Academic journal article Attention, Perception and Psychophysics

Abnormal Pitch-Time Interference in Congenital Amusia: Evidence from an Implicit Test

Academic journal article Attention, Perception and Psychophysics

Abnormal Pitch-Time Interference in Congenital Amusia: Evidence from an Implicit Test

Article excerpt

Congenital amusia, characterized by a severe problem in detecting anomalies in melodies, is a lifelong disorder that has been ascribed to an acoustical pitch deficit. In the present study, we investigated how the perception of a duration is altered when it is bounded by tones varying in pitch. The results show that temporal accuracy is impaired by pitch variations as small as a quarter of a semitone in control participants, whereas it is impaired only when pitch variations are increased to 4 semitones in congenital amusics. Furthermore, control participants associate intervals bounded by low- and high-pitched tones with long and short durations, respectively. Amusic participants do not make this connection, even with large pitch differences, pointing to a deficit in pitch-time integration. Thus, our results are consistent with the notion that congenital amusia is linked to a neurogenetic anomaly that impairs pitch processing, independently of task factors.

Humans are born with the potential both to speak and to make music. For the majority of those who are musically untrained, this fundamental human trait is expressed by avid listening and by occasional dancing and singing. The propensity to engage in music ultimately gives rise to a sophisticated music processing system that is largely acquired implicitly by experience (Peretz, 2006). However, a minority of individuals never acquire this core musical system, either in part or in total. This condition, termed congenital amusia (Peretz, 2001), affects 4% of the general population (Kalmus & Fry, 1980) and is akin to other congenital developmental disorders, such as prosopagnosia, dyscalculia, dysphasia, and dyslexia, and is thought to result from a musical pitch disorder (Foxton, Dean, Gee, Peretz, & Griffiths, 2004; Hyde & Peretz, 2004).

The nature of the pitch disorder remains, however, unsettled. It has been shown that amusic individuals cannot detect pitch changes that are smaller than 1 semitone, which represents the difference in frequency between adjacent pitches in Western music and is the building block of musical scales. Yet, there are indications that amusic individuals might be able to use pitch information, albeit implicitly. Amusics are able to reproduce pitch directions vocally, although being unable to report these explicitly (Loui, Guenther, Mathys, & Schlaug, 2008). Similarly, the brain of amusics responds to quarter-tone (i.e., 50-cent) pitch violations, by exhibiting an early right-lateralized negative electrical response, although the individual is unable to overtly detect these violations (Peretz, Brattico, Järvenpää, & Tervaniemi, 2009). These data point to the possibility that pitch sensitivity is normal in congenital amusia and that lack of confidence might be the origin of the observed behavioral failures. In normal participants, confidence and discriminability typically are related. However, in amusics, there might be a dissociation, as is the case in blindsight: Their discrimination abilities might be higher than what they think they are. Amusic individuals are often underconfident about their perceptual experiences. They may treat uncertainty as a lack of perception and report no awareness, even when more objective measures show that they can detect the presence of pitch changes.

Pitch perception without awareness raises the question of the nature of the neural representation that supports it. One possibility is that pitch-tracking mechanisms are normal up to the level of the auditory cortex, but the cortical neural representation of pitch is too weak to support reliable discrimination and memory. This would be consistent with the anatomical anomalies observed in the auditory and inferior frontal cortex of amusic individuals (Hyde, Zatorre, Griffiths, Lerch, & Peretz, 2006; Hyde et al., 2007; Mandell, Schulze, & Schlaug, 2007). Another possibility, as noted above, is that the auditory cortex computes pitch changes normally, but lack of confidence and decision factors are the origin of the observed behavioral failures. …

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