Double dissociation in monocular blindness: Enhanced contrast but impaired motion perception

Abstract

Previous research has shown that early monocular blindness from unilateral enucleation (surgical removal of one eye) results in equivalent or enhanced form perception but impairments in aspects of motion processing (see Steeves et al., 2008). To further investigate the effects of early monocular blindness on form and motion processing, we compared binocularly and monocularly viewing controls to individuals who were unilaterally enucleated within the first few years of life. Thresholds were measured on three tasks that had not before been tested in this population; 1) contrast discrimination, 2) horizontal speed discrimination, and 3) horizontal coherent motion discrimination. Preliminary data are consistent with previous research showing early monocular blindness results in equivalent or enhanced sensitivity compared to binocularly and monocularly viewing controls at some contrasts. It also results in higher motion discrimination thresholds for lower speeds and a nasalward bias in the perception of coherent motion. These results add to the literature showing that the loss of one eye early in life can enhance low contrast form processing, presumably through a lack of binocular interactions. In contrast, this same lack of binocularity can impede the normal maturation of motion processing suggesting that binocularity is required for normal maturation of this system.

Footnotes

 NSERC to JKS and OGSST to KRK.