No EEG evidence for subconscious detection during Rapid Serial Visual Presentation

Electroencephalography (EEG) is widely used to study visual and auditory perception. It has the benefit of high temporal resolution allowing one to detect the earliest moments of neural processing of a stimulus. In some detection tasks EEG signals precede overt behavioral response by as much as 200 ms, i.e. at times when stimuli may not yet have been consciously detected by the subjects, leading some to speculate that EEG may reveal also subconscious target detection. We thus asked if there are EEG signals associated with detection of a stimulus even in the absence of an overt (conscious) report. Rapid Serial Visual Presentation (RSVP) of images elicits strong EEG responses shortly after a target image is presented and these evoked responses can be detected on a single trial basis using dedicated pattern recognition techniques previously developed. Here we record EEG during RSVP where we vary detection performance by varying presentation parameters such as eccentricity or size of the target on an image. We find that under these manipulations the behavioral detection performance of subjects largely tracked the detection of evoked responses in the EEG. More specifically, we show that EEG detection performance is high for those trial in which subject successfully report the presence or absence of a target, while EEG detection performance is indistinguishable from chance when subjects failed to provide a correct response. In short, when the subjects sees the target, we also see this in their EEG; if the subjects do not see the target then their EEG remains also unafected by the target stimulus. In summary, contrary to the often-held believe, we have found no EEG evidence for subconscious detection of a target stimulus during RSVP.