Auditory Scene Analysis Account

MR exhibited impaired sequential streaming. A critical aspect of music function is the analysis of perceptual patterns where individual notes are combined sequentially to form melodies (Bregman, 2002; Griffiths, 2003). Without this ability, one would expect a difficulty in forming coherent musical information streams that could be analysed for contour content. Accordingly, MR's inability to form contour representations in fast sequences may not only be due to a pitch perception deficit for brief tones, but also a sequential streaming deficit. Given that MR was unable to stream pitches according to Gestalt grouping rules, his cognitive system may have lacked the necessary patterned streams from which to mentally abstract the contour of melodies. MR's lesion location supports the proposition that the STG anterior to Heschl's gyrus is instrumental in processing patterns of information from one sound source (Warren et al., 2003). In this way, an auditory scene analysis account affords lower-level insight into the potential anatomical-functional correlations of contour representation.

MR's impaired intervallic processing accords with a sequential streaming deficit. Impaired sequential streaming, despite preserved pitch perception for patterns within a longer temporal window, would prevent the cognitive system from eliciting contour representations from which to anchor intervallic information. A sequential streaming deficit also explains MR's impaired tonal processing for slow pitch sequences by virtue of the relationship between intervals and the musical scale.

MR exhibited an impaired ability to perceive simultaneous streams correctly. Griffiths (2003) purports that simultaneous formation of perceptual patterns is crucial to chord formation and harmonic structure. According to MR's subjective report, the richness of his perception of grand orchestral works has been attenuated post-stroke. A simultaneous streaming deficit may explain MR's sense of diminished sound for large musical works by way of an impaired ability to synthesise separate components of chords and harmonies. A simultaneous streaming focus also provides a plausible explanation for MR's agnosia for slow familiar orchestral music (Beckwith, 2003) despite preserved pitch pattern perception for slow sequences.

Abnormal grouping mechanisms have been proposed to underlie perceptual pattern organisation deficits (Johnsrude et al., 2000). Given the weight of evidence from MR's impaired sequential and simultaneous streaming, it is reasonable to conclude that MR is unable to reconstruct an accurate representation of sound patterns. Nevertheless, the conclusion that faulty grouping mechanisms are the sole cause does not automatically follow, given the confounding influence of his pitch perception problems. While normal functioning Gestalt grouping mechanisms are paramount to an accurate representation of reality (Bregman, 2002), correct pitch perception enables the rules of proximity, similarity, symmetry, good continuation, and common fate to be applied to the correct incoming pitches (Deutsch, 1999). MR's impaired auditory scene analysis offers a powerful and novel explanation of his higher level musical deficits. Yet the contribution of this impairment, independent of an account based on MR's pitch perception deficit, is impossible to assess in the musical domain since there is no feasible way to examine either in isolation.

Strong inferences based on MR's impaired auditory scene analysis cannot be made in relation to his deficits for slow musical sequences. As the streaming tasks contained rapidly presented tones, it is indeterminable whether MR's inability to elicit the streaming effect is due to a streaming impairment of a general nature, or to a streaming impairment specific to tone patterns of brief durations.

Home - FAQ - Register - Forums - My Feedback - Contact Us - Terms and Conditions
Free Personality Tests : Relationships - Personality - Beliefs - Wellbeing - Attitudes - Behaviour - Cognitive Abilities
Scientific Research - Psychlopedia