An event-related potential study of sensory representations of unfamiliar tonal patterns.

Tonal patterns were delivered to 17 subjects instructed to read a self-selected book and to ignore the auditory stimuli. The standard pattern contained eight 50-ms segments differing in frequency. Infrequent changes of single segments within the pattern elicited negative modulations of the event-related brain potentials (ERPs) as compared with the ERPs elicited by the standard pattern. The change consisted of either a duplication of a single segment or an interchange of two segments within the pattern. Because of the nature of the change, the ERP modulation cannot be explained by a simple refractoriness mechanism or by assuming that the mechanism generating the negative modulation relies on representations of only the spectral but not the temporal information of the pattern. Therefore, the spectral and the temporal information of the tonal patterns were represented by the information processing system on a grain of single segments.