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Biomedical subjects

N Osaka

Publications and source records attributed to N Osaka.

At least 55 records · Page 3Linked to original sources
PubMed1982

Exponent of the Broca-Sulzer flash duration as a function of retinal eccentricity.

The flash duration producing maximum brightness-enhancement changes as a power function of luminance, that is, the time locus of the Broca-Sulzer flash duration TB, decreases as luminance L increases: TB = k x L beta , where beta is the duration exponent. The exponent of TB was estimated for 1-deg white flash fovea, 10-, 20-, 30-, 40-, 50-, and 60-deg temporal eccentricities of the dark-adapted human right eye. The following method of brightness maximization was used: the observer adjusted the duration of constant luminance flashes to produce a maximally bright flash. Duration was adjusted by rotating a microprocessor-based potentiometer. The results showed that the duration of the brightest flash TB decreased as L increased with the negative power exponent. Furthermore, the size of the negative exponent decreased as a function of increasing retinal eccentricity. Time-dependent brightness processing in the fovea and periphery is discussed in terms of the psychophysical brightness power function.

Dark Adaptation↗
PubMed1982

Exponent of the latency of brightness power functions in the fovea and periphery of the visual field.

RT and perceived brightness against log luminance, covering the range between 3.4 and - 1.6 log cd/m2 in steps of 1 log unit, were measured at the fovea, 20 degrees, and 40 degrees in the periphery. The RT and brightness data were fitted to the RT and brightness power function, respectively. It was found that (a) asymptotic RT increased as eccentricity increased and that (b) the RT exponent decreased as retinal eccentricity increased: Estimated mean RT exponent was found to be approximately - .31 in the fovea, but - .25 and - .17 in the 20 degrees, and 40 degrees periphery, respectively. Further, (c) the brightness exponent tended to increase as eccentricity increased. The RT exponent in the fovea was in agreement with the exponent for perceived brightness (.36); however, the RT exponent in the periphery was about 1/2 to 2/3 as small as that in the fovea. This implies that as luminance changes equal RT contour changes as a function of eccentricity. That is, RT in the periphery does not primarily depend on the target's brightness but its luminance.

Adult↗
PubMed1980

Effect of peripheral visual field size upon visual search in children and adults.

Twenty observers in each of the age groups, three, four, five, and twenty-one years, were asked to identify pictures displayed through five different sizes of peephole. Recognition latency changes as a cube-root power function of aperture area. It was found that latency decreased as age and area increased. However, the exponent of the power function showed little age-related change. Effectiveness of the peripheral visual field size was discussed in terms of magnitude of the exponent.

Adult↗
PubMed1980

Human intelligence and power spectral analysis of visual evoked potentials.

The relationship between intelligence and power spectra of visual evoked potential was investigated using 8 normal and 8 mentally retarded children as subjects. The results showed the power spectrum of mentally retarded has a peak at 4 to 6 Hz, whereas that of normal has two apparent peaks at 4 and 12 Hz. It appears the peak at 12 Hz reflects the difference of intelligence.

Adolescent↗
PubMed1980

Luminance range effect on brightness exponent in the fovea and periphery.

Using a method of magnitude estimation, the exponent of the brightness power function has been determined for functions describing the brightness of stimuli presented at the fovea and the following peripheral retinal locations: 10, 20, 30, 40, and 50 degrees nasally eccentric to the fovea along the horizontal meridian of the right eye. The exponent for a 1-sec. flash was significantly increased as a function of increasing eccentricity at the lower luminance ranges whereas slightly increased at the higher luminance ranges.

Discrimination Learning↗
PubMed1979

[Brightness power function and equal brightness contour for dark- and light-adapted eye in the peripheral visual field (author's transl)].

To test whether the equal brightness contour at supra-threshold runs parallel with the contour at threshold, magnitude estimation and the staircase procedure were employed for estimating brightness power function under dark- and light-adaptation. The luminance was changed from 43 to 83 dB re 10(-6) cd/m2 with the light adapting luminance at 53 dB. The retinal loci tested were 0 degrees to 70 degrees periphery in steps of 10 degrees. The exponent of the power function gradually increased from .37 to .73 as eccentricity and adapting luminance increased. The equal brightness contour decreased for dark-adaptation and increased for light-adaptation as eccentricity increased at supra-threshold but at threshold did not follow the parallel hypothesis for both adapting conditions.

Adaptation, Ocular↗
PubMed1978

VEP latency and RT as power functions of luminance in the peripheral visual field.

Behavioral correlates of P1 latency of visual evoked potentials (VEPs) were investigated using visual reaction time (RT) as a measure at the fovea, 20 degrees and 40 degrees nasal retinal eccentricities along the horizontal meridian of the right eye. Three luminances of the target in steps of 1 log units were used: 26, 260 and 2600 cd/m2. As luminance increased VEP latency and RT decreased. Further, as eccentricity increased VEP latency and RT increased. The highest product-moment coefficient of correlation (r = 0.998) was found between RT and P1 latency in the fovea, whereas the coefficient of correlation was found to be slightly small in the peripheral loci. The data (both VEPs and RTs) were fitted by the power function of the form: T = kLB + T0 where T, k, L T0 and B indicate VEP latency (or RT, scaling constant, luminance, asymptotic latency and exponent of the power function, respectively. This shows how the VEP latency and the RT can be related to luminance with exponent B. It was found that psychophysical power law governs VEP latency as well as RT with an exponent of about -0.32. It was suggested that both RT AND P1 latencies of VEP originate in the similar nonlinear visual system.

Adult↗
PubMed1978

Brightness exponent for the periphery in the Bloch region.

Using a method of direct magnitude estimation, perceived brightness was measured in the dark-adapted eye with brief flashes of varying duration in the Bloch region (1-100 ms) and retinal lock (0 degrees-40 degrees) for the photopic luminance levels covering the range between 140 and 0.14 cd/m2 in steps of 1 log unit. Perceived brightness increased as a function of flash luminous energy (product of luminance and duration) up to critical duration of approximately 100 ms. The brightness power exponent for brief flash was found to be 0.48 +/- 0.01 in the fovea, whereas about 0.44 +/- 0.01 in the periphery.

Humans↗
PubMed1977

Effect of refraction on perceived locus of a target in the peripheral visual field.

A target of 44 min of arc with luminance of 1.03 log cd/m2 of 50 msec duration was presented to the loci along each of nasal, temporal, superior, and inferior half retinal meridians covering the eccentricity between 10 degrees and 50 degrees in steps of 10 degrees units. Two graduate students, serving as Ss, were instructed to point out the perceived locus where the target had appeared. The visual angles between the perceived and physical locus of the target were increased as a function of retinal eccentricity due to refraction.

Humans↗