Holmes and Griffiths (2019) found that fundamental auditory grouping processes-assessed by an abstract figure-ground task-helped to explain variability in speech-in-noise perception after accounting for the audiogram. Sub-clinical variability in pure-tone thresholds has been estimated to account for approximately 15% of the variance in speech-in-noise performance among people ( Holmes & Griffiths, 2019), meaning that the remainder of the variance must originate from other processes.Ĭentral processes are likely to affect the ability to parse target speech from simultaneously occurring background sounds. Yet, difficulties with speech-in-noise perception cannot be fully accounted for by the pure-tone audiogram, which is the most common clinical measure of peripheral hearing ability: Even people who perform normally on clinical tests of peripheral auditory function frequently visit the clinic reporting difficulties understanding speech in noisy places ( Cooper & Gates, 1991 Hind et al., 2011 Kumar, Amen, & Roy, 2007). Understanding speech when competing sounds are present (“speech-in-noise perception”) is particularly difficult for people with sensorineural hearing loss ( Dubno, Dirks, & Morgan, 1984 Gatehouse & Noble, 2004 Helfer & Freyman, 2008). Here, we report a rare case of a young patient who experienced a right hemisphere infarct and subsequently reported difficulty listening in environments containing multiple sounds, such as understanding speech in noisy places and picking out melodies in music. Yet, we do not fully understand which brain regions are required to carry out these processes. The auditory system faces the challenge of parsing these sounds, so that we can focus on the voice of a particular person or a particular melody that we wish to hear out. In our everyday lives, we are often in environments that contain multiple competing sounds-from the sound of someone's voice in a noisy café, to a violin melody that emerges from a large orchestra. Further, the work demonstrates a (partial) lateralisation of the necessary anatomical substrate for segregation that has not been previously highlighted. Consistent with functional imaging studies on normal listeners, the work implicates non-primary auditory cortex. These symptoms are analogous to the visual symptom of simultaneous agnosia. This is the first demonstration of an acquired deficit in the segregation of complex acoustic patterns due to cortical damage, which we argue is a causal explanation for the symptomatic deficits in the segregation of speech and music. Testing with a stochastic figure-ground task-a way of estimating generic acoustic foreground and background segregation-demonstrated that this was also abnormal. Follow-up tests confirmed difficulties with auditory segregation in her left ear that spanned multiple domains, including words-in-noise and music streaming. Clinical tests showed no evidence for abnormal cochlear function. She reported chronic difficulties with segregating speech from noise and segregating elements of music. This led to damage to auditory cortex including planum temporale that spared medial Heschl's gyrus, and included damage to the posterior insula and inferior parietal lobule. We investigated auditory processing in a young patient who experienced a single embolus causing an infarct in the right middle cerebral artery territory.
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