The delayed consolidation hypothesis of all-or-none conscious perception during the attentional blink, applying the ST2 framework

The delayed consolidation hypothesis of all-or-none conscious perception during the attentional blink, applying the ST 2 framework H. Bowman 1 , P. Craston 1 , S. Chennu 1 , B. Wyble 2 Centre for Cognitive Neuroscience and Cognitive Systems, University of Kent, UK Department of Brain and Cognitive Sciences, MIT, USA Abstract There is evidence that conscious perception during the attentional blink is all-or-none, which contrasts with the finding of a continuum of perceptual strength in masking experiments. This seems to reveal the underlying representation of strength that can be found in the brain in the absence of attentional enhancement. We provide electrophysiological support for this all-or-none theory. Then, using principles from the ST 2 model of temporal attention and working memory, we show how this all-or-none pattern can be explained by the delayed target consolidation that is known to arise during the attentional blink. Keywords: Attentional Blink, P300, ST 2 Introduction Intuitively, it would seem that conscious perception is all- or-none. For example, bistable visual stimuli, e.g. the Necker cube or binocular rivalry, exhibit a dichotomy in perception: one or other stable percept is perceived in its entirety, without access to intermediate images. In other words, we either see all of a particular stable percept or none of it. Consistent with this perspective, (Sergent & Dehaene, 2004; Sergent, Baillet & Dehaene, 2005) have argued that conscious perception during the attentional blink (AB) is all-or-none; that is, targets presented during the attentional blink deficit are either completely perceived or completely missed, as revealed by subject visibility ratings. However, masking experiments in which strength is systematically varied suggest a continuous (although probably non-linear) gradation of visibility (Sergent & Dehaene, 2004, Del Cul, Baillet & Dehaene, 2007). This paper seeks to explain this seeming inconsistency in experimental findings, by arguing that all-or-none conscious perception during the attentional blink (AB) arises because of the delayed consolidation that is known to occur during the AB (Sessa et al., 2006; Vogel & Luck, 2002; Bowman et al., 2008). We do this by presenting a neural model of all-or- none consolidation during the AB, which reuses principles from the simultaneous type, serial token (ST 2 ) model of temporal attention (Bowman & Wyble, 2007; Wyble et al., Why, though, should we be interested in the attentional blink? The AB is the deficit in reporting a second target (T2) if it is presented between 100 and 500 ms after a reported first target (T1), when a rapid serial visual presentation (RSVP) format is employed. The first reason is that the AB reflects a late stage deficit; that is, T2s that are missed during the AB are processed for visual and semantic features (Vogel et al., 1998). Thus, the AB seems to isolate the extra processing step that is required to encode an otherwise preconscious representation into working memory, i.e. to consciously perceive it. A second reason for being interested in the AB, is that it enables bottom-up strength and attention to be independently manipulated. A first requirement for an item to be consciously perceived is sufficient bottom-up strength. Under normal viewing conditions, most stimuli are strong enough to be consciously perceived. However, if stimulus representations are fleeting, as in RSVP, they will sometimes be too weak to enter consciousness. Hence, the weaker a neural representation of a stimulus, the less the likelihood it will enter awareness (Kanwisher, 2001). However, this cannot be the sole requirement for conscious perception, as stimuli that are equally strong in perceptual terms, in some cases succeed but in others fail to enter consciousness (Luck et al., 1996, Rees et al., 2000). In particular, the neural representation of a stimulus also needs to be attended to before it can enter awareness. Koch & Tsuchiya (2007) have argued that attention and consciousness ‘are distinct phenomena that need not occur together and can be manipulated using distinct paradigms. ’ To investigate the influence of target strength and attention on conscious perception, we thus require an experimental paradigm where the availability of attention and bottom-up strength can be manipulated independently (Kim & Blake, 2005); the AB is such a paradigm. A key aspect of modern cognitive neuroscience is the identification of neurophysiological correlates of conscious perception. Within the context of the AB, the P3 component of the event-related potential (ERP) is viewed as such a correlate. A P3 component is only evoked by those targets in RSVP that can be correctly reported (e.g. Kranczioch et al., 2003). Target items that are missed do not evoke a P3. The P3 is thus generally seen as an EEG correlate of encoding items into working memory (Vogel et al., 1998) and, by the same logic, a number of studies have proposed that the P3 serves as an index of conscious perception (e.g. Sergent et al., 2005, Kranczioch et al., 2007). In line with these previous studies, we use the P3 component as a correlate of conscious perception for targets in RSVP. We present EEG data investigating how bottom-up target strength and the availability of attention modulate conscious perception of targets in RSVP. We compare the EEG signatures (specifically, the P3 components) of targets presented outside and during the AB. We find that bottom up strength of targets affects the P3 for targets presented outside the AB, but does not influence the P3 evoked by