A common sensorimotor map underlying counting, visual-spatial working memory 
and trans-saccadic perception

David Melcher
Center for Mind/Brain Sciences, University of Trento, Italy

Real-world perception is typically trans-saccadic: we see the same object 
across multiple fixations. Yet saccadic eye movements can dramatically change 
the location in which an object is projected onto the retina. In a series 
of experiments using eye tracking, psychophysics, neuroimaging and TMS, we 
have investigated how information from a previous fixation can influence 
perception in the subsequent fixation. Specifically, we have tested the idea 
that the “remapping” of receptive fields around the time of saccadic eye 
movements might play a role of trans-saccadic perception. Our results suggest 
that two mechanisms interact to produce stable, “object-otopic” perception 
across saccades. First, a limited number of objects that are individuated in 
a scene (treated as unique objects potentially subject to action, as opposed 
to being part of the background gist) are represented and updated across 
saccades in a sensorimotor “saliency map” (including areas in posterior 
parietal cortex and frontal eye fields).

Second, and more controversially, we suggest that the updating of these 
“pointers” in the map leads to the remapping of visual receptive fields in 
intermediate visual areas. We have found that perception can be described as 
retinotopic, spatiotopic or even—in the case of moving objects or immediately 
before saccades —neither of the above. At the same time, however, the visual 
system must give priority to retinal information, which tends to be most 
reliable during fixation of stable objects.