Attention without awareness: Attentional modulation of perceptual grouping without awareness

Perceptual grouping is the process through which the perceptual system combines local stimuli into a more global perceptual unit. Previous studies have shown attention to be a modulatory factor for perceptual grouping. However, these studies mainly used explicit measurements, and, thus, whether attention can modulate perceptual grouping without awareness is still relatively unexplored. To clarify the relationship between attention and perceptual grouping, the present study aims to explore how attention interacts with perceptual grouping without awareness. The task was to judge the relative lengths of two centrally presented horizontal bars while a railway-shaped pattern defined by color similarity was presented in the background. Although the observers were unaware of the railway-shaped pattern, their line-length judgment was biased by that pattern, which induced a Ponzo illusion, indicating grouping without awareness. More importantly, an attentional modulatory effect without awareness was manifested as evident by the observer’s performance being more often biased when the railway-shaped pattern was formed by an attended color than when it was formed by an unattended one. Also, the attentional modulation effect was shown to be dynamic, being more pronounced with a short presentation time than a longer one. The results of the present study not only clarify the relationship between attention and perceptual grouping but also further contribute to our understanding of attention and awareness by corroborating the dissociation between attention and awareness.

     

Influencing choice without awareness

Forcing occurs when a magician influences the audience’s decisions without their awareness. To investigate the mechanisms behind this effect, we examined several stimulus and personality predictors. In Study 1, a magician flipped through a deck of playing cards while participants were asked to choose one. Although the magician could influence the choice almost every time (98%), relatively few (9%) noticed this influence. In Study 2, participants observed rapid series of cards on a computer, with one target card shown longer than the rest. We expected people would tend to choose this card without noticing that it was shown longest. Both stimulus and personality factors predicted the choice of card, depending on whether the influence was noticed. These results show that combining real-world and laboratory research can be a powerful way to study magic and can provide new methods to study the feeling of free will.     

无觉知条件下的客体注意效应

采用双矩形范式变式考察在对客体无觉知的条件下的客体注意效应,共包括两个实验：实验一考察对完整矩形客体无觉知的条件下能否出现客体注意效应,发现在完整矩形客体不可见的情况下依然出现了客体注意效应。实验二考察对虚拟矩形客体无觉知的情况下是否能够出现客体注意效应,发现在虚拟矩形客体不可见的情况下也能够出现客体注意效应。研究结果表明客体注意效应在无觉知条件下依然存在,为注意与觉知在功能上相互分离的观点提供了新的证据。     

无觉知条件下的客体注意效应

采用双矩形范式变式考察在对客体无觉知的条件下的客体注意效应,共包括两个实验：实验一考察对完整矩形客体无觉知的条件下能否出现客体注意效应,发现在完整矩形客体不可见的情况下依然出现了客体注意效应。实验二考察对虚拟矩形客体无觉知的情况下是否能够出现客体注意效应,发现在虚拟矩形客体不可见的情况下也能够出现客体注意效应。研究结果表明客体注意效应在无觉知条件下依然存在,为注意与觉知在功能上相互分离的观点提供了新的证据。     

Specificity of face processing without awareness

The recognition memory for inverted faces is especially difficult when compared with that for non-face stimuli. This face inversion effect has often been used as a marker of face-specific holistic processing. However, whether face processing without awareness is still specific remains unknown. The present study addressed this issue by examining the face inversion effect with the technique of binocular rivalry. Results showed that invisible upright faces could break suppression faster than invisible inverted faces. Nevertheless, no difference was found for invisible upright houses and invisible inverted houses. This suggested that face processing without awareness is still specific. Some face-specific information can be processed by high-level brain areas even when that information is invisible.     

False recognition and perception without awareness

Jacoby and Whitehouse (1989) demonstrated that the probability of calling new test words "old" (i.e., false recognition) is biased by context words. When context words were briefly exposed and subjects were not informed of their presence, new words were called "old" more often if the context and test words were identical than if the context and test words were different. When the context words were presented at longer exposure durations and subjects were informed of their presence, the opposite pattern of results occurred. In Experiment 1, we replicated the critical qualitative difference across conditions reported by Jacoby and Whitehouse. In addition, the combined results of Experiments 2 and 3 demonstrated that the exposure duration of the context words, and not the instructions to the subjects, is the primary factor determining which pattern of false recognition occurs. However, in contrast with the findings of Jacoby and Whitehouse, both patterns of false recognition were associated with significant recognition memory for the context words. The latter finding presents problems for any interpretation of false recognition, which implies that the briefly exposed context words are perceived without awareness.     

Implicit and explicit memory without awareness

Summary Three experiments are reported which investigate the conscious status of subjects during an implicit-memory test. In all experiments the subjects either named each visually presented target item or generated each item from an anagram in a first phase of incidental learning. In a second phase, they were either given a visual word-stem completion task as an implicit-memory test or given a recognition task (Experiment 1), or a cued-recall task (Experiments 2 and 3) as explicit-memory tests. Finally, in a third phase the subjects were required to make decisions about the input status (i. e., they had to decide whether the item was present in the first phase) as well as about the output status of information (i. e., they had to decide whether the item had been completed, recognized or recalled in the second phase). A generation effect (i. e., generated items were remembered better than named items) was evident in the recognition and recall data, but only for items whose recognition or recall was accompanied by conscious recollection of their previous occurrence in the study list. Judgments about the input status were more precise, given that items had been consciously recognized or recalled rather than completed. The same pattern of findings was observed for judgments about the output status. The results are interpreted as evidence that subjects in implicit-memory tests are less aware of the fact that some of their productions are relevant to prior experiences. In addition, they are less aware of the fact that they are retrieving information from their memories. However, the same state of nonawareness may be present in explicit-memory tests, as was revealed by the performance of subjects on those items whose recognition or recall was not accompanied by conscious recollection.     

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).     

Another look at semantic priming without awareness

In a recent study, McCauley, Parmelee, Sperber, and Carr (1980) reported results indicating that semantic priming had been produced by visual stimuli that were backward masked at durations too brief for greater than chance report. The conclusions drawn from such an experiment are critically dependent upon whether or not the primes were actually masked below the thresh-old for identification during priming trials. The three experiments reported here provide evidence that this requirement was not met. Rather, McCauley et al.’s (1980) methodology allowed for an uncontrolled increase in light adaptation during the actual testing of prime efficacy in the priming session. This increase in light adaptation reduced the effectiveness of the backward mask and resulted in an increase in prime visibility during priming trials. Thus, semantic priming probably occurred under conditions in which commensurate visual information was actually available.     

Vection can be induced without global-motion awareness

A new vection illusion is reported. Vection was induced even though there was no consciously perceived global display motion corresponding to the self-motion. The resulting experience can be summarised as: "I feel that I am moving but I do not know why".     

Temporal structure coding with and without awareness

In order to interpret a constantly changing environment, visual events far apart in space and time must be integrated into a unified percept. While spatial properties of invisible signals are known to be encoded without awareness, the fate of temporal properties remains largely unknown. Here, we probed temporal integration for two distinct motion stimuli that were either visible or rendered invisible using continuous flash suppression. We found that when invisible, both the direction of apparent motion and the gender of point-light walkers were processed only when defined across short time periods (i.e., respectively 100 ms and 1000 ms). This limitation was not observed under full visibility. These similar findings at two different hierarchical levels of processing suggest that temporal integration windows shrink in the absence of perceptual awareness. We discuss this phenomenon as a key prediction of the global neuronal workspace and the information integration theories of consciousness.     

Context-dependent brightness priming occurs without visual awareness

Our visual systems account for stimulus context in brightness perception, but whether such adjustments occur for stimuli that we are unaware of has not been established. We therefore assessed whether stimulus context influences brightness processing by measuring unconscious priming with metacontrast masking. When a middle-gray disk was presented on a darker (or brighter) background, such that it could be consciously perceived as brighter (or darker) via simultaneous brightness contrast (SBC), reaction times were significantly faster to a bright (or dark) annulus than to a dark (or bright) annulus. We further show that context-dependent brightness priming does not correlate with visibility using an objective measure of awareness (Experiment 1) and that context-dependent, but not context-independent brightness priming, occurs equally strongly for stimuli below or above the subjective threshold for awareness (Experiment 2). These results suggest that SBC occurs at early levels of visual input and is not influenced by conscious perception.