Lesion correlates of impaired acoustic-phonetic perception after unilateral left hemisphere stroke.

Acoustic-phonetic perception refers to the ability to perceive and discriminate between speech sounds. Acquired impairment of acoustic-phonetic perception is known historically as 'pure word deafness' and typically follows bilateral lesions of the cortical auditory system. The extent to which this deficit occurs after unilateral left hemisphere damage and the critical left hemisphere areas involved are not well defined. We tested acoustic-phonetic perception in 73 individuals with chronic left hemisphere stroke and performed multivariate lesion-symptom mapping incorporating controls for non-specific task confounds, pure tone hearing loss, response bias and lesion size. Separate analyses examined place of articulation, manner of articulation, voicing and vowel discriminations. Overlap of the lesion map with transcallosal pathways linking left and right temporal lobes was examined using a probabilistic diffusion tensor tractography map of these pathways obtained from a healthy control cohort. Compared to an age- and education-matched control sample, 18% of the patients had impaired acoustic-phonetic perception overall, with 44% impaired on voicing, 26% on manner, 15% on place and 14% on vowel discrimination. Lesion-symptom mapping revealed the most critical areas to be the transverse temporal gyrus (TTG) and adjacent medial belt cortex, the acoustic radiation and the posterior superior temporal sulcus (pSTS). There were notable differences between lesion correlates for the different types of discrimination, with place discrimination linked to medial TTG, vowel discrimination to lateral TTG and planum temporale, manner discrimination to posterior planum temporale and voicing discrimination to pSTS. Overlap of the main lesion map with transcallosal temporal lobe pathways was minor but included a deep white matter component at the base of the middle and inferior temporal gyri. The extent of overlap between individual lesions and the transcallosal pathway map was not correlated with acoustic-phonetic perception. The results add further evidence that acoustic-phonetic impairments, particularly impairments of voicing perception, are relatively common after unilateral left temporal lobe damage, and they clarify the lesion correlates of these deficits. Differences between the lesion maps for the discrimination types likely reflect differential reliance on spectral versus temporal analysis for these discriminations.