| Research Abstract |
The receptive fields of retinal bipolar cells (BCs) comprise concentrically organized, opponent center and surround regions, indicating a crucial role for BCs in spatial information processing. The purpose of this study is to examine the central receptive fields and surround receptive fields of BCs under various intensities of background light, and to clarify how the BCs modify their spatial property under natural light environment. The BC's surround receptive is due to the input from horizontal cells (HCs). Our physiological experiments using carp retinae showed that HC receptive fields, measured by scanning the retina with a flash of slit, shrink after the prolonged background illumination of more than 5 min. The spatio-temporal receptive fields of HCs, estimated by applying a light stimuli modulated in both space and tine, shrank with time lag, so that an after image appeared in the HC layr to a moving pattern is inhibited. The central receptive field of BCs was physiologicaly examined by scanning the retina with a small slit (50・ 200 mum). The results showed that the central receptive field size of BCs was slightly enlarged under the background illumination, but usually the change of receptive field size was smaller than those of HCs
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