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T S Aiba

Publications and source records attributed to T S Aiba.

7 recordsLinked to original sources
PubMed1995

The spatiotemporal range of inhibitory interaction in flicker detection.

The flicker thresholds of luminous bars were measured as a function of the spatial and/or temporal separation of two flickering stimuli. Each of the bars had an intensity profile of one-half cycle of a sinusoidal wave subtending 2.26 x 0.45 arc deg and each bar was presented twice at two positions with a duration of 10 msec. The spatial separation was defined as the distance between the adjacent flanks of two flickering stimuli, while the temporal separation was determined as the time-lag between the offset of the first flickering stimulus and the onset of the second. We found that the thresholds increased asymptotically with the spatial separation in such a way as to suggest that the spatial extent over which inhibitory interaction could be effective was as large as about 2 arc deg. We also found that the threshold gradually decreased with greater temporal separation; this indicated that the temporal proximity of successive stimuli effects less suppression on the temporal response. These two effects were seemingly additive. These findings suggest that the visual system involves not only local spatial interaction, but also a global mechanism capable of spreading inhibition over several local units after a delay of several msec.

Flicker Fusion↗
PubMed1987

Temporal integration in human vision and the opponent-color systems.

The present study demonstrated that the temporal integration time (t.i.t.) could be prolonged even if the background energy was increased, provided that the background consisted of the colors opponent to each other. This was found, more or less, irrespective of the test stimulus size. These results suggest that the t.i.t. is not determined solely at receptor sites in the visual system, but that the chromatically-opponent systems are heavily involved. Mechanisms based upon a two-sites adaptation with one detection pathway model were briefly discussed.

Adaptation, Ocular↗
PubMed1987

Color-opponent characteristics revealed in temporal integration time.

The critical durations for temporal integration at threshold were obtained for lights of various wavelengths, presented both against darkness and against achromatic or chromatic backgrounds of different luminances. The critical duration (tc) was defined by a point of intersection of the two lines with the slopes of zero and unity in a log I.t-t plot, fitted by means of an algorithm implemented by computer program. tc was short for the lights of middle wavelengths, longer for the lights at the ends of the spectrum, and became shorter as the background luminance increased. tc also depended on the background wavelength, generally showing color-opponent characteristics when the difference was taken between tc's for the chromatic background and those for the achromatic one. The results were interpreted as the manifestation of chromatically-opponent system activities in temporal integration.

Color Perception↗
PubMed1985

Positional acuity with chromatic stimuli.

Theoretical reasons are presented for expecting a high precision spatial acuity task (vernier acuity) to be more difficult with an equiluminous stimulus than with stimuli containing luminance cues. This prediction was verified in Experiment 1. In a second experiment, it was shown that the result of the first experiment could not be explained by reduced detectability of the equiluminous target bar. We explain these results by the conflicting demands of chromatic and spatial differencing within a single mechanism, and propose that this also explains the similarities between long and medium wavelength cones in their spectral sensitivities.

Color Perception↗
PubMed1985

Vernier acuity predicted from changes in the light distribution of the retinal image.

If two thin bars of different luminance are placed side by side, their joint spatial position in a Vernier alignment task is determined simply by their relative luminances. The threshold luminance contrast difference required to produce a just detectable change in spatial position corresponds to a spatial shift of 5-20 arcsec in the centroid of the retinal light distribution, depending upon contrast relative to the background. This technique may be used to measure acuity with a display that has a spatial resolution considerably worse than the Vernier offset threshold. We have also extended the centroid technique to components that differ both in wavelength and luminance. Colour was found to make no essential difference to the task. Taking into account the spread of light in the retinal image, the manifest contrast thresholds are equivalent to threshold intensity increments between adjacent foveal receptors of less than 1% comparable to the values reported by Hecht and Mintz for dark line detection.

Contrast Sensitivity↗
PubMed1967

The electroretinogram evoked by the excitation of human foveal cones.

1. A 2 degrees test stimulus foveally fixed and viewed against a blue background (40 degrees in extent and producing 2.0 x 10(4) scotopic td of retinal illuminance) evokes a small voltage which can be recorded from the human eye with a conventional contact lens electrode if the test stimulus is flashed at a rate of 15 c/s, and the responses to at least several hundred flashes are averaged.2. The action spectrum of the response obtained in this way agrees reasonably well with the observer's psychophysical foveal luminosity curve.3. For the peripheral retina, the action spectrum is similar to that of the fovea when allowance is made for differences in screening macular pigment.4. Such responses diminish when the test stimulus is focused on to the peripheral retina and disappear when the test light is focused on the blind spot.5. Therefore, the response to the test light fixated centrally is the result of the excitation only of cones mainly, if not exclusively, in the fovea.6. When the intensity of the background is reduced by a factor of 10, the action spectrum shows evidence of the effect of excitation of rods in the blue part of the spectrum and of cones in the red. These red and blue responses add linearly when combined together, provided they are adjusted to coincide in phase.

Journal Article↗