Prefrontal fNIRS hemodynamic correlates of attentional load during rapid serial visual presentation tasks

Despite the growing interest in functional near-infrared spectroscopy (fNIRS) for practical brain-computer interface (BCI) applications, prefrontal hemodynamic responses during rapid serial visual presentation (RSVP) tasks remain poorly characterized, even though these tasks demand sustained attentional engagement under fast-paced visual streams.

We examined prefrontal cortex (PFC) activation and functional connectivity as indices of attentional monitoring during an RSVP task using a 15-channel prefrontal fNIRS device in 50 participants. Trials either contained one target image among nontargets or consisted entirely of nontarget images. Eleven statistical activation features from oxygenated (HbO) and deoxygenated (HbR) hemoglobin changes, and Fisher's r-to-z transformed inter-channel connectivity values were compared between conditions using paired-samples t-tests with false discovery rate correction. Response time and exploratory correlations between behavioral latency and hemodynamic features were also analyzed.

The nontarget condition showed slightly higher HbO activation, mainly in amplitude-related features such as max and mean, suggesting increased sustained processing demands when target absence had to be confirmed. In contrast, HbR differences were more strongly characterized by distributional and transient-related features, including kurtosis, skewness, and peak-related features, suggesting complementary HbO and HbR sensitivity to task conditions. Connectivity analysis revealed condition-dependent inter-channel coupling patterns, with generally stronger HbO connectivity in the nontarget condition and a partially different HbR pattern. Response times were significantly longer in the nontarget condition and were more closely associated with temporal and distributional hemodynamic features than with amplitude-based features.

These findings provide an initial exploratory characterization of condition-dependent prefrontal activation and connectivity differences during RSVP tasks, highlighting the potential of fNIRS as a practical tool for attentional monitoring and informing future multimodal neuroimaging approaches.