Intermediate Level Theory of Consciousnesskind of deficits are found in touch, as well; patients are able to match two different objects by
how they feel, but are totally unable to categorize those objects (as, say, cubes or cylinders). These
patients, then, suffer from an associative agnosia: they are able to experience the world consciously,
but cannot classify these experiences as belonging to this category or that. This is strong evidence
for the existence of an intermediate level of processing in these modalities, and evidence also for
consciousness arising at that intermediate level.
2 Attention Is the Mechanism by Which IRs Become ConsciousOne main worry for Prinz about the intermediate level hypothesis is that there is ample evi-
dence of activations at the intermediate level and beyond that does not coincide with conscious
experience. For example, Pessiglione et al. (2007) show the existence of subliminal motivation;
we can be motivated by stimuli of which we are unaware. These motivation-relevant structures
are in the forebrain, well after the processing of visual stimuli (at the intermediate level). Berti
et al. (1999) describe a subject with brain damage who can make accurate judgments about
whether objects he holds in his hands are the same or different, but who, due to the damage,
has no tactile experiences in one hand. The ability to make these comparative judgments, as
we have seen, is associated with intermediate level structures. Since we have good evidence for
intermediate level processing in the absence of consciousness, we have reason to believe that IRs
are not sufficient for consciousness. This is not necessarily a big surprise. So far, we have only been
concerned with figuring out where conscious states can be found in the information processing
going on in the brain, not necessarily with trying to theorize about what conditions or features
constitute consciousness.
To begin this extra theoretical work, there is a simple strategy to follow: compare those cases
where IRs are unconscious with those cases where IRs are conscious and see what the differ-
ence is. Whatever difference we find will give us interesting clues about the further constitutive
question. Not only will we (already) know where consciousness arises, we might also find out
how these IRs become conscious. For example, if we can find cases of people who are blind to
stimuli that other people usually see (or deaf to stimuli other people normally hear, etc.), so long
as the former process information through the intermediate level the same as the latter, we will
be in a perfect position to implement the strategy.
One locus of evidence that fits the strategy comes from unilateral neglect. In this condition,
patients usually suffer from damage to the right inferior parietal cortex. Given the wiring of
the brain, visual information that comes in from the left visual field is processed by the right
side of the brain (and vice versa)—even through to the parietal cortex. As a result, these patients
have a visual deficit for items in their left visual field. For example, if you present a subject with
unilateral neglect a series of lines and ask her to bisect the line exactly in the middle, she will
invariably bisect those lines with a mark that is far closer to the right end of the line than the
middle. Or, even more strangely, suppose you present such a subject with a series of pictures,
where the right side of each picture is the same front of a horse, while the left side of the picture
varies—sometimes it is the back of a cow, sometimes the back of a bicycle, and sometimes the
(normal) back of a horse. A patient with unilateral neglect will experience them as all the same;
the left side of the pictures and their obvious differences are invisible to such patients. Yet, and
this part is crucial, there is strong evidence that the invisible stimuli are being processed right on
through the intermediate level. Not only do these subjects fail to see what most people typically
see, but they appear to process these unseen stimuli in ways that others process stimuli that are
seen. To obtain evidence for all the processing, let us stick with the horse example. When asked
which of these identical horses seems the most real, patients typically select the correct horse