Human auditory source discrimination.

Abstract

The aim of this study is to examine the auditory system's ability to process low energy frequency transpositions of complex sounds. The auditory processing of complex sounds such as musical instruments, voice, or environmental events is currently an active area of research. Some propose that auditory "objects" are represented by neurons which encode the `invariant' spectro-temporal acoustic properties (Griffiths & Warren,2004). These sound features tend to be heavily damped and very transient and, therefore, frequency rich. This study shows the auditory's sensitivity to detect these adjustments by detecting the pre-attentive magnetic mismatch response (MMNm) from 8 subjects passively listening to complex audio stimulations. Responses were detected from most subjects even though participants could not attentively discriminate the sounds. This result is somewhat controversial in that current views suggests that a mismatch response indicates processing that is available for higher processing i.e. should be attentively discriminable (Näätänen et al., 2010). Localization results suggest the mismatch processing is performed in the auditory associations regions (superior temporal sulcus, insula) of the auditory cortex. These results suggest that transient sounds might be essential to auditory object identification, and that the auditory system is able to distinguish at a sensory level, shifts in the heavily damped spectral structure of complex sounds even though some cannot do so attentively. This could be due to the greater analysis given by the human brain to determining the pitch center rather then the sound timbre, yet some trained musicians have the ability to distinguish these subtle differences (i.e. differences between manufacturers of the same kinds of instruments).