Figure 1.

Eye dominance assessed from OKN responses. (A) Cats were placed on a recording table and their head fixed by means of an implanted bolt (see Materials and Methods). In front of the head two mirrors were mounted such that each eye was viewing a separate monitor. (B) Recordings of horizontal OKN from cat 1 evoked by dichoptic presentation of gratings moving in opposite directions for four different contrast conditions. Phases devoid of saccades are underlaid with gray if they exceed 500 msec and those classified as smooth phases of OKN are marked with black bars whose position indicates which eye controls OKN (Top, left eye; Bottom, right eye). When only one grating is presented to either the left or the right eye, OKN is unidirectional, smooth phases of OKN reflecting the movement direction of the grating. If both eyes are stimulated with gratings of equal contrast (l = 0.5, r = 0.5), OKN is entirely dominated by the left eye. OKN is controlled by the two eyes in alternation only when contrast ratios are very asymmetric (l = 0.1, r = 0.9) indicating a pronounced dominance of the left eye. (C) Eye dominance ratios (see Materials and Methods) expressed as the fraction of time during which OKN was dominated by the left eye stimulus (ordinate) as a function of the contrast ratio (abscissa) between dichoptically presented gratings for all three cats. The curves correspond to significantly fitted sigmoidal functions. In two cats the deviated eye was dominant and in one cat the nondeviated eye. At equal contrast of the two gratings, eye dominance ratios are for cat 1, 0.96; cat 2, −0.53; and cat 3, −0.85. Bars = SEM. Dashed vertical lines are drawn at the contrast ratios shown in B.