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Lecture 22

PHIL-UA 73 Lecture Notes - Lecture 22: Confabulation, Ataxia, Ned BlockPremium

2 pages74 viewsFall 2017

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Ned Block

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Two Visual Systems
Ned Block
1) Fast
a. Feeds to the top the head, dorsal visual systems
2) Slow
a. Feeds to ventral visual system in the occipital lobe and then into the temporal lobe
The most dramatic discovery was the one found by Andy Clark, in which 2 classes of patients were discovered:
- Patients have one function without the other (vise-versa)
- Rarest/most unclear patient: D.F.
o Something in DF’s shower emitted carbon dioxide, which destroyed a part of her brain between
the temporal and occipital lobes the lateral occipital complex.
She had visual-form agnosia. She could distinguish colors, shapes, and textures, but
not shades or forms. In particular, she was at chance on saying whether something
was horizontal or vertical. She could push a card through a rotating slot almost as
good at this as a normal person, but she could not say whether the slot was
horizontal or vertical.
Dorsal activity = good; ventral activity = bad
She can draw, but cannot recognize her own drawing.
- Optic ataxia: people who can describe what they see, but cannot pick things up or move them. They are
less pure than the other in that the areas that control motion are much larger. You need a lot of damage
- Dorsal has almost no memory, but the ventral system does
o If she is starting to post something and then closes her eyes, she cannot remember where
things and her actions are due to chance
- Dorsal specialized for fast behavior (ex: dribbling a ball)
o Clark: “the purpose of the ventral system is to plan visually guided actions. But the execution of
them is done by the dorsal system.”
- Dorsal feeds to peripheral
o Some people have the experience of running down the beach and avoiding the stones without
realizing it. You are seeing the stones unconsciously and feet are guided to miss them
- Illusions of the ventral system that do not fool the dorsal system
o A few of these are ones that fool the eye, but not the hand
Ex 1) Group of circles one of the circles
bigger to the eye because there are a
group of smaller circles around it. However, the hand is not fooled and the person
reaches for the bigger one (not surrounded by circles)
Ex 2) Series of lights the subjects hand was below them, and when one of the lights
lit up, subject was supposed to move his hand to the location and touch it.
Intervention: while the subject’s hand was in motion, the researcher
changed the light. The subjects found themselves reaching for the right one,
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