AN EVENT-RELATED POTENTIAL EXAMINATION OF ATTENDED AND UNATTENDED STIMULI IN VISUAL SELECTION USING BILATERAL STIMULUS-PRESENTATION

The experiment reported here examined an interference paradigm using a bilateral stimulus presentation in which stimuli were presented simul taneously in the left and right visual fields. The lateralization of t he early visual components allowed an ERP examination of material pres ented in each field. Attention was directed to one field or the other on each trial by a 100% valid cue. Two letters were nominated as targe ts and the simultaneous presentation allowed presentation of material compatible, incompatible or neutral with reference to the target. A ne gative peak was observed at 230 ms post stimulus at occipital and temp oral sites. There was a variation in this peak for unattended stimuli, with compatible and incompatible target letters being significantly d ifferent to non-target letters. Contrary to previous research, this fi nding suggests that material is not filtered out at an early stage as proposed by early selection. It was found that the response to unatten ded target material also varied according to the type of item presente d at the attended location. These findings were discussed in relation to previous studies which found no difference in the processing of una ttended target and non-target material, and also in relation to sugges tions that automatic processing of unattended material occurs only whe n there is controlled processing occurring simultaneously.