Perceptual enhancement as a result of a top-down attentional influence in a scene viewing task: Evidence from saccadic inhibition

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.

Saccadic inhibition during free viewing in macaque monkeys

Through the process of saccadic inhibition, visual events briefly suppress eye movements including microsaccades. In humans, saccadic inhibition has been shown to occur in response to the presentation of parafoveal or peripheral visual distractors during fixation and target-directed saccades and to physical changes of behaviorally relevant visual objects. In monkeys performing tasks that controlled eye movements, saccadic inhibition of microsaccades and target-directed saccades has been shown. Using eye data from three previously published studies, we investigated how saccade rate changed while monkeys were presented with visual stimuli under conditions with loose or no viewing demands. In two conditions, animals passively sat while an LED lamp flashed or screen-wide images appeared in front of them. In the third condition, images were repeated semiperiodically while animals had to maintain their gaze within a wide rectangular area and detect oddballs. Despite animals not being required to maintain fixation or make saccades to particular targets, the onset of visual events led to a temporary reduction of saccade rate across all conditions. Interestingly, saccadic inhibition was found at image offsets as well. These results show that saccadic inhibition occurs in monkeys during free viewing.NEW & NOTEWORTHY We investigated the time courses of saccade rate following visual stimuli during three conditions of free viewing in macaque monkeys. Under all conditions, saccade rate decreased transiently after the onset of visual stimuli. These results suggest that saccadic inhibition occurs during free viewing.

Neurocognitive analyses reveal that video game players exhibit enhanced implicit temporal processing

Winning in action video games requires to predict timed events in order to react fast enough. In these games, repeated waiting for enemies may help to develop implicit (incidental) preparation mechanisms. We compared action video game players and non-video game players in a reaction time task involving both implicit time preparations and explicit (conscious) temporal attention cues. Participants were immersed in virtual reality and instructed to respond to a visual target appearing at variable delays after a warning signal. In half of the trials, an explicit cue indicated when the target would occur after the warning signal. Behavioral, oculomotor and EEG data consistently indicate that, compared with non-video game players, video game players better prepare in time using implicit mechanisms. This sheds light on the neglected role of implicit timing and related electrophysiological mechanisms in gaming research. The results further suggest that game-based interventions may help remediate implicit timing disorders found in psychiatric populations.

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

The choice of where to look next is determined by both exogenous (bottom-up) and endogenous (top-down) factors, but details of their interaction and distinct contributions to target selection have remained elusive. Recent experiments with urgent choice tasks, in which stimuli are evaluated while motor plans are already advancing, have greatly clarified these contributions. Specifically, exogenous modulations associated with stimulus detection act rapidly and briefly (∼25 ms) to automatically halt and/or boost ongoing motor plans as per spatial congruence rules. These stereotypical modulations explain, in quantitative detail, characteristic features of many saccadic tasks (e.g. antisaccade, countermanding, saccadic-inhibition, gap, and double-step). Thus, the same low-level visuomotor interactions contribute to diverse oculomotor phenomena traditionally attributed to different neural mechanisms.

Saccadic inhibition interrupts ongoing oculomotor activity to enable the rapid deployment of alternate movement plans

Diverse psychophysical and neurophysiological results show that oculomotor networks are continuously active, such that plans for making the next eye movement are always ongoing. So, when new visual information arrives unexpectedly, how are those plans affected? At what point can the new information start guiding an eye movement, and how? Here, based on modeling and simulation results, we make two observations that are relevant to these questions. First, we note that many experiments, including those investigating the phenomenon known as "saccadic inhibition", are consistent with the idea that sudden-onset stimuli briefly interrupt the gradual rise in neural activity associated with the preparation of an impending saccade. And second, we show that this stimulus-driven interruption is functionally adaptive, but only if perception is fast. In that case, putting on hold an ongoing saccade plan toward location A allows the oculomotor system to initiate a concurrent, alternative plan toward location B (where a stimulus just appeared), deliberate (briefly) on the priority of each target, and determine which plan should continue. Based on physiological data, we estimate that the advantage of this strategy, relative to one in which any plan once initiated must be completed, is of several tens of milliseconds per saccade.