Individuals with congenital amusia respond to fractal music differently from normal listeners

Congenital amusia is a neurogenetic disorder predominately defined by impaired perception of musical tonal relationships. This study examined amusics’ responses to a gradient of pitch interval complexity in fractal music. Eighteen Mandarin-speaking amusics and 18 controls rated random tone sequences for perceptual (complexity, melodicity) and affective (interest, ease, mood) attributes, and performed a recognition memory task. Sequences were created using fractal model (1/fß) with ß-values ranging from 0.0 (most complex) to 2.6 (least complex). As predicted, both groups rated complexity based on the ß-values, demonstrating that amusics perceived the gradient of pitch interval complexity. However, amusics’ ratings deviated from controls in measures of melodicity, affect, and memory performance. For controls, moderately complex sequences (fractal ß-values =1.4–1.6) were rated the most melodious, drove the highest emotional responses, and were the easiest to remember, whereas amusics’ ratings did not respond to this range, but rather followed a more linear trend. These findings suggest that amusics not only have problems with perception of pitch interval relationships (not complexity), but also lack heightened sensitivity to the moderate range in fractal music. This deficit is reflected in broader musical processing including the perception of melody, affective response, and memory for musical sequences. [This work was supported by National Science Foundation Grant BCS-0719666 to P.C.M.W. and Shanghai Normal University funding to C.J.]