Naghmeh Mostofi


VSS Best Poster Awards 2013

Space-time characteristics of visual input modulations resulting from saccades.

Naghmeh Mostofi1, Marco Boi1,Martina Poletti1, Jonathan D. Victor3, Michele Rucci1,2 ;1-Department of Psychology, Boston University, 2-Graduate Program in Neuroscience, Boston University, 3-Department of Neurology and Neuroscience, Weill Cornell Medical College.

Under natural viewing conditions, eye movements continually modulate the input signals to the retina. Saccades occur 2-3 times per second, and microscopic eye movements are present during the intersaccadic periods of visual fixation. It is critical to characterize the spatiotemporal input resulting from this incessant alternation between large and small eye movements, as this is the input signal to the visual system. In a previous study, we have focused on fixational eye movements (Kuang et al., 2012) and shown that, during viewing of natural scenes, microscopic eye movements carry out a crucial information-processing step: they remove predictable correlations in natural scenes by equalizing the spatial power of the retinal image within the frequency range of ganglion cells’ peak sensitivity, a transformation, previously attributed to center-surround receptive field organization.

Here, we focus on the temporal modulations resulting from saccades, which strongly affect neural responses at fixation onset. We show that the space-time transformation due to saccades consists of two distinct regimes. Below a critical low spatial frequency, K, saccades amplify spatial frequency; that is, like ocular drift, the amount of temporal power they yield increases with the spatial frequency of the stimulus. Above K, instead, saccadic temporal modulations equally transform all spatial frequencies. The cut-off frequency K depends on the amplitude of saccades, it is smaller with larger saccades.

Furthermore, for any saccade there is a critical high spatial frequency (related to its amplitude) above which the temporal modulations resulting from ocular drift contain more power than those given by saccades. These results suggest that saccades and ocular drift contribute to encoding different frequency ranges, with saccades enhancing low spatial frequencies and drift fi lling in high spatial frequencies. We present the results of psychophysical experiments which support this hypothesis.

Acknowledgement: NIH EY018363, NSF 1127216, NSF 0843304, NIHR90DA0333460.

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