Two experiments were carried out to determine the functional relation between the critical flicker frequency (CFF) of two identical intermittent targets, binocularly superimposed, and the phase difference between the targets. Binocular CFF is a monotonic decreasing function of phase difference, positively accelerated for phase differences between 0° and 180", and negatively accelerated for phase differences between 360° and 180°. It is postulated that the results can be accounted for by assuming the existence of something akin to the "isodynamic" cells of Cajal, and that more weight is attached to the input to these cells from one eye than from the other.

A method of graphic recording was used to determine the effect of inspection time on the initial magnitude and rate of decay in the spiral after-effect (SAE). Graphic recordings of 14 Ss were obtained for the SAE as die inspection period was varied. A mathematical formula representing the SAE was proposed on the basis of experimental data. The decay of the SAE was approximately exponential with time; the exponential constant was an inverse function of the duration of the inspection period. The initial magnitude, inferred from the total apparent expansion in the after-effect, varied directly with the inspection period. Implications for research were presented.

The neurological and behavioural factors which are integral for an explanation of the spiral after-effect are derived from a review of recent literature. A functional mechanism which must underlie interocular transfer and binocular superimposition effects is described and related to the neurological and behavioural factors presented. A probable neurological basis for the spiral after-effect is suggested.