In an effort to supply widespread cutaneous stimulation, a multiple contactor system permitting application of vibratory signals to 10 body loci simultaneously was devised. 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 relative pattern complexity, and degree of communality. 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 2 factors apparently responsible. With number of stimulus positions held constant, confusions between patterns arise when there is relatively large overlap of elements in the patterns. No single locus, of the 10 employed, contributes to error production more than would be dictated by chance.