VLSI processor for reliable stereo matching based on adaptive window-size selection

科研費報告書収録論文(課題番号:12555119・基盤研究(B)(2) ・H12～H14/研究代表者:亀山, 充隆/最適構成理論に基づく高安全知能自動車用VLSIプロセッサチップファミリの開発

Effect of background luminance on visual responses to strong flashes : perceived brightness and the early rise of photoreceptor responses

The threshold intensity for large-long incremental stimuli rises proportionally to adapting background luminance IB (Weber adaptation), but the intensity required to evoke a criterion high-brightness sensation rises much less steeply. We propose that this difference originates in the very first stage of visual processing, in the phototransduction and adaptation properties of the retinal photoreceptor cells. A physiological model previously found to account for visual latency and brightness as functions of stimulus intensity in the dark-adapted state [Donner, K. (1989). Visual Neuroscience, 3, 39–51] is extended to cover different states of adaptation. It is assumed that the neural coding of high intensities is based on the rate of rise (quasi-derivative) of the photoreceptor response just after it reaches a small threshold amplitude. The shallow background adaptation functions for high-brightness criteria emerge as a consequence of the relative constancy of the leading edge of large responses under backgrounds, a phenomenon that can be formally described by compensating changes in photoreceptor sensitivity and time scale. We first test the model on supra-threshold responses in the frog retina, where the discharge rate of ganglion cells (a possible neural code for brightness) and the primary rod hyperpolarizations can be recorded under identical conditions. The two are related as predicted over at least 3 log units of background intensity. We then show that published data on the background adaptation of human foveal high brightness judgments conform to the same model, assuming that human cones accelerate as IB−b with b = 0.14–0.15

Spectral characteristics and regionalization of the eye of the satyrid Bicyclus anynana

The ommatidial characteristics of the eyes of many insects are non-uniform (Stavenga, 1992). The retinal heterogeneity has been investigated in the satyrid Bicyclus anynana by in vivo microspectrophotometry of the eye shine from individual ommatidia. The ommatidial reflectances fall into two classes. The reflectance of the first, yellow-green (YG) class has a main band peaking at 570 nm (width ca 50 nm) and a subsidiary band in the violet; the second, red (R) class has a broad band from 580 to 680 nm. All ommatidia in the dorsal part of the eye belong to the YG-class. The ommatidia of the ventral part of the eye belong to either the YG- or the R-class. The density of the R-class is highest in the downward-looking area. The eye shine is maximal in the dark-adapted eye, but it rapidly decreases upon illumination with bright light, due to migration of pigment granules towards the light guiding rhabdom. The time constant of this pupil mechanism is in the order of a few seconds. The reflectance also exhibits distinct spectral changes due to changes in the content of the visual pigments in the rhabdom. This phenomenon allows studying the decay and renewal of visual pigment in vivo