Perception and identification of tones in different timbres: Using pupil diameter to investigate absolute pitch ability

Absolute pitch (AP) is the ability to effortlessly identify or produce pitches without reference. However, behavioral research has shown that pitch perception and identification in certain timbres are more difficult for AP possessors. In this study, we investigate whether pitch identification and labeling in different timbres (piano and voice) would require different amounts of cognitive resource allocation. We measured accuracy, response time, and pupillary responses of 18 musicians with varying degrees of AP while performing a pitch identification test. We also examined whether behavioral and psychophysiological responses were related to aspects of musical experience, such as the age of onset of musical training, daily hours of practice, and years of musical training. Behavioral results revealed significantly longer response time for vocal tones compared to piano tones. However, there was no difference in accuracy when comparing pitch labeling in piano and vocal tones. On the psychophysiological level, pupillary responses were significantly different across timbre conditions, with larger pupil dilation for vocal tones than piano tones. We also observed an effect of key color (whether the tones corresponded to diatonic or chromatic tones in a C major scale) on pupil dilation, with greater dilation for pitches corresponding to black keys compared to white keys. These findings expand the current knowledge regarding how pitches in different timbres are processed by musicians with varying degrees of AP and open new avenues for the investigation of potentially different cognitive mechanisms involved in the processing of the human voice and musical timbres by AP possessors.