Transient and sustained effects of stimulus properties on the generation of microsaccades

Abstract

Saccades shift the gaze rapidly every few hundred milliseconds from one fixated location to the next, producing a flow of visual input into the visual system even in the absence of changes in the environment. During fixation, small saccades called microsaccades are produced 1-3 times per second, generating a flow of visual input. The characteristics of this visual flow are determined by the timings of the saccades and by the characteristics of the visual stimuli on which they are performed. Previous models of microsaccade generation have accounted for the effects of external stimulation on the production of microsaccades, but they have not considered the effects of the prolonged background stimulus on which microsaccades are performed. The effects of this stimulus on the process of microsaccade generation could be sustained, following its prolonged presentation, or transient, through the visual transients produced by the microsaccades themselves. In four experiments, we varied the properties of the constant displays and examined the resulting modulation of microsaccade properties: their sizes, their timings, and the correlations between properties of consecutive microsaccades. Findings show that displays of higher spatial frequency and contrast produce smaller microsaccades and longer minimal intervals between consecutive microsaccades; and smaller microsaccades are followed by smaller and delayed microsaccades. We explain these findings in light of previous models and suggest a conceptual model by which both sustained and transient effects of the stimulus have central roles in determining the generation of microsaccades.

Oculomotor freezing reflects tactile temporal expectation and aids tactile perception

“…This limitation to trials with high temporal predictability suggests that precise temporal planning is needed to proactively schedule microsaccades. Usually, microsaccade triggering is characterized either as automatic, elicited by neural noise [66][67][68] , or as reactive, e.g., driven by current changes in visual input [69][70][71] , top-down signals from spatial attention 39,72,73 (but see ref. 74 ), or accumulated fixation error signals 46,72 .…”

Oculomotor freezing reflects tactile temporal expectation and aids tactile perception

“…This limitation to trials with high temporal predictability suggests precise temporal planning is needed to proactively schedule microsaccades. Usually microsaccade triggering is characterized either as automatic, elicited by neural noise 66–68 , or as reactive, e.g., driven by current changes in visual input 69–71 , top-down signals from spatial attention 39,72,73 (but see 74 ) or accumulated fixation error-signals 46,72 . A proactive component has not been included yet in models of microsaccade generation.…”

A unified model of the task-evoked pupil response

“…In our model, it was important to include a post-saccade refractory period because real saccades exhibit an approximately 125 ms refractory period [144], whereas the Gaussian noise added to the generator function could generate saccades in rapid succession with unrealistically short inter-saccadic intervals. Saccades exhibit a refractory period that resembles the one commonly observed in neural spiking, suggesting it is neural in origin [141, 142, 144].…”

“…In our model, it was important to include a post-saccade refractory period because real saccades exhibit an approximately 125 ms refractory period [144], whereas the Gaussian noise added to the generator function could generate saccades in rapid succession with unrealistically short inter-saccadic intervals. Saccades exhibit a refractory period that resembles the one commonly observed in neural spiking, suggesting it is neural in origin [141, 142, 144]. The inter-saccadic interval distribution for microsaccades and small fixational saccades differ [141], with the former following an exponential distribution as expected for a Poisson process (i.e., random timing, fixed rate) and the latter approximating a gamma distribution.…”