Biased competition

Question 1

Crowding

Answer 1

Inability to identify objects when surrounded by other objects in the peripheral vision.

Small RFs can resolve this problem (eg in foveal)
RF in peripheral are larger, which is why they can’t resolve it. The surrounding letters are crowding the RF, interfering with the middle stimuli

Question 2

Neural firing in V4

Answer 2

When preferred stimulus is shown with a non-preferred in the same RF, the response is reduced, almost to none. When the contrast of that non-preferred is lowered it fires again.

Question 3

Biased competition

Answer 3

Model of attentional selection (desimone)

High level neurons have large RF, so when there’s two stimuli there’s competition.
Attention can bias this competition so that the response is the same as when the stimulus is presented alone.

This is why you can see the T if you use covert attention

Question 4

fMRI proof

Answer 4

Experiment with fMRI signals in two conditions:

Sequential condition (SEQ) where stimuli are presented 250 ms each after each other

Simultaneous condition (SIM) where stimuli are presented all together for 250 ms

Due to low temporal resolution, you’d expect the same response for both conditions
- Is the case in V1 neurons (small RF, so same stimuli)
- in V4, you see the effect of crowding, The SEQ condition gives stronger response, the SIM remains same due to crowding.
- Resolved if attention is focussed to 1 area, result similar to V1 case.

Question 5

Attentional causes

Answer 5

1. Increase firing rate and synchrony of attended locations/features/objects
2. Allow for feature binding and faster responses
3. Mostly: resolve competition between responses in the same RF, so better discrimination and less crowding.