Abstract
Functional near-infrared spectroscopy (fNIRS) is a silent, non-invasive neuroimaging technique that is potentially well suited to auditory research. However, the reliability of auditory-evoked activation measured using fNIRS is largely unknown. The present study investigated the test-retest reliability of speech-evoked fNIRS responses in normally-hearing adults. Seventeen participants underwent fNIRS imaging in two sessions separated by three months. In a block design, participants were presented with auditory speech, visual speech (silent speechreading), and audiovisual speech conditions. Optode arrays were placed bilaterally over the temporal lobes, targeting auditory brain regions. A range of established metrics was used to quantify the reproducibility of cortical activation patterns, as well as the amplitude and time course of the haemodynamic response within predefined regions of interest. The use of a signal processing algorithm designed to reduce the influence of systemic physiological signals was found to be crucial to achieving reliable detection of significant activation at the group level. For auditory speech (with or without visual cues), reliability was good to excellent at the group level, but highly variable among individuals. Temporal-lobe activation in response to visual speech was less reliable, especially in the right hemisphere. Consistent with previous reports, fNIRS reliability was improved by averaging across a small number of channels overlying a cortical region of interest. Overall, the present results confirm that fNIRS can measure speech-evoked auditory responses in adults that are highly reliable at the group level, and indicate that signal processing to reduce physiological noise may substantially improve the reliability of fNIRS measurements.
Highlights
Functional near-infrared spectroscopy has emerged as a popular method for imaging the haemodynamic response to neuronal activity in the human brain (Boas et al, 2014)
We have found application of this algorithm to be beneficial in earlier work (Wiggins and Hartley, 2015), and here we aimed to establish whether it can improve the test-retest reliability of Functional near-infrared spectroscopy (fNIRS) measurements, compared to the conventional approach of assessing HbO and HbR separately
The speech intelligibility data (Fig. 2) collected immediately after the fNIRS measurements confirmed that participants were readily able to understand the auditory speech material with or without visual cues
Summary
Functional near-infrared spectroscopy (fNIRS) has emerged as a popular method for imaging the haemodynamic response to neuronal activity in the human brain (Boas et al, 2014). This noninvasive technique uses near-infrared light to illuminate the brain through the intact scalp; the intensity of light returning to the surface is measured to detect changes in cerebral haemoglobin concentrations. The present study aimed to quantify the test-retest reliability of temporal-lobe fNIRS responses to auditory speech (with and without matching visual cues) in normally-hearing adults. Since visual speech cues are known to activate auditory regions in the superior temporal cortex (Calvert et al, 1997; Hall et al, 2005; MacSweeney et al, 2000), we aimed to quantify the reliability of temporal-lobe responses to visual speech (i.e. silent speechreading)
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