Abstract
Sound localization is an essential part of auditory processing. However, the cortical representation of identifying the direction of sound sources presented in the sound field using functional near-infrared spectroscopy (fNIRS) is currently unknown. Therefore, in this study, we used fNIRS to investigate the cerebral representation of different sound sources. Twenty-five normal-hearing subjects (aged 26 ± 2.7, male 11, female 14) were included and actively took part in a block design task. The test setup for sound localization was composed of a seven-speaker array spanning a horizontal arc of 180° in front of the participants. Pink noise bursts with two intensity levels (48 dB/58 dB) were randomly applied via five loudspeakers (–90°/–30°/–0°/+30°/+90°). Sound localization task performances were collected, and simultaneous signals from auditory processing cortical fields were recorded for analysis by using a support vector machine (SVM). The results showed a classification accuracy of 73.60, 75.60, and 77.40% on average at –90°/0°, 0°/+90°, and –90°/+90° with high intensity, and 70.60, 73.6, and 78.6% with low intensity. The increase of oxyhemoglobin was observed in the bilateral non-primary auditory cortex (AC) and dorsolateral prefrontal cortex (dlPFC). In conclusion, the oxyhemoglobin (oxy-Hb) response showed different neural activity patterns between the lateral and front sources in the AC and dlPFC. Our results may serve as a basic contribution for further research on the use of fNIRS in spatial auditory studies.
Highlights
Auditory perception is one of the most important sensory modalities in creatures
Since localization acuity is higher for broadband than for narrowband sounds and the neural sound location encoding was influenced by the attention of listening (Butler, 1986), here, we presented pink noise bursts with different sound intensities and sources randomly in blocks of a run, allowing participants to attend the sound localization task and avoid speech understanding
We extracted two sets of functional near-infrared spectroscopy (fNIRS) data for analysis based on behavioral results, used a dichotomous classification method to differentiate the fNIRS signals in different conditions, and presented them in the form of figure legends, which are presented below as part of the results of this experiment
Summary
Auditory perception is one of the most important sensory modalities in creatures. There are multiple types of information presented in sounds. Identifying the source of the sound makes wild animals aware of the danger or its prey and is important in communicative interactions in human society. Auditory neuroscientists have examined the neuronal mechanisms underlying spatial hearing (Middlebrooks and Green, 1991; Skottun, 1998; Grothe et al, 2010). The localization and identification of sounds are constructed from the precise relative intensity and timing between the two ears [two binaural cues mostly play roles in the horizontal plane: interaural. Cerebral Representation Sound Localization fNIRS time difference (ITD) and interaural level difference (ILD)] as well as from patterns of frequencies mapped at the two ears (play roles mostly in the vertical plane) (Middlebrooks and Green, 1991). Humans integrate input from the ears and cognitive processes to derive the location of sound sources (Nothwang, 2016; Zhang and Liu, 2019). The neural encoding of sound locations and especially the processing of sound sources in the cortex remains a matter of ongoing discussion, and there are still divergent views (Ahveninen et al, 2014)
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