Cortical mechanisms of speech perception in noise

Purpose: The present study examines the brain basis of listening to spoken words in noise, which is a ubiquitous characteristic of communication, with the focus on the dorsal auditory pathway. Method: English-speaking young adults identified single words in 3 listening conditions while their hemodynamic response was measured using fMRI: speech in quiet, speech in moderately loud noise (signal-to-noise ratio [SNR] 20 dB), and in loud noise (SNR -5 dB). Results: Behaviorally, participants' performance (both accuracy and reaction time) did not differ between the quiet and SNR 20 dB condition, whereas they were less accurate and responded slower in the SNR -5 dB condition compared with the other 2 conditions. In the superior temporal gyrus (STG), both left and right auditory cortex showed increased activation in the noise conditions relative to quiet, including the middle portion of STG (mSTG). Although the right posterior STG (pSTG) showed similar activation for the 2 noise conditions, the left pSTG showed increased activation in the SNR -5 dB condition relative to the SNR 20 dB condition. Conclusion: We found cortical task-independent and noise-dependent effects concerning speech perception in noise involving bilateral mSTG and left pSTG. These results likely reflect demands in acoustic analysis, auditory-motor integration, and phonological memory, as well as auditory attention.