The nonlinearity of the yellow-blue color opponent system was tested by determining the hue cancellation code for yellow and blue lights on a white background light of 84 ~ 41000 td. The nonliearity depends on the intensity of background white light and the wavelength of yellow lights. The effect of the adaptation of the background can be ascribed to difference between the changing Properties with light adaptation of S cone system and those of M and L cone systems. The wavelength dependencies cannot be ascribed to the nonlinearities of the cones system, but to the distinct nonlinear properties of the two yellow components at the post-receptor site.

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The system of human postural control is a nonlinear open system in which there are dynamical interactions between the visual system, the vestibular system and somatic sensation. Here we examine the effects of depth information in visual stimuli on postural control by measuring "body sway". Our purpose is to construct a mathematical model of postural control in order to design visual display systems which are well-matched to human visual perception. Postural changes of standing subjects were measured during presentation of moving visual stimuli for two depth conditions : disparity or no disparity. Data analysis consisted of estimation of locus length, Lyapunov spectra and variance. Clear effects of depth information were found. To addition, we present related data for eye and head movement, and investigate the effect of disparity information on OKN.

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Using a CRT display we investigated how the color of a region influences on the perceptual colors of neibouring regions. When we displayed two neiboring strip regions, the color of a region appeared to invade the neiboring region and, spreading therein, caused the region to have an altered uniform color This suggests that the visual system, after decomposing the visual picture into elementary uniform regions on the basis of the brightness pattern, assign a color to every elementary region on the basis of the color information of poor spatial resolution. We propose a simple mathematical model of such a visual process and Show that the model roughly predicts exprimental data on the perceptual color alteration.

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The MST region of the visual cortex responds to visual stimuli in motion. Research using monkeys has shown that MST neurons are direction sensitive. Within this region is a subset of neurons which are also sensitive to stimulus size. consequently, we assume that MST neurons play an important role in the perception of relative motion. Using this information about MST neuron properties, we have developed and evaluated a visual processing model.

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A new mathematical spatio-temporal model of the human vision system has already been proposed which can quantitatively simulate spatio-temporal visual responses to flickering and drifting sinusoidal waves. In this paper, for applying the model to images with any motion, the X-channel's temporal impulse response and the Y-channel's one of the vision system are estimated by using Hilbert transform and incorporated into the model. As an appropriate example, this model is applied to flashed sinusoidal waves with various exposure durations, arid it is shown that the model can theoretically reproduce spatial frequency characteristics of contrast sensitivities and relations between contrast threshold and exposure duration.

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