Abstract
The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). The modulation frequency was 4, 16, 64, 256, or 1024 Hz. Measurements of intensity discrimination thresholds for white noise were performed as a control task. In both tasks, white noise stimuli had a 2-s duration and were presented monaurally at 75 dB SPL. Two adult listeners with left- or right-hemisphere damage and three normal-control adult listeners were tested in each ear. Lesions encompassed the primary auditory cortex in the two patients. All listeners had normal audiometric thresholds. The modulation detection data showed no sign of ear asymmetry. For all listeners, the TMTFs displayed a typical low-pass characteristic. Modulation detection was 10–14 dB poorer-than-normal at modulation frequencies between 4 and 256 Hz in the patient with left-hemisphere damage. In contrast, modulation detection was normal in the patient with right-hemisphere damage. Intensity discrimination was within the normal range (0.5–1 dB) for both patients. These results support the hypothesis that cortical structures within the left hemisphere play a crucial role in temporal envelope processing. [Work supported by the Fondation de l’Avenir and the Cognitique Program.]
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