Early cortical interactions between chromatic and luminance signals: an ERP study of object classification J Martinovic, B Jennings |
|---|
School of Psychology, University of Aberdeen, United Kingdom
|
| While luminance and chromatic pathways remain largely separate at subcortical levels, their signals are combined from V1 onwards. This event-related potential (ERP) study examined how luminance and chromatic signals combine in early cortical processing. Participants discriminated between Gaborised images of nameable objects, novel objects and patches of randomly scattered Gabors. These stimuli were presented at mean threshold or at twice the threshold. They excited either the luminance pathway alone, luminance and L-M pathways or luminance, L-M and S-(L+M) pathways. While classification accuracy for the three types of stimuli was comparable across pathways at threshold, increases in performance at suprathreshold were less pronounced for objects defined by the full combination of pathways. The first ERP component, an N1 peaking 200-300ms after stimulus onset, occurred earlier and had larger amplitude at suprathreshold for luminance only and luminance and L-M stimuli. The full combination at suprathreshold elicited only a shift in latency but same amplitude as at threshold. Object-selectivity in the N1 was found only for the full combination. Therefore, the addition of S-(L+M) information at suprathreshold might both suppress the amplitude gain mechanism of the other two channels and enhance sensitivity to some mid-level property of objects, relating to lower accuracy rates. |
| Up Home |
|---|