Recognition without awareness: An elusive phenomenon

Two recent studies described conditions under which recognition memory performance appeared to be driven by nondeclarative memory. Specifically, participants successfully discriminated old images from highly similar new images even when no conscious memory for the images could be retrieved. Paradoxically, recognition performance was better when images were studied with divided attention than when images were studied with full attention. Furthermore, recognition performance was better when decisions were rated as guesses than when decisions were associated with low or high confidence. In three experiments, we adopted the paradigm used in the earlier studies in an attempt to repeat this intriguing work. Our attempts were unsuccessful. In all experiments, recognition was better when images were studied with full attention than when images were studied with divided attention. Recognition was also better when participants indicated high or low confidence in their decision than when they indicated that their decision was a guess. Thus, our results conformed to what typically has been reported in studies of recognition memory, and we were unable to demonstrate recognition without awareness. We encourage others to explore this paradigm, and to try to identify conditions under which the phenomenon might be demonstrated.Declarative memory refers to the capacity to recollect facts and events, and can be contrasted with a collection of nondeclarative memory abilities, including skills, habits, and the phenomenon of priming, which are expressed through performance rather than recollection (Squire et al. 2004). Declarative memory depends on the integrity of medial temporal lobe structures, while the various forms of nondeclarative memory depend on other brain systems (Schacter and Tulving 1994; Eichenbaum and Cohen 2001; Squire 2004). The best-studied example of declarative memory is recognition memory—the ability to judge items as having been encountered previously. Successful recognition is ordinarily accompanied by a conscious experience of familiarity, and sometimes by conscious memory of the prior encounter itself (Gabrieli 1998).One interesting idea that has been explored in some detail is that recognition memory decisions based on familiarity might also benefit from priming. Priming refers to an improved ability to produce or identify an item on the basis of a recent encounter with the same item or a related item, but without a requirement that there be conscious knowledge of the prior encounter (Tulving and Schacter 1990; Schacter and Buckner 1998). In early studies, it was suggested that previously encountered items might be processed more fluently (e.g., with greater speed and with more ease), and that improved fluency might influence familiarity judgments. Specifically, items perceived with greater fluency might tend to be identified as familiar (Mandler 1980; Jacoby and Dallas 1981; Johnston et al. 1991).This idea encountered difficulty when it was found that severely amnesic patients can perform at chance on conventional recognition tests despite exhibiting intact perceptual priming (Hamann and Squire 1997; Stark and Squire 2000). If fluency facilitates recognition, severely amnesic patients who exhibit intact perceptual priming should perform better than chance on recognition memory tests. Thus, it has seemed that the perceptual fluency that mediates priming does not also support familiarity-based recognition judgments, at least not to a measurable degree. Indeed, the contribution of perceptual fluency appears to be too weak to drive recognition performance noticeably above chance (Conroy et al. 2005).Nonetheless, it remains possible that conditions might be found under which recognition decisions can benefit from perceptual fluency, and in this way be linked to nondeclarative memory. Two recent studies (Voss et al. 2008; Voss and Paller 2009) described conditions under which recognition memory appeared to be significantly driven by nondeclarative memory. Participants studied difficult-to-verbalize images (Fig. 1) with either full attention or divided attention. At test, each image was paired with a highly similar new image, and participants made a speeded forced-choice decision. The striking finding was that, under these conditions, accurate recognition memory performance occurred, but without the awareness that ordinarily accompanies successful recognition. Specifically (and paradoxically), performance was better under divided-attention conditions (which ordinarily degrade memory performance) than under full-attention conditions (Fig. 2A). Furthermore, in one study (Voss et al. 2008), recognition was better when participants reported that they were guessing than when they reported conscious memory of the images (combined high- and low-confidence trials) (Fig. 2B). Notably, this phenomenon occurred only when the test was given in a forced-choice format, and not in a yes/no format. The other study (Voss and Paller 2009) reported a similar advantage for guessing in the divided-attention condition. These two reports appear to demonstrate recognition without awareness and a significant contribution of nondeclarative memory to recognition performance.Open in a separate windowFigure 1.In the full-attention condition, participants studied 14 images for 2 sec each (1.5-sec intertrial interval). Alternatively, in the divided-attention condition, participants studied the images while deciding whether a digit heard during the previous trial was odd or even. The forced-choice recognition test probed memory for the middle 10 images presented in the study sequence. Each studied item was presented together with a highly similar new item, and participants selected the old item by responding “left” or “right.” After each response, participants indicated how confident they were in their recognition decision (G, guess; L, low confidence; H, high confidence).Open in a separate windowFigure 2.Data from Experiment 2 in Voss et al. (2008), estimated from their Figure 2. (A) When recognition was probed using a forced-choice format, performance was more accurate in the divided-attention condition than in the full-attention condition. (B) In both conditions, forced-choice recognition was more accurate in trials where participants indicated that their recognition decision was a guess (G) than in trials where participants indicated low or high confidence (L/H) in their decision. Asterisks indicate performance significantly above chance (P < 0.05). Error bars indicate SEM.These findings challenge the conventional view that recognition memory is more effective when full attention is given to a task than when attention is divided (Anderson 1980), that recognition memory is associated with a conscious experience of familiarity (Gabrieli 1998), and that recognition memory accuracy is positively correlated with ratings of confidence (Reed et al. 1997; Mickes et al. 2007). Because the reported findings are exceptional, we explored the phenomenon further in three separate experiments in an attempt to replicate it and identify its boundary conditions. We adopted the same paradigm as was used in the original study (Voss et al. 2008).