Strongly masked content retained in memory made accessible through repetition

Abstract

A growing body of evidence indicates that information can be stored even in the absence of conscious awareness. Despite these findings, unconscious memory is still poorly understood with limited evidence for unconscious iconic memory storage. Here we show that strongly masked visual data can be stored and accumulate to elicit clear perception. We used a repetition method across a wide range of conditions (Experiment 1) and a more focused follow-up experiment with enhanced masking conditions (Experiment 2). Information was stored despite being masked, demonstrating that masking did not erase or overwrite memory traces but limited perception. We examined the temporal properties and found that stored information followed a gradual but rapid decay. Extraction of meaningful information was severely impaired after 300 ms, and most data was lost after 700 ms. Our findings are congruent with theories of consciousness that are based on an integration of subliminal information and support theoretical predictions based on the global workspace theory of consciousness, especially the existence of an implicit iconic memory buffer store.

Figure 1

Procedure for Experiment 1. A focus signal (F) was shown followed by a series of masks (M), target letters (T), and blanks (B). The mask duration was adjusted according to target repetition-interval timings. (Experiment 2 added blank frames (7 ms) before and after the targets).

Figure 2

Experiment 1 results of subjective and objective measures of awareness based on the number of presentations and repetition interval timings. Results for all measures were significantly higher when masked stimuli were repeated (10 and five presentations) but decreased as repetition intervals lengthened: (a) Mean results of subjective perception ratings measured through the perception-awareness scale (PAS). Objective measures showed the same effects: (b) depicts the percentage of correct content reports (CR) while (c) shows the percentage of correct forced-choice task (FCT) responses.

Figure 3

Experiment 2 results. More data points for each number of target presentation and repetition interval pair and stronger masking corroborated the findings from Experiment 1: Repetition had a significant impact on PAS reports (a), as well as the percentage of correct CR (b) and FCT responses (c). Repetition interval length had a significant impact on perception even among relatively short intervals.