Abstract
A purely temporal aspect of masking by light was studied using a modified Crawford paradigm.1 A 0.01-s pulse (the probe) was presented before, during, or after the flash, a 0.5-s pulse of intensity fixed at 25 or 100% of dc luminance (120 cd/m2). Either pulse incremented the luminance over the whole field (12° diameter). The observer’s task was to detect the probe as a change in the temporal shape of the brightness fluctuation due mainly to the flash. Probe thresholds were determined in a yes/no experiment with the probe and flash going to both eyes, the same eye, or opposite eyes. Masking was always strongest near flash onset and offset. Differences among the binocular, ipsilateral, or contralateral masking effects were small indicating the predominance of cortical on and off responses to spatially coextensive incremental pulses of luminance.2,3 Also, a binocular flash was not a stronger masker for a monocular probe, than the ipsilateral flash, although the binocular flash was brighter than a monocular flash at nominally identical luminance, area, and duration. An incremental flash is defined as a temporal interval limited by on and off responses and filled in by brightness.
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