For the price of a song: How pitch category learning comes at a cost to absolute frequency representations

For the price of a song: How pitch category learning comes at a cost to absolute frequency representations Melody Dye, Michael Ramscar & Edward Suh Department of Psychology, Stanford University 450 Serra Mall, Stanford, CA 94305. Abstract Appreciating music is cognitively demanding: listeners must learn to divide a continuous space of sound into culturally defined, discrete categories, and maintain a high degree of accuracy in their representations of those sounds. Here, we present a formal analysis of pitch category learning that reveals the trade-offs associated with learning the relative pitch categories that make music possible. Consistent with this, an empirical study reveals how under normal circumstances, people’s ability to represent absolute frequency information is lost as a consequence of the learning processes that facilitate relative pitch acquisition, a finding which may help explain the rarity of absolute pitch among the general population. Understanding the contradictory computational demands of conceptual and perceptual learning can inform the design of musical training and may offer insight into the development of phonological categories in language. Keywords: Musical Cognition, Relative Pitch, Absolute Pitch, Concepts, Categories, Learning Theory Introduction Most hearing people have the ability to learn musical pitch categories and the relationships between them. With training, listeners of every age can learn to distinguish types of musical intervals from one another and to identify and reproduce melodies from different starting notes, a skill known as “relative pitch” (RP). Far rarer, and virtually unknown outside the musical community, is “perfect” or “absolute pitch” (AP): the ability to accurately label a given note by its fundamental frequency (Takeuchi & Hulse, 1993). The acquisition of AP is overwhelmingly associated with musical training early in life (Chin, 2003), which has led to the suggestion that learning to label notes according to their absolute frequencies may be subject to a biological critical period (Trainor, 2005; Deutsch et al., 2006). Here, we examine whether the loss of many listeners’ ability to represent absolute frequency information may be a consequence of learning to discriminate relative pitch categories, as an inherent part of the processes that make RP acquisition possible. Musical sounds are initially encoded in the cochlea as tonotopic representations of frequency, then passed through the auditory pathway to cortex (Merzenich & Reid, 1974; Wessinger et al., 1997). Although initial sound representations are based on frequency, few listeners conceptualize music this way. Rather, most listeners make use of relative pitch (RP) systems: identifying, remembering, and producing music relative to the differences, or intervals, in culturally defined systems of pitch. The number of listeners able to recognize or produce tones in terms of their absolute frequencies (AF) varies by culture and task. While nearly half of music conservatory students in China can name pitches in terms of AF, the estimated rate in North American conservatory students is just 15%, and less than 0.01% for the general population (Deutsch et al., 2006). However, when tasks do not include a naming component—e.g., identifying whether familiar musical excerpts are in the correct key, or singing or humming familiar songs from memory—evidence of sensitivity to AF more widespread (Terhardt & Seewann, 1983; Halpern, 1989; Levitin, 1994; Schellenberg & Trehub, 2003). Further, speakers of tonal languages, such as Vietnamese, display a high degree of pitch consistency in their speech production across test sessions (Deutsch et al., 2004) and North Americans without musical training are even sensitive to the AF of the telephone dial tone (Smith & Schmuckler, 2008). Interestingly, just as infants are initially able to detect and respond to the full spectrum of sounds employed in the world’s languages before later losing this ability (Werker & Tees, 1984; Kuhl et al., 2006) as they acquire the sound categories of their native tongues, it appears that infants initially favor musical representations based on absolute rather than relative pitch, and that processing tends to switch over to relative as they develop (Saffran & Griepentrog, 2001). Thus, despite the popular belief that AF sensitivity in music is a special ability, mysteriously acquired by a few, it would appear that the potential for absolute pitch possession is widespread. The mystery, then, is not why so few people have it, but rather, why so many lose it (Deutsch, 2002; Miyazaki, 2004; Levitin & Rogers, We propose that one answer lies in the nature of pitch categories, and the way they are learned. In music, melodies are usually produced and described in relation to conventionalized systems of abstract musical categories, such that melody can be appreciated independently of any particular instrument, singer or key. Chroma—musical pitch categories—do not exist in nature; rather, they are culturally determined ways of dividing up a continuous sound space. Here, we suggest that the computational demands of learning to recognize discrete structure in continuous perceptual space stands in direct opposition to the preservation of AF information.