Chapter 8

Question 1

What is attention capture?

Answer 1

When motion attracts our attention and forces us to notice something (also of evolutionary importance)

Question 2

What are some of the functions of motor perception?

Answer 2

Different viewpoints can help disambiguate an ambiguious retinal image (motion provides information about objects).

Question 3

How quickly does it take us to detect gender and mood respectively in a point light display?

Answer 3

Gender: 100ms.
Mood: 1/2 second.

Question 4

What is real motion versus illusory motion versus apparent motion?

Answer 4

Real motion: Actual motion of an object through space
Illusory Motion: Perception of motion when there is none physically
Apparent Motion- Two (or more) stimuli in different locations alternately flash on/off-with correct timing, there is a perception of motion

Question 5

What are some examples of apparent motion?

Answer 5

movies and TV, flipbooks, theatre marquee

Question 6

What are motion after effects?

Answer 6

Watching a continuously moving stimulus for 30-60s, then switching to look at a stationary object often produces the illusion of movement in the opposite direction.

Question 7

What was the study that Larsen et al did to see if real and illusory motion were actually separate?

Answer 7

fMRI study with 3 conditions: a) 2 flashing lights simultaniously. B) real motion. C) Apparent motion (illusory motion timed to produce apparent).

Question 8

What did Larsen et al find in their study?

Answer 8

Both real and apparent motion activate similar regions-apparent motion activates the area in between the two regions even though there was no stimulus.

Question 9

What is the Reichardt Detector theory proposed by Werner Reichardt?

Answer 9

Early hypothetical model for how a neural circuit could code for specific patterns of motion-must include some sort of delay mechanism. Modern ones use an inhibitory connection. Found in primates in V1 and some retinal ganglion cells of other species.

Question 10

Why do we need a delay between the two neurons to detect motion?

Answer 10

To tune neurons to specific directions and speeds of motion-delay in signal 1 slows down the impulse so that signal 1 and 2 can fire at the same time, causing increased excitation. Neurons are tuned to specific directions (where delay is) and speed (length of delay)

Question 11

Can the Reichardt detector also be stimulated by apparent motion?

Answer 11

YES. Explains why it is perceived like real motion.

Question 12

What is one of the issues with the Reichardt detector theory?

Answer 12

The theory involves something moving across our field of vision, and we dont track it with our eyes. The issue is, if we do track it with our eyes, the object remains in the fovea, so how do we perceive motion then?

Question 13

What is the corollary discharge theory?

Answer 13

Theory that takes into account eye movements- movement of object+movement of eyes = 3 different types of neural signals

Question 14

What are the 3 different types of neural signals in corollary discharge theory?

Answer 14

Image displacement, motor signal, corollary signal

Question 15

What is image displacement?

Answer 15

When the object moves across the receptive field

Question 16

What is the motor signal?

Answer 16

Sent from the brain-eye muscles (allows us to track the object)

Question 17

What is the corollary signal?

Answer 17

Copy of the motor signal, but goes everywhere else in the brain (usually visual cortex).

Question 18

What do we have to have in order for us to see motion in the corollary discharge theory?

Answer 18

Have to have 1/3 of the signals. If all are present, then there is no motion because they cancel each other out!

Question 19

What is some behavioural evidence for the corollary discharge theory?

Answer 19

Afterimages move with our eyes-there is no image displacement signals in this, but there are motor/corollary signals. Can also see motion when pushing on the eyelid (image displacement due to eye rotating slightly with pressure0

Question 20

What is some physiological evidence for the corollary discharge theory?

Answer 20

Patient R.W.-had damage to medial superior temporal area-environment appeared to swirl around him. Loss of corollary discharge signal, so, therefore, would see things move but would have nothing to cancel out the image displacement.
Single-cell recordings in monkeys- neurons respond when a bar moves across the receptive field. Then, have the monkey track a fixation point while the bar is stationary (move receptive field across the bar). Neuron doesn’t fire, suggests corollary signal cancelling image displacement.

Question 21

What is area MT?

Answer 21

Middle temporal area, part of the dorsal stream. Neurons respond selectively to motion, tuned to different directions and speeds. Does not respond to shape, curvature, or colour. Receptive fields are 5-10X larger than those in V1 (good to detect large scale motion)

Question 22

What happens when there is damage to area MT?

Answer 22

Akinetopsia-inability to perceive motion (when things move, it looks like a strobe light)

Question 23

What happens when area MT is stimulated?

Answer 23

Shifted motion perception (vertigo like)

Question 24

What is the aperture problem?

Answer 24

Each motion detector has a receptive field that only covers a small portion of a larger object-makes direction of motion of the object ambiguous.

Question 25

What is the solution to the aperture problem?

Answer 25

Combine inputs across several different “Motion detectors” each tuned to a different direction. MT neurons combine inputs from cells in V1 to solve the aperture problem