Abstract
Purpose: The magnocellular (M) pathway's contributions to PPmfVEPs was examined by comparing VEP characteristics with isoluminant (ISO) colour and diffuse red background dartboards against Luminance Contrast (LC) dartboards.
Methods: Participants (n=5) observed stimuli through a stereoscopic display (two screens viewed via mirrors at 45°; lenses gave an effective infinity viewing distance). Stimulus was an 84 region cortically scaled dartboard, eccentricity 23° 4x4 checkerboards briefly pulsed pseudo-randomly (mean frequency 2/second/region). Ten conditions were tested with 30 or 60 cd/m2 mean luminance and grey or chromatic (red-green) checks yielding six LC and four ISO conditions. RGB values were selected with a photometer. Participants viewed a 30Hz reversing dartboard of all regions; for ISO they made it not flicker; for LC they verified it flickered, they then viewed PP dartboards (four 1 minute segments per condition). 64 channels were recorded at 256Hz.
Results: ISO produced a response delayed in initial rise and in peak relative to LC reflecting the absence of faster M pathway transmission for ISO. 90% of the channels were significant (pConclusions: PP presentation has better SNR than traditional contrast reversing stimuli, allowing for more conditions in a reasonable length session. This research is the first usage of PPmfVEPs to identify M pathway effects. Potential applications include Dyslexia and Schizophrenia, which have a correspondence with dysfunctional M pathways.
ARC Centre of Excellence in Vision Science.