MULTIPLE CUTANEOUS STIMULATION: THE DISCRIMINATION OF VIBRATORY PATTERNS.

Abstract

In an effort to supply widespread cutaneous stimulation and thus make possible systematic study of the limits of spatial discrimination through this channel, there has been devised a multiple contactor system permitting application of vibratory signals to 10 bodily loci simultaneously. Patterns comprising from 1 to 9 stimuli were presented in successive pairs, the subject's task being to report whether the patterns were perceived as “same” or “different.” Members of pairs were separated by 500 msec and burst duration was 200 msec. Two synchronized Western Union tape transmitters presented 20 programs of 50 pairs of patterns, 500 “same” and 500 “different” pairs being randomly intermixed in the 1000 presentations. A pilot experiment, in which many types of pattern changes were explored, revealed errors to be associated with (a) relative pattern complexity (large numbers of vibrators) and (b) high degree of communality (many elements in common). A formal experiment, involving a stratified sample with all combinations of numbers of loci and degrees of communality represented equally, verified the preliminary finding, and permitted, in addition, separation of the two factors apparently responsible. The relation between errors and communality, with number of stimulus positions held constant, proves to be an intimate one; confusions between patterns arise when there is relatively large overlap of elements in the patterns to be discriminated. A supplementary analysis, directed at whether particular receptive areas may be especially prone to error, shows no single locus, of the 10 employed, contributing to error production more than would be dictated by chance.