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Perceptual continuity

We take it for granted that the visual world is stable, yet we move our eyes almost continuously. Moreover, we only have high-resolution vision in a small region at the centre of our visual field, yet we believe that we see the entire visual image in high resolution. How does the brain give us the impression of visual stability and uniform high spatial definition? Answering these questions has been one of the most fundamental tasks for vision scientists and psychologists for over a century.

The NVRI conducts experiments both at its Carlton site and in its satellite laboratory at Monash University that investigate these fundamental issues. Drs Markus Hietanen and Adam Morris form the core of this research group. They work closely with our collaborators at Monash University, Professor Marcello Rosa and Dr Nicholas Price. We have established that visual processing undergoes very fundamental changes at the time of saccadic eye movements. Saccades are eye movements that shift our gaze from one location in the visual scene to another and occur at a rate of three times per second. We have shown that certain areas of the brain are attenuated during these eye movements, which assists in removing the blurred signals of a moving world that would otherwise occur during saccades, which can move the eyes at speeds of 500 degrees per second.

Perhaps more exciting is the observation that immediately after saccades those same brain areas become hyperactive and respond more strongly to visual stimulation than normal. Our observations suggest that attenuating visual sensitivity during saccades and improving visual sensitivity after saccades are integral parts of maintaining visual stability in the face of continuous gaze changes. Therefore, we get the best of both worlds: we can change our gaze direction to maximize our capacity for high-resolution vision across the entire visual field, while not losing our sense of visual stability. The other exciting conclusion to be drawn from this work is that the motor system is influencing how the visual system takes in information: we are not passive observers – rather we actively search each visual scene for what we want and tune our visual systems to see what we need.