title: Interlateral asymmetry in the time course of the effect of a peripheral prime stimulus.
abstract: Evidence exists that both right and left hemisphere attentional mechanisms are mobilized when attention is directed to the right visual hemifield and only right hemisphere attentional mechanisms are mobilized when attention is directed to the left visual hemifield. This arrangement might lead to a rightward bias of automatic attention. The hypothesis was investigated by testing male volunteers, wherein a "location discrimination" reaction time task (Experiments 1 and 3) and a "location and shape discrimination" reaction time task (Experiments 2 and 4) were used. Unilateral (Experiments 1 and 2) and unilateral or bilateral (Experiments 3 and 4) peripheral visual prime stimuli were used to control attention. Reaction time to a small visual target stimulus in the same location or in the horizontally opposite location was evaluated. Stimulus onset asynchronies (SOAs) were 34, 50, 67, 83 and 100 ms. An important prime stimulus attentional effect was observed as early as 50 ms in the four experiments. In Experiments 2, 3 and 4, this effect was larger when the prime stimulus occurred in the right hemifield than when it occurred in the left hemifield for SOA 100 ms. In Experiment 4, when the prime stimulus occurred simultaneously in both hemifields, reaction time was faster for the right hemifield and for SOA 100 ms. These results indicate that automatic attention tends to favor the right side of space, particularly when identification of the target stimulus shape is required.
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, 05508 900 Sao Paulo, SP, Brazil. bia@icb.usp.br
authors.forename: B A
authors.initials: BA
authors.lastname: Castro-Barros
authors.forename: L L
authors.initials: LL
authors.lastname: Righi
authors.forename: G
authors.initials: G
authors.lastname: Grechi
authors.forename: L E
authors.initials: LE
authors.lastname: Ribeiro-do-Valle
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology*; D003463:Cues; D005364:Field Dependence-Independence; D005556:Form Perception / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values; D013028:Space Perception / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*