exogenous signal arrives ∼80 ms after cue onset and rapidly accelerates the (incorrect) plan toward the cue, whereas the informed endogenous signal arrives ∼25 ms later to favor the (correct) plan away from the cue. Here, we scrutinize a key mechanistic hypothesis about this dynamic, that the exogenous and endogenous signals act at different times and independently of each other. We test quantitative model predictions by comparing the performance of human participants instructed to look toward a visual cue or away from it under high urgency. We find that, indeed, the exogenous response is largely impervious to task instructions; it simply flips its sign relative to the correct choice, and this largely explains the drastic differences in psychometric performance between the two tasks. Thus, saccadic choices are strongly dictated by the alignment between salience and behavioral goals.