Stimuli presented on the fringe of awareness do not cause proactive interference

A key question in consciousness studies is what is distinct about a conscious as opposed to a sub-conscious percept. The experiments presented here provide evidence for the hypothesis that only conscious percepts enable the formation of episodic memories. We do this by assessing proactive interference (PI) in rapid serial visual presentation (RSVP) streams. Specifically, in a post-stream recognition memory test, we quantify memory for items presented in the RSVP stream close in time to the memory test. PI is demonstrated if performance on long RSVP streams is worse than on short streams, where long streams have many more items presented before the item probed in the recognition memory test. We demonstrate PI on reaction times for slow streams [stimulus onset asynchrony (SOA) 350 ms], but not for fast streams (SOA 83 or 100 ms). We investigate the implications of this reaction time difference by fitting drift diffusion models. The failure to see PI in fast streams raises the possibility that stimuli presented below the threshold of awareness are not episodically encoded.