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Abstract

Natural images have a characteristic second order statistics since their amplitude spectra fall with spatial frequency (f) as 1/fα, where α is about 1.0. It is thought that visual neurones may exploit this statistical redundancy in order to process visual information efficiently. We examined whether the responses of V1 neurons to gratings in their classical receptive field (RF) are affected by the α of images surrounding their RF.
Single neurons in V1 of anaesthetised paralysed marmosets were stimulated with a static grating of optimal orientation, spatial frequency and phase, which covered the RF. The contrasts of the grating varied between 0 and 100%. Gratings were surrounded by 10ox10o images which were either natural images, natural images filtered to an α of 0, 0.5, 1.0, 1.5, 2.0 and 2.5 or a control uniform background of the same mean luminance as the grating. Stimuli were presented for 250ms simultaneously and extra cellular activity was recorded.
Mean firing rate in the 250ms window showed little effect of surround α on the responses of our population of neurons to gratings. Analysis of response latencies revealed a small effect of surround image statistics on response latency of V1 neurons to gratings, but only below 50% grating contrast. At α values less than 1.0, latencies tended to be shorter than the control while above 1.0, latencies were about 30ms longer. We discuss these findings in terms of corresponding psychophysical experiments and optimal processing of information in real world scenes.