Abstract
We perceive a continuous, stable visual environment in spite of frequent saccadic eye movements. Saccadic suppression, i.e. a reduction in the sensitivity of the visual system at the time of the eye movement, is widely believed to support this perceptual stability. The neuronal basis of this phenomenon is not well understood yet. Psychophysical data suggested an early suppression site, like the LGN or area V1, while electrophysiological studies provided mixed results pointing rather toward higher extrastriate and parietal areas. In this study we investigated the hypothesis, that the diversity of the reported results might be due to methodological reasons: In studies, in which strong saccadic suppression was observed, typically a brief single stimulus was flashed at random times in different trials ('flash stimulation'); no or only weak suppression was found when some form of continuous stimulation that started well before the eye movement (e.g. permanent natural images or ongoing flicker) was used ('continuous stimulation'). In the present study, we recorded multi-unit activity in area V1 of the macaque monkey and compared the perisaccadic response modulations in conditions of flash and continuous stimulation. Continuous stimulation caused rapid neuronal adaptation during fixation, i.e. an initial transient response after stimulation onset was followed by a rapid decline until a stable level of sustained activity was reached. This level was only slightly modulated perisaccadically. Typically, a small reduction in activity during the eye movement was followed by a postsaccadic enhancement. For flashed stimuli, however, we observed a strong modulation: perisaccadic stimuli elicited a response that was reduced in amplitude by more than half of the value obtained during fixation. Our results provide evidence that strong saccadic suppression effects can be observed early in the visual system, at least as early as in V1.
Meeting abstract presented at VSS 2014