Abstract

Excitability functions were determined by measuring the threshold luminance of a circular test flash (43′, 5 msec) at various temporal intervals before and after the onset of a larger concentric 25-msec conditioning flash. The paired stimuli were presented in maxwellian view to the right eye, either centrally, or 7° or 15° in the nasal field. The conditioning flash was either 57′, 1°50′, 2°43′, or 3°30′ in diameter, and was either scotopic, or one of two photopic luminances. The results show that (1) luminance is the most powerful nontemporal determinant of the increment threshold, (2) as the conditioning diameter increases, test threshold decreases with central or 7° photopic stimuli, but with scotopic peripheral stimuli, the test threshold increases and then decreases. For photopic stimuli at 15°, increasing the CF diameter generally raises the increment threshold. In general, the diameter for maximal increment threshold becomes progressively larger as luminance is decreased or as stimulation occurs farther in the periphery. These results are discussed in terms of the neural organization under different conditions of luminance and retinal position.

© 1968 Optical Society of America

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