Abstract

Assuming that the internal response to a brief change of luminance is biphasic,¹ it has been proposed² that responses to binocular stimuli must be interocularly in phase to produce a hypothetical fused effect represented psychophysically as binocular summation (e.g., at threshold). Binocular summation has been demonstrated³ for stimuli that were both spatially and temporally in 0 or 180° phase. These observations are in agreement with the model.² To test it further, we measured differential luminance thresholds for binocular stimuli of like and opposite polarity as a function of interocular delay (SOA). Pulse duration was a parameter between 5 and 150 ms. With no delay, thresholds were lower for like than for opposite polarity stimuli: the usual finding. The relationship was reversed at a critical delay, near SOA = 50 ms. This effect was at maximum for pulses of 50-ms duration, which suggests that (1) both on and off parts of a pulse contribute to the net response and (2) there is a limit (a temporal window) of phase dependent binocular interaction.

© 1987 Optical Society of America