Impaired pitch matching for different waveforms after right hemisphere damage

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Abstract
Studies of dichotic pitch discrimination in normal and neurologically impaired subjects have suggested that the nondominant hemisphere plays a significant role in complex pitch perception. However, despite the fact that pitch deficits can typically be demonstrated in patients with right hemisphere damage, such patients rarely report gross difficulties with functions that use pitch information, suggesting that some capacity for this process is spared. To test this, a series of pitch matching tests were administered to a 61-year-old subject who suffered a right hemisphere stroke, and was found to have normal speech but impaired pitch discrimination on dichotic testing. The frequency of one function generator was controlled by the subject and the frequency of a second generator that produced the target was controlled by the experimenter. Tones were presented continuously at 60 dBA, and the subject was free to alternate between the target and matching tones. Four conditions were tested: sine waves were matched, square waves were matched, sine waves were matched to square waves, and square waves were matched to sine waves. Mean accuracies for sine and square wave matches were 0.01 and 0.34 semitones, respectively. In contrast, matches between wave types ranged from 6.43–17.33 semitones. These results suggest that different types of pitch processing may be dissociable after focal brain damage. [Work supported by NIH.]

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