EQUIDISTANCE SETTINGS AT PHOTOPIC RETINAL-ILLUMINANCE LEVELS AS A FUNCTION OF TARGET VELOCITY IN A FRONTAL PLANE.

Abstract

Equidistance settings for a black vertical rod oscillating in a given frontal plane have been obtained at three photopic levels of binocular retinal illuminance. The magnitude of the constant (localization) errors and that of the variable errors (average deviations) of the equidistance settings have been studied as functions of target velocity. For the two observers used, the magnitude of both the constant errors and the variable errors progressively increased as target velocity was increased. The effects were noted for settings obtained at each of the three retinal-illuminance levels. The direction of the localization errors, however, was opposite for the two observers. The effect of retinal-illuminance level on the depth settings was less systematic, due probably to the high photopic levels used. The data obtained on the constant errors suggest that, regardless of the direction of the localization error, the comparison rod was adjusted progressively closer to the actual plane of target oscillation as the level of retinal illuminance was increased. The variability of the settings for a given target velocity remained relatively constant at each of the three retinal-illuminance levels. The present results are discussed in relation to comparable data obtained in earlier experiments on stereoscopic acuity and on the Pulfrich stereophenomenon.