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Representations of abstract attributes of auditory stimuli in the human brain were demonstrated using the mismatch negativity (MMN), an event-related potential component elicited by a change in a repetitive sound. Stimuli were pairs of sinusoidal tones. There were two types of tone pairs in each block, standard (p = 85%) and deviant pairs (p = 15%), delivered in a random order. Standard and deviant tone pairs differed only in the direction of within-pair frequency change. In addition, the frequency levels of both the standard and deviant pairs varied randomly within a wide range in a block; thus the standard pairs shared the direction of the within-pair frequency change but not the absolute frequency level. Correspondingly, the deviant pairs only shared the opposite direction of the within-pair change. Nevertheless, the deviant tone pairs elicited MMN, implying that even the direction of the within-pair frequency change of the standard stimuli, and not just their absolute frequencies, developed a neural representation.
Saarinen et al. (Tue,) studied this question.