^Two aspects are essential to externalist theories.
] They make reliable accuracy the central quality for determining whether a certain cognitive process is a source of knowledge. In the case of sense perception, this means that only those sensory processes that reliably give us accurate information about the world will count as potential sources of knowledge.
] They don’t require us to be aware of the operations of the processes that give us information. This means that externalist theories—in contrast with internalist theories—allow that it is possible that we can be unaware of the process we are employing to acquire information and of whether that process is in fact reliably accurate. In the case of sense perception, this means that we at least sometimes acquire information on the basis of sensory processes of which we’re unaware or about whose accuracy we’re unaware.
^There is a great deal of support from cognitive psychology and neurobiology for both of these components of externalism.
One example is the existence of dual streams of cognition for the
processing of visual information, and another involves what neurologists call brain bilateralization, the fact that the two halves of the brain are specialized for different tasks that they can perform independently.
] One way that brain functions are specialized is between the dorsal and ventral streams. The visual cortex, the region of the brain that is responsible for receiving information from the eyes, is located at the back of the brain.
The dorsal stream—or the “where”
pathway—runs along the top of the cortex. It’s the visual system that aids in determining the spatial location of the objects around us, preparing us for any actions that we might want to perform with those objects. The other pathway is called the ventral stream—or the “what”
pathway—and it is located on the underside of the cortex. It’s the network responsible for the visual identification of objects.
Theories of Knowledge LECTURE 8 Perception: foundationalism and externalism
] The brain has two halves, or hemispheres, which are joined by a very densely packed strand of nerve cells called the corpus callosum.
There are some neurosurgical procedures, called split-brain surgeries, that require cutting the corpus callosum so that the two hemispheres of the brain can no longer communicate. For many years after the first split- brain surgeries were performed, neurosurgeons didn’t think that cutting the corpus callosum had any effect on brain function.
Certainly, split-brain patients didn’t claim to notice any difference before or after the surgery. That was the thought until neuroscientist Michael Gazzaniga began studying split-brain patients and found that the two sides of the brain are unable to make sense of what the opposite side is aware of.
^The phenomena of dual-stream pathways for visual information processing and of split-brain cases seem to provide evidence for both of the aspects of sense perception that support externalism.
] Both involve evidence that some cognitive systems are more reliably accurate in either gathering or evaluating information in perception.
] Both support the idea that we are often unaware of the processes we actually employ in sense perception and that we are often equally unaware of whether or why the processes we employ are reliably accurate.
^This suggests that, at least in the case of sense perception, externalism provides the best account for explaining the structure of knowledge.
T o study the inability of the two sides of the brain to make sense of what the opposite side is aware of, Michael Gazzaniga and his team of researchers flashed an image to each eye of a split-brain patient while keeping that image hidden from the other eye. At the same time, they gave each patient’s hand an option to choose from one of four pictures that best matched the image. In other words, the left hand could choose from the pictures that matched the image that the left eye saw, and the right hand could choose from the pictures that matched the image that the right eye saw.
Theories of Knowledge LECTURE 8 Perception: foundationalism and externalism
One very dramatic illustration of the results of
Gazzaniga’s research with split-brain patients is the case of a subject referred to as P.S.:
P.S. had seen a chicken claw with his left brain, and his right hand chose a picture of a chicken.
His right brain had seen a picture of a snow scene, and his left hand picked up a picture of a shovel. When asked why he had done all of this, he said from his left hemisphere, ‘The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.’
This suggested to Gazzaniga that there is a special mechanism in the brain—which he calls the interpreter—
that is responsible for explaining our behavior to
ourselves. It concocts a plausible story for us about what is going on in our heads when we pause to think about what we’re perceiving or thinking. But importantly, what the interpreter concocts is just a story—one that’s often not very accurate.
]Jackson, Perception.
Noe, Action in Perception.
]
reAdings
yTheories of Knowledge LECTURE 8 Perception: foundationalism and externalism
QUIZ
1 What is the type of foundationalism that claims that the basis of sensory knowledge is our immediate, qualitative experiences of phenomena like color patches, shapes, or regions of light?
a Experience-based internalist foundationalism
b Naive internalist foundationalism 2 TrUe or fAlse
Patrick Cavanagh’s work on the physics of shadows provides evidence in favor of the claim that the inferences on which our sensory knowledge is based are the result of the sort of personal processes that the experience-based internalist foundationalist suggests.
3 TrUe or fAlse
The problem for naive internalist foundationalism is that the naive foundationalist cannot appeal to the reliable accuracy of sense perception to explain why sense perception supports knowledge.
4 If you see an object in your vicinity and track its location relative to you, that’s a result of what?
a Your brain’s dorsal stream b Your brain’s ventral stream 5 According to Michael Gazzaniga,
our conscious experiences are a result of which of the following?
a The intrinsic experiential qualities in the objects themselves b A special module in the left
hemisphere of the brain that makes up an explanation of the information processed in the brain
c Brain activities distributed across both brain hemispheres
d All of the above e None of the above
Theories of Knowledge LECTURE 8 QUIZ