Directed attention and perceptual asymmetry to monaurally presented tones

Forty-eight right-handed Ss were tested for simple reaction time (RT) to a monaurally presented 1000 Hz tone of 250 msec duration. Each S was tested in 3 series comprising 7, 11 and 15 stimulus presentations (trials). In each series all stimuli but one (probe) were presented to a single ear. Ss were divided equally into right or left-ear attention groups on the basis of the ear receiving the non-probe trials. Right-ear attention resulted in equally good RTs to either attended or non-attended ear. Left-ear attention resulted in slower RTs than right-ear attention and showed a significant discrepancy between ears in favor of the non-attended ear. The results are interpreted as showing that neither simulus competition nor language processing are necessary conditions for eliciting auditory asymmetry. The data indicate that a cortically-mediated process of selective attention operates in the production of auditory asymmetries for some non-language sounds and that, as with language perception, it is the left cerebral hemisphere that is primarily involved.