Motion perception

Affordance

possibilities for action that an object or environment provides to an organism

Akinetopsia

a rare condition in which an individual is unable to detect motion despite intact visual perception of stationary stimuli, caused by damage to area MT

Anterior intraparietal (AIP) area

a region of the posterior parietal lobe involved in the act of grasping

Apparent motion

the appearance of real motion from a sequence of still images

Corollary discharge theory

the theory that the feedback we get from our eye muscles as our eyes track an object is important to the perception of motion

Correspondence problem (motion perception)

how the visual system knows if an object seen at Time 1 is the same object at Time 2

Focus of expansion

the destination point in an optic flow display, from which point perceived motion derives

Gradient of flow

the difference in the perception of the speeds of objects moving past us in an optic flow display

Induced motion

an illusion whereby one moving object may cause another object to look as if it is moving

Lateral intraparietal (LIP) area

an area of the primate parietal cortex involved in the control of eye movements

Medial intraparietal (MIP) area

an area of the posterior parietal lobe involved in the planning and control of reaching movements of the arms

Motion

a change in position over time

Motion aftereffect

a motion-based visual illusion in which a stationary object is seen as moving in the opposite direction of real or apparent motion just observed

Point-light walker display

an experiment in which small lights are attached to the body of a person or an animal, which is then filmed moving in an otherwise completely dark environment

Real motion

motion in the world created by continual change in the position of an object relative to some frame of reference

Reichardt detectors

neural circuits that enable the determination of direction and speed of motion by delaying input from one receptive field, to determine speed, to match the input of another receptive field, to determine direction

Phi motion

perception of motion produced by quickly alternating presentation of stimuli; illusory “shadow” image the same colour as background

ex: circle of dots, each dot disappearing and reappearing one by one, making it look like the circle is moving

Beta motion

perception of motion produced by sequential presentation of stationary images; these images appear to move

ex: three red dots presented at once, looking like a snake

Interstimulus interval

time between offset of frame 1 and onset of frame 2

SOA

time difference between the start of one stimulus and the start of another

Nearest-neighbor principle

select alternative that minimizes overall “traveling distance” of elements

Image displacement signal

detects motion across retina

Motor signal

muscle-movement info sent to eye muscles

Comparator

determines perception of motion; occurs when IDS is present or CDS is present but never both

Kinetoscope

first motorized film projector, co-invented by Thomas Edison

Critical flicker fusion

frequency at which a succession of stimuli appear to be on continuously

Short-range

low-level; occurs within the small visual angles (15-20’); governs real motion of stimuli

Long-range

higher-level; occurs in larger visual angles (20’-6 degrees); mechanism for apparent motion

Ecological approach

emphasized evolution, considered perception in the natural world, understanding motion of observer is important

Optic flow

stimulus array changes in a logical way as observer moves through the environment