Behavioural and electrophysiological modulations of onset primacy in visual change detection.

Generally, newly appearing objects attract observers' attention more effectively than other types of change in an environment. While there is consensus about the existence of this phenomenon, it has been debated whether the new objects attain their primacy in an endogenous or an exogenous fashion. To contribute to this debate, the current study measured participants' behavioural performance in detecting object appearance (onset) and disappearance (offset) while recording their electroencephalography. Some participants were trained to give priority to detecting offsets, and their data were compared against those of neutral (i.e., untrained) participants. This comparison revealed that the difference in behavioural response times between onset and offset detection was reduced after training, reflecting the degree to which onsets had attentional advantage over offsets in each group of participants. At the same time, amplitudes of the P100 event-related potential component were more differentiated between onset and offset detection in the trained participants than in the neutral participants. Critically, the modulations of the response times and the P100 amplitudes were not attributed to stimulus-driven effects because all participants were exposed to the same set of stimuli when the post-training results were obtained. Thus, these findings offer evidence that the relative efficacy of object onset in visual change detection is not purely a bottom-up phenomenon but is instead modulated by top-down processes.