Metacognition in Putative Magno- and Parvocellular Vision

A major distinction in early visual processing is the magnocellular (MC) and parvocellular (PC) pathways. The MC pathway tends to process motion, transient events, and low spatial frequencies, while the PC pathway mostly processes color, sustained events, and high spatial frequencies. Prior work suggests that the PC pathway more strongly contributes to conscious object recognition via projections to the ventral “what” visual pathway, whereas the MC pathway contributes to non-conscious motion and localization processing via the dorsal stream “where/how” pathway. This invites the question: Are we equally aware of activity in both pathways? And if not, do task demands interact with which pathway is more accessible to awareness? We investigated this question in a set of two studies measuring participant’s metacognition (their ability to judge the accuracy of their own perceptual decisions) for stimuli biased towards MC or PC processing. The “Steady/Pulsed Paradigm” presents brief, near-threshold stimuli under two conditions thought to favor either pathway. In the “pulsed” condition, the target appears atop a brief luminance pedestal which theoretically saturates the transient MC response and leaves the PC pathway to process the stimulus. In the “steady” condition, the stimulus is identical except the luminance pedestal is constant throughout the trial, rather than flashed along with the target. This theoretically adapts the PC neurons and leaves MC for processing. Experiment 1 was a spatial localization task thought to rely on information relayed from the MC pathway. Using a model-based approach to quantify participants’ metacognition about their task performance, we found higher metacognition in the steady (MC-biased) condition. Experiment 2 was an orientation-discrimination task more reliant on PC pathway information. Preliminary results show an abolishment of the MC pathway advantage seen in experiment 1 and suggests that the metacognitive advantage for MC processing may hold for stimulus localization tasks only. (edited)