On the degree of attention and capacity limitation in tactile processing

Two conditions were used to evaluate Os’ ability to detect near-threshold vibrotactile stimuli. In both conditions, a signal was presented at one of three skin loci, the O stating which locus received the stimulus. In the simultaneous condition, there was a single observation interval during which a signal occurred at one of the three loci. In the sequential condition, there were three observation intervals presented successively at 800-msec intervals, with a signal presented at one of the three loci during one of the three observation intervals. Each observation interval was associated with a particular locus. Theories postulating attentional control and limitations of capacity during this type of vibrotactile information processing predict performance to be inferior in the simultaneous condition, since that condition requires sharing of attention among the three possible sources of tactile stimulation. The data showed performance to be identical in the two conditions. This result not only disconfirms the single-channel model proposed by Franzen, Markowitz, and Swets (1970), but also argues for an unlimited-capacity nonattention model of tactile perceptual processing. The results are in accord with similar findings for visual processing by Shiffrin and Gardner (1972).