chapter 8 part 2

Question 1

ecological approach to motion perception

Answer 1

approach to motion perception that focuses on aspects of the environment that we use for perception

Gibson - information for perception isn’t location on the retina, but rather “out there” in the environment

Question 2

optic array

Answer 2

the optic array is the structure created by the surfaces, textures and contours of the environment (basically the scene) - the ecological approach to motion perception focuses on how the movement of the observer (moving eyes?) causes changes in the optic array

Question 3

global optic flow

Answer 3

information for movement that occurs when all elements in a scene move - the perception of global optic flow indicates that it is the observer that is moving and not the scene

Question 4

local disturbance in the optic array

Answer 4

occurs when an object moves relative to the environment, so that the stationary background is covered and uncovered by the moving object - this local disturbance indicates that the object is moving relative to the environmentin

Question 5

corollary discharge

Answer 5

a copy of the motor signal that causes eye muscles to move - it gets sent to the comparator so that it knows that our eyes were moving

Question 6

three neural signals in corollary discharge theory

Answer 6

1. image displacement signal, which occurs when an image moves across the retina
2. motor signal, which is sent from the motor area to the eye muscles which cause the eye to move
3. corollary discharge signal, which is a copy of the motor signal

Question 7

when do we perceive movement under the corollary discharge theory?

Answer 7

when a brain structure called the comparator (number of structures) receives just one signal

Question 8

use corollary discharge theory to explain why we perceive movement when we follow moving objects with our eyes

Answer 8

because our eye movement causes a corollary discharge signal

but there is no displacement signal because the image stays in the same place on our retina - bc we are moving our eyes w it

means that the comparator receives only one signal = movement perception

Question 9

use corollary discharge theory to explain why we perceive movement when we keep our eyes stationary as something moves past us

Answer 9

no corollary discharge signal because our eyes aren’t moving

there is a displacement/image movement signal because the object in motion moves across the retina

only one signal reaches to comparator = movement perception

Question 10

use corollary discharge theory to explain why we don’t perceive movement when we scan our eyes around a room

Answer 10

moving our eyes = corollary discharge signal

there is also an image movement/displacement signal because everything we scan moves across our retinas

2 signals sent to the comparator = no movement perception

Question 11

the reichardt detector

Answer 11

a neural circuit proposed by werner reichardt in which signals caused by movement of a stimulus across the receptors are processed by a delay unit and an output unit so that signals are generated in one direction but not in the opposite direction

Question 12

single neuron responses to motion

Answer 12

certain complex cells in the brain respond to specific movement in a particular direction

these neurons are found in the visual cortex and in other areas of the brain - middle temporal area (MT) is a big one

Question 13

reichardt detector output unit

Answer 13

component of the detector that compares signals received from two or more neurons - activity in the unit is necessary for motion perception

it is also able to multiply responses from neurons in order to create the movement signal that results in the perception of motion

Question 14

reichardt detector delay unit

Answer 14

component of the reichardt detector proposed to explain how neural firing occurs to different directions of movement - the delay unit delays the transmission of nerve impulses as they travel from receptors toward the brain

Question 15

how does the reichardt circuit explain movement from left to right (example)

Answer 15

movement from the left activates neuron A - response moves towards the output but is slowed by the delay unit - during delay movement continues and stimulates neuron B which reaches the output unit at the same time as the delayed signal from neuron A - output unit multiplies the responses and a large movement signal is created

Question 16

evidence for motion perception in the middle temporal area (MT)

Answer 16

moving dot displays
lesioning MT cortex
transcranial magnetic stimulation
microstimulation

Question 17

moving dot displays

Answer 17

• group of dots moving randomly
  -coherence indicates the degree to which dots move in the same direction
• activity in MT/ability to identify direction goes up with coherence - can see it in brain scans of monkeys

shows relationship between perception of motion and neural firing in the MT cortex

Question 18

motion detection in lesioned MT cortex

Answer 18

monkeys who have had their MT cortex lesioned require much more coherence (10 to 20 percent as opposed to 1 or 2) before they can detect the direction of motion

Question 19

Transcranial magnetic stimulation of MT cortex

Answer 19

temporarily disrupts the normal functioning of neurons

ps have difficulty determining the direction in which a random pattern of dots was moving - temporary form of akinetopsia

Question 20

microstimulation of MT cortex

Answer 20

enhances normal neural activity
- small wire electrode gets placed into the cortex and delivers a weal electrical charge that stimulates neurons and causes them to fire

can stimulate different neurons in the MT cortex to influence how we perceive motion