Subliminally and Supraliminally Acquired Long-Term Memories Jointly Bias Delayed Decisions

Abstract

Common wisdom and scientific evidence suggest that good decisions require conscious deliberation. But growing evidence demonstrates that not only conscious but also unconscious thoughts influence decision-making. Here, we hypothesize that both consciously and unconsciously acquired memories guide decisions. Our experiment measured the influence of subliminally and supraliminally presented information on delayed (30-40 min) decision-making. Participants were presented with subliminal pairs of faces and written occupations for unconscious encoding. Following a delay of 20 min, participants consciously (re-)encoded the same faces now presented supraliminally along with either the same written occupations, occupations congruous to the subliminally presented occupations (same wage-category), or incongruous occupations (opposite wage-category). To measure decision-making, participants viewed the same faces again (with occupations absent) and decided on the putative income of each person: low, low-average, high-average, or high. Participants were encouraged to decide spontaneously and intuitively. Hence, the decision task was an implicit or indirect test of relational memory. If conscious thought alone guided decisions (= H₀), supraliminal information should determine decision outcomes independently of the encoded subliminal information. This was, however, not the case. Instead, both unconsciously and consciously encoded memories influenced decisions: identical unconscious and conscious memories exerted the strongest bias on income decisions, while both incongruous and congruous (i.e., non-identical) subliminally and supraliminally formed memories canceled each other out leaving no bias on decisions. Importantly, the increased decision bias following the formation of identical unconscious and conscious memories and the reduced decision bias following to the formation of non-identical memories were determined relative to a control condition, where conscious memory formation alone could influence decisions. In view of the much weaker representational strength of subliminally vs. supraliminally formed memories, their long-lasting impact on decision-making is noteworthy.

Keywords: decision-making; hippocampus; long-term memory; relational learning; subliminal stimulation; unconscious processing.

Figure 1

Experimental Design. Participants were presented with subliminal combinations of faces and written high- (blue) or low-wage (red) occupations or consonant strings (light gray: control condition). Subliminal encoding was followed by a rest period of 20 min. Next, participants consciously encoded the same faces presented supraliminally now combined with either the same occupations, congruous or incongruous occupations. The decision task followed after another break. All faces were shown again, without any occupations, for participants to rate each person's putative income and then to try to recall the person's occupation as learned before. The individuals depicted in this figure gave written informed consent to publication of their image.

Figure 2

Schematic illustration of experimental tasks. Unconscious Encoding: One subliminal encoding episode in which one subliminal stimulus (S: face with occupation word) is presented 12 times in between masks (M). One encoding episode consists of 6 attention task trials. In one of these trials, the fixation screen (F) contains a target stimulus (“−” or “|” instead of “+”); Conscious Encoding: Sequence of three supraliminal encoding trials. Participants indicated by button press how well the indicated occupation matched a person ([C]: “poor,” [V]: “poor-average,” [B]: “good-average,” or [V]: “good” match); Decision Task and Cued Recall: Participants first decided on the suspected income of the person ([C]: “low,” [V]: “low-average,” [B]: “high-average,” or [V]: “high” income), then tried to remember and say the occupation associated to this face, and finally indicated whether they randomly guessed, had a hunch but were unsure, or certainly remembered the occupation; The individuals depicted in this figure gave written informed consent to publication of their image.

Figure 3

Influences of unconscious and conscious encoding on decision-making. (A) Plotted is the difference in income ratings for faces consciously encoded with high- vs. low-wage occupations (i.e., [high]-[low]). This difference reflects the decision bias toward consciously encoded occupations. Results are shown for the between-subjects manipulated experimental condition (identical, congruous, incongruous) and the within-subject manipulated unconscious encoding condition (faces with occupations vs. consonants). The figure illustrates a strong decision bias following unconscious and conscious encoding of identical information, and a reduced or absent bias following encoding of congruous or incongruous unconscious and conscious information. (B) Plotted is the change in the bias toward consciously encoded occupations ([high]-[low]) for faces that were unconsciously encoded with occupations instead of consonant strings (i.e., [bias for faces encoded with occupations]-[bias for faces encoded with consonant-strings]). This change reflects the unconscious influence on decision bias: positive scores indicate increased, negative scores decreased decision bias toward the consciously seen occupations due to subliminal encoding of face-occupation pairs. The figure illustrates an increased decision bias following unconscious and conscious encoding of identical occupations, and a reduced bias following encoding of non-identical (congruous or incongruous) information. Displayed are group means with SEMs. #p < 0.10, ^*p < 0.05 (uncorrected two-tailed t-tests).