Event-related potentials reveal an early advantage for luminance contours in the processing of objects
Martinovic, J., and Wuerger, S. M.
School of Psychology, University of Liverpool, UK
The speed of object recognition is driven by luminance information. Do event-related potentials (ERPs) reflect this luminance superiority? We measured ERPs in response to line drawings of familiar and unfamiliar objects. Contours were defined along three directions in cardinal colour space: 1) S-cone-isolating (S), or 2) intermediate isoluminant direction (S and L-M), or 3) an additional achromatic component (S; L-M; L+M+S), providing a luminance signal. Stimuli along different colour directions were equated in terms of discrimination thresholds (familiar/unfamiliar objects). A prominent central parieto-occipital N1 component was found; its amplitude correlated with contrast thresholds. N1 occurred with an earlier latency for stimuli containing luminance signal; meanwhile, its amplitude was modulated by object identity. As N1 is a marker of visual discriminative processing, we conclude that high-level discrimination starts early (200 msec) and exhibits object-selective effects if luminance information is provided, consistent with the superiority of the magnocellular pathway in object recognition.