[Lateralization of attention in the acoustic modality].

Posner reported that knowledge of where in space a visual stimulus will occur ("expected" condition), improves detection ("benefit"), as measured by response latencies, while response latencies became longer ("cost") when visual stimulus position is "unexpected" and intermediate when the visual stimulus position is "neutral". The authors have tried to replicate this finding in the acoustical modality. One hundred-twenty acoustical stimuli (clicks) were presented to the right and the left ear of ten right handed subjects, preceded by the biaural verbal warnings "right", "left" or "center". After the "center" verbal warning, the clicks could be presented to the right or the left ear equally often (50%): "neutral" condition; after the "right" or "left" verbal warnings, the clicks could be presented in 80% of cases to the "expected" ear and in 20% of cases in "unexpected" ear. The results suggested that: a) reaction times are significantly faster when the clicks are presented to the right ear; b) the "cost" effect is present but not the "benefit" effect, since no difference was shown between reaction times in the "neutral" and in the "expected" conditions; c) the right ear advantage disappears in the "unexpected" condition after the "right" verbal warning only. The authors discuss the results in relation to the attentional interhemispheric theories.