Abstract
PurposePrevious studies have revealed increased frontal brain activation during speech comprehension in background noise. Few, however, used tonal languages. The normal pattern of brain activation during a challenging speech-in-nose task using a tonal language remains unclear. The Mandarin Hearing-in-Noise Test (HINT) is a well-established test for assessing the ability to interpret speech in background noise. The current study used Mandarin HINT (MHINT) sentences and functional magnetic resonance imaging (fMRI) to assess brain activation with MHINT sentences.MethodsThirty native Mandarin-speaking subjects with normal peripheral hearing were recruited. Functional MRI was performed while subjects were presented with either HINT “clear” sentences with low-level background noise [signal-to-noise ratio (SNR) = +3 dB] or “noisy” sentences with high-level background noise (SNR = −5 dB). Subjects were instructed to answer with a button press whether a visually presented target word was included in the sentence. Brain activation between noisy and clear sentences was compared. Activation in each condition was also compared to a resting, no sentence presentation, condition.ResultsNoisy sentence comprehension showed increased activity in areas associated with tone processing and working memory, including the right superior and middle frontal gyri [Brodmann Areas (BAs) 46, 10]. Reduced activity with noisy sentences was seen in auditory, language, memory and somatosensory areas, including the bilateral superior and middle temporal gyri, left Heschl’s gyrus (BAs 21, 22), right temporal pole (BA 38), bilateral amygdala-hippocampus junction, and parahippocampal gyrus (BAs 28, 35), left inferior parietal lobule extending to left postcentral gyrus (BAs 2, 40), and left putamen.ConclusionIncreased frontal activation in the right hemisphere occurred when comprehending noisy spoken sentences in Mandarin. Compared to studies using non-tonal languages, this activation was strongly right-sided and involved subregions not previously reported. These findings may reflect additional effort in lexical tone perception in this tonal language. Additionally, this continuous fMRI protocol may offer a time-efficient way to assess group differences in brain activation with a challenging speech-in-noise task.
Highlights
Understanding speech in background noise is a challenging task involving multiple brain areas, including regions involved in auditory processing, interpreting language, maintaining attention, and using working memory (Bronkhorst and Plomp, 1992; Narayan et al, 2007; Shetake et al, 2011; Moore et al, 2014)
Noisy versus Clear Brain activation during noisy speech processing in contrast to clear speech processing is presented in Figure 3 and Table 1
Reduced activation was seen in secondary auditory, language, auditory, memory, and somatosensory areas, including bilateral superior temporal gyrus (STG) (BA 22) and middle temporal gyrus (MTG) (BA 21), left Heschl’s gyrus (BAs 41 and 42), right temporal pole (BA 38), bilateral amygdala-hippocampus junction and PHG (BAs 28 and 35), left inferior parietal lobule extending to left postcentral gyrus, and putamen (BA 40)
Summary
Understanding speech in background noise is a challenging task involving multiple brain areas, including regions involved in auditory processing, interpreting language, maintaining attention, and using working memory (Bronkhorst and Plomp, 1992; Narayan et al, 2007; Shetake et al, 2011; Moore et al, 2014). Adank et al (2012) investigated spoken sentence comprehension in Dutch, and revealed more activity in bilateral IFG and frontal operculum (FO) during noisy (SNRs = +2 dB, 0 dB, or −2 dB) speech processing than clear speech processing, less activity was found in primary auditory and language networks. These results suggest that, in addition to the temporal areas involved in auditory and language processing, frontal areas become increasingly activated with higher levels of background noise during speech processing (Adank et al, 2012): increased frontal activation, especially in the left IFG and FO, were consistently found when additional noise processing was required in speech comprehension
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