ABSTRACT

In order to consider the relative roles of the hemispheres in timbre perception, I presented two split-brain patients (neither of whom was an accomplished musician) five different musical instrument sounds I had used in a New York City recording studio (a Yamaha DX-7 piano sound, a Roland TR-505 snare drum sound, and Ensoniq Mirage violin, trumpet, and bell samples). The instrument sounds were presented in free field in the

context of five eight-note melodies (ascending diatonic scale, ascending chromatic scale, variable diatonic set, variable chromatic set, and monotonic) played at one note per second in the registers of C4 (piano, trumpet, bell) and C5 (violin) (A4=440cps); of course, the snare drum was presented in a monotonic sequence only. Figure 2 illustrates the experimental procedure. During the playing of the sixth or seventh note, the subject was reminded to fixate a central dot on a Macintosh Plus computer screen, and a picture of a musical instrument was flashed for 150msec in one or the other visual field. Subjects were instructed to press the space bar on the computer keyboard if what they saw was what they heard. Thus, in this match-to-sample task, the match was made available to only one hemisphere, and it matched the sample in 50% of trials. The visual field the picture was flashed in, the hand used to respond, the instrument sound, the melodic context, and whether or not the picture matched the sound were counterbalanced across two hundred trials. The results are illustrated in Figure 3. In both patients, the left hemisphere and the right hemisphere performed significantly better than chance, revealing that each half-brain was able to discriminate and recognize musical instrument timbre. In addition, the results indicated that in both patients the left hemisphere was superior to the right hemisphere.