Psyc 367 (UAlberta- Farley) Ch. 8 Perceiving Motion

Akinetopsia

A condition in which damage to an area of the cortex involved in motion perception causes blindness to motion.

an inability to perceive motion

Aperture Problem

Occurs when only a portion of a moving stimulus can be seen, as where the stimulus is viewed through a narrow aperture or through the "field of view" of a neurons' receptive field. This can result in misleading information about the direction in which the stimulus is moving.

Apparent Motion/Movement

An illusion of movement that occurs when two objects separated in space are presented rapidly, one after another, separated by a brief time interval.

Biological Motion

Motion produced by biological organisms. Most of the experimenrs have used walking humans with light attached to their joints and limbs as stimuli.

Self-produced motion of a person or other living organism

Coherence

In research on movement perception in which arrays of moving dots are used as stimuli, the degree of correlation between the direction of moving dots. 0% means all the dots are moving independently, 100% means all the dots are moving in the same direction.

Comparator

A structure hypothesized by the corollary discharge theory of movement perception. The corollary discharge signa; and the sensory movement signal meet here to determine whether movement will be perceived.

Corollary Discharge Signal (CDS)

A copy of the motor signal that is sent to the eye muscles to cause movements of the eye. The copy is sent to the hypothetical comparator of corollary discharge theory.

It gets sent to a different part of the brain for another purpose

Corollary Discharge Theory

The theory that explains motion perception as being determined both by movements of the image on the retina and by signals that indicate movement of the eyes.

Delay Unit

A component of the Reichardt detector proposed to explain how neural firing occurs to different directions of movement. Delays the transmission of nerve impulses as they travel from the receptors toward the brain.

Event Boundary

The point in time when one event ends and another begins.

Event

A segment of time at a particular location that is perceived by observers to have a beginning and an ending.

Global Optic Flow

Information for movement that occurs when all elements in a scene move. The perception indicated that it is the observer that is moving and not the scene.

Without any local disturbances

Illusory Motion

Perception of motion when there is actually none.

aka apparent movement/phi phenomenon

stationary stimuli are presented in slightly different locations

Image Displacement Signal (IDS)

In corollary discharge theory, the signal that occurs when an image moves across the visual receptors (across the retina)

Implied Motion

When a still picture depicts an action that involves motion, so that an observer could potentially extend the action depicted in the picture in their mind based on what will most likely happen next.

Induced Motion

The illusory movement of one object that is caused by the movement of another object that is nearby and moving in the opposite direction

Local Disturbance in the Optic Array

Occurs when one object moves relative to the environment, so that the stationary background is covered and uncovered by the moving object. This disturbance indicates that the object is moving relative to the environment.

Motion Aftereffects

An illusion that occurs after a person views a moving stimulus and then sees movement in the opposite direction when viewing a stationary stimulus immediately afterward.

Relates to fatiguing neurons tuned to motion in one direction = less sensitive to neurons in other directions

Motion Signal (MS)

In corollary discharge theory, the signal that is sent to the eye muscles when the observer moves or tries to move their eyes.

Optic Array

The structured pattern of light created by the presence of objects, surfaces, and textures in the environment.

Output Unit

A component of the Reichardt detector that compared signals received from 2 or more neurons. According to Reichardt's model, activity in the unit is necessary for motion perception.

If those signals reach the output unit together = motion detected

Point-Light Walkers

A biological motion stimulus created by placing lights at a number of places on a person's body and having an observer view the moving-light stimulus that results as the person moves in the dark.

Real Motion

The physical movement of a stimulus. Constrats with apparent motion.

occurs when an object is physically moving

Real-motion Neuron

Neuron in the monkey's cortex that responds when movement of an image across the retina is caused by movement of a stimulus, but does not respond when movement across the retina is caused by movement of the eyes.

Reichardt Detector

A neural circuit proposed by Werner Reichardt, in which signals caused by movement of a stimulus across the receptors are processes by a delay unit and an output unit so that signals are generated by movement in one direction but not in the opposite direction.

Directional: each one can only detect motion in one direction

Representational Momentum

Occurs when motion depicted in a still picture continues in an observer's mind.

Shortest Path Constraint

In the perception of apparent motion, the principle that apparent movement tends to occur along the shortest path between 2 stimuli.

Striate cortex (v1)

The region of the occipital lobe where information from the retinas first reach the cortex

Function related to motion = direction of motion across small receptive fields

Complex cortical cells (in v1)

Respond to movement of the ends of objects

Middle temporal area (MT)

Implicated in other aspects of motion perception

region of the visual cortex that plays a key role in perceiving the motion of objects in the visual field

Waterfall Illusion

An aftereffect of movement that occurs after viewing a stimulus moving in one direction. Viewing it makes other objects appear to move in the opposite direction.

Up + down motion sensitive neurons

Have similar levels of activity

Downward motion = more activation in “down” neurons

Continue staring = fatigue + weaken signals; look away, “up” sensitive neurons generate stronger signals

Ecological approach

From Gibson

Focuses on what/how information directly available in the environment is useful to guide perception/action

Corollary Discharge Theory: movement is perceived

Perceived when comparator receives input from either (but not both)

• Corollary discharge signal

  OR

• Image displacement signal

Corollary Discharge Theory: movement isn’t perceived

Isn’t perceived when comparator receives input at the same time, from both

• Corollary discharge signal

  AND

• Image displacement signals

Superior temporal sulcus (STS)

Perception of motion related to animals + people (biological motion)

Medial superior temporal area (MST)

Processing optic flow; locating moving objects reaching for moving objects