Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amp litude modulation (SAM) applied to a white noise, as a function of modulati on rate (i.e. her 'temporal modulation transfer function' or TMTF); (2) dis criminate between two white noises amplitude modulated by time-reversed tem porally asymmetric envelopes; and (3) identify white noises amplitude modul ated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to nor mal data, the results obtained with the brain-damaged patient showed: (1) i ncreased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identifi cation of speech-envelope noise stimuli. In contrast, intensity discriminat ion thresholds were within the normal range. Taken together, the results in dicate a general impairment in auditory temporal acuity, which is now speci fied as a deficit in the coding of envelope rate and shape, and a deficit i n the ability to use temporal envelope cues in speech processing. These res ults support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligib ility disorders.