Matthias Michel

This chapter is about the role of introspection in the production of scientific data for consciousness research. I address the following question: does introspection provide a special kind of data—subjective data—that are indispensable for studying consciousness? Subjectivists answer that consciousness is a special phenomenon, and should be studied with this special kind of introspective data. Objectivists deny the existence of subjective scientific data. Some objectivists are pessimists. They argue that scientists can only study people's beliefs and reports about their experiences, not conscious experiences themselves. Others are optimists. They deny the existence of subjective scientific data, but hold that scientists can nevertheless study consciousness as a subjective phenomenon. This is both an introduction to this debate and a plea for optimism.

Rapid progress in artificial intelligence (AI) capabilities has drawn fresh attention to the prospect of consciousness in AI. There is an urgent need for rigorous methods to assess AI systems for consciousness, but significant uncertainty about relevant issues in consciousness science. We present a method for assessing AI systems for consciousness that involves exploring what follows from existing or future neuroscientific theories of consciousness. Indicators derived from such theories can be used to inform credences about whether particular AI systems are conscious. This method allows us to make meaningful progress because some influential theories of consciousness, notably including computational functionalist theories, have implications for AI that can be investigated empirically.

The question of which mental functions require consciousness has recently come to the forefront because of its relevance for investigating animal consciousness. Finding out that an animal can perform a function associated with consciousness would count as evidence that it has conscious states. I argue that most of the empirical research interpreted as showing that some functions are associated with consciousness fails to show this. Instead, it merely shows that the relevant functions falter when based on degraded sensory signals—which is unsurprising. This issue hinders empirical research on the functions associated with consciousness. I explain how consciousness research can do better when investigating the functions that require consciousness. Until the relevant research is properly carried out, the presence of functions supposedly associated with consciousness in non-human animals should not convince the skeptics one bit.

It is not obvious why we are conscious. Why can't all of our mental activities take place unconsciously? What is consciousness for? We aim to make progress on this question, focusing on conscious vision. We review evidence on the timescale of visual consciousness, showing that it is surprisingly slow: postdictive effects reveal windows of unconscious integration lasting up to 400 milliseconds. We argue that if consciousness is slow, it cannot be for online action-guidance. Instead, we propose that conscious vision evolved to support offline cognition, in tandem with the larger visual sensory horizons afforded by the water-to-land transition. Smaller visual horizons typical in aquatic environments require fast, reflexive actions of the sort that are guided unconsciously in humans. Conversely, larger terrestrial visual horizons allow benefits to accrue from “model-based” planning of the sort that is associated with consciousness in humans. We further propose that the acquisition of these capacities for internal simulation and planning provided pressures for the evolution of reality monitoring—the capacity to distinguish between internally and externally triggered signals, and to solve “Hamlet's problem” in perception—the problem of when to stop integrating evidence, and fix a particular model of reality. In line with higher-order theories of consciousness, we associate the emergence of consciousness with the emergence of this reality monitoring function. We discuss novel empirical predictions that arise from this account, and explore its implications for the distribution of conscious (vs. unconscious) vision in aquatic and terrestrial animals.

Anosognosia for visual deficits—cases where significant visual deficits go unnoticed—challenges the view that our own conscious experiences are what we know best. We review these widespread and striking failures of awareness. Anosognosia can occur with total blindness, visual abnormalities induced by brain lesions, and eye diseases. We show that anosognosia for visual deficits is surprisingly widespread. Building on previous accounts, we introduce a framework showing how apparently disparate forms of anosognosia fit together. The central idea is that, to notice a deficit, individuals need to form expectations about normal vision, compare expectations and visual input, and judge any mismatch at the metacognitive level. A failure in any of these three steps may lead to unawareness of visual deficits.

To study consciousness, scientists need to determine when participants are conscious and when they are not. They do so with consciousness detection procedures. A recurring skeptical argument against those procedures is that they cannot be calibrated: there is no way to make sure that detection outcomes are accurate. In this article, I address two main skeptical arguments purporting to show that consciousness scientists cannot calibrate detection procedures. I conclude that there is nothing wrong with calibration in consciousness science.

Psychiatric research is in crisis because of repeated failures to discover new drugs for mental disorders. Lack of measurement validity could partly account for these failures. If researchers do not actually measure the effects of drugs on the disorders they aim to investigate, one should expect suboptimal treatment outcomes. I argue that this is the case, focusing on depression, and fear & anxiety disorders. In doing so, I show how psychiatric research illustrates a more general phenomenon that I call “validity drift.” A validity drift occurs when, in the course of developing new measurement procedures, researchers end up studying something different from what they originally aimed to study. I analyze the different ways in which scientists attempt to validate procedures for measuring mental disorders for the purpose of testing drugs in animal models. I show how those validation efforts might fail, thereby leading to validity drifts. Overall, this analysis highlights the complex interplay between the development of new measurement procedures, their calibration, and scientific theories of the target phenomena.

Negative subjective reports such as “I didn’t see the stimulus” can be interpreted as indicating either that the subject didn’t see the stimulus, or as indicating that, while the subject did see the stimulus, the strength of sensory signals associated with the stimulus fell below a conservative criterion for answering “seen”. Determining which of these two interpretations is correct is the criterion problem. I present two ways in which researchers can solve this problem. But there’s more. What I call the “new criterion problem” consists in determining whether criteria effects reflect perceptual changes, or changes in response strategy. Through case studies, I argue that this new version of the problem can be solved as well, although there is currently no systematic way to solve it. I conclude that criterion problems do not constitute good reasons for skepticism about the scientific study of consciousness.

This chapter presents the perceptual reality monitoring theory of consciousness (PRM). PRM is a higher-order theory of consciousness. It holds that consciousness involves monitoring the reliability of one’s own sensory signals. I explain how a perceptual reality monitoring mechanism computes the higher order representations that are crucial for consciousness. While PRM accounts for the difference between conscious and unconscious states, it does not explain, on its own, why experiences feel the way they do—the phenomenal character of experience. PRM is compatible with multiple theories of phenomenal character. Here, I show how to combine it with ‘Mental Quality Space’ theory. I finish by presenting empirical evidence for PRM, as well as some of its predictions.

Introspection is the capacity by which we know our own conscious mental states. Several theories aim to explain it. According to acquaintance theory, we know our experiences by being acquainted with them. Acquaintance is non-causal, non-inferential, and non-observational. I present a dilemma for the acquaintance theory of introspection. Either subjects are always acquainted with all their experiences; or some attentional mechanism selects the relevant experiences (or aspects of experiences) for introspection. The first option is implausible: it implies that subjects are omniscient about their own experiences. The second option is also implausible: if acquaintance is a non-causal relation, introspection cannot target specific (aspects of) experiences without violating the principle of causal closure of the physical.

To study (un)conscious perception and test hypotheses about consciousness, researchers need procedures for determining whether subjects consciously perceive stimuli or not. This article is an introduction to a family of procedures called ‘confidence-based procedures’, which consist in interpreting metacognitive indicators as indicators of consciousness. I assess the validity and accuracy of these procedures, and answer a series of common objections to their use in consciousness research. I conclude that confidence-based procedures are valid for assessing consciousness, and, in most cases, accurate enough for our practical and scientific purposes.

Is perceptual processing in dedicated sensory areas sufficient for conscious perception? Localists say ‘Yes—given some background conditions.’ Prefrontalists say ‘No: conscious perceptual experience requires the involvement of prefrontal structures.’ I review the evidence for prefrontalism. I start by presenting correlational evidence. In doing so, I answer the ‘report argument’, according to which the apparent involvement of the prefrontal cortex in consciousness stems from the requirement for reports. I then review causal evidence for prefrontalism and answer the ‘lesion argument’, which purports to show that prefrontalism is wrong because lesions to the prefrontal cortex do not abolish consciousness. I conclude that multiple sources of evidence converge toward the view that the prefrontal cortex plays a significant role in consciousness.

Conscious experiences involve subjective qualities, such as colours, sounds, smells and emotions. In this Perspective, we argue that these subjective qualities can be understood in terms of their similarity to other experiences. This account highlights the role of memory in conscious experience, even for simple percepts. How an experience feels depends on implicit memory of the relationships between different perceptual representations within the brain. With more complex experiences such as emotions, explicit memories are also recruited. We draw inspiration from work in machine learning as well as the cognitive neuroscience of learning and decision making to make our case and discuss how the account could be tested in future experiments. The resulting findings might help to reveal the functions of subjective experience and inform current theoretical debates on consciousness.

Studying consciousness requires contrasting conscious and unconscious perception. While many studies have reported unconscious perceptual effects, recent work has questioned whether such effects are genuinely unconscious, or whether they are due to weak conscious perception. Some philosophers and psychologists have reacted by denying that there is such a thing as unconscious perception, or by holding that unconscious perception has been previously overestimated. This article has two parts. In the first part, I argue that the most significant attack on unconscious perception commits the criterion content fallacy: the fallacy of interpreting evidence that observers were conscious of something as evidence that they were conscious of the task-relevant features of the stimuli. In the second part, I contend that the criterion content fallacy is prevalent in consciousness research. For this reason, I hold that if unconscious perception exists, scientists studying consciousness could routinely underestimate it. I conclude with methodological recommendations for moving the debate forward.

Phillips argues that blindsight is due to response criterion artefacts under degraded conscious vision. His view provides alternative explanations for some studies, but may not work well when one considers several key findings in conjunction. Empirically, not all criterion effects are decidedly non-perceptual. Awareness is not completely abolished for some stimuli, in some patients. But in other cases, it was clearly impaired relative to the corresponding visual sensitivity. This relative dissociation is what makes blindsight so important and interesting.

Some proponents of the Integrated Information Theory of consciousness profess strong views on the Neural Correlates of Consciousness, namely that large swathes of the neocortex, the cerebellum, at least some sensory cortices, and the so-called limbic system are all not essential for any form of conscious experiences. We argue that this connection is not incidental. Conflation between strong and weak versions of the theory has led these researchers to adopt definitions of NCC that are inconsistent with their own previous definitions, inadvertently betraying the promises of an otherwise fruitful empirical endeavour.

Having a confirmation bias sometimes leads us to hold inaccurate beliefs. So, the puzzle goes: why do we have it? According to the influential argumentative theory of reasoning, confirmation bias emerges because the primary function of reason is not to form accurate beliefs, but to convince others that we’re right. A crucial prediction of the theory, then, is that confirmation bias should be found only in the reasoning domain. In this article, we argue that there is evidence that confirmation bias does exist outside the reasoning domain. This undermines the main evidential basis for the argumentative theory of reasoning. In presenting the relevant evidence, we explore why having such confirmation bias may not be maladaptive.

Local theories of consciousness state that one is conscious of a feature if it is adequately represented and processed in sensory brain areas, given some background conditions. We challenge the core prediction of local theories based on long-lasting postdictive effects demonstrating that features can be represented for hundreds of milliseconds in perceptual areas without being consciously perceived. Unlike previous empirical data aimed against local theories, localists cannot explain these effects away by conjecturing that subjects are phenomenally conscious of features that they cannot report. We also discuss alternative explanations that localists could offer.

Consciousness is currently a thriving area of research in psychology and neuroscience. While this is often attributed to events that took place in the early 1990s, consciousness studies today are a continuation of research that started in the late 19th century and that continued throughout the 20th century. From the beginning, the effort built on studies of animals to reveal basic principles of brain organization and function, and of human patients to gain clues about consciousness itself. Particularly important and our focus here is research in the 1950s, 1960s, and 1970s involving three groups of patients—amnesia, split brain, and blindsight. Across all three groups, a similar pattern of results was found—the patients could respond appropriately to stimuli that they denied seeing (or in the case of amnesiacs, having seen before). These studies paved the way for the current wave of research on consciousness. The field is, in fact, still grappling with the implications of the findings showing that the ability to consciously know and report the identity of a visual stimulus can be dissociated in the brain from the mechanisms that underlie the ability to behave in a meaningful way to the same stimulus.

The intuition that consciousness is hard to explain may fade away as empirically adequate theories of consciousness develop. We review socio-historical factors that account for why, as a field, the neuroscience of consciousness has not been particularly successful at developing empirically adequate theories. Based on this we argue that the meta-problem may be a self-fulfilling prophecy, created in part because we inadvertently focused too much on the so-called 'hard problem', limiting scientific progress.

Opponents to consciousness in fish argue that fish do not feel pain because they do not have a neocortex, which is a necessary condition for feeling pain. A common counter-argument appeals to the multiple realizability of pain: while a neocortex might be necessary for feeling pain in humans, pain might be realized differently in fish. This paper argues, first, that it is impossible to find a criterion allowing us to demarcate between plausible and implausible cases of multiple realization of pain without running into a circular argument. Second, opponents to consciousness in fish cannot be provided with reasons to believe in the multiple realizability of pain. I conclude that the debate on the existence of pain in fish is impossible to settle by relying on the multiple realization argument.

Consciousness scientists have not reached consensus on two of the most central questions in their field: first, on whether consciousness overflows reportability; second, on the physical basis of consciousness. I review the scientific literature of the 19th century to provide evidence that disagreement on these questions has been a feature of the scientific study of consciousness for a long time. Based on this historical review, I hypothesize that a unifying explanation of disagreement on these questions, up to this day, is that scientific theories of consciousness are underdetermined by the evidence, namely, that they can be preserved “come what may” in front of (seemingly) disconfirming evidence. Consciousness scientists may have to find a way of solving the persistent underdetermination of theories of consciousness to make further progress.