Understanding the Higher-Order Approach to Consciousness
Authors: Richard Brown, Hakwan Lau, Joseph E. LeDoux
Journal: Trends in Cognitive Sciences (2019)

Misunderstandings about HOT have marginalized it relative to other approaches.We clarify some of the key misunderstandings, including assumptions about the equivalence between consciousness and metacognition, and the role of introspection and the self.We reply to several objections, including those concerning the nature of perception in the visual periphery and issues raised about the value of so-called 'no report' paradigms.We also address issues regarding the involvement of prefrontal cortex, including questions about whether it is necessary, and whether its deactivation during dreams and psychedelic states is incompatible with it contributing to higher-order awareness.We propose a reconceptualization of lower-order states that contribute to higher-order awareness, including states of prefrontal cortex and multimodal and mnemonic states processed in posterior cortical areas.We provide arguments as to why the HOT of consciousness may be superior to both GWT and local recurrency theory regarding its ability to account for subjective experiences, especially of complex states such as memories and emotions that occur in everyday life and that are hallmarks of psychopathological conditions. The higher-order theory (HOT) of consciousness has often been misunderstood by critics. Here, we clarify its position on several issues, and distinguish it from other views, such as the global workspace theory (GWT) and early sensory models (e.g., first-order local recurrency theories). For example, HOT has been criticized for overintellectualizing consciousness. We show that, while higher-order states are cognitively assembled, the requirements are in fact considerably less than often presumed. In this sense, HOT may be viewed as an intermediate position between GWT and early sensory views. We also clarify that most proponents of HOT do not stipulate consciousness as equivalent to metacognition or confidence. Furthermore, compared with other existing theories, HOT can arguably account better for complex everyday experiences, such as emotions and episodic memories. This makes HOT particularly useful as a framework for conceptualizing pathological mental states. The higher-order theory (HOT) of consciousness has often been misunderstood by critics. Here, we clarify its position on several issues, and distinguish it from other views, such as the global workspace theory (GWT) and early sensory models (e.g., first-order local recurrency theories). For example, HOT has been criticized for overintellectualizing consciousness. We show that, while higher-order states are cognitively assembled, the requirements are in fact considerably less than often presumed. In this sense, HOT may be viewed as an intermediate position between GWT and early sensory views. We also clarify that most proponents of HOT do not stipulate consciousness as equivalent to metacognition or confidence. Furthermore, compared with other existing theories, HOT can arguably account better for complex everyday experiences, such as emotions and episodic memories. This makes HOT particularly useful as a framework for conceptualizing pathological mental states. Consciousness (see Glossary), as used here, refers to subjective experience, or what is sometimes called phenomenal consciousness [1.Chalmers D. The Conscious Mind. Oxford University Press, 1996Google Scholar, 2.Nagel T. What is it like to be a bat?.Philos. Rev. 1974; 83: 4435-4450Crossref Google Scholar], as opposed to the condition of merely being awake and alert and behaviorally responsive to external stimuli. To be phenomenally conscious is for there to be something that it is like to be the entity in question, that is, something that it is like for the entity itself [2.Nagel T. What is it like to be a bat?.Philos. Rev. 1974; 83: 4435-4450Crossref Google Scholar]. Subjective experience is the stuff of novels, poems, and songs, of our emotions and memories, the essence of being a human. It is hard to imagine what it would be like to not be sentient in the way we are. Unsurprisingly, then, the science of consciousness is currently a vibrant and thriving area of research. However, there is no generally accepted theory of the phenomena being studied, and the phenomena themselves often do not include many of the kinds of complex experiences that we normally have in the course of day-to-day life, such as of our emotions and memories. Here, we argue that the foundation for a viable theory of such experiences exists but has not been given the credit it deserves. We are referring to various ideas known collectively as HOT. HOT is often overlooked, or lumped in with other cognitive theories of consciousness, such as GWT. Even worse, it is sometimes dismissed out of hand as not empirically plausible compared with other theories. Our main goal here is to identify and answer some of the most common questions concerning the theory. First, however, we briefly describe key features of HOT. Theories of consciousness can be categorized as either first-order theories or HOTs. In general, there are two features that make a theory of consciousness a HOT rather than a first-order theory. The first feature is a commitment to the claim that a mere first-order representation is not sufficient for conscious experiences to arise; some higher-order mechanism or mechanisms are also needed. For example, having a first-order perceptual state about an external object is often crucial for the organism to respond meaningfully to it. However, according to HOT, such first-order states can occur nonconsciously and are insufficient for phenomenally conscious experiences to occur [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar]. This requirement of HOT distinguishes it from local versions of first-order theories, such as recurrent processing theories [4.Dretske F. Naturalizing the Mind. MIT Press, 1995Google Scholar, 5.Block N. Empirical science meets higher order views of consciousness: reply to Hakwan Lau and Richard Brown.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 199-213Google Scholar, 6.Lamme V.A. How neuroscience will change our view on consciousness.Cogn. Neurosci. 2010; 1: 204-220Crossref PubMed Scopus (124) Google Scholar, 7.Tye M. Consciousness, Color, and Content. MIT Press, 2000Crossref Google Scholar]. The second requirement of HOT comes from the common-sense claim that if an organism is in no way aware of itself as being in a certain first-order state, then it is not phenomenally conscious of the content of that state. This is a logical consequence of what is called the Transitivity Principle [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar]. The basic idea, according to HOT, is that conscious experiences entail some kind of minimal inner awareness of one's ongoing mental functioning, and this is due to the first-order state being in some ways monitored or meta-represented by a relevant higher-order representation. This requirement of HOT distinguishes it from cognitive theories, such as GWT [8.Baars B.J. Franklin S. An architectural model of conscious and unconscious brain functions: Global Workspace Theory and IDA.Neural Netw. 2007; 20: 955-961Crossref PubMed Scopus (76) Google Scholar, 9.Dehaene S. Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts. Penguin Books, 2014Google Scholar, 10.Naccache L. Dehaene S. Reportability and illusions of phenomenality in the light of the global neuronal workspace model.Behav. Brain Sci. 2007; 30: 518-520Crossref Scopus (0) Google Scholar, 11.Naccache L. Why and how access consciousness can account for phenomenal consciousness.Philos. Trans. R. Soc. Lond. Ser. B Biol. Sci. 2018; 373: 20170357Crossref PubMed Scopus (6) Google Scholar], which also invoke additional cognitive processes as a crucial element of conscious experience, but which do not posit this type of inner awareness. For this reason, GWT is a variant of first-order theory. HOT is not a single entity. It in fact comes in many varieties [12.Rosenthal D. Varieties of higher-order theory.in: Gennaro R.J. Higher-Order Theories of Consciousness: An Anthology. John Benjamins, 2004: 17-44Crossref Google Scholar, 13.Lau H. Rosenthal D. Empirical support for higher-order theories of conscious awareness.Trends Cogn. Sci. 2011; 15: 365-373Abstract Full Text Full Text PDF PubMed Scopus (208) Google Scholar, 14.Rosenthal D. Weisberg J. Higher-order theories of consciousness.Scholarpedia. 2008; 3: 4407Crossref Google Scholar] that are distinguished by the different ways in which they define the relevant higher-order mechanism (Table 1). For example, the traditional view, sometimes attributed to John Locke and Immanuel Kant, refers to the mechanism of inner awareness as an Inner Sense, akin to perception [15.Armstrong D.M. A Materialist Theory of the Mind. Routledge, 1968Google Scholar, 16.Lycan W.G. The superiority of Hop to HOT.in: Gennaro R.J. Higher-Order Theories of Consciousness: An Anthology. John Benjamins, 2004: 93-114Crossref Google Scholar]. However, Inner Sense HOTs, also referred to as Higher-Order Perception theories, have somewhat fallen out of favor because of a failure to find a neural implementation of an Inner Sense [17.Sauret W. Lycan W.G. Attention and internal monitoring: a farewell to HOP.Analysis. 2014; 74: 363-370Crossref Scopus (2) Google Scholar]. Another variety, Dispositional HOT, posits that the mere availability of first-order content to higher-order mechanisms accounts for consciousness [18.Carruthers P. Phenomenal Consciousness: A Naturalistic Theory. Cambridge University Press, 2000Crossref Google Scholar]. Other versions of HOT include the Phenomenal Self theory [19.Metzinger T. Being No One. MIT Press, 2003Crossref Google Scholar], the Radical Plasticity Hypothesis [20.Cleeremans A. The Radical Plasticity Thesis: how the brain learns to be conscious.Front. Psychol. 2011; 2: 86Crossref PubMed Scopus (0) Google Scholar], and variants of Higher-Order Thought Theory (HOTT) [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar, 12.Rosenthal D. Varieties of higher-order theory.in: Gennaro R.J. Higher-Order Theories of Consciousness: An Anthology. John Benjamins, 2004: 17-44Crossref Google Scholar, 14.Rosenthal D. Weisberg J. Higher-order theories of consciousness.Scholarpedia. 2008; 3: 4407Crossref Google Scholar, 21.Kriegel U. Subjective Consciousness: A Self-Representational Theory. Oxford University Press, 2009Crossref Google Scholar, 22.Brown R. The HOROR theory of phenomenal consciousness.Philos. Stud. 2015; 172: 1783-1794Crossref Scopus (13) Google Scholar, 23.Lau H. Brown R. The emperor's new phenomenology? The empirical case for conscious experience without first-order representations.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 171-197Google Scholar, 24.LeDoux J.E. Brown R. A higher-order theory of emotional consciousness.Proc. Natl. Acad. Sci. U. S. A. 2017; 114: E2016-E2025Crossref PubMed Scopus (63) Google Scholar, 49.LeDoux J. The Deep History of Ourselves: How Ancient Microbes Became Conscious Brains. Viking, 2019Google Scholar]. HOTT postulates that the higher-order state is thought-like, and is the subject of much current discussion and debate [5.Block N. Empirical science meets higher order views of consciousness: reply to Hakwan Lau and Richard Brown.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 199-213Google Scholar, 23.Lau H. 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The merits of higher-order thought theories.Trans/Form/Ação. 2018; 41: 31-48Crossref Scopus (1) Google Scholar, 30.Rosenthal D. Misrepresentation and mental appearance.Trans/Form/Ação. 2018; 41: 49-74Crossref Scopus (0) Google Scholar].Table 1Differences between HOTs and Other Theories of ConsciousnessTheoryaThis table only covers a few theories to highlight contrasts between different HOTs and between HOT and other theories in the literature. The issues in question are as follows. (i) Is the theory a variety of HOT? (ii) Does first-order content need to be re-represented at a later stage to become conscious? (iii) Does everyday experience mean that many thought-like representations are involved at one moment? (iv) Does consciousness require capacity for conceptual processing? (v) Does consciousness require explicit (contra subpersonal-level) metacognition? (vi) What is the function of consciousness?Is it a variety of HOT?Is first-order content re-represented?Are complex 'thoughts' required?Is conceptual processing involved?Is explicit metacognition required?What is the function of consciousness in the theory?Higher-Order Thought Theory (HOTT) 3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar, 13.Lau H. Rosenthal D. Empirical support for higher-order theories of conscious awareness.Trends Cogn. Sci. 2011; 15: 365-373Abstract Full Text Full Text PDF PubMed Scopus (208) Google ScholarYesYes, but redescribed in different formatYesYesNoLittle is assumed by the theoryHigher-Order Representation of a Representation (HOROR) 22.Brown R. The HOROR theory of phenomenal consciousness.Philos. Stud. 2015; 172: 1783-1794Crossref Scopus (13) Google Scholar, 23.Lau H. Brown R. The emperor's new phenomenology? The empirical case for conscious experience without first-order representations.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 171-197Google Scholar, 24.LeDoux J.E. Brown R. A higher-order theory of emotional consciousness.Proc. Natl. Acad. Sci. U. S. A. 2017; 114: E2016-E2025Crossref PubMed Scopus (63) Google ScholarYesYes, possibly redescribed in different formatNot clearYesNoWhatever the function of the right kind of higher-order representations of representations turns out to bePerceptual Reality Monitoring Theory 42.Lau H. Consciousness, metacognition, & perceptual reality monitoring.PsyArXiv. 2019; (10 June)Google ScholarYesNoNo, relevant higher-order states are mere indexesNoNoFormation of subjectively justified beliefsMulti-State Hierarchical Model of Subjective Self-Awareness 49.LeDoux J. The Deep History of Ourselves: How Ancient Microbes Became Conscious Brains. Viking, 2019Google ScholarYesDiverse hierarchically organized lower-order states are re-representedNot required, but can resultYes, in the form of schemaNoThoughts, beliefs, memories, feelings, and attributions about the world, and about oneself as an object and a subjectRadical Plasticity Thesis 20.Cleeremans A. The Radical Plasticity Thesis: how the brain learns to be conscious.Front. Psychol. 2011; 2: 86Crossref PubMed Scopus (0) Google ScholarYesYes, but redescribed in different formatNo, relevant higher-order states are not thoughtsTypically noNoControl of behavior and learning in novel situationsFirst-order local recurrency view 1.Chalmers D. The Conscious Mind. Oxford University Press, 1996Google Scholar, 6.Lamme V.A. How neuroscience will change our view on consciousness.Cogn. Neurosci. 2010; 1: 204-220Crossref PubMed Scopus (124) Google Scholar, 78.Block N. Consciousness and cognitive access.Proc. Aristot. Soc. 2008; 108: 289-317Crossref Scopus (0) Google Scholar, 87.Block N. Consciousness, accessibility, and the mesh between psychology and neuroscience.Behav. Brain Sci. 2007; 30 (discussion 499–548): 481-499Crossref PubMed Scopus (12) Google ScholarNoNoNoNoNoMinimalGlobal Workspace Theory (GWT) 8.Baars B.J. Franklin S. An architectural model of conscious and unconscious brain functions: Global Workspace Theory and IDA.Neural Netw. 2007; 20: 955-961Crossref PubMed Scopus (76) Google Scholar, 9.Dehaene S. Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts. Penguin Books, 2014Google Scholar, 10.Naccache L. Dehaene S. Reportability and illusions of phenomenality in the light of the global neuronal workspace model.Behav. Brain Sci. 2007; 30: 518-520Crossref Scopus (0) Google Scholar, 11.Naccache L. Why and how access consciousness can account for phenomenal consciousness.Philos. Trans. R. Soc. Lond. Ser. B Biol. Sci. 2018; 373: 20170357Crossref PubMed Scopus (6) Google ScholarNoPropagated but not necessarily metarepresentedNoNoNoGlobal sharing and stabilization of informationGlobal Workspace Plus Metacognition 50.Shea N. et al.Supra-personal cognitive control and metacognition.Trends Cogn. Sci. 2014; 18: 186-193Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar, 131.Shea N. Frith C.D. The global workspace needs metacognition.Trends Cogn. Sci. 2019; 23: 560-571Abstract Full Text Full Text PDF PubMed Scopus (1) Google ScholarNoNoNoNoYesGlobal sharing and stabilization of information and interpersonal communicationa This table only covers a few theories to highlight contrasts between different HOTs and between HOT and other theories in the literature. The issues in question are as follows. (i) Is the theory a variety of HOT? (ii) Does first-order content need to be re-represented at a later stage to become conscious? (iii) Does everyday experience mean that many thought-like representations are involved at one moment? (iv) Does consciousness require capacity for conceptual processing? (v) Does consciousness require explicit (contra subpersonal-level) metacognition? (vi) What is the function of consciousness? Open table in a new tab HOT emerged from a philosophical theory, but is not simply an intriguing philosophical hypothesis. It is also broadly compatible with empirical findings in neuroscience. For example, under highly controlled conditions, a difference in perceptual awareness is better correlated with activity in brain areas responsible for high-level cognition rather than in early sensory regions [31.Lau H.C. Passingham R.E. Relative blindsight in normal observers and the neural correlate of visual consciousness.Proc. Natl. Acad. Sci. U. S. 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Cogn. 2018; 62: 34-41Crossref PubMed Scopus (2) Google Scholar] or lesion [35.Fleming S.M. et al.Domain-specific impairment in metacognitive accuracy following anterior prefrontal lesions.Brain. 2014; 137: 2811-2822Crossref PubMed Scopus (82) Google Scholar] can change subjective aspects of the perceptual experience. These findings have been reviewed previously [13.Lau H. Rosenthal D. Empirical support for higher-order theories of conscious awareness.Trends Cogn. Sci. 2011; 15: 365-373Abstract Full Text Full Text PDF PubMed Scopus (208) Google Scholar, 36.Lau H. Rosenthal D. The higher-order view does not require consciously self-directed introspection: response to Malach.Trends Cogn. Sci. 2011; 15: 508-509Abstract Full Text Full Text PDF Google Scholar], and there have also been recent updates [23.Lau H. Brown R. The emperor's new phenomenology? The empirical case for conscious experience without first-order representations.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 171-197Google Scholar, 37.Odegaard B. et al.Should a few null findings falsify prefrontal theories of conscious perception?.J. Neurosci. 2017; 37: 9593-9602Crossref PubMed Scopus (12) Google Scholar], in which some standard philosophical objections have also been addressed. Here, we discuss some of these findings and replies to objections in details. However, instead of providing yet another broad review, we go through these issues in the context of clarifying some common misunderstandings by framing them in terms of questions about HOT. Given that much of the evidence supporting HOT is also compatible with other cognitive theories of consciousness, such as GWT, it has not been obvious how to arbitrate between the two. Our goal is to make clear this distinction to allow further experiments to arbitrate between the different theories. According to HOT, cognitive access, in the form of a kind of inner awareness, is necessary for phenomenal consciousness. A common objection then is that HOT makes consciousness require overly sophisticated mechanisms [4.Dretske F. Naturalizing the Mind. MIT Press, 1995Google Scholar, 38.Seager W.E. A cold look at HOT theory.in: Gennaro R.J. Higher-Order Theories of Consciousness: An Anthology. John Benjamins, 2004: 255-275Crossref Google Scholar]. One version of this criticism is that HOTT appears to commit itself to the cognitive requirement of having concepts about mental states that constitute the content of higher-order thoughts. Various HOTTs respond differently to this challenge. Some appeal to innate concepts. Others deny that the relevant conceptual capacities are sophisticated [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar]. Still others question whether concepts are required at all [23.Lau H. Brown R. The emperor's new phenomenology? The empirical case for conscious experience without first-order representations.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 171-197Google Scholar]. Another version of this objection argues that, given the richness of everyday experience, and the fact that the human capacity for thoughts is limited, consciousness under HOTT would require too many higher-order thoughts [18.Carruthers P. Phenomenal Consciousness: A Naturalistic Theory. Cambridge University Press, 2000Crossref Google Scholar]. However, the exact level and degree of complex processing required to generate relevant higher-order thoughts is not currently known. Some higher-order theorists propose that the relevant higher-order states may use relational concepts ('x is bluer than y') [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar], which would reduce both the amount of processing and number of thoughts required relative to what might at first be expected. Confusion also results in part from the ways 'thought,' 'introspection', and 'self,' as used in HOT, are interpreted by critics [28.Malach R. Conscious perception and the frontal lobes: comment on Lau and Rosenthal.Trends Cogn. Sci. 2011; 15 (author reply 508–509): 507Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar]. Traditionally, introspection refers to an active process in which one becomes conscious of their inner states [39.Jack A.I. Shallice T. Introspective physicalism as an approach to the science of consciousness.Cognition. 2001; 79: 161-196Crossref PubMed Scopus (133) Google Scholar, 40.Nelson T.O. Narens L. Why investigate metacognition?.in: Metcalfe J. Shimamura A.P. Metacognition: Knowing about Knowing. The MIT Press, 1994: 1-25Google Scholar]. Similarly, 'self' is often used to refer to conscious awareness of one's self. The fact that higher-order philosophers tend to use propositional statements involving personal pronouns ('I see red') to describe the higher-order thought has led to the idea that HOT implies a conscious self that has introspective knowledge of its experiences [41.Dennett D. Not just a fine trip down memory lane: comments on the essays on content and consciousness.in: Muñoz-Suárez C. De Brigard F. Content and Consciousness Revisited: With Replies by Daniel Dennett. Springer International Publishing, 2015: 199-220Crossref Scopus (1) Google Scholar]. However, HOTT proponents, in fact, typically call upon a cognitively 'lean' conception of both thought and self. In some versions, a monitoring mechanism that works at the subpersonal level is postulated [42.Lau H. Consciousness, metacognition, & perceptual reality monitoring.PsyArXiv. 2019; (10 June)Google Scholar], while, in other versions, the thoughts are at the personal level but are arrived at automatically and without appearing to be the product of inference [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar]. Importantly, both the leaner/passive and thicker/active versions of self and introspection relevant to HOT are distinct from more basic biological mechanisms referred to with terms such as 'self as object' (as opposed to subject) [43.Damasio A. Self Comes to Mind: Constructing the Conscious Brain. Pantheon Books, 2010Google Scholar, 44.Baker L.R. Naturalism and the First-Person Perspective. Oxford University Press, 2013Crossref Google Scholar], 'core self' [45.Panksepp J. The Archaeology of Mind: Neuroevolutionary Origins of Human Emotion. W.W. Norton & Company, 2012Google Scholar], or the 'machinery of self' [46.Lewis M. The Rise of Consciousness and the Development of Emotional Life. The Guilford Press, 2013Google Scholar]. As such, the thoughts involved in higher-order representations are not usually themselves viewed as ones we are conscious of being in [3.Rosenthal D.M. Consciousness and Mind. Oxford University Press, 2005Google Scholar, 15.Armstrong D.M. A Materialist Theory of the Mind. Routledge, 1968Google Scholar, 23.Lau H. Brown R. The emperor's new phenomenology? The empirical case for conscious experience without first-order representations.in: Pautz A. Stoljar D. Blockheads! Essays on Ned Block's Philosophy of Mind and Consciousness. MIT Press, 2019: 171-197Google Scholar, 24.LeDoux J.E. Brown R. A higher-order theory of emotional consciousness.Proc. Natl. Acad. Sci. U. S. A. 2017; 114: E2016-E2025Crossref PubMed Scopus (63) Google Scholar, 36.Lau H. Rosenthal D. The higher-order view does not require consciously self-directed introspection: response to Malach.Trends Cogn. 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