Rapid processing of complex natural scenes: A role for the magnocellular visual pathways?

Monkeys and humans were tested on a rapid categorization task of briefly flashed (30 ms) previously unseen natural images. They had to respond only when a target (animal or food) was present. Removing color information had no effect on the monkey's performance. For humans, a strong correlation between the use of color information and the RT duration appeared. Accuracy was identical with chromatic and achromatic photographs for the fastest humans, whereas subjects with longer RTs showed an increasing impairment when color was removed. Rapid identification may rely mainly on the fast feed-forward processing of coarse achromatic information in the magnocellular stream. These results impose strong constraints for modeling the first stages of visual processing. (C) 1999 Elsevier Science B.V. All rights reserved.