The influence of eye movements and their retinal consequences on bistable motion perception
Eye related movements such as blinks and microsaccades are modulated during bistable perceptual tasks, however, the role of such movements in these purely internal perceptual switches is not known. We conducted two experiments involving an ambiguous plaid stimulus, wherein participants had to continuously report their motion percept. To dissociate the effect of blinks and microsaccades from the visual consequences of such eye movements, we added external blanks and microshifts. Our results showed that while blanks facilitated a switch to the coherent motion percept, this was not the case for a switch to component percept. A similar difference was found with respect to blinks. While both types of perceptual switches were preceded by a decrease in blinks, only the switch to coherent percept was followed by an increase in blinks. These blink related findings, which we largely replicated and refined in a second study, indicate distinct internal processes underlying the two perceptual switches. Microsaccade rates, on the other hand, only showed a weak relation with perceptual switches but their direction was modulated by the perceived motion direction. Additionally, our data showed that microsaccades are differently modulated around internal (blinks) and external events (blanks, microshifts), indicating an interaction between different eye related movements. This study shows that eye movements such as blinks and microsaccades are modulated by purely internal perceptual events independent of task related motor or attentional demands. Eye movements therefore can uncover distinct internal perceptual processes that might otherwise be hard to dissociate.