It is hypothesized that a steady light in one eye will lower or inhibit the critical rate (CFF) of contralateral intermittent flashes of light in a manner consonant with the effect of an adapting field on the discrimination of single flashes. Luminances spanning a 6-log-unit range were variously combined in two 1.5° fields. Results indicate that there is an inhibitory effect which depends in part on relative luminances: except with very dim stimuli, an adapting light dimmer than a given flicker light reduces CFF somewhat; and CFF decreases progressively as adapting luminance increases. Viewed with bright adapting light, a moderately bright flicker field shows a 10–20% reduction in CFF and a dim flicker light (whose CFF is 8 cps or less) shows a 100% reduction in CFF. However, the data, when plotted in a ΔI/I format, show only partial similarity to curves of steady-field and single-flash luminance discrimination. Moreover, the upper limb in each of the family of binocular CFF-logI curves, in which adapting luminance is the parameter, parallels the monocular curve and may be fitted to a similar exponential equation.
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