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Helene Gauchou, Agnieszka Wykowska, Anna Schubö, Kevin O'Regan; An ERP study of visual change detection. Journal of Vision 2007;7(9):666. doi: 10.1167/7.9.666.
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Numerous studies employed event-related brain potential (ERP) in order to understand the time course of neural events underlying the change detection of a visual stimulus. It has been reported that change detection would be related with an increase of negativity at posterior sites peaking around 200ms after stimulus onset (Kaernbach, Schröger, Jacobsen & Roeber, 1999; Koivisto & Revonsuo, 2003) and with an enhanced positivity in the P3 time range (Niedeggen, Wichmann & Stoerig, 2001; Turatto, Angrilli, Mazza, Umilta & Driver, 2002). The posterior negativity is described as an electrophysiological correlate of phenomenal visual change awareness and the enhanced positivity as a later postperceptual processing stage involved in response-related decision processes.
In the present ERP study participants were presented for 100ms with a sample screen composed of four colored squares and after a 1s delay appeared a test screen. The task was to detect the color change of one of the items that was cued on the test screen by the use of a frame. The use of this cue allowed us to assess if the N2 increased amplitude is correlated with the change detection mechanism or with the attentional processes related with target detection.
Moreover in a second time the participants had to rate the level of confidence of their change/non-change detection answer. This scale allowed us to study separately three kinds of trials: 1) High level of confidence trials corresponding to the situation where participants saw the change/no-change; 2) Medium level trials where they had no visual experience but a feeling of change/no-change; 3) Low level trials where participants were guessing. This categorization allowed us to investigate the ERP difference between correct and non correct answers as a function of the different levels of visual experience.
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