Deficits in melodic contour visualization in individuals with congenital amusia

People with congenital amusia have difficulty with melodic contour processing, even when the pitch changes involved exceed their threshold for pitch discrimination. Patel et al. (2005) proposed the “Melodic Contour Deafness Hypothesis”, which posits that congenital amusia results from insensitivity to the direction of pitch movement rather than impaired processing of pitch change detection. Given that melodic processing requires both accurate perception of pitch change direction as well as the capacity to represent a succession of contour changes, it is unclear whether impairments in melodic contour processing observed in individuals with congenital amusia occur at a perceptual stage or at a stage of representing a contour pattern in memory. To disentangle these two stages, the present study examined cross-modal mapping using an audio-visual mismatch detection task. Twelve participants with congenital amusia and 12 matched controls were presented with tone sequences (tonal and atonal) and visual contours that corresponded to the melodic contour of the tones (i.e., sequences of dots that vary in spatial height corresponding to pitch changes). Participants were asked to respond as quickly as possible when they detected an audio-visual mismatch. Compared with control participants, amusic individuals made more errors in both tonal and atonal sequences. The finding suggests that individuals with congenital amusia are impaired in perceiving the up-down pattern of a melody. Furthermore, all participants showed a better performance on tonal sequences than atonal ones. In other words, tonal structure facilitated melodic contour processing.