Biomedical subjects

Hirohisa Yaguchi

Publications and source records attributed to Hirohisa Yaguchi.

3 recordsLinked to original sources

PubMed2006

Stereo channels with different temporal frequency tunings.

To investigate the spatial and temporal frequency tunings for stereopsis, we measured the contrast sensitivity for depth discrimination with variable spatiotemporal frequencies and disparities using drifting sinusoidal gratings. The results showed that the contrast sensitivity changed with the stimulus disparity and the disparity tuning function varied with the spatial frequency. The disparity in the peak sensitivity decreased proportionally with the spatial frequency (size-disparity correlation). Although the temporal frequency exhibited a limited influence on the peak disparity, the temporal frequency tuning varied with the spatial frequency. The shape of the temporal frequency tuning function was lowpass for higher spatial frequencies, whereas it was bandpass for low spatial frequencies. These results suggest that more than one channel with different temporal as well as spatial frequency tunings contribute to stereopsis.

Contrast Sensitivity↗

PubMed2002

Smooth shifts of visual attention.

To examine whether visual attention shifts continuously across the visual field, we measured sensitivity to a small flash presented at various locations while the observer was tracking a moving target in an ambiguous apparent motion display. The sensitivity peaked near the target and the peak shifted smoothly along the apparent motion path. Since the peak-shift speed varied with the speed of the tracked target, we conclude that the attention mechanism selects the location to facilitate processing by tracking the target disk continuously. Attention does not simply select a location for enhanced processing, but rather predicts the future location of the object of interest based on its velocity.

Attention↗

PubMed2002

Detection of relative and uniform motion.

We measured the lowest velocity (velocity threshold) for discriminating motion direction in relative and uniform motion stimuli, varying the contrast and the spatial frequency of the stimulus gratings. The results showed significant differences in the effects of contrast and spatial frequency on the threshold, as well as on the absolute threshold level between the two motion conditions, except when the contrast was 1% or lower. Little effect of spatial frequency was found for uniform motion, whereas a bandpass property with a peak at approximately 5 cycles per degree was found for relative motion. It was also found that contrast had little effect on uniform motion, whereas the threshold decreased with increases in contrast up to 85% for relative motion. These differences cannot be attributed to possible differences in eye movements between the relative and the uniform motion conditions, because the spatial-frequency characteristics differed in the two conditions even when the presentation duration was short enough to prevent eye movements. The differences also cannot be attributed to detecting positional changes, because the velocity threshold was not determined by the total distance of the stimulus movements. These results suggest that there are two different motion pathways: one that specializes in relative motion and one that specializes in uniform or global motion. A simulation showed that the difference in the response functions of the two possible pathways accounts for the differences in the spatial-frequency and contrast dependency of the velocity threshold.

Journal Article↗