Deficits of musical timbre perception after unilateral temporal-lobe lesion revealed with multidimensional scaling

Thirty patients with unilateral temporal lobe excisions and 15 normal control subjects were tested in a task involving judgements of timbre dissimilarity in single tone and melodic conditions. Perceptual correlates of spectral and temporal parameters resulting from changing the number of harmonics and rise-time duration, respectively, were investigated by using a multidimensional scaling technique. The results of subjects with left temporal lobe lesion suggest that they were able to use the spectral and temporal envelopes of tones independently in making perceptual judgements of single tones. In the melodic condition, their results were significantly different from those of normal control subjects, suggesting that left temporal lesions do affect subtle aspects of timbre perception, despite these patients' preserved ability to make discrimination judgements using traditional paradigms. The major finding of this study concerns perceptual ratings obtained by subjects with right temporal lobe lesion, which revealed a disturbed perceptual space in both conditions. The most distorted results were obtained with single tones, in which the temporal parameter was less prominent. Tones were grouped according to their spectral content, but the results did not reflect a coherent underlying perceptual dimension. In general, the data from both patient groups (left lesions and right lesions) showed that the extraction of temporal cues was easier in the melodic than in the single tone condition, suggesting that the different durations and frequencies heard in a musical phrase enhance the importance of certain physical parameters. The findings of the present study replicate and extend previous results showing that timbre perception depends mainly upon the integrity of right neocortical structures, although a contribution of left temporal regions is also apparent. These data also demonstrate that multidimensional techniques are sensitive to more subtle perceptual disturbances that may not be revealed by discrimination paradigms.