Change blindness is one of those surprising things that cognitive science has revealed about the nature of conscious experience. It turns out th at there can be rather large changes in the visual scene a person is looking at and that most people will completely miss them! I am not talking about small changes but rather very large changes right in front of the faces that are actively looking for changes (for some nice examples see this link). Once one sees the difference it is so obvious that ones attentionis drawn to it every time, but for a while it really looks as though there is no difference between the two pictures.
Any theory of consciousness should be able to account for this phenomena. Fred Dretske, in his well known paper “Change Blindness” (requires a password), gives the following account of what is going on in instances of change blindness. He distinguishes between thing-awareness and fact-awareness. Thing awareness is our being conscious of some physical thing in the world. Examples include seeing blue, hearing music, etc. Fact-awareness is our being conscious of some fact. From the way that Dretske talks about fact-awareness it sounds like it consists in having the appropriate belief, but to be honest I am not sure exactly what his view is on this (especially given that he seems doubtful as to whether or not having a belief makes one conscious of anything in the first place).
Given these distinctions he then gives his account of change blindnessas follows. When one is looking at the two pictures one is thing aware of them, where this means that one sees the two pictures. But one is not fact-aware that there is a difference between them. This view is contrasted with what he calls the ‘object view’ which claims that one sees both of the pictures and the difference between them but does not notice that one is seeing the difference.
The object view is pretty much what the higher-order thought theory of consciousness predicts. On that kind of theory one is in a first-order visual state that represents both pictures but one is also in a higher-order state that (mis)-represents the first-order states as not differing. That is, one is conscious of the difference between the two pictures but one is not conscious of it AS the difference. Dretske takes change blindness to be a counter-example to the transitivity principle as he thinks that what we have is a case of a conscious experience (the experience of the thing that is different as between the two pictures) but that we are not conscious of having.
So which of these two accounts is right? This recent article on change blindness and priming seems to me to offer evidence against Dretske’s account (not to mention evidence against ‘naive realist’ and anto-representationalist views generally). In the experiments subjects were presented with two alternating pictures of numbers arranged in rows and columns. In the second picture one of the numbers was changed and subjects failed to notice this change. Nonetheless both the unchanged number and the changed number showed a priming effect. What this suggests is that both pictures are represented by the visual system even though both are not consciously experienced. When one looks at the two pictures they look the same! One can spend minutes examining those pictures convinced that there really isn’t any difference between them and the whole thing must be a joke. But it isn’t. There is a difference and it is a strikingly large difference. So even though there is nothing that it is like for you to be conscious of the thing that makes the difference between the two pictures, you are conscious of it; just not as the difference. How is this going to be explained on a first-order view like Dretske’s
The other interesting thing about this study was that they found that when the change is detected, that is when one sees the two pictures and notices that the second one is different, then it is only the second picture’s information that does any priming. They suggest that the first representation is still there but is inhibited…this might pose a problem for Rosenthal’s argument that conscious states do not have any fucntion…but I will leave that for another time…