2 - Perceptual illusions Flashcards
Explain why the original receptive field belief is incorrect
The original receptive field belief is the belief that a neuron only reacts to what is inside of its RF. Van der Heydt’s study has shown that a neuron can also respond to an illusory contour. In order to react to an illusory contour, the neuron needs to have information from outside its RF. Therefore it not only reacts to what is inside its RF but apparently also reacts to what is outside its RF.
Explain why contour/object processing is not a high-level process
In the high-level contour processing view, it is thought that cognition is needed to know that there is an object or a contour. Van der Heydt has shown that this processing happens way earlier as the V2 neurons respond to both real contours and illusory contours. Especially the fact that they react to illusory contours means that the V2 neurons somehow know that the parts outside of its RF, that make the illusory contours visible, somehow belong together to the same object.
As the distance between the target and the mask increases, what happens to suppression?
Suppression is only obtained with greater target/mask delays as edge distance increases
As target size increases, what happens to suppression and masking?
Brightness suppression increases as the size of the target increases. As size of target increase, masking is obtained at longer delays
Why is it logical that there is a shorter latency when CRF was at boundary than when it was centered?
The spreading starts at the edge, therefore the response is fast. It takes time to get to the center, therefore the response is slow.
What is the method of Van der Heydt?
Electrophysiological study on monkeys. doing a visual fixation task. edges, bars and illusory contours were moved back and forth across the RF. Activity of V2 and V1 neurons were measured.
What is the method of Paradiso?
target -white disk, mask - white circle. should produce an illusory percept. Subjects were instructed to make brightness match between specified area of the target and a pallette of gray tones from black to white
What is the method of Huang?
Recordings in monkeys, fixation task. Examined temporal response pattern of V1 neurons to uniform surfaces and compared response timing with stimulus borders at different locations relative to RF.
Stimuli : uniform surface and oriented bar of light - temporal response patterns. large uniform disk with boundary and center condition - comparing response latencies to surface interiors and boundaries
changing uniform disk in size - comparing response latencies to uniform disks of different sizes
