Human Discrimination and Categorization of Emotions in Voices: A Functional Near-Infrared Spectroscopy (fNIRS) Study.

Thibaud Gruber,Didier Grandjean,Leonardo Ceravolo,Sascha Frühholz,Kinga Igloi,Blanca Marin Bosch,Coralie Debracque

doi:10.3389/fnins.2020.00570

Abstract

Functional Near-Infrared spectroscopy (fNIRS) is a neuroimaging tool that has been recently used in a variety of cognitive paradigms. Yet, it remains unclear whether fNIRS is suitable to study complex cognitive processes such as categorization or discrimination. Previously, functional imaging has suggested a role of both inferior frontal cortices in attentive decoding and cognitive evaluation of emotional cues in human vocalizations. Here, we extended paradigms used in functional magnetic resonance imaging (fMRI) to investigate the suitability of fNIRS to study frontal lateralization of human emotion vocalization processing during explicit and implicit categorization and discrimination using mini-blocks and event-related stimuli. Participants heard speech-like but semantically meaningless pseudowords spoken in various tones and evaluated them based on their emotional or linguistic content. Behaviorally, participants were faster to discriminate than to categorize; and processed the linguistic faster than the emotional content of stimuli. Interactions between condition (emotion/word), task (discrimination/categorization) and emotion content (anger, fear, neutral) influenced accuracy and reaction time. At the brain level, we found a modulation of the Oxy-Hb changes in IFG depending on condition, task, emotion and hemisphere (right or left), highlighting the involvement of the right hemisphere to process fear stimuli, and of both hemispheres to treat anger stimuli. Our results show that fNIRS is suitable to study vocal emotion evaluation, fostering its application to complex cognitive paradigms.

Highlights

While the majority of the studies investigating cognitive processes in cortical regions have relied on functional magnetic resonance imaging or electroencephalography (EEG), the use of functional near-infrared spectroscopy as an imaging technique has developed over the last 25 years
In this study we showed that Functional Near-Infrared spectroscopy (fNIRS) is a suitable method to study cognitive paradigms related to emotions, categorization and discrimination, in the human frontal regions using mini-block design and event related stimuli
Our first goal was to estimate whether it was possible to isolate significant activity in the inferior frontal gyrus (IFG) using fNIRS, whose activity has been highlighted in previous functional magnetic resonance imaging (fMRI) studies investigating emotional prosody processing, and in particular during categorization and discrimination of emotional stimuli (Schirmer and Kotz, 2006; Frühholz et al, 2012)

Summary

Introduction

While the majority of the studies investigating cognitive processes in cortical regions have relied on functional magnetic resonance imaging (fMRI) or electroencephalography (EEG), the use of functional near-infrared spectroscopy (fNIRS) as an imaging technique has developed over the last 25 years (Chance et al, 1993; Hoshi and Tamura, 1993; Kato et al, 1993; Emotion Processing Analysis Through fNIRSVillringer et al, 1993; Boas et al, 2014; Buss et al, 2014; Homae, 2014). Similar to fMRI, fNIRS is a non-invasive and non-ionizing method that investigates the brain hemodynamics (Boas et al, 2014). Using the principle of tissue transillumination, fNIRS indirectly measures via near-infrared light the oxygenated hemoglobin (Oxy-Hb) and deoxygenated hemoglobin (DeoxyHb) sustaining the hemodynamic response function (HRF). Research findings using fNIRS suggest that this method can be an appropriate substitute to fMRI to study brain processes related to cognitive tasks (Cui et al, 2011; Scholkmann et al, 2014) with a more realistic approach (Strait and Scheutz, 2014). Similar to other neuroimaging techniques such as fMRI, a growing number of fNIRS studies use mini-block or event-related paradigms rather than block designs (Aqil et al, 2012; Aarabi et al, 2017). We aimed to advance knowledge on the use of fNIRS in complex cognitive paradigms relying on mini-block design by evaluating its use in emotional evaluation paradigms, which previous work suggested could constitute a relevant field to evaluate the suitability of fNIRS

Objectives

Methods

Results

Conclusion