On pure word deafness, temporal processing, and the left hemisphere
Pure word deafness (PWD) is a rare neurological syndrome characterized by severe difficulties in understanding and reproducing spoken language, with sparing of written language comprehension and speech production. The pathognomonic disturbance of auditory comprehension appears to be associated with a breakdown in processes involved in mapping auditory input to lexical representations of words, but the functional locus of this disturbance and the localization of the responsible lesion have long been disputed. We report here on a woman with PWD resulting from a circumscribed unilateral infarct involving the left superior temporal lobe who demonstrated significant problems processing transitional spectrotemporal cues in both speech and nonspeech sounds. On speech discrimination tasks, she exhibited poor differentiation of stop consonant-vowel syllables distinguished by voicing onset and brief formant frequency transitions. Isolated formant transitions could be reliably discriminated only at very long durations (>200 ms). By contrast, click fusion threshold, which depends on millisecond-level resolution of brief auditory events, was normal. These results suggest that the problems with speech analysis in this case were not secondary to general constraints on auditory temporal resolution. Rather, they point to a disturbance of left hemisphere auditory mechanisms that preferentially analyze rapid spectrotemporal variations in frequency. The findings have important implications for our conceptualization of PWD and its subtypes. (JINS, 2005, 11, 456–470.)(Received March 17 2004)
(Revised February 10 2005)
(Accepted April 5 2005)
Key Words: Word deafness; Auditory agnosia; Left hemisphere; Temporal processing; Speech perception.
c1 Reprint requests to: Gerry A. Stefanatos, D. Phil., Director, Cognitive Neurophysiology Laboratory, Moss Rehabilitation Research Institute, Albert Einstein Medical Center, 1200 West Tabor Road, Philadelphia, PA 19141. E-mail: Stefanag@Einstein.edu