35-36 What is Perception?

Question 1

What percentage of the brain is involved in vision?

Answer 1

30% of 100,000,000,000 brain cells

Question 2

What is the function of the V4 area of the visual cortex?

Answer 2

It’s the colour module

Question 3

How about the medial temporal area (MT) of the cortex? What’s it for, doofus?

Answer 3

Detecting motion

Question 4

Where is the fusiform face area (FFA)?

Answer 4

It’s located in the fusiform gyrus, which runs from the temporal to occipital lobe

Question 5

What happens as we ascend the hierarchy of the visual cortex?

Answer 5

Receptive fields get larger - less spatial resolution

Receptive fields get more complex - complex selectivities

Receptive field responses correlate with perception (V4 - colour, FFA - face etc.)

Question 6

What is a Reichardt detector?

Answer 6

It’s a delay system neuron used for detecting direction and speed of movement

Question 7

How many saccades per second does the eye make?

Answer 7

Around 3 per second.

Question 8

What is the Waterfall Effect?

Answer 8

The effect whereby if you look at something moving in constant unidirectional motion for a long time (such as waterfall or movie credits), then look away, you see static objects move in opposite direction

Question 9

How can the Waterfall Effect be explained?

Answer 9

Motion detecting cells adapt to downward movement, causing less downward activity in sum of motion detectors. When stimulus ceases, cells return to below their resting level firing rate , causing the opposite effect (population of motion detectors is biased. Upward sum). It’s a motion aftereffect.

Question 10

How does colour constancy work?

Answer 10

While reflected wavelengths changes, relative brightness remains constant - brain processes colour in context.

Question 11

How can we focus on blue if there are no blue cones at the fovea?

Answer 11

Blue is filled in - brain extrapolates. Plus, their small number (5%) is enhanced by “blue amplifier” somewhere in brain.

Question 12

Why can’t we see 180 degrees in high resolution?

Answer 12

Brain not big enough to process all that data! We compensate by eye saccades.

Question 13

What features of the face are (not) detected by the FFA?

Answer 13

Size, colour, contrast don’t matter.

What’s important is oval exterior shape, presence of eyes and mouth.

FFA cells are also sensitive to viewpoint - some like front on, others 3/4, others profile. They show view dependence.

Question 14

What does FFA encode apart from face identity?

Answer 14

The FFA also encodes

expression

gaze direction

Question 15

What disorders are associated with face recognition deficits?

Answer 15

Autism; schizophrenia

Question 16

What does a local legion of FFA cause?

Answer 16

Prosopagnosia - inability to recognise faces

Question 17

What do inverted face tests such as the Thatcher illusion demonstrate?

Answer 17

Our facial recognition detectors show:

Strong orientation dependence (inverted face is harder to recognise)

Strong tendency to holistic processing (overrides sensitivity to parts - Thatcher illusion; composite illusion)

Question 18

What is perception?

Answer 18

Perception is the process of attaining awareness of our environment from sensory information

Question 19

What evidence is there for the existence of separate perceptual modules for vision?

Answer 19

Neurophysiology, fMRI and lesion studies

Question 20

What are the three kinds of colour blindness?

Answer 20

Protanopia – L-cone (red) missing

Deuteranopia - M-cone (green) missing

Tritanope - S-cone missing.

Question 21

What is perceptual bistability (rivalry)?

Answer 21

The bistable state produced by visual ambiguity

Question 22

What is binocular rivalry?

Answer 22

When two different images are simultaneously presented to the two eyes, you will only be conscious of one of the two images at a time.

Question 23

Why study binocular rivalry?

Answer 23

If you find the brain activity fluctuating with the switches in percept you’ve found the “neural correlate of consciousness”

Question 24

How does the Ames room work?

Answer 24

Viewer looks through a pinhole, and so the only depth cues are monocular - all of these suggest a square room. Interpretation: If the two people are at the same distance, but very different in retinal size, one must be a giant, and the other tiny!

Question 25

What are the two neural pathways for vision?

Answer 25

The dorsal and ventral

Question 26

What is the dorsal action (where) pathway?

Answer 26

The dorsal stream is proposed to be involved in the guidance of actions and recognizing where objects are in space. It’s fast & veridical motor “action” path. It goes directly from the retina, via the superior colliculus and the pulvinar, into the posterior parietal lobe, where it also gets input from V1.

Question 27

What is the ventral (what) pathway?

Answer 27

The ventral pathway is the slow perceptual path, prone to illusions. It is associated with object recognition and form representation. It stretches from the retina to the lateral geniculate nucleus to V1 to the inferotemporal cortex.

Question 28

If someone with lesion to lateral occipital cortex tries to match a letter to a letter slot, what happens?

Answer 28

Interference, as this task activates the ventral “what” pathway

Question 29

What is someone with lateral occipital lesion tries to post a letter?

Answer 29

Fine, as this action activates the dorsal “where” pathway - lateral occipital cortex not involved.