Ocular interaction in its relation to measurements of brightness threshold

Abstract

The question to which an answer is here sought is how far, if at all, the sensations from the two eyes of a subject add together in the measurement of brightness threshold. That is, do two eyes see better than one, or only equally well? Two aspects of the question have been investigated; first, the measurement of brightness threshold when the eyes are in equilibrium with a visual field of fixed brightness (steady state of adaptation); secondly, the measurement of the variation of brightness threshold with time after cutting off a conditioning field of more or less high brightness (changing state of adaptation). In an investigation of this kind the action of the eye pupils must be eliminated. This was done by the use of Maxwellian view for all visual fields, though the method of fixing the eye pupil at its maximum size by a mydriatic could also be used (Lythgoe and Phillips 1938). It was felt, however, that the Maxwellian view method was more generally satisfactory, though it necessitated more complicated apparatus and great care in equalizing the beams entering the two eyes. Consideration is also given to the effect of a light stimulus applied to one eye on threshold measurements made with the other eye.