Visually Evoked Response Correlates of Perceptual Masking and Enhancement

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Paired flashes, evoked potentials, paired reponse

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The perception of some characteristic of a brief test flash (TF) such as brightness, form, or orientation, can be influenced by the subsequent presentation of a second closely following and overlapping brighter flash (BF). If the interflash interval ([FI) is brief (90 msec or less) the TF will be masked by the BF (see review by Raab 1963). It the IFI is longer than that required for masking of the TF (100-150 msec), the brightness of the TF can be enhanced (Donchin and Lindsley 1965). The IFI values for both masking and enhancement effects depend upon a difference in luminance between the TF and the BF; in general the higher the luminance of the BF relative to the TF, the higher the IFI at which masking and enhancement will occur. The development of new techniques has made it possible to follow the changes induced in at least one aspect of neural activity in human subjects as stimulus conditions are varied (see Whipple 1964 for numerous studies of sensory evoked response in man). Using the computer averaging technique, we have recorded evoked potentials elicited by paired flashes which gave rise to the perceptual phenomena described above and it was found (Donchin et al. 1963), by visual inspection of the records, that average evoked potentials elicited by paired flashes can be classified into three groups as a function of the interval between the two flashes. In the present study the responses obtained to paired flashes have been further analyzed by attempting to separate the components contributed by each flash of the pair. In addition, in order to compare t Supported by NSF grant GB-1844, NASA contract NsG-623, and aided by Navy contract Nonr 233 (32). 2 Present address: Division of Neurology, Stanford University Medical School, Palo Alto, Calif. the observed modifications of the TF evoked potential to the observed perceptual changes, the analysis was performed for three different values of TF luminance. Specifically, average evoked potentials were computed from EEGs recorded from the surface of the scalp over the visual area in human subjects when paired flashes were presented with different IFls and also when the two different flashes comprising the pair were presented separately, Then the average evoked potential of the BF was subtracted from the combined re.- sponse to the pair of flashes allowing a delay corresponding to the IFI. The remainder was assumed to be the contribution of the TF to the paired response. It was predicted that the remaining evoked potential associated with the TF would vary in relation to the way the TF was perceived, thus reflecting the retroactive effect of the second flash upon the first when the interval between the flashes was varied.


Electroencephalography and Clinical Neurophysiology, V. 19, Issue 4, P. 325-335.

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Donchin, E., & Lindsley, D. B. (1965). Visually evoked response correlates of perceptual masking and enhancement. Electroencephalography and Clinical Neurophysiology, 19, 325-335.