Abstract
Our perceptual systems are exceptionally good at searching our sensory environments for salient stimuli. A key question is the extent to which this search is performed subliminally. We explore this using Rapid Serial Visual Presentation (RSVP), by comparing detection performance with the memory left for distractors, the stimuli that have to be rejected as non-targets in the process of searching for targets. To assess the impact that conscious perception has on the fragility of memories, we explore three Stimulus Onset Asynchronies (SOAs): 117ms, 230ms, and 350ms. 26 participants were instructed to search for a target word in each RSVP stream. At the end of the trial, they indicated the presence/absence of the target. In half of the trials, they responded to a free-recall or a recognition memory question. We calculated accuracy (for Free-recall) and d-prime (for Recognition) for each of the last 3 distractors presented in the stream in order to contrast the recency effect (a key marker of the fragility of memory representations) between the two memory tasks. Recall performance at 117ms was extremely low: the -1 item was correctly recalled on approximately one in five streams and, on average, a -1 to -3 item was recalled correctly on less than one in ten streams. Recognition performance was higher and less subject to recency, but still substantially lower than Detection performance. Comparing the recency effect across the three SOAs, it seems that there is a large change in free recall performance from 117ms SOA to 230ms SOA that is not present for recognition. We argue that these findings suggest that the brain subliminally searches for salient stimuli, and are also consistent with a theory we call the tokenized-percept hypothesis, which links conscious perception to the process of episodically marking experiences.