Differences in Prefrontal Cortex Activity and Behavioral Response Over Time During Visual and Auditory Working Memory Tasks: A Functional Near-Infrared Spectroscopy Pilot Study

This study aims to investigate the effects of different stimulus modalities on brain activity, behavioral responses, and fatigue perception over time, explicitly comparing visual n-back and auditory n-back tasks in healthy adults using functional near-infrared spectroscopy (fNIRS). Nineteen healthy adults participated in the study, and all participants performed 20 blocks each of a visual n-back task and an auditory nback task with a load condition (3-back) while being recorded with fNIRS. The z-score of oxyhemoglobin (oxy-Hb) at channel 16 was initially higher during the auditory n-back task compared to the visual n-back task; however, this difference did not remain significant after false discovery rate (FDR) correction. Additionally, oxy-Hb levels exhibited a general decline over time across multiple channels. In terms of behavioral performance, participants demonstrated lower accuracy and longer reaction times in the auditory n-back task compared to the visual n-back task. However, subjective fatigue scores did not differ significantly between the two modalities. The findings of this study elucidate the effects of working memory load, across different modalities and over time, on local brain dynamics and behavioral responses. This insight contributes to the understanding of modality-dependent mechanisms of cognitive load in the prefrontal cortex.