From a study by L Mottron, I Peretz, and E Ménard:
A multi-modal abnormality in the integration of parts and whole has been proposed to account for a bias toward local stimuli in individuals with autism (Frith, 1989; Mottron and Belleville, 1993). In the current experiment, we examined the utility of hierarchical models in characterising musical information processing in autistic individuals. Participants were 13 high-functioning individuals with autism and 13 individuals of normal intelligence matched on chronological age, nonverbal IQ, and laterality, and without musical experience. The task consisted of same-different judgements of pairs of melodies. Differential local and global processing was assessed by manipulating the level, local or global, at which modifications occurred. No deficit was found in the two measures of global processing. In contrast, the clinical group performed better than the comparison group in the detection of change in nontransposed, contour-preserved melodies that tap local processing. These findings confirm the existence of a “local bias” in music perception in individuals with autism, but challenge the notion that it is accounted for by a deficit in global music processing. The present study suggests that enhanced processing of elementary physical properties of incoming stimuli, as found previously in the visual modality, may also exist in the auditory modality.
This one took even me a while to figure out! However, after careful reading, this study says that autistic individuals are more adept at processing local changes to music than average people, and just as adept at processing global changes. Therefore, we see here that autistic individuals are more sensitive to small changes in music than average people.
And how does classical music tie into this? We can speculate that thanks to the large developmental sections in classical music, in which small manipulations of the music are used to advance the piece, this kind of music is more likely to stimulate the brains of the autistic individual than the brains of normal people. Popular music simply does not have the kind of complexity that occurs in classical music, and therefore does not have the capacity that classical music does to exercise the processing abilities.