Perceptual consciousness and cognitive access: an introduction

Abstract

The problem of perceptual consciousness—the question of how our subjective experiences (colours as we see them; sounds as we hear them; tastes, etc., as we feel them) could be accounted for in terms of brain processes—is often regarded as the greatest unsolved mystery of our times. In recent literature, one of the most pressing questions in this regard is whether the neural basis of perceptual consciousness is independent of the neural basis of cognitive access mechanisms that make reporting and reflecting on conscious experiences possible. The Theme Issue focuses on this central problem of consciousness research and aims to contribute to the field by critically discussing state-of-the-art empirical findings, identifying methodological problems and proposing novel approaches.

This article is part of the theme issue ‘Perceptual consciousness and cognitive access’.

1. Consciousness and its neural basis

Consciousness is often described as a mystery because there are no clear explanatory links connecting it to material processes, and thus accounting for subjective conscious experiences in terms of certain features of ‘underlying’ brain states and neural interactions appears to be an intractable problem for scientific endeavours [1]. The problem stems from the fact that the phenomenal aspect of consciousness seems to be dissociable from its purported functional aspects. As Ned Block famously argues, the notion of phenomenal consciousness (referring to the experiential characteristics of consciousness) is conceptually distinct from the notion of access consciousness (referring to the functions that can be associated with consciousness) [2]. Consequently, functional descriptions of proclaimed neural bases of consciousness can always be seen as descriptions of the mere information processing and representational capacities of certain brain states, while it can be denied that the brain states in question correspond to consciousness in any way.

Owing to this conceptual puzzle, scientific endeavours aiming to anchor conscious experiences to brain processes rely on correlational studies to find the neural basis of consciousness. The goal of such correlational studies is twofold.

First, to find the constituents (as opposed to the causal background conditions or causal consequences) of the total neural basis of a conscious state (e.g. the experience of a particular stimulus)—that is, the totality of those neural states that are jointly sufficient for being in the conscious state in question. And second, to find the core neural basis of a conscious state, i.e. that part of the total neural basis that is responsible for being in the particular conscious state under scrutiny (as opposed to being in another conscious state with different phenomenal character or content) [3].

A problem with such correlational studies is that they need to contrast conscious and non-conscious conditions or conditions differing in a specific content. However, as conscious experiences are directly available only to the individual having them, in order to determine whether a subject is conscious of a specific stimulus or not (or what it is that the subject is conscious of) one needs to rely on subjective reports: verbal descriptions or other behavioural indications by the subject of his or her own conscious experiences. But relying on subjective reports threatens to jeopardize the very goal of these endeavours, i.e. to delineate the neural underpinnings of consciousness and to distinguish them from causal antecedents (pre-conscious activity) and consequences (post-conscious activity). Subjective reports require certain cognitive processes to be in operation accessing the information reported, which then might show up in the neural activity identified by this methodology as the total or even core neural basis of a conscious state [4,5]. This would also, then, cause a problem from a conceptual, a methodological and a theoretical perspective.

From a conceptual perspective, cognitive access to the information registered by the perceptual system, introspecting it and preparing verbal or other behavioural reports about it are all parts of those functions that consciousness is often associated with but from which its phenomenal aspect is claimed to be dissociable. But then how could pure phenomenal consciousness ever be the subject of scientific investigations if it can only be studied via the very functions that it is supposed to be distinct from? Or perhaps even more pressingly, how could this idea of pure phenomenal consciousness ever find support if without access even the subject purportedly experiencing it cannot introspect it and form beliefs about it? [6]

From a methodological perspective, the cognitive access mechanisms in question are all candidates of possible post-conscious activities that might not be constitutive parts of the neural basis of consciousness but are only downstream processes acting on the information content of independently conscious states. From this perspective, relying on subjective reports possibly confounds the findings, resulting in an overestimation of the neural basis of consciousness and rendering delineating the neural basis of phenomenal consciousness itself likely out of reach [4,5].

From a theoretical perspective, the question of whether the operation of cognitive access mechanisms is a constitutive condition of being in a conscious state is in the very centre of the main debate in contemporary literature as one of the key differences that distinguish major theories of consciousness is exactly how they think about this issue. For instance, while ‘global workspace’ [7], ‘higher order thought’ [8] or ‘intermediate level representation’ [9] accounts build different varieties of cognitive access or accessibility into the definition of consciousness, ‘local recurrence’ [10] theory denies that such global processing or global availability would be a constitutive part of being conscious. From this perspective, then, relying on a methodology that is unable to clarify the relation between phenomenal consciousness and cognitive access means that crucial predictions of different theories of consciousness remain untestable, and hence the evaluation of these theories becomes unattainable, ultimately resulting in a stalemate between views that find cognitive access necessary for consciousness and those that do not.

2. The context and focus points of the Theme Issue

The present Theme Issue focuses on this central question of whether cognitive access to perceptual information processing is necessary for the occurrence of conscious experience of perceived stimuli.

The ongoing debate between the two opposing positions with regard to this question has inspired insightful empirical investigations and innovative theoretical approaches. In recent years, a variety of novel studies and systematic reviews have been published that try to settle the debate in one way or another. Against the essential role of access it has been argued that the typical neural signatures of cognitive access are not required for conscious perception [11–14] or that conscious experiences are richer than what can be reported and thus consciousness overflows cognitive access [15–17]. For the essential role of access it has been argued that the alleged richness of consciousness is overestimated [18,19], and unreportable information is only present in conscious experiences in a generic form [20,21]. At the same time, recent work on distributed, resource and activity-silent models of working memory has started to reframe the whole debate [22,23], while newly raised methodological worries are pushing the field towards novel, so-called no-report paradigms [4,5].

It is, thus, particularly timely to directly confront the contradictory findings and incompatible interpretations, to compare competing theoretical frameworks and experimental paradigms and to address methodological issues from multiple perspectives to set the direction for future research. This is exactly what this Theme Issue aims to achieve.

The first part focuses on the core question regarding the relation between perceptual consciousness and cognitive access. The two opposing views are introduced and reevaluated by their originators [24,25]. Then the role of access is further discussed in the light of the possibility of offline information processing [26]. Finally, this part is concluded by a critical examination of how different ways of understanding the notion of cognitive access might affect the prospects of the opposing views with regard to the core question [27].

The second part focuses on the issue of whether conscious perception is rich or sparse. If the content of perceptual consciousness is richer than the content that can be cognitively accessed, then consciousness overflows access and thus access cannot be necessary for consciousness. This part confronts empirical reasons for thinking that conscious perception is rich [28] with reasons for thinking that it is sparser than often thought [29,30].

Next, the Theme Issue takes a closer look at the methodological problems arising from the empirical approaches dominating the field. Pessimistic conclusions are drawn with regard to whether the major methodological puzzle can be circumvented [31] and an alternative methodological approach is proposed [32].

The next part revisits the question of how to understand the notion of cognitive access. Attention and working memory are key concepts in this regard. For instance, the richness of perceptual consciousness implies that access is not necessary for consciousness only given specific assumptions about the link between cognitive access and the operation of working memory. This part first focuses on the role attention plays [33,34], then clarifies how recent advancements in understanding the operations of working memory and the activities of the neural substrates of working memory functions can affect the debate [35,36].

The Issue concludes with a part that considers the broader context of the topic. An alternative approach to consciousness, in general, and to the problem of consciousness and cognitive access, in particular, is discussed [37]. Then the very concern about the connection between the phenomenal and the functional that lies in the core of contemporary theorizing and dictates the standard way of thinking about consciousness is revisited and reassessed [38]. And finally, features of conscious perception are used to re-evaluate the increasingly popular general framework according to which perceptual representations are probabilistic [39].

Via confronting opposing theoretical approaches and empirical findings, analysing methodological pitfalls and proposing guidelines for developing novel research paradigms, we expect the Theme Issue to trigger waves of new experimental studies, stimulate model building and lead to the formation of novel theoretical frameworks.

Data accessibility

This article has no additional data.

Competing interests

We declare we have no competing interests.

Funding

This study was supported by the FWO Postdoctoral Fellowship 1.2.B39.14N (P.F.).