Hysteresis effects in visual and auditory perception and the comparison of underlying neural mechanisms - an EEG study.

Perceptual hysteresis-the tendency to maintain a current percept even as sensory input shifts towards an alternative interpretation-provides a useful model for studying how recent perceptual history stabilises ongoing perception. The present EEG study, to our best knowledge, provides the first side-by-side examination of the neural correlates of visual and auditory hysteresis within a common experimental and analytical framework. In two experiments, participants viewed ambiguous Necker cubes or listened to ambiguous Shepard tones. In both modalities, stimuli were presented either in a sequential order designed to induce hysteresis or in a randomised order serving as a baseline condition. Behavioural analyses revealed robust order-dependent perceptual biases in both experiments, with hysteresis effects being markedly stronger in the sequential than in the randomised condition, and, in general, more pronounced in the auditory task. This pattern is a central contribution of the present work, as it shows that ordered stimulus presentation induces a stronger history-dependent stabilisation of perception than the local micro-sequences present in random stimulus sequences. At the neural level, inter-trial coherence (ITC) analyses revealed hysteresis-related differences in both modalities, but the oscillatory profiles differed between tasks. In the visual experiment, perception of sequential orders was associated primarily with enhanced alpha and beta band ITC over posterior and frontal electrode sites, without corresponding differences in oscillatory power. In the auditory experiment, hysteresis-related ITC differences were more extensive, including fronto-central alpha band and sustained right-posterior beta band effects, and were accompanied by robust power differences: The baseline condition showed stronger posterior alpha power, whereas the hysteresis condition showed temporally sustained frontal beta power increases. Supplementary source analyses provided supportive evidence for a bilateral involvement of dorsolateral prefrontal and inferior frontal regions. Together, these findings point to partly convergent fronto-posterior involvement in visual and auditory hysteresis, but also suggest modality-specific involvement of sensory-association, attentional, and working-memory-related processes.