^The second problem with indirect perceptual realism is that it sees the role of the senses as being able to provide us with phenomenal sensory experiences. But this is simply mistaken. Rather, the role of the senses is to provide us with information about the world around us.
^These two problems may seem bad enough for indirect perceptual realism, but there is an even bigger problem for the view, at least from our perspective: According to indirect perceptual realism, all we immediately perceive is our own perceptual experiences, rather than the objects that those experiences are about. But that’s a claim about the immediate objects of our experiences.
^The technical term for that subject matter is metaphysics—the study of the basic building blocks of reality and their relations to each other.
That’s not what we’re primarily concerned with. We’re interested in knowledge and how to get it. So, we’re interested in the building blocks of knowledge, such as beliefs, and what makes some beliefs count as knowledge.
^And the point now is that the beliefs we form on the basis of sense perception are not primarily beliefs about our experiences. They’re beliefs about phenomena in the world that we care about: people, places, and things.
^But indirect perceptual realism is a theory about the objects of our perceptual experiences, not about the objects of the beliefs based on those experiences. So, even if indirect perceptual realism were true, that would have no direct bearing on the relation between sense perception and knowledge.
I n the remainder of this lecture, we’ll begin to tackle the first question. In particular, we’ll
consider whether there is a good reason to suppose that coherentism offers the best explanation for how sense perception supports knowledge.
In the next lecture, we’ll first consider whether there is good reason for thinking that internalist foundationalism offers the best explanation for how sense perception supports knowledge or whether we ought to endorse some form of externalist explanation instead.
^There are two different types of distinctions that we can make when we talk about perceptual processes, and the relation between those two types of distinctions is liable to cause confusion.
^First, it’s important to distinguish between computations that you perform and computations that your brain performs but that you have no access to. Philosophers sometimes call the first type of processes—the ones that you normally have access to and at least some control over—personal processes. And they call the second type of processes—the ones that are performed by organs or systems of organs in the body, without direct access or control by the person whose body it is—subpersonal ones.
^The second distinction is between what cognitive psychologists refer to as top-down and bottom-up processes.
^A bottom-up process is one that arrives at a result from more basic inputs, where each of those inputs is computed independently. A bottom- up theory of visual perception would suggest that information is transmitted in one direction from the retina to the visual cortex. On this type of theory, each stage in the mechanism for the processing of visual information involves increasingly complex analysis of the information transmitted from the immediately preceding stage.
Theories of Knowledge LECTURE 7 does sense Perception support Knowledge?
^Common versions of bottom-up theories include the idea that the neurons involved in each stage of visual information processing are highly specialized to perform a very specific type of computation. For example, there are neurons that just perform detection of light versus dark, or of edges that are oriented in a certain direction, or of motion.
^In opposition to bottom-up views of perceptual information processing are top-down views. According to top- down theories, the brain is able to use higher-level information as feedback for more basic sensory processing mechanisms in the brain. Top-down theorists reject the idea that the processing of sensory information in the brain moves in only one direction, from the more basic to the more complex. Instead, they suggest that the more complex computational mechanisms in the brain can provide feedback for earlier mechanisms.
^A number of the pieces of evidence cited in favor of top-down theories have to do with the fact that your semantic knowledge—your knowledge of concepts and meaning—can affect what you perceive.
^There seems to be at least some evidence for top-down processing of sensory information in the brain. And top-down processing involves taking context into account before deciding how to interpret information. And this, in turn, should remind you of coherentism—about the way in which beliefs can be justified enough to count as knowledge.
^Remember, coherentism says that what makes an instance of true belief count as knowledge is that the belief fits together with the rest of your information. And the top- down theory says that your sensory processing system takes different pieces of information and interprets them based on how they best fit together given the context.
^Does that mean that the cognitive science of perception supports coherentism? That would be very strong support for the theory, but unfortunately for coherentism, top- down theories don’t offer support for any theory of the structure of knowledge.
Theories of Knowledge LECTURE 7 does sense Perception support Knowledge?
I f all sense perception involved top-down processing, then we would expect newborns not to be able to perceive anything at all until they developed the concepts to help them make sense of what William James called the “blooming, buzzing confusion” of their immediate sensory stimuli.
This, however, is not the case. For example, newborn human infants seem to show a preference for face shapes over scrambled stimuli—as early as a few minutes after they’re born.
^One problem is that top-down theories cannot tell the whole story of sense perception. There must be at least some room for bottom-up explanations as well.
^The second problem for coherentism is even more serious. In order for some empirical evidence to support one of the theories of internalist justification, such as coherentism, it would have to involve personal computational mechanisms. That’s because coherentism is a theory about what goes on in the mind, rather than about the subpersonal mechanisms
that are plugging away below the surface of your awareness or control.
^The debate between top-down and bottom-up explanations, however, is best understood as involving just those sorts of subpersonal mechanisms.
That’s because the debate is supposed to involve the sorts of computational processes to which you normally have no access and over which you normally have no control. So, even if the best explanation of sense perception is top- down—and there is reason to question whether that’s even the case—it would still not support coherentism.
]Lehrer, “Coherence, Truth, and Undefeated Justification.”
Russell, The Problems of Philosophy.
]
reAdings
Theories of Knowledge LECTURE 7 does sense Perception support Knowledge?
QUIZ
1 TrUe or fAlse
The argument from illusion attempts to establish that what you immediately perceive in sense perception is your own subjective experiences.
2 TrUe or fAlse
People with visual agnosia can accurately sketch the features of the objects that they see, but they cannot recognize those objects.
3 TrUe or fAlse
The most plausible understanding of our sensory systems is that their role is to provide us with phenomenal sensory experiences that enrich our inner mental lives.
4 What does the discussion of the Citizen Kane example tell us?
a Indirect perceptual realism really is the only correct view of sense perception.
b Indirect perceptual realism only makes sense in the case of viewing movies, photographs, etc.
c Even if indirect perceptual realism is true as a theory in metaphysics, it is in fact irrelevant to discussions in epistemology.
5 David Hubel and Torsten Wiesel’s research establishing the existence of specialized neurons for the detection of very specific features of visual stimuli would seem to be an example of which of the following?
a Subpersonal, top-down processing
b Subpersonal, bottom-up processing
c Personal, top-down processing d Personal, bottom-up processing
Theories of Knowledge LECTURE 7 QUIZ