Sinusoïdal current and perceived brightness II

Vision Rrs. Vol. 12,p. 363.Pergamon Press1972. Printedin GreatBritain.

LETTER SINUSOIDAL

CURRENT

TO THE EDITORS AND

PERCEIVED

BRIGHTNESS

II

(Received 1 Ociober 1971)

IN OURprevious letter (BROEKHUIJSEN and VERINGA,1971) we have stated that upon injection of a sinusoldal alternating current of properly chosen amplitude at about 90 Hz into a person’s eye, adapted to and observing a 35” white screen at (0.5-50) x 10m3 cd/m*, the visual field seems to darken considerably and to remain darkened for the duration of current injection. Rightly it has been brought to our attention that our experiments could hardly have distinguished a persistent darkening phenomenon from a slowly decreasing darkening, which-after the current is switched off-is inverted to a slowly extincting brightness increase. By means of a binocular experiment we have ruled out the latter possibility. For this purpose we offered the adaptating light alternatingly to the right and the left eye and adjusted for a binocular match of brightness impressions. At repetition rates of 05-l Hz it appeared that during the time of current injection into one eye, the brightness impression of that eye did remain less than the brightness impression in the other eye. At repetition rates over 1 Hz the reported phenomenon was hardly or not detectable. At this moment we are not able to explain the latter effect. MAARTJXN L. BROEKHUIJSEN FRANS T. VERINGA

Dept. of Neurophysiology, State University of Groningen, The Netherlands

REFERENCE BROEKHUIJSEN, M. L. and VERINGA,F. T. (1971). Sinusoidal current and perceived brightness. Vision Res. 11,

479483.

363