Readings 8-10 Flashcards
Reading 8: why did they study patient CB?
CB has damage to his right occipital lobe (right visual cortex, damage to V1). So, he has no vision in the left visual field. They used this to study his visuomotor task performance in his blind field with and without a 2s obstruction/delay of visual information.
Reading 8: what were the results?
Without the delay, CB performed similarly to controls in his sighted field and blind field (was able to reach for a target while avoiding obstacles).
With the delay, CB was no longer able to perform well in his blind field. He still performed similarly to the controls in his sighted field.
Reading 8: what are the mechanisms that explain the results?
Due to the blindsight phenomenon and subcortical visual pathways, CB could avoid the obstacles in his blind field without noticing their presence.
CB’s dorsal/motor system is intact, while is ventral/perceptual stream is affected. When vision is obstructed 2s before the reaching movement, he is forced to work off memory, and therefore has to work off the damaged visual system. Therefore, the blindsight effect is abolished with the 2s delay.
Reading 9: what illusion did they study? What was their hypothesis?
It was a depth perception illusion: a normal protruding face, a hollow face that looked hollow, and a hollow face that looked normal (illusionary).
They hypothesized that when doing fast, motor tasks (flicking off targets on the faces), people will rely on the dorsal stream, and reach for the targets’ true locations. While doing perceptual tasks (deliberate pointing, drawing where they think the targets are), people will point to/draw the illusionary target position.
Reading 9: what were the results?
Drawing task: a robust illusion effect. People drew the illusionary face target locations similar to the normal face target locations, meaning that they perceived the illusionary face to be protruding. They perceived the hollow face to be hollow.
Flicking task: People were able to flick the targets at their true locations for all the faces.
Pointing task: similar effects as the drawing task. They fell for the illusion.
Reading 9: what mechanisms explain the illusion effect?
Motor tasks (flicking) trigger the automatic system, where motor information is received before it reaches conscious awareness. Perceptual tasks (deliberate pointing, drawing) don’t trigger the automatic system, and rely on conscious perception/the ventral stream/immediate memory. This presents a dissociation between visual systems.
Reading 10: how does patient SB differ from the controls?
SB has callosal agenesis, where she has impaired communication between brain hemispheres. Therefore, she experiences latency in contralateral/crossed tasks (where the target appears in the visual hemisphere opposite to the responding limb).
Reading 10: what were the results for the simple RT tasks and reach adjustment tasks?
SB showed an increased latency difference between crossed and uncrossed conditions (36ms) compared to the controls (2ms). However in the reach adjustment task, SB showed no latency differences compared to the controls.
Reading 10: what mechanisms allow SB to have similar reach adjustments to the controls?
Due to the involvement of subcortical structures in automatic movements, and the saccadic eye movement system.
The automatic process is only triggered during movements, not in simple RT tasks.