It is expected that the properties of human visual receptive field change due to the state of adaptation. The receptive field properties may be described by the line spread function
l (χ). However we have no easy direct psychophysical method to measure
l (χ). Instead of the autocorrelation function of
l (χ) can be decided directry if we utilize the two stimuli method. In this method the additivity of two narrow line stimuli is measured and then the auto-correlation function of
l (χ) is calculated from the degree of additivity for various stimuli separations. The auto-correlation function of
l (χ) were investigated for three kinds of adapting field. Then it was found that on high adapting field luminance the auto-correlation functions of
l (χ) had positive and negative phases which represented the excitatory and inhibitory property of receptive field. On the contrary the auto-correlation function of
l (χ) on low luminance adapting field had no negative phase. Therefore it was suggested that the excitatory area enlarged and the inhibitory response decreased when the adapting field luminance lowered.
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