Selective Effects of Ongoing Alpha-Band Activity on Magno- and Parvo-Mediated Detection.

Spontaneous fluctuations in cortical excitability, as reflected in variation in occipital alpha-band activity (8-12 Hz), have been shown to explain trial-to-trial variability in perception. Specifically, observers typically report seeing a stimulus more often during states of weak alpha power, likely due to a shift in detection criterion. However, prior work has paid little attention to the specific stimulus properties mediating detection. In early vision, different stimulus properties are preferentially processed along the magnocellular (MC) and parvocellular (PC) pathways, which vary in their preference for spatial and temporal frequency content and chromatic information. The goal of this study was to understand how spontaneous alpha power affects the detection of stimuli which are preferentially processed by either the MC or PC pathway. To achieve this, we used the "Steady/Pulsed Paradigm" which presented a brief, near-threshold stimulus in two conditions intended to bias processing to one or the other pathway. Our results showed an interaction effect of pre-stimulus alpha power on detection between the two conditions. While weak alpha power was predictive of seeing the stimulus in the steady condition (MC-biased), no significant effect was found in the pulsed condition (PC-biased). This interaction was driven by a selective alpha-related criterion shift in the steady condition, with no effect of pre-stimulus alpha on sensitivity (d') in either condition. Our results imply that alpha oscillations may differentially regulate excitability in the MC and PC pathways.