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The Present Study

Dawn Senathi-Raja

The overarching aim of this project was to compare Peretz's higher-level cognitive emphasis of audition to a lower-level emphasis of pitch perception and auditory scene analysis according to their explanatory power in relation to MR's musical illusions and pattern of agnosia/s in various auditory domains. This is the first formal attempt, known to the author, to investigate perceptual deficits underpinning a pattern of auditory agnosias.

The first aim of the present study was to accurately classify MR's auditory agnosia along the dimensions of music, speech prosody, and environmental sounds. Within the musical domain, MR was expected to exhibit instrumental agnosia based on his reported difficulty for distinguishing instruments of similar pitch ranges. Within the melodic dimension, past testing found that the preservation of MR's ability to process melodic contour was inconsistent with current theories that attribute contour function to the right STG (Beckwith, 2003). However, thorough assessment of MR's contour ability was expected to reveal a contour processing deficit and subsequent intervallic and tonality deficits consistent with Peretz's theory. Within the prosody domain, the proposed association between rhythmic/melodic aspects of spoken sentences and that of music (Patel et al., 1998) led to the hypothesis that MR would have impaired prosodic function. Within the domain of environmental sounds, the finding that environmental sounds provoked MR's auditory illusions (Beckwith, 2003), gave rise to the prediction that he would show environmental agnosia.

The second aim of this study was to thoroughly examine MR's low-level perceptual deficits. Auditory processing of music, environmental sounds, and speech prosody rely on aspects of complex pitch perception and auditory scene analysis to varying degrees. As such, MR's pattern of perceptual processing deficits was expected to account for his higher-level pattern of agnosias. Based on preliminary evidence that MR exhibited a basic pitch processing deficit (Beckwith, 2003), it was anticipated that he would have a pitch perception deficit for the complex pitch of individual notes and for complex pitch patterns. Given MR's impaired ability to detect the direction of two individual notes (Beckwith, 2003), which is thought to be the simplest form of pattern organisation (Johnsrude, Penhune, & Zatorre, 2000), he was predicted to have an auditory scene analysis deficit.

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