Motion Perception

Question 1

texture-defined (contrast-defined) object

Answer 1

An object that is defined by changes in contrast, or texture, but not by luminance.

Question 2

smooth pursuit

Answer 2

A type of voluntary eye movement in which the eyes move smoothly to follow a moving object.

Question 3

akinetopsia

Answer 3

A rare neuropsychological disorder in which the affected individual has no perception of motion.

Question 3

correspondence problem

Answer 3

In motion detection, the problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a particular feature in frame 1.

Question 3

microsaccade

Answer 3

An involuntary, small, jerklike eye movement.

Question 4

saccade

Answer 4

A type of eye movement, made both voluntarily and involuntarily, in which the eyes rapidly change fixation from one object or location to another.

Question 5

middle temporal area (MT)

Answer 5

An area of the brain thought to be important in the perception of motion.

Question 6

motion aftereffect (MAE)

Answer 6

The illusion of motion of a stationary object that occurs after prolonged exposure to a moving object.

Question 7

superior colliculus

Answer 7

A structure in the midbrain that is important in initiating and guiding eye movements.

Question 8

saccadic suppression

Answer 8

The reduction of visual sensitivity that occurs when we make saccadic eye movements. Saccadic suppression eliminates the smear from retinal image motion during an eye movement.

Question 8

second-order motion

Answer 8

The motion of an object that is defined by changes in contrast or texture, but not by luminance.

Question 8

vergence

Answer 8

A type of eye movement in which the two eyes move in opposite directions; for example, both eyes turn toward the nose (convergence) or away from the nose (divergence).

Question 9

apparent motion

Answer 9

The illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession.

Question 10

optic array

Answer 10

The collection of light rays that interact with objects in the world that are in front of a viewer. Term coined by J. J. Gibson.

Question 12

aperture

Answer 12

An opening that allows only a partial view of an object.

Question 14

interocular transfer

Answer 14

The transfer of an effect (such as adaptation) from one eye to the other.

Question 15

tau (τ)

Answer 15

Information in the optic flow that could signal time to collision (TTC) without the necessity of estimating either absolute distances or rates. The ratio of the retinal image size at any moment to the rate at which the image is expanding is tau, and TTC is proportional to tau.

Question 16

time to collision (TTC)

Answer 16

The time required for a moving object (such as a cricket ball) to hit a stationary object (such as a batsman’s head). TTC = distance/rate.

Question 18

focus of expansion

Answer 18

The point in the center of the horizon from which, when we’re in motion (e.g., driving on the highway), all points in the perspective image seem to emanate. The focus of expansion is one aspect of optic flow.

Question 19

comparator

Answer 19

An area of the visual system that receives one copy of the command issued by the motor system when the eyes move (the other copy goes to the eye muscles). The comparator compares the image motion signal with the eye motion signal and can compensate for the image changes caused by the eye movement.

Question 20

luminance-defined object

Answer 20

An object that is delineated by changes in reflected light.

Question 22

first-order motion

Answer 22

The motion of an object that is defined by changes in luminance.

Question 23

biological motion

Answer 23

The pattern of movement of living beings (humans and animals).

Question 24

aperture problem

Answer 24

The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous.

Question 25

optic flow

Answer 25

The changing angular positions of points in a perspective image that we experience as we move through the world.

Question 26

reflexive eye movement

Answer 26

A movement of the eye that is automatic and involuntary.