اثرات طولانی مدت آغازگر عاطفی پنهان از حالات صورت

Abstract Unconscious processing of stimuli with emotional content can bias affective judgments. Is this subliminal affective priming merely a transient phenomenon manifested in fleeting perceptual changes, or are long-lasting effects also induced? To address this question, we investigated memory for surprise faces 24 h after they had been shown with 30-ms fearful, happy, or neutral faces. Surprise faces subliminally primed by happy faces were initially rated as more positive, and were later remembered better, than those primed by fearful or neutral faces. Participants likely to have processed primes supraliminally did not respond differentially as a function of expression. These results converge with findings showing memory advantages with happy expressions, though here the expressions were displayed on the face of a different person, perceived subliminally, and not present at test. We conclude that behavioral biases induced by masked emotional expressions are not ephemeral, but rather can last at least 24 h.

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Results 3.1. Strictly-Subliminal prime presentations Given the possibility that some participants were aware of prime faces during the priming phase, we took several steps to determine the relevance of this for both short- and long-lasting effects of affective priming. In particular, we attempted to identify a subset of participants most likely to have processed prime faces in a subliminal manner. Although there are many methods to use in such circumstances (Seth et al., 2008), there is reason to be skeptical of using subjective reports alone or of relying only on objective tests of prime processing. Therefore, we elected to adopt a conservative approach analogous to that used by Szczepanowski and Pessoa (2007), in which we selected a subgroup of participants based on both types of criteria together. We reasoned that strictly-subliminal presentation is most likely when (1) participants’ attempts to discriminate among emotional expressions of primes were not accurate, and (2) their subjective reports gave no indication of conscious perception of primes. Performance data on emotional-expression discrimination were subjected to Χ2 analyses. Above chance-levels of expression discrimination were indicated by significant Χ2 (p < .05) for 23 participants. Awareness of prime faces was evident in the subjective reports obtained from 24 participants. A total of 28 of the 43 participants demonstrated either above-chance discrimination abilities or provided subjective reports of prime awareness (18 participants satisfied both criteria). These participants thus formed the Not-Strictly-Subliminal (NSS) group. The remaining 15 participants comprised the Strictly-Subliminal (SS) group. Of course, it remains possible that prime awareness was missed by the subjective reports (e.g., because of forgetting), or that prime awareness occurred despite chance-level discrimination abilities (e.g., because different strategies were used in this test versus in the priming phase, or because an inaccurate estimate of true discrimination abilities was obtained due to unexplained variability in responses and/or an insufficient number of trials). Nonetheless, these procedures were advantageous because conscious perception of primes was more likely, overall, for the NSS group than for the SS group. 3.2. Priming results Surprise faces were rated as more positive when primed by happy faces than when primed by fearful faces, but only in the SS group (Fig. 2). To assess priming, we compared mean surprise-face ratings across pairs of conditions in separate contrasts within each group as planned comparisons based on our prior study (Li et al., 2008). Happy face primes led to more positive ratings than fearful face primes in the SS group [t(14) = 2.58, p < .05], but not in the NSS group [t(27) = 0.65, n.s.]. No other differences between pairs of different prime categories were significant (t-values < 1.24). There were no main effects of group [SS vs. NSS, F(1, 41) = 0.30, n.s.], or prime expression [F(2, 82) = 2.62, p = .07], nor was there an interaction between group and prime expression [F(2, 82) = 1.01, n.s.]. There were no differences in mean surprise-face ratings between the SS and NSS groups with fearful primes [t(41) = 1.08, n.s.], happy primes [t(41) = 0.03, n.s.], or neutral primes [t(41) = 0.50, n.s.]. Mean ratings of surprise faces (1=most negative, 6=most positive) for the ... Fig. 2. Mean ratings of surprise faces (1 = most negative, 6 = most positive) for the Strictly-Subliminal group and the Not-Strictly-Subliminal group as a function of prime expression. Strictly-Subliminal participants rated surprise faces primed by happy faces as significantly more positive than surprise faces primed by fearful faces. ∗Indicates p < .05. Error bars indicate ±1 SEM with baseline individual variability removed. Figure options Affective priming in the SS group was particularly strong early in the priming phase. The magnitude of affective priming, defined as the mean rating difference between surprise faces primed by happy faces and those primed by fearful faces, was high in the first three blocks [M = 0.24, SD = 0.31, t(14) = 2.99, p < .01], whereas affective priming in the second three blocks was non significant [M = 0.11, SD = 0.32, t(14) = 1.31, n.s.]. This may reflect habituation of priming or a change in response strategy regarding the affective evaluation of the surprise faces. Further analyses were run to address the concern that the post-hoc sorting of participants into SS and NSS groups might have skewed results by disrupting assignment of stimulus sets to participants (i.e., the counterbalanced pairings of the three groups of surprise faces with each category of emotional prime). Results provided strong evidence for dismissing this concern. First, SS participants were distributed across all three stimulus-set assignments (7, 5, and 3 participants per stimulus set). Second, the magnitude of affective priming (mean ratings of happy-primed faces minus fear-primed faces) did not differ reliably across the three stimulus sets [F(2, 40) = 2.20, p = .13]. Moreover, the stimulus set that produced the largest magnitude of affective priming in the SS group had only three participants. Incomplete counterbalancing can thus be ruled out as a potential explanation for priming for the SS group. Magnitude of affective priming was not associated with the degree of objective discrimination ability for participants within either the SS group [r = −0.40, p = .13] or the NSS group [r = −0.11, n.s.]. Thus, the ability to discriminate facial affect when intentionally attempting to do so after being informed about the presence of primes (Day 2) was not associated with increased priming magnitude in the absence of any instructions to attend specifically to prime faces (Day 1). The non significant correlation in the SS group is in the opposite direction to the correlation that would be expected if priming were merely a weak reflection of participants’ abilities to extract affective information from emotional expressions that can be used both for affective discrimination and awareness of facial affect. Although these correlational results are only null findings, they are consistent with the inference supported above that priming effects in the SS group arose due to subliminal processing. 3.3. Memory results In the SS group, surprise faces primed by happy faces were remembered better than surprise faces primed by fearful faces (Fig. 3). In an initial analysis of recognition results, we computed recognition hit rates irrespective of confidence level and separately as a function of the expression of the prime from Day 1. Mean hit rate was significantly higher for happy-primed surprise faces than for fearful-primed surprise faces [t(14) = 2.95, p < .05], and for neutral-primed surprise faces [t(14) = 2.28, p < .05], but did not differ between fearful-primed and neutral-primed surprise faces [t(14) = 1.28, n.s.]. In the NSS group, hit rate differences between pairs of priming conditions were all non significant (t-values < 1.43). Hit rates averaged across conditions were well above the false alarm rates for trials with new faces for both the SS group [t(14) = 4.34, p < .01] and the NSS group [t(27) = 10.40, p < .01]. Furthermore, the finding that memory results varied with prime status (fearful versus happy) in the SS group but not in the NSS group was confirmed by a significant interaction between prime status and group [F(1, 41) = 4.52, p < 0.05]. There were no differences in recognition hit rates between the SS and NSS groups with fearful primes [t(41) = 0.34, n.s.], happy primes [t(41) = 1.79, n.s.], or neutral primes [t(41) = 0.78, n.s.]. Mean hit rates for “old” surprise faces for the Strictly-Subliminal group and ... Fig. 3. Mean hit rates for “old” surprise faces for the Strictly-Subliminal group and the Not-Strictly-Subliminal group as a function of prime expression from the priming phase on Day 1. Ratings of “mildly confident old” and “very confident old” were classified as hits. Dashed lines indicate false alarm rates (new faces endorsed as “mildly confident old” or “very confident old”). Strictly-Subliminal participants displayed significantly better memory for surprise faces primed by happy faces than surprise faces primed by fearful or neutral faces. We observed the same pattern when hits included only “very confident old” responses to old faces (see Fig. 4). ∗Indicates p < .05. Error bars indicate ±1 SEM with baseline individual variability removed. Figure options We observed the same pattern of results when recognition hits were counted just for faces endorsed as old with high confidence, or when all four levels of recognition confidence were taken into account (Fig. 4). To differentially weight the memory experiences expressed by confidence ratings in each condition, we calculated memory scores using mean numerical ratings—4 = “very confident old,” 3 = “mildly confident old,” 2 = “mildly confident new,” and 1 = “very confident new.” A higher memory score thus reflects stronger memory. Mean memory scores in the SS group were 2.64, 2.87, and 2.70 for fearful, happy, and neutral conditions, respectively. Pairwise analyses showed higher scores for the happy condition compared to the fearful condition [t(14) = 2.96, p < .05], and compared to the neutral condition [t(14) = 2.36, p < .05], with no differences between fearful and neutral conditions [t(14) = 0.79, n.s.]. Mean memory scores in the NSS group were 2.71, 2.65, and 2.73 for fearful, happy, and neutral conditions, respectively, with no significant differences between scores (t-values < 1.09). There were no differences in memory scores between the SS and NSS groups with fearful primes [t(41) = 0.62, n.s.], happy primes [t(41) = 0.09, n.s.], or neutral primes [t(41) = 0.78, n.s.]. Proportion of responses for the four levels of memory confidence for “old” ... Fig. 4. Proportion of responses for the four levels of memory confidence for “old” surprise faces as a function of prime expression (F = fearful, H = happy, and N = neutral) from the priming phase on Day 1, shown separately for the Strictly-Subliminal group (A) and the Not-Strictly-Subliminal group (B). Ratings of “mildly confident old” and “very confident old” were classified as hits, and ratings of “mildly confident new” and “very confident new” were classified as misses. These findings confirm the pattern of results shown in Fig. 3. Error bars indicate ±1 SEM with baseline individual variability removed. Figure options We also found that affective evaluation per se influenced subsequent recognition memory. We calculated mean affective ratings for each surprise face across trials for each participant. We then segregated these ratings for faces rated more negatively and those rated more positively, collapsing across data from all three prime conditions, with a median split made separately for each participant. Surprise faces rated more negatively were remembered better than surprise faces rated more positively. This result was obtained using either the four levels of memory confidence [t(42) = 3.12, p < .01] or hit rates alone [t(42) = 3.25, p < .01]. When analyzed by group, the recognition advantage for negatively rated faces was apparent in the NSS group [t(14) = 4.23, p < .01], but not in the SS group [t(27) = 0.11, n.s.], and was significantly larger for the NSS group than the SS group [t(41) = 2.56, p < .05]; these results were computed using four levels of memory confidence, but the same pattern was also clear when measured with hit rates (likewise for subsequent analyses). These recognition differences between the SS and NSS groups were not due to differences in the variability (SD) of affective evaluations between the groups [t(41) = 0.24, n.s.]. To determine if these effects varied with prime condition, a further analysis was conducted using median splits of affective ratings of surprise faces made separately for each prime condition from each participant (Fig. 5). In the SS group, there was a marginally significant tendency for surprise faces rated more negatively to be remembered better than surprise faces rated more positively for the fearful prime condition [t(14) = 2.07, p = .05], but not for the happy prime condition [t(14) = 0.60, n.s.] or neutral prime condition [t(14) = 0.56, n.s.], when the four levels of recognition confidence were taken into account. In the NSS group, surprise faces rated more negatively were remembered better than surprise faces rated more positively in all three prime conditions [fearful; t(27) = 2.92, p < .01, happy; t(27) = 4.78, p < .01, neutral; t(27) = 2.69, p < .05]. There were no differences in the variability of affective evaluations (SD) between prime conditions in the SS group [F(2, 28) = 0.88, n.s.] and the NSS group [F(2, 54) = 0.18, n.s.]. Mean memory confidence scores (1=very confident new, 2=mildly confident new, ... Fig. 5. Mean memory confidence scores (1 = very confident new, 2 = mildly confident new, 3 = mildly confident old, 4 = very confident old) for old surprise faces for the Strictly-Subliminal group (A) and the Not-Strictly-Subliminal group (B) as a function of prime expression and affective evaluation from the priming phase on Day 1. Trials were segregated into most negative (-) and most positive (+) affective evaluations for each participant based on a median split (trials with an affective evaluation equal to the median were excluded). ∗Indicates p ⩽ .05, ∗∗indicates p < .01. Error bars indicate ±1 SEM with baseline individual variability removed. Figure options This same question was also approached with a regression analysis, in which we computed the slope for the linear correlation between mean affective rating and memory score for each participant (outliers outside the 95% confidence ellipse were eliminated before computing the correlation for each participant). Collapsing across data from all three priming conditions and both groups, the mean slope was negative and significantly different from zero [M = −0.22, SD = 0.30, t(42) = 4.88, p < .01], demonstrating better memory for more negatively rated surprise faces. In separate analyses, mean slopes were significantly negative for both the SS group [M = −0.19, SD = 0.33, t(14) = 2.16, p < .05] and the NSS group [M = −0.24, SD = 0.28, t(14) = 4.52, p < .01]. With SS participants, mean slopes were significantly negative in the fearful prime condition [M = −0.32, SD = 0.10, t(14) = 3.25, p < 0.01], but not in the happy or neutral prime conditions (t-values < 0.15). With NSS participants, mean slopes were significantly negative in the fearful [M = −0.23, SD = 0.52, t(27) = 2.30, p < .05], happy [M = −0.25, SD = 0.34, t(27) = 3.97, p < .01], and neutral [M = −0.19, SD = 0.42, t(27) = 2.44, p < .05] conditions. Together, these analyses converge to show that negative affective evaluation was associated with better recognition memory, but preferentially for participants most likely aware of prime faces. Importantly, these results also show that the recognition advantage for surprise faces primed by happy faces in the SS group occurred independently of affective evaluation per se.