Motion-Induced Blindness and the Concepts of Consciousness
Excerpt on motion-induced blindness from my “The Neurophilosophy of Consciousness” (forthcoming in Max Velmans and Susan Schneider (eds.) The Blackwell Companion to Consciousness. Oxford: Basil Blackwell. ):
Regarding the question of qualia, of whether there is anything it is like for blindsight subjects to have stimuli presented to the blind regions of their visual fields, I take it that it is quite natural to reason as follows. Since they are not conscious of the stimuli and since the states that represent the stimuli are not conscious states, there must not be anything its like to have stimuli presented to those regions. Of course, the reader may doubt this claim if the reader is not a blindsight subject. It will be useful in this regard to consider a case that readers will be more likely to have first-person access to. For precisely this reason it is instructive to look at the phenomenon of motion induced blindness (Bonneh et al2001).
Motion induced blindness may be elicited in normal subjects under conditions in which they look at a computer screen that has a triangular pattern of three bright yellow dots on a black background with a pattern of blue dots moving “behind†the yellow dots. As subjects fixate on center of the screen it appears to them that one or more of the yellow dots disappear (although in reality the yellow dots remain on the screen). The effect is quite salient and readers are encouraged to search the internet for “motion induced blindness†and experience the effect for themselves. There are several lines of evidence that even during the “disappearance†the yellow dots continue to be represented in visual areas of the brain. The effect can be influenced by transcranial magnetic stimulation to parietal cortex (a relatively late stage of visual processing in the brain). Additionally, the effect can be shown to involve non-local grouping of the stimulus elements. So, for example, if the yellow dots are replaced with a pair of partially overlapping circles, one yellow and one pink—sometimes an entire circle will disappear leaving the other behind even though some parts of the two different circles are very close in the visual field. As mentioned previously, the brain mechanisms thought to mediate such object groupings are relatively late in the visual processing hierarchy.
We may turn now to the applications of the concepts of transitive consciousness, state consciousness, and qualia to motion induced blindness. First off, motion induced blindness looks to be a phenomenon involving transitive consciousness since in the one moment the subject is conscious of the yellow dot, in the next they are not conscious of the yellow dot, and along the way they are conscious of a yellow dot seeming to disappear. Second, we can see that motion induced blindness allows for applications of the concept of state consciousness, since studies of motion induced blindness provides evidence of conscious states that represent the presence of yellow dots as well as unconscious states that represent the presence of yellow dots.
Let us turn now to ask how the concept of phenomenal character applies in the context of motion induced blindness. The best grip we can get on this question is simply by asking what it is like is like see yellow dots disappear. When there is an unconscious state that represents the yellow dots or no transitive consciousness of yellow dot, there is, with respect to the yellow dot, nothing it is like to see it. Or, more accurately, what this instance of motion induced blindness is like is like not seeing a yellow dot. When the state representing the yellow dot is conscious, what it is like to be in that state is like seeing a yellow dot. One might suppose, then, as will be discussed later, that what it is like to be in the conscious state is determined, at least in part, by the representational content of that state. In this case, it is the content of the representation of a yellow dot.
Fig. 1: Motion-induced blindness ahead. Please slow down.
August 15th, 2006 at 6:29 am
[…] First off, according to advocates of the transitivity thesis it is supposed to be intuitively obvious that it is a requirement on having a conscious state that one is conscious of that state. If the transitivity thesis is true it should be obviously incorrect to say of a state that is was conscious before any one was conscious of it. However, if we consider a particular example, it seems that the transitivity thesis is not obviously correct (which is not, of course, to say that it is obviously incorrect). Consider, for example, how one might describe what happens in motion induced blindness experiments when the yellow dots pop into and out of consciousness. [See the demo at the end of “Motion-Induced Blindness and the Concepts of Consciousness“] It seems equally plausible to say either (1) that first the perception of the yellow dot becomes conscious and then you become conscious of your perception of the yellow dot or (2) the perception of the yellow dot becomes conscious only if you also become conscious of your perception of the yellow dot. If the transitivity thesis were pre-theoretically obvious, then option (1) would be obviously incorrect and (2) would be obviously correct. However, since neither (1) nor (2) seem obviously correct (or obviously incorrect), the transitivity thesis is not pre-theoretically obvious. […]