Parallel and independent attentional facilitation of color and orientation S Andersen1, M Müller2, S A Hillyard3 |
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1School of Psychology, University of Aberdeen, United Kingdom |
| We examined sustained attentional selection of stimuli defined by conjunctions of color and orientation. Participants attended to one out of four concurrently presented superimposed fields of randomly moving horizontal or vertical bars of red or blue color in order to detect brief intervals of coherent motion. Stimulus processing in early visual cortex was assessed by recordings of steady-state visual evoked potentials (SSVEPs) elicited by the flickering stimuli. Attentional selection of conjunction stimuli was found to be achieved by parallel enhancement of the two defining features. This finding was confirmed and extended in a second experiment, in which we directly contrasted selection of single features and feature-conjunctions. We found that conditions in which selection was based on color or orientation only exactly predicted the magnitude of attentional enhancement when attending to a conjunction of both features. Furthermore, enhanced SSVEP amplitudes of attended stimuli were accompanied by equal sized reductions of SSVEP amplitudes of unattended stimuli in all cases. In conclusion, attentional modulation of stimulus processing in early visual cortex could be fully explained by parallel and independent facilitation of both feature dimensions. |
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