William R. Biersdorf

Quantitative functions for size and distance judgments

A psychophysical approach was used to obtain judgments of visual extent under three conditions. In tuvo conditions a comparison stimulus at each of two distances was matched in size to a standard which varied in distance. Stimuli were presented on a well-lighted table and were judged by two observers under Objective instructions. Both the standard and comparison were located in either a frontal or longitudinal plane. In a third condition relative distance estimates were given of two stimuli which varied in their relative positions along the table. The mean results for all conditions were described as a power function of physical stimulus measures. The exponent was greater than 1.0 for frontal size and usually less than 1.0 for flat size and distance. The position of the comparison affected the magnitude of the exponents to a lesser degree. These findings have relevance for interpretations of size and distance judgments.

Flicker and Color Adaptation in the Human Electroretinogram

Flickering ten millisecond light stimuli have been used to elicit the human electroretingram under conditions of chromatic adaptation. The resulting records have been examined both for participation of photopic and scotopic mechanisms, and for selective wavelength effects. With slowly flickering stimuli (4 flashes per second) the ERG (electroretinogram) exhibited distinct photopic and scotopic components even when recorded from eyes that were well light adapted. More rapidly flickering stimuli (20 flashes per second) elicited pre-eminently photopic potentials. It was found that the adaptation stimuli, depending upon their color, were effective in reducing the sensitivity of one or the other component, but that specific chromatic effects within either component were quite small. The results are discussed in relation to psychophysical data and earlier ERG experimentation.

Luminance-duration relationships in the light-adapted electroretinogram.

The applicability of the Bunsen-Roscoe law to the components of the human electroretinogram was investigated under conditions of moderate light adaptation. Simultaneous X and B waves were obtained with red test stimulation and A and B waves with white test stimulation. Both response amplitude and implicit time were measured. The A and X waves were found to adhere to the Bunsen-Roscoe law and have relatively constant implicit times. The response amplitude of the B waves showed systematic departures from a simple Bunsen-Roscoe model and their implicit times varied with both stimulus duration and luminance.

Effects of an Artificial Pupil and Accommodation on Retinal Image Size

A very small artificial pupil in front of the eye allows a distinct view of an object when accommodation is incorrect. Helmholtz reported that the retinal image size of the object is changed when the eye is not accommodated for the object. Binocular size matching with an artificial pupil before one eye is used to provide quantitative data relating image-size change to accommodation and distance of the artificial pupil from the eye. Control experiments, including paralysis of accommodation in one eye, establish that the phenomenon is related to accommodation and is not an artifact of other variables.

Level of Light Adaptation and the Human Electroretinogram

This report deals with the effects of two adaptational variables upon the human electroretinogram. First, further investigation of a temporal increase in electroretinogram amplitude during light adaptation is reported. The effects of red and white test flashes were compared at several adaptation levels. The temporal increase was found only for high luminance adaptation levels and only for white test flashes. Second, the effects of constant luminance test flashes upon a wide range of adaptation levels were investigated. It was found that increasing levels of light adaptation produced decreases in the amplitudes of the components of the electroretinogram. Long latency components were affected by lower levels of light adaptation and to a greater extent than short latency components. The results are considered in relation to the duplicity theory and to the resting potential of the eye.

Response of the Human Eye to Sudden Changes in the Wavelength of Stimulation

The human electroretinogram (ERG) was elicited by an abrupt replacement of a chromatic adaptation stimulus with a long duration test stimulus. It was found that the relative spectral sensitivity of the ERG was strongly dependent upon the color and luminance of the adaptation stimulus with adaptation to a particular color lowering sensitivity to the same part of the spectrum. Clear-cut responses were produced by test luminances below an adaptation luminance only when the two were far apart in the spectrum. Analysis of the data gave definite evidence for two spectral processes with maxima near 500 and 620 mμ. There was evidence for other possible processes in the green and blue but their maxima were not well defined.

Effects of stimulus duration upon spectral sensitivity of the human electroretinogram.

The effects of three stimulus durations on spectral sensitivity of the electroretinogram were examined under moderate light adaptation. The durations were 11, 42, and 109 msec. At a low criterion amplitude of response, the 11-msec duration showed lower sensitivity in the green and blue regions of the spectrum than the two longer durations. At the red end of the spectrum all curves showed elevated sensitivity of approximately equal amounts. For a moderate criterion amplitude, the curves for the various durations retained their relative positions at the shorter wavelengths. At the red end of the spectrum, sensitivity decreased for all durations, but to a greater amount for the two longer durations. For a high criterion response, the 11-msec duration became more sensitive throughout the spectrum; however, it retained a form similar to that for the two longer durations. The curves were presumed to include at least two components: a scotopic process and a red-sensitive process. Possible interpretations of the duration effects on the spectral curves included the Bunsen–Roscoe law and the summation of on- and off-responses.

Electrical responses of the human eye following intense chromatic pre-exposures

Abstract The spectral sensitivity of the human electroretinogram was investigated in early dark-adaptation following high-luminance pre-exposures of yellow, blue and green light. The scotopic contribution to the spectral curves was greatly reduced, with maximum sensitivity occurring at longer wavelengths. For low-criterion a -waves the peak sensitivity was near 555 mμ, while low-criterion b -waves tended to have higher sensitivity in the red region of the spectrum. Selective effects from the chromatic pre-exposures were small for the b -wave and not apparent for the a -wave. Comparison of the a - and b -wave sensitivities showed that the b -wave retained more responsiveness at short wavelengths.

The spectral sensitivity of the human electroretinogram during the temporal course of dark-adaptation

Abstract Threshold curves derived from the b-wave of the ERG show similarities to analogous psychophysical data. There is an immediate decrease in threshold for the first minute and then a leveling off at about 8–12 min depending on the color of the stimulus light. For shorter wavelengths there is a clear break in the curve, the threshold decreasing again and becoming asymptotic between 22 and 30 min. This total change of threshold covers a range of over 3 log units. With longer wavelengths, the break in the curve is scarcely evident. Peak latency curves of threshold responses show pronounced breaks for all tested wavelengths. The a-waves show little evidence of breaks. Spectral curves derived early in dark-adaptation show a characteristic scotopic function plus a long wavelength process for the b-wave. The a-wave at this time shows scotopic plus elevated middle and long wavelength activity. For both waves, with more time in the dark, the longer wavelength processes tend to diminish in sensitivity The spectral curves here tend to conform more closely to the scotopic function.