Saturday, July 28, 2012

Attention and Consciousness Rely on Distinct Neural Mechanisms

The information in this post is related to my ongoing series on Bernard Baars' Global Workspace Theory of consciousness (see Part One, Part Two, and Part Three - part four is in process). In Baars' model, attention and consciousness are not identical, whereas many other cognitive models of consciousness do see them as either identical, or view attention as an inseparable aspect of consciousness (Posner, 1994; Jackendoff, 1996; Velmans, 1996; Merikle and Joordens, 1997; Mack and Rock, 1998; Chun and Wolfe, 2000; O’Regan and Noe, 2001; Mole, 2008; De Brigard and Prinz, 2010; Prinz, 2010).

In a 2010 article, Christof Koch and his team (Consciousness and attention: On sufficiency and necessity) reviewed an extensive body of research showing that attention and consciousness can be examined independently. Here is the abstract for that paper:
Recent research has slowly corroded a belief that selective attention and consciousness are so tightly entangled that they cannot be individually examined. In this review, we summarize psychophysical and neurophysiological evidence for a dissociation between top-down attention and consciousness. The evidence includes recent findings that show subjects can attend to perceptually invisible objects. More contentious is the finding that subjects can become conscious of an isolated object, or the gist of the scene in the near absence of top-down attention; we critically re-examine the possibility of “complete” absence of top-down attention. We also cover the recent flurry of studies that utilized independent manipulation of attention and consciousness. These studies have shown paradoxical effects of attention, including examples where top-down attention and consciousness have opposing effects, leading us to strengthen and revise our previous views. Neuroimaging studies with EEG, MEG, and fMRI are uncovering the distinct neuronal correlates of selective attention and consciousness in dissociative paradigms. These findings point to a functional dissociation: attention as analyzer and consciousness as synthesizer. Separating the effects of selective visual attention from those of visual consciousness is of paramount importance to untangle the neural substrates of consciousness from those for attention.
In order to help explicate how consciousness and awareness inter-relate, Koch has created a 2x2 visual representation (attention × consciousness design matrix). The graph allows for the categorization of different objects, stimuli, or features in terms of whether they give rise to consciousness and if they require attentional top-down conscious processing.
Previously, we argued that each behavior or percept can be categorized within a 2 × 2 design matrix, defined by whether it gives rise to consciousness and whether it requires top-down attentional amplification (Koch and Tsuchiya, 2007).

The lower right quadrant of our attention × consciousness design matrix (Table 1) is filled with behaviors or percepts in which attention is necessary for them to give rise to consciousness. For example, an unexpected and unfamiliar stimulus requires top-down attention in order to be consciously perceived. Otherwise, such a stimulus goes unnoticed, a phenomenon called inattentional blindness (Mack and Rock, 1998).

Table 1. A four-fold classification of percepts and behaviors depending on whether or not top-down attention is necessary and whether or not these percepts and behaviors give rise to phenomenal consciousness. Different percepts and behaviors are grouped together according to these two, psychophysically defined, criteria.

At the top-left of the table are behaviors or percepts that do not require the deployment of top-down attention, and that can occur in the absence of conscious perception. For instance, a perceptually invisible grating that is not attended will still lead to a visible afterimage (e.g., van Boxtel et al., 2010). That is, the formation of afterimages can be independent of paying attention to the inducer nor of consciously perceiving it.

In the first half of the review, we focus on the rest of the matrix: attention without consciousness (bottom-left) and consciousness without attention (top-right). We examine whether attention is necessary and/or sufficient for consciousness.

While many scholars agree that attention and consciousness are distinct, it is popular to assume that attention is necessary for consciousness. For example, Dehaene et al. (2006) argue that without top-down attention, an event cannot be consciously perceived and remains in a preconscious state. Another view is that attention and consciousness are so intertwined that they cannot be operationally separated (O’Regan and Noe, 2001; De Brigard and Prinz, 2010; Prinz, 2010).
The conclusion of the first half of their paper is the point I am after here: "Attention to a stimulus or an attribute of this stimulus is neither strictly necessary nor sufficient for the stimulus or its attribute to be consciously perceived."

As I mentioned above, Baars (2005) is one of the cognitive theorists of consciousness who believe that attention and consciousness are not only separable but rely on unique neural systems - others, as cited by Koch, include Wundt, 1874; Iwasaki, 1993; Hardcastle, 1997; Naccache et al., 2002; Lamme, 2003; Woodman and Luck, 2003; Kentridge et al., 2004; Koch, 2004Block, 2005; Bachmann, 2006; Dehaene et al., 2006; Koch and Tsuchiya, 2007; Tsuchiya and Koch, 2008a,b.

A more recent paper, On the Neural Mechanisms Subserving Consciousness and Attention, by Catherine Tallon-Baudry (2012, Jan, online), offers additional support for this perspective. Here is her abstract:
Consciousness, as described in the experimental literature, is a multi-faceted phenomenon, that impinges on other well-studied concepts such as attention and control. Do consciousness and attention refer to different aspects of the same core phenomenon, or do they correspond to distinct functions? One possibility to address this question is to examine the neural mechanisms underlying consciousness and attention. If consciousness and attention pertain to the same concept, they should rely on shared neural mechanisms. Conversely, if their underlying mechanisms are distinct, then consciousness and attention should be considered as distinct entities. This paper therefore reviews neurophysiological facts arguing in favor or against a tight relationship between consciousness and attention. Three neural mechanisms that have been associated with both attention and consciousness are examined (neural amplification, involvement of the fronto-parietal network, and oscillatory synchrony), to conclude that the commonalities between attention and consciousness at the neural level may have been overestimated. Last but not least, experiments in which both attention and consciousness were probed at the neural level point toward a dissociation between the two concepts. It therefore appears from this review that consciousness and attention rely on distinct neural properties, although they can interact at the behavioral level. It is proposed that a “cumulative influence model,” in which attention and consciousness correspond to distinct neural mechanisms feeding a single decisional process leading to behavior, fits best with available neural and behavioral data. In this view, consciousness should not be considered as a top-level executive function but should rather be defined by its experiential properties.
At the recent Evolution and Function of Consciousness Summer School ("Turing Consciousness 2012") held at the University of Montreal as part of Alan Turing Year, Tallon-Baudry lectured on the topic of this paper: Is Consciousness an Executive Function?

The reason this is important (as I will discuss further in the series of posts on Global Workspace Theory and the Future Evolution of Consciousness) is that this model offers extensive neurobiological support for a variety of human development theories.

For example, the ability to focus attention on the self as an object and to experience this distal part of the self subjectively in consciousness - the adult development model of Robert Kegan - is given a neurobiological substrate that has been missing so far.

Likewise, if consciousness and attention operate with distinct neural systems, then we are able to explain how the brain is able to focus attention on other brain functions (such as the verbal stream of consciousness) and hold them as objects in consciousness, which is the basis of meditation and mindfulness practice.

According to Baars and others, we can focus attention on any brain function and make it conscious - the proof of this is those monks who have demonstrated an ability to alter their brainwave functions, the quality and quantity of brain function, and so on. The take-home message is that we can use attention to "evolve" our own brain function and potentially increase our developmental level through focused attention, mindfulness, and other practices.

Equally important, meditation can increase the holding space of working memory (which is roughly 7 unrelated objects), and working memory is essentially the space of our momentary consciousness. Van Leeuwen, Singer, and Melloni (2012), in Meditation increases the depth of information processing and improves the allocation of attention in space, demonstrated essentially what the title of their paper indicates.

These authors hypothesized that the process of meditation, which requires that we learn to ("respond to the dual demand") focus our attention on a specific object (mantra, the breath, flame, etc.) and also learn how to recognize and stop intrusive thoughts ("disengaging quickly from distracters"), can strengthen the efficiency of how we allocate attention. The length of their study was basically a four-day meditation retreat (they used focused attention meditation and open monitoring meditation). They conclude:
[T]hese results suggest that practicing meditation enhances the speed with which attention can be allocated and relocated, thus increasing the depth of information processing and reducing response latency.
In a related study, Metta McGarvey at Harvard (2010) argues that "mindful awareness catalyzes transformational change through optimally integrating conceptual and pre-conceptual ways of knowing" (Mindful Leadership Study). Part of her research compared an Integral Practice with basic mindfulness practice and found IP more highly correlated with mindfulness scores (brief results here).

Anyway, I will have more to say about attention and consciousness in a future post.

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