Does Attention Accompany the Conscious Awareness of Both Location and Identity of an Object

The question of whether consciousness and attention are the same or different phenomena has always been controversial. In trying to find an answer to this question, two different measures for consciousness and attention were used to provide the potential for dissociating between them. Conscious awareness of either the location or the identity of the object was measured as the percentage of correct reports of that aspect. The location of the focus of attention, on the other hand, was determined using the shooting-line illusion (SLI). In the SLI, a static line is perceived as growing from the location of a preceding cue (i.e., the location of the focus of attention). To investigate whether conscious awareness of the location of an object could be dissociated from conscious awareness of its identity, the attentional blink (AB) was used. It is known that during the AB, identification of the second of two consecutively and briefly presented targets (T1 and T2) is impaired if the temporal lag between the two targets is less than about 500 ms. In three experiments, an SLI was induced during the AB to determine whether attention was at the location of T2 when the observer was consciously aware of its location, its identity, or both. Observers were instructed to report the identity and location of the targets, and the direction of the SLI. Three important findings emerged. First, the SLI was seen as growing from T2 only when T2 was identified correctly. Second, observers could report T2 location even when unaware of its identity. Third, the SLI occurred from T2 only when T2 identity – not its location – could be reported correctly. These results indicate that focal attention does not necessarily accompany conscious awareness of some aspects of the object, while it does accompany conscious awareness of its identity. ATTENTION AND AWARENESS OF LOCATION AND IDENTITY 3 It can readily be argued that attention and consciousness are tightly interlinked and serve parallel functions in our day-to-day experience. Attention, for instance, is selective, excluding objects or locations that fall outside its focus. Those unattended objects or locations are seen less clearly, processed less well, and reacted to more slowly than they would be if attended. Consciousness can be argued to serve a similar selective function – we are never aware of all of the information available to us in the world, and we are provided with a filtered view of that world by the information that does reach our consciousness. There is substantial evidence to support the proposal that consciousness and attention are inseparably linked (e.g., Dehaene et al., 2006; Taylor & Fragopanagos, 2007). Consider, for example, the phenomenon of change blindness in which observers watch repeated alternations of two versions of a single photograph, in which one element in the photo is different in the two versions. The task is simply to identify what is changing; that change can be quite substantial, such as the disappearance and reappearance of the engine in a photograph of an airplane. It has been shown that in this task, the change is only detected when attention is directed specifically to the element that is changing. In other words, without attention, the element does not reach conscious awareness and hence the change is not detected (O’Reagan et al., 2000; Rensink, 2000; Rensink, O’Reagan, & Clark, 1997; Simons & Levin, 1997; Simons & Rensink, 2005). Mack and Rock (1998) reported the phenomenon of inattentional blindness in which objects which are not attended, even when substantial and surprising, do not reach conscious awareness. Given evidence such as this, many have concluded that attention and consciousness are one and the same. Other scientists and philosophers, however, have questioned whether it is justified to say that attention and consciousness are inseparably linked. Is it really necessary to pay attention to something in order for it to reach consciousness? Can items which have not reached consciousness attract attentional processes? Research has shown that observers can become conscious of an isolated object or the gist of a scene despite the near absence of top-down attention; conversely, observers can attend to perceptually invisible objects which do not reach consciousness (Koch & Tsuchiya, 2007). Along the same lines, stimuli that are attended are not always consciously perceived (Super et al., 2001). Given the continued debate as to whether attention and consciousness are linked at theoretical and conceptual levels, it is especially difficult to dissociate them at an empirical level (Koch & Tsuchiya, 2007). This is particularly true when one considers the phenomenological diversity of both attention and consciousness as well as the dynamic nature of the attention-consciousness relationship. In this sense, dissociating attention and consciousness is one of the items in the list of fundamental problems in the field. To answer this question, some recent studies have used procedures that manipulate consciousness and attention independently, and the current research follows this trend. In the present paper, we will build on the distinction between conscious awareness of the location of an object and conscious awareness of the identity of that same object as proposed by Atkinson and Braddick (1989). Further, we will use an index of attention that will enable us to distinguish whether attention accompanies both aspects of conscious awareness (suggesting that attention and conscious awareness are fully linked) or whether conscious awareness of the location of an object and conscious awareness of its identity are differentially accompanied by attention (suggesting that attention and conscious awareness can be dissociated). In determining whether attention accompanies conscious awareness of both location and identity, we employed two separate measures, one for attention and one for consciousness. Specifically, we utilized the attentional blink (AB) paradigm to manipulate the observers’ conscious awareness of the identity of an object, and the shooting-line illusion (SLI) to index the location of attention. In a rapid serial visual presentation (RSVP) when there are two targets (T1 and T2) embedded in a stream of distractors and the task is to report those two targets, a deficit in the perception of the second target is usually observed if the inter-target lag is not longer than about half a second (e.g., Chun & Potter, 1995; Raymond, Shapiro, & Arnell, 1992). Most studies on this phenomenon, known as the attentional blink, have shown that what was impaired during the AB was the identification (e.g., Potter, Chun, Banks, & Muckenhoupt, 1998) of the second target. The attentional blink is an ideal tool for ATTENTION AND AWARENESS OF LOCATION AND IDENTITY 4 manipulating an observer’s conscious awareness of the identity of a stimulus (Sergent, Baillet, & Dehaene, 1995) as the change from being aware of the identity of the stimulus to being unaware of its identity appears to be an all-or-none process (Sergent & Dehaene, 2004). Hence, in the current experiments we used the attentional blink in order to manipulate and measure whether or not the observers were consciously aware of the identity of the target stimuli. In the current research we used a second phenomenon known as the shooting-line illusion to index the location of attention. In the SLI (Hikosaka, Miyauchi, & Shimojo, 1993a, b), a line that is displayed all at once is perceived as if drawn progressively from one end to the other. A temporallyleading cue – the inducing stimulus – is used to orient the observer’s attention to one end of the line, and the line then appears to grow from that end. Hence, the SLI is critically dependent on attention being focused at the location of the inducing stimulus, and we can therefore use the occurrence and direction of the SLI to index the location of the focus of attention. In combining the SLI and the AB to test the interaction between attention and conscious awareness of identity and location, we built on the paradigm developed by Kawahara (2002). In his study, Kawahara presented distractor digits in three separate RSVP streams located at the apices of an imaginary triangle. Two of these streams also contained a letter-target. A line was also displayed simultaneously with T2, and it could appear in one of three locations: 1) between the stream that contained T1 and the stream that contained T2, 2) between the stream that contained T1 and the stream that contained neither target, or 3) between the stream that contained T2 and the stream that contained neither target. The results revealed a pronounced AB deficit in that T2 was identified more accurately at a long inter-target lag than a short inter-target lag. More importantly, observers perceived the line as shooting from the T1-stream regardless of whether the other stream contained T2 or a distractor. This led to the conclusion that T1 acted as a spatial cue, which focused the observers’ attention on the location of the T1-stream, thus mediating the SLI. In this study, we use the same basic method as Kawahara (2002) did, to examine the observers’ conscious awareness of the location of the target, conscious awareness of the identity of the target, and whether attention accompanied both forms of conscious awareness. The critical difference between the current experiments and those of Kawahara (2002) is that the inducing stimulus was T2 instead of T1 so that we could use the attentional blink to control whether observers had conscious awareness of the identity of T2. Specifically, at short inter-target lags, observers would not be consciously aware of the identity of T2 whereas at long inter-target lags they would be. EXPERIMENT 1A The current research aims to separate the conscious awareness of the identity of a stimulus from the conscious awareness of its location, and to determine whether attention equally accompa