Colour and qualia

5. Objections to functionalism

The basic objection to a functionalist account of subjective colour, or of any qualitative experience, is that it just seems intuitively plausible that functional red and subjective red could come apart. The mismatch goes in both directions. That is, according to the famous absent and inverted qualia hypotheses, it seems quite possible that a creature could satisfy the conditions for functional red even though not experiencing subjective red, or, for that matter, having any qualitative experience at all. On the other hand, it also seems quite possible that a creature could experience subjective red even though most of the causal relations it normally maintains were absent (this is less emphasized in the literature).

An example of the first sort of problem is the famous ‘inverted spectrum’ thought experiment. As we noted above, colour experience is a function of three basic features: hue, brightness and saturation. Colour quality space can be modelled then as a three-dimensional solid; in fact, a cone. The vertical dimension represents brightness, the horizontal represents saturation, and the circular dimension represents hue. Given this model, there seems to be a mapping of points in the space onto their complements around an axis that bisects the cone through the middle. Reds would be mapped onto greens, blues onto yellows, and so on. The resulting cone would be isomorphic to the original in the sense that all the distance/similarity relations among points would be maintained.

Given this characterization of an inversion, take two creatures, one of whom has a colour quality space described by the original cone and the other of whom has one described by the inverted cone. If we are just looking at the relational properties – those involving causal relations to external stimuli, internal mental states, and behaviour – it seems that the two creatures would be functionally isomorphic. Yet, when looking at a red fire engine one would be having a reddish experience and the other would be having a greenish one. In other words, while they would both satisfy the criteria for functional red, one would be having an experience of subjective red and the other of subjective green. So, subjective red cannot be identical to functional red.

The ‘absent qualia’ hypothesis represents an even more extreme possibility. Ned Block (1980) asks us to imagine the entire nation of China (or any similarly large group of individuals) organized, say, by telephone, so as to realize the functional organization of a human brain. Let us also imagine that this vast network is connected to a robot which has a video camera for an ‘eye’. When the robot is stimulated by light from a fire engine the network will go into a state of functional red, by hypothesis. Yet, it seems quite bizarre to claim that the robot, the network, or the system comprising both, is having a qualitative experience. Thus we have a case of functional red without subjective red (or any qualitative character at all).

An example of subjective red without the normal causal connections could occur if someone’s normal functioning were disturbed, so that various relations between their colour experience and memory, belief and the like no longer held. It seems possible that this could happen while the qualitative character of their experience remained unchanged. One concrete case of this is colour blindness. The fact that someone cannot distinguish red from green obviously affects the structure of their colour space, yet it is not obvious that this makes their experiences of blue any different from mine.