Selective attention to conjunctions of color and shape of alphanumeric versus non-alphanumeric stimuli: a comparative electrophysiological study.
We compared multi-dimensional selection on the basis of the color, the global shape and the local shape of alphanumeric (letters) and non-alphanumeric (non-letters) stimuli. We investigated whether letters are selected on the basis of name codes or on the basis of highly familiar local shape codes. Participants responded to a single conjunction of color, global shape and local shape occurring in a randomized stream of other conjunctions of these attributes. Dependent variables were reaction time and measures derived from event-related brain potentials (onset latencies and peak amplitudes of the occipital selection negativity, SN). The SN results showed that, for both letters and non-letters, color and global shape were selected first and local shape was selected later. Reaction times were faster, and SN to the local shape occurred earlier for letters than for non-letters. The SN to the local shape of letters was larger than the SN to the local shape of non-letters. In contrast, the SN to the global shape of letters was smaller than the SN to the global shape of non-letters. Selection of the global shape of letters, but not of non-letters, depended on whether they occurred in the relevant color. Selection of the color of both letters and non-letters was independent of shape relevance, and selection of the local shape of both letters and non-letters was independent of color relevance. These results suggest that, (1) both letter and non-letter shapes are initially analyzed in a feature-specific manner; and (2) letters are selected for task-directed processing on the basis of highly familiar local shape codes and not on the basis of name codes.
Rotte
M
M
Department of Clinical Neurophysiology, Otto-von-Guericke University, Magdeburg, Germany. michael.rotte@medizin.uni-magdeburg.de
Heinze
H J
HJ
Smid
H G
HG
D000328:Adult; D001288:Attention / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D003118:Color Perception / Q000502:physiology*; D005071:Evoked Potentials; D005260:Female; D005556:Form Perception / Q000502:physiology*; D007839:Functional Laterality; D006801:Humans; D008297:Male; D011930:Reaction Time