The equivalent background and retinal eccentricity

Abstract

The validity of the equivalent background concept was tested for 8 retinal loci ranging from 3° to 70° on the nasal half of the horizontal meridian. Dark adaptation and increment threshold curves were obtained for two different test field conditions: 2°175msec and 0.5°40msec, both monochromatic at 550 nm. Results show that the equivalent background follows its own time course at each location. In photopic vision, the equivalent background for the inner periphery is lower than for the outer periphery. In scotopic vision, this relationship reverses. The findings suggest that the equivalent background concept may obtain only for loci having comparable spatial and temporal properties.