Neural Mechanisms of Intersensory Switching: Evidence for Delayed Sensory Processing and Increased Cognitive Effort

Intersensory switching (IS), the ability to shift attention between different sensory systems, is essential for cognitive flexibility, yet leads to slower responses compared to repeating the same sensory modality. The underlying neural mechanisms of IS remain largely unknown. In this study, high-density EEG was used to investigate these mechanisms in healthy adults (n=53) performing a speeded reaction time (RT) task involving visual and auditory stimuli. Trials were categorized as Repeat (same preceding modality) or Switch (different preceding modality). Switch trials showed slower RTs and delayed sensory responses (N1 and P2 components). Furthermore, across both Repeat and Switch trials, RT correlated with the latency of these neural responses. Additionally, lower alpha-band inter-trial phase coherence (ITPC) in primary sensory regions was noted for Switch compared to Repeat trials, suggesting reduced efficiency of sensory processing. Greater induced theta activity over fronto-central scalp regions in Switch trials suggested increased cognitive control demands, potentially involving the anterior cingulate cortex (ACC). These findings reveal that IS is characterized by delayed sensory processing and heightened cognitive load, supporting a model where prior stimulus primes the sensory cortex for faster processing in Repeat trials, while Switch trials demand more cognitive resources for adjustment. The similarity of effects across both auditory and visual sensory modalities suggests that IS effects represent core features of sensory processing, potentially reflecting a fundamental, modality-independent mechanism of attentional switching across sensory domains.