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Neural Synchrony and the Causal Efficacy of Consciousness

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Abstract

The purpose of this paper is to address a well-known dilemma for physicalism. If mental properties are type identical to physical properties, then their causal efficacy is secure, but at the cost of ruling out mentality in creatures very different to ourselves. On the other hand, if mental properties are multiply realizable, then all kinds of creatures can instantiate them, but then they seem to be causally redundant. The causal exclusion problem depends on the widely held principle that realized properties inherit their causal powers from their realizers. While this principle holds for functional realization, it fails on a broader notion of realization that permits the realization of complex qualitative properties such as spatial and temporal patterns. Such properties are best seen as dependent powerful qualities, which have their causal roles in virtue of being the qualities they are, and do not inherit powers from their realizers. Recent studies have identified one such property—neural synchrony—as a correlate of consciousness. If synchrony is also partially constitutive of consciousness, then phenomenal properties are both multiply realizable and causally novel. I outline a version of representationalism about consciousness on which this constitution claim holds.

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Notes

  1. See Crane (1995) for the idea that the problem of mental causation should be treated as a mutually inconsistent set of plausible claims about the mind. I focus on phenomenal properties, but the problem generalises to other mental properties. See Yates (2012) for more on causal exclusion, especially in relation to functionalism.

  2. When I say that a property P causes an effect E, this should be taken to mean that P bestows upon E’s cause C (which might be an event, state, or object) the power to cause E.

  3. Jackson and Pettit (1990).

  4. Lewis (1966); Kim (1992).

  5. Putnam (1967). Multiple realizability has been placed under significant pressure recently by Polger and Shapiro (2016). I lack the space to address their arguments here, but will briefly discuss their views in Sects. 2 and 4.

  6. Bennett (2003); Kallestrup (2006).

  7. Yablo (1992); List and Menzies (2010).

  8. Kim (1998) makes this point, and argues that the resulting overdetermination is no less problematic.

  9. Kim (1992).

  10. Wilson (1999, 2011, 2015); Shoemaker (2001).

  11. This point is argued at length in Wilson (2015). See Yates (2016) for full discussion of causal inheritance as a condition on realization.

  12. On the theory suggested in Sect. 4, phenomenal properties are complex properties that are partially functional, and derive their causal novelty from their non-functional parts.

  13. Crook and Gillett (2001).

  14. Heil (2003); Martin (2007).

  15. Bird (2007).

  16. Armstrong (1983).

  17. Jacobs (2011).

  18. Smith (2016).

  19. And of course it may not. See Yates (2017) for more on this issue.

  20. I present a simplified version of the argument here; see Yates (2016) for the details.

  21. Image courtesy of Wikipedia. File: Tetrahedral Structure of Water.png. (2017, February 20). https://commons.wikimedia.org/w/index.php?title=File:Tetrahedral_Structure_of_Water.png&oldid=234459610.

  22. This account owes much to Gillett’s (2003).

  23. A referee objects that molecular geometry is realized by “relative spatial relations”, which are common to both H2O molecules and molecular models. I am not sure what ‘relative spatial relations’ means, but it seems to me that it is most naturally taken to refer to the directions of the relata in relation to each other, in which case it is simply another way of referring to geometric structure. That is common to both cases, but its realizers—the relata themselves and the specific distance relations between them—are not.

  24. Polger and Shapiro (2016).

  25. Gillett (2003) argues—and I agree—that because rigidity is itself multiply realizable, aluminium and steel waiter’s corkscrews do count as different implementations of the same function.

  26. I thank an anonymous referee for pressing me on this point.

  27. See Yates (2012) for full discussion.

  28. For something to have a power simpliciter is for it to be disposed to behave in a certain way, when appropriately related to certain stimuli. For something to have a conditional power is for it to be such that if it had certain other properties, it would have the relevant power simpliciter, where the other properties in question are not independently sufficient for this. See Shoemaker (2001, pp. 25–26).

  29. For details see Yates (2016); for similar arguments see Gillett (2016a, pp. 221–223).

  30. Shoemaker (2002).

  31. See Yates (2016) for more on this issue.

  32. Gillett (2016a, b).

  33. It isn’t clear where properties like geometric structure fit into Gillett’s ontology, and I don’t attribute to him the claim that they are capable of machresis.

  34. Image courtesy of Wikipedia. File:SimulationNeuralOscillations.png. (2011, September 7). https://commons.wikimedia.org/w/index.php?title=File:SimulationNeuralOscillations.png&oldid=59030332.

  35. I focus on same-frequency oscillations for now. I return to the issue of phase lag below, and briefly discuss cross-frequency coupling in Sect. 5.

  36. Engel et al. (2001); Fries (2005).

  37. I return to this in Sect. 4.

  38. Gray and Singer (1989); Fries et al. (2001).

  39. See Fries (2015, pp. 221–222); Singer (2013, pp. 6–7), for summaries; and Tiesinga and Sejnowski (2009) for details.

  40. Tiesinga and Sejnowski (2009); Wang (2010).

  41. In some models, long-range gamma coherence is established by a chain of the same inhibitory interneuron networks that give rise to local gamma coherence in the PING model; in others, it is mediated by slower rhythmic oscillations that act as pacemakers. For details, see Buzsáki and Wang (2012). To get a sense of the intricacies of synchronization between coupled oscillators in general, see Arenas et al. (2008).

  42. Following Fries’ influential (2005) paper.

  43. Reproduced from Fries (2015).

  44. Fries (2005, 2015).

  45. Fries (2015, p. 224), suggests a pulsatile coding system in which spatial activity patterns carry representational content and are refreshed in the receiving population at the frequency of oscillation.

  46. Srinivasan et al. (1999).

  47. The frequency tags were in the range 7–12 Hz. Such flicker-induced oscillations are not those that the brain uses to represent the gratings themselves, but a different rhythm occurring in the same network. As explained in Sect. 3, neural networks can oscillate at several frequencies at once.

  48. Op. Cit. p. 5446.

  49. In this condition one eye is dominant and the other suppressed when different stimuli of equal contrast are presented to each eye, and this fact can be used in a similar way to binocular rivalry studies, but rather than relying on reports, we simply assume that the dominant eye image is perceived during rivalry.

  50. Fries et al. (1997). Details of further such studies can be found in Engel et al. (1999); for a recent and wide-ranging review, see Engel and Fries (2016).

  51. Melloni et al. (2007).

  52. Fries et al. (2001).

  53. Roy et al. (2007).

  54. See Engel et al. (2001) for a detailed review of the role of neural synchrony in top–down attentional processing. They suggest that visual search might work by top–down induced synchrony in the sub-threshold membrane potential of visual populations, so that when their preferred stimulus is detected, its representation is automatically synchronous with the higher cognitive systems guiding the search.

  55. I won’t summarise them here, but see Engel and Fries (2016) for a survey of several such theories.

  56. Chalmers (2004). Chalmers speaks of pure and impure representational properties as representations of content rather than states of affairs. I don’t think this is a particularly perspicuous way of putting things, and prefer to think of intentional states as representing objects (properties, events…), not contents.

  57. One can also be a Russellian or a Fregean representationalist, depending on whether one identifies phenomenal character with phenomenally representing an object simpliciter, or with representing it under a given mode of presentation. For present purposes, I’m neutral between these alternatives. See Chalmers (2004).

  58. Tye (1995).

  59. Op. cit. p. 101.

  60. Tye (2000, p. 62).

  61. GWT was first proposed in Baars (1988).

  62. Dehaene and Naccache (2001), p. 1.

  63. This is the central message of Dennett (1991).

  64. This suggestion is made in Dennett (2001, p. 224), and I’ll return to it later.

  65. Op. cit. pp. 224–225.

  66. The suggestion that synchrony realizes the global workspace is made in Newman and Baars (1993).

  67. Millikan (1984); Papineau (1984).

  68. Cummins (1996).

  69. It’s independently plausible that the visual system uses a combinatorial semantics, which in turn gives rise to the feature binding problem. See Treisman (1999) for an introduction, and the other papers in the same volume for further discussion.

  70. The account given in Sect. 2 allows for the realization of abstract structure.

  71. Content so understood may also be causally novel, if the arguments of Sect. 2 are correct. A structural representation may have certain causal powers in virtue of the very same abstract structure that endows it with representational content, and not in virtue of the realizers of that structure. I lack the space to develop this proposal here, however, and shall not assume any causal novelty on the part of content.

  72. Rao and Lowenstein (2015).

  73. Murphy et al. (2011). I thank an anonymous referee for drawing my attention to this.

  74. Crick and Koch (1990); see also Engel et al. (1999).

  75. I thank an anonymous referee for pressing me on the nature of these couplings.

  76. Block (1978). Searle (1980) famously raises the same concern for the classical computational theory of mind, but we can safely view this as a version of functionalism for present purposes.

  77. Block (1978).

  78. Polger and Shapiro (2016).

  79. It also doesn’t require a commitment to representationalism about phenomenal character, although I’ll continue to assume representationalism here.

  80. See Friston and Stephan (2007) for details.

  81. Bastos et al. (2012).

  82. It’s worth noting that some who endorse predictive coding models of perception eschew mental representation altogether, for instance Hutto (2018). See Kiefer and Hohwy (2018) for a diametrically opposed view, according to which mental representation, construed in terms of causal-structural isomorphism, arises naturally within Bayesian predictive coding systems.

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Acknowledgements

Based primarily on research funded by the Fundação para a Ciência e a Tecnologia (IF/01736/2014), and in part on earlier work funded by a British Academy Postdoctoral Fellowship. I am very grateful to Peter Dayan for discussion of downward causation in neuroscience, and for introducing me to CTC, but do not attribute any of the views presented here to him. For helpful discussions and comments, I am grateful to David Chalmers, Carl Gillett, Matteo Grasso, Jim Hopkins, William Jaworski, Robert Koons, David Papineau, and two anonymous referees.

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    David Yates

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Yates, D. Neural Synchrony and the Causal Efficacy of Consciousness. Topoi 39, 1057–1072 (2020). https://doi.org/10.1007/s11245-018-9596-7

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