Do “Magnocellular Tasks” Measure “Magnocellular Function”?

Abstract

Magnocellular deficit theories propose that certain cognitive disorders, such as developmental dyslexia, arise from a generalised deficit in the visual dorsal–magnocellular system and its auditory homologue. Psychophysical tasks requiring rapid temporal processing are often used to probe magnocellular function in this context. However, it is not clear whether performance on these various tasks is actually supported by a common substrate. This study investigated whether different putative measures of magnocellular function produce mutually consistent results, and thus evaluated the extent to which they target the same neural mechanisms. Within the PERGENIC project, 1060 participants completed four psychophysical tasks: detection of ‘frequency-doubled’ gratings (FD); detection of pulsed gratings of low spatial frequency on a steady luminance pedestal (SP); detection of coherent motion (CM); and auditory discrimination of temporal order (TO). Although all measures exhibited good test–retest reliability, only...