Abstract
Neurons in the primary visual cortex (V1) change their responses depending on stimulus parameters such as orientation, spatial frequency (SF), size and so on. In this study, we investigated how stimulus size effects on SF tuning property of neurons in V1 and lateral geniculate nucleus (LGN) of cats. First, we found that V1 neurons increased sensitivity to high SF stimuli when small gratings were used and that SF selectivity of V1 neurons was sharpened when large gratings were used, according to the shifts of peak and high cut-off of SF tuning curves. Second, we measured area summation tuning curves under several SF grating conditions, and found that a higher SF stimulus caused a reduction of the receptive field size and an increase of the surround suppression. The same tendency was observed in LGN, which is the main source of excitatory input to V1. This implies that the relationship between SF and area summation properties observed in V1 has its origin in LGN and is modified in the intracortical network. These results suggest how neural circuit in early visual pathway changes its way of information processing and how it reduces redundancy in various visual environments; for small visual objects, neurons increase SF sensitivity to get fine resolution, on the other hand, for large ones, they sharpen SF selectivity to reduce redundancy. [J Physiol Sci. 2006;56 Suppl:S176]
