Blindsight

Question 1

Hemianopia

Answer 1

Patiens with unilateral lesions to V1 (CS & GY)
- Didn’t see anything in half of visual field

Tested motion perception, (15-20 degr./sec)
- accurately reporting stimuli
- If slower, not visible BUT when forced to guess, 80% correct

Shape discrimination
- Will always say I don’t see anything BUT guessing is always above chance.

Target position
- Eye movement and target finger pointing is almost fully correct

Other
- Spatial summation across the midline, faster RT to two stmuli in bland and intect than to one in intact (like normal)
- Attentional blink: still intact

Question 2

Blindsight

Answer 2

Even though it’s not the same as blind, result is a lot lower than ‘normal subjects’ so what is blindsight.

They’re best at locallization, motion and properties carried by the dorsal stream

Idea now:
- blindsight has lesion to primary visual cortex,, but it has a bypass to the posterior parietal cortex / MT (part of dorsal stream) through the SC and pulvinar.

Question 3

Support for alternative pathway

Answer 3

MT neuron responses in monkeys after V1 lesion. If stimuli shown in lesion zone, there’s still neurons showing weak response in MT. goes down but not gone.

Combined V1 and SC removal would cut that bypass, and result: totally abolishes the response. Max response of MT is mostly by V1 but also the SC

Pulvinar lesion (muscimol) also abolished the reaction.

Question 4

Monkey blindsight tasks

Answer 4

Dissociation is more difficult to know bc monkey can’t talk. Two tasks:

Forced choice task (FC)
- Fixation spot, target shown in affected hemifield. Monkeys have to make eyemovement to either up/down

Yes/no task (YN)
- Maintain fixation, shown target (so basically FC) OR no target is shown, in which case they have to maintain fixation (no task)

If trained to do this, they show the same dissociations as humans

Question 5

False alarm / correct rejection

Answer 5

Normal
- FC situation 100% correct
- YN situation (w stimulus) 100% correct
- YN situation (no stimulus) 100% correct

Affected
- FC is still high
- YN w stimulus is a lot lower (lots of miss)
- YN situation wo stimulus is still high

Meaning there’s blindsight in monkeys
Also; SDT reveals taht affected hemi shows drop in Da (sensitivity), independent of decision criterion. Meanign it’s unconscious vision (d’ of YN drops significanlty

Question 6

Superblindsight

Answer 6

Bilateral V1 lesion, still behaving almost normal *mostly monkeys, people tend not to trust their capabilities