Early unilateral enucleation disrupts motion processing

Previous research has shown that unilaterally enucleated observers demonstrate better luminance-defined form perception compared to monocularly viewing controls, and similar performance to control observers viewing binocularly (Vision Res. 37(17) (1997) 2465). In Experiment 1 we asked whether the perception of form, where form is defined by other attributes than luminance, is also improved compared to monocularly viewing controls. We tested 16 enucleated observers and 25 controls viewing monocularly and binocularly for their ability to detect and recognize form from texture (texture-defined (TD) form) and form from motion (motion-defined (MD) form). There was no difference between the three groups for TD form perception. However, enucleated observers had significantly poorer MD form perception than did binocularly viewing controls. In Experiment 2 we asked whether poor performance on the perception of MD form might be due to a general reduction in motion processing abilities. To examine this possibility, we used a motion coherence task. We tested eight unilaterally enucleated and 14 monocularly and binocularly viewing control observers on a horizontal coherent motion discrimination task. The monocularly viewing controls showed no naso-temporal asymmetry in direction discrimination for coherent motion. In contrast, the enucleated group showed an asymmetry in direction discrimination where temporalward motion coherence thresholds were significantly higher than those for nasalward motion. These latter findings are discussed in terms of the absence of binocular competition during the development of motion processing pathways.