Independent perceptual learning in monocular and binocular motion systems

Abstract

Investigations of eye-specificity of perceptual learning in judging motion direction of moving luminance-defined objects have found a substantial degree of transfer from trained to untrained eyes, implying a largely binocular site of learning (1–4). These results appear to be incompatible with the proposal that motion direction of moving luminance-defined objects is extracted by highly sensitive monocular systems and a less sensitive binocular motion system (5). We conjecture that the seemingly contradictory results may be a consequence of different eye-specificities of different learning mechanisms: a monocular learning mechanism in clear displays and a binocular learning mechanism in noisy displays. Eye-transfer tests, external noise manipulations (6) and observer models (7) were used to systematically characterize learning mechanisms and to investigate the eye specificity of each mechanism. Perceptual learning in one eye was measured over ten practice sessions. Transfer to and subsequent learning in the untrained eye were assessed in five transfer sessions. Learning in the trained eye improved performance (reduced contrast thresholds) in that eye with virtually equal magnitude across a wide range of external noise levels. The improvements were accounted for by a mixture mechanism of stimulus enhancement and template retuning. The degree of transfer of perceptual learning from the trained eye to the untrained eye depended on the amount of external noise added to the signal stimuli. In high external noise conditions, learning transferred completely to the untrained eye. In low external noise conditions, a large degree (about 46%) of eye-specific learning was found. During the transfer sessions, performance in the untrained eye further improved via stimulus enhancement with smaller though significant contribution of template retuning. The results suggest that perceptual learning of motion direction judgments involves two independent mechanisms at different processing stages of the visual system.

Footnotes

 The research is supported by NSF and NIMH.