Using functional near-infrared spectroscopy in measuring the hearing thresholds in sleeping infants

Abstract

Functional near-infrared spectroscopy (fNIRS) is a developing technology that uses near-infrared light to image brain activity in the surface layers of the cortexIt measures changes in oxy- haemoglobin (HbO) and deoxy-haemoglobin (HbR) in response to stimuli, which makes it suitable for objectively assessing hearing thresholds by examining the morphology of sound-evoked fNIRS response. This study recruited twelve sleeping infants with no known hearing loss. A natural recording of the /ba/ speech token was used as the stimulus, which was trimmed and concatenated into a 5.4 s stimulus block. The stimulus was presented monaurally between 35 and 80dB SPL using an insert earphone. fNIRS responses were recorded from bilateral pre-frontal and temporal regions. We observed a positive peak at around 5–6 s from stimulus onset and followed by a negative trough at around 10–20 s from stimulus onset. The amplitudes and latencies of this response varied with different stimulus intensity levels. Results showed how features of the fNIRS response changed systematically with intensity level. Characterizing the response differences to different stimulus intensity levels will facilitate the development of a model for assessment of hearing thresholds in this population.