No abstract

Onset primacy is a robust behavioural phenomenon whereby humans identify the sudden appearance of an object in the environment (onset) with greater speed and accuracy than other types of visual change, such as the sudden disappearance of an object from the environment (offset). The default mode hypothesis explains this phenomenon by postulating that onset detection is the default processing mode of the attentional system. The present study aimed to test this notion by investigating whether onset primacy is also reflected on a neural level, as indicated by the comparative efficiency of neural processing for onsets, using electroencephalography. It was hypothesised that this relative efficiency would be reflected in the P300 event-related potential as a greater amplitude across temporal, parietal, and occipital regions during onset detection, compared to offset detection. This prediction was tested through a change detection task in which participants were required to identify the location of onset or offset between paired images of naturalistic scenes. Results showed that P300 amplitude differed between onset and offset conditions in the anticipated direction, supporting the default mode hypothesis. These results suggest that the P300 is a neural marker of onset primacy in visual change detection.