Evolving Phenomenal Consciousness

As part of the argument for the superiority of his HOT (Higher Order Thought) theory of phenomenal consciousness, Carruthers offers an answer to the question of how phenomenal consciousness evolved, and he claims that this answer is superior to alternatives based upon other theories. I wish to demur. Evolutionary considerations are the cornerstone of Carruthers' rejection of alternative HOE (Higher Order Experience) accounts of phenomenal consciousness, which he argues do not successfully explain the cognitive role of phenomenal consciousness. They are also a cornerstone of his denial that nonhuman animals, young children, and autistic individuals are phenomenally conscious. The conjectured evolutionary story is too weak for either role.

In Carruthers' story, phenomenal consciousness emerges as an evolutionary "by-product, not directly selected for" (2000:230) of a two-stage selection process: First there was selection for first-order sensory representations (unconscious experiences), then there was selection for a "mind-reading" capacity which required conceptualization of mental states. On Carruthers' view, once the organism's own first-order sensory representations become directly available for conceptualization they are de facto phenomenally conscious. Once experiences become phenomenally conscious, then further adaptive benefits may follow -- particularly, Carruthers thinks, for making appearance-reality distinctions (2000:232; see also Allen & Bekoff 1997).

We have a huge range of phenomenally conscious experiences, from pains and orgasms, to the taste of sour milk and the feeling of breathlessness caused by the thin air and the staggering view from atop a snow-capped mountain. I shall argue that Carruthers' account fails to explain why we are phenomenally conscious in all the ways that we are. In other words, I shall put pressure on the alleged generality of this account, which is in evidence in this passage from chapter 8:

Now the important point for our purposes is that the mind-reading faculty would have needed to have access to a full range of perceptual representations. It would have needed to have access to auditory input in order to play a role in generating interpretations of heard speech, and it would have needed to have access to visual input in order to represent and interpret people's movements and gestures, as well as to generate representations of the form, `A sees that P' or `A sees that [demonstrated object/event]'. Mere conceptual events wouldn't have been good enough. For often what needs to be interpreted is a fine-grained gesture or facial expression, for which we lack any specific concept. It seems reasonable to suppose, then, that our mind-reading faculty would have been set up as one of the down-stream systems drawing on the integrated first-order perceptual representations, which were already available to first-order concepts and indexical thought. .... Once this had occurred, then nothing more needed to happen for people to enjoy phenomenally conscious experiences, on a dispositionalist HOT account. (2000:231)

In this passage, the phrase "access to a full range of perceptual representations" seems to be playing a dual role. First, although only two forms of perception -- hearing and sight -- are mentioned explicitly they seem to be standing service for all the forms of perception which give rise to phenomenally conscious experience, and the full range of perceptual representations should therefore encompass odor, taste, and touch, as well as nociception and other somatic sensations. Second, Carruthers' reference to those elements of perception for which we lack specific concepts indicates another sense in which the range of perceptual representations available for second order thought is supposed to be construed broadly.

I shall have little to say about this second sense of breadth, although I do think there are questions that might be raised about the limits of this account of phenomenal consciousness in the light of such phenomena as chicken-sexing (Biederman & Shiffrar 1987) where the question of how it is accomplished cannot be answered by introspection on the part of the expert chicken-sexers (Harnad 1996). Instead, I shall focus on the first notion of breadth -- the idea that Carruthers has outlined here an account of the evolution of phenomenal consciousness that applies across a wide variety of experiences from different perceptual systems.

Carruthers draws attention to interpretive acts based on speech and gesture, as well as to a more general class of attributive acts that seem to have less to do with communication per se. Because intentional communication between humans takes place predominantly in the modalities of hearing and vision (and perhaps to some extent using touch), Carruthers' focus on these two modalities in the quoted passage seems designed to enhance the plausibility of his thesis that interpretation constitutes a driving force for evolution. But the thesis seems considerably less plausible with respect to other sensory modalities, particularly smell and taste. The way others look to us, sound to us, and the sensations they produce when they touch us are all possible targets of interpretation. But there seems little to interpret in the way other people smell and taste to us. I conclude that the mind-reading faculty has no need for access to smell and taste for interpretive purposes.

What about more general forms of attribution? Well, it seems trivially easy to think of scenarios in which it would be adaptively useful to know what another individual is smelling or tasting. And we also know that natural selection can operate on very small margins, so it is not out of the bounds of possibility that there could have been selection for mind reading with respect to smell and taste. But this just-so story needs fleshing out, especially in light of the fact that it is not a foregone conclusion that these perceptual systems should give rise to phenomenally conscious experience, for there is at least one perceptual system, the vomeronasal system (Monti-Bloch et al. 1998), which responds to pheromones and affects human behavior but with respect to which we utterly lack phenomenal consciousness. Indeed it seems much more straightforward to think of cases where it would be adaptively advantageous (not to mention potentially pleasurable) to know whether one's pheromones have been detected and are generating an intense desire for intercourse in a conspecific, than it is to think of adaptive scenarios for more mundane odors. It is far from clear why we have phenomenally conscious smell and taste but are oblivious to "vomerolfaction" (Cooper & Burghardt 1990).

At best, then, the