Chapter 8: Perceiving Movement Flashcards
akinetopsia
the difficulty or inability to perceive motion (rare condition)
event
a segment of time at a particular location that is perceived by observers to have a beginning and an end
event boundary
the point in time when each event ends and the next one begins
when are event boundaries most likely to occur?
event boundaries are more likely to occur when there is a change in speed or acceleration of the movement
functions of motion perception
- Detecting things (important for survival)
- Perceiving objects (we perceive things more accurately when an object is moving)
- Perceiving events
- Social perception (we use the characteristics of movement to interpret emotions)
- Taking action
point-light walker
a method of presenting human motion by placing small lights on people’s joints and filming the patterns created when they move
can people determine if people are acting socially based on point-light walkers?
participants were able to indicate if the people were interacting socially, but those with autism had more difficulties doing so.
geometric shapes and movement perception experiment (Heider & Simmel, 1944)
showed an animated film to participants and asked them to describe what was happening. Although the characters were geometric objects, participants made up stories describing them as having feelings, motivations, and personalities
real motion
the physical movement of a stimulus
illusionary motion
the perception of the motion of stimuli that aren’t actually moving.
3 types of illusionary movement
apparent motion, induced motion, and motion aftereffects
apparent motion
an illusion of movement that occurs when two objects separated in space are presented rapidly, one after another, separated by a brief time interval
induced motion
when the motion of one object causes a nearby stationary object to appear to move
motion aftereffects
occur when a moving stimulus causes a stationary stimulus to appear to move
waterfall illusion
the aftereffect of movement that occurs when one views a waterfall moving in one direction. Viewing the waterfall makes other objects appear to move in the opposite direction
activation of real vs. apparent motion study
presented participants with either a control condition, a real motion display, or an apparent motion display and found that the activation associated with apparent and real motion were similar
gibson’s ecological approach to motion perception
involves looking for information that is “out there” in the environment. focuses on how movement of what’s being observed changes in the optic array.
optic array
the structure created by the surfaces, textures, and contours of the environment
local disturbance
the covering and uncovering of the optic array
global optic flow
the fact that everything moves at once in response to the movement of the observer’s eyes
corollary discharge approach to motion perception
States that if the comparator receives just one signal (either image displacement or corollary discharge), movement will be perceived.
3 types of signals according to the corollary discharge approach
image displacement, motor, and corollary discharge signals
image displacement signal
occurs when an image moves across the retina
motor signal
is sent from the motor area to the eye muscles to cause the eye to move
corollary discharge signal
a copy of the motor signal that is sent to the eye muscles to cause the movement of the eye
comparator
a brain structure hypothesized by the corollary discharge theory to determine whether movement will be perceived
the Reichardt detector
A neural circuit proposed by Werner Reichardt in which signals caused by the movement of a stimulus across the receptors are processed by a delay unit and an output unit so that signals are generated by movement in one direction but not in the opposite direction
output unit
compares the signal it receives from neurons A & B
delay unit
slows down the signals from neuron A as they travel toward the output unit & multiplies the responses from A to B to create the movement signal that results in perception
what type of signals does the Reichardt detector respond to?
movement from left to right
does the Reichardt detector exist in other species?
Some more complicated versions of this circuit exist in other species, where neurons only fire to particular directions of motion
medial temporal (MT) area
a brain area in the temporal lobe that is responsible for the direction and speed of object motion
what happens when coherence is increased?
monkeys judged the direction of motion more accurately and MT neurons fired more vigorously. Demonstrates relationship C (the physiology perception relationship
coherence
the degree to which the dots move in the same direction
(0%- you can’t detect a particular direction of movement; 100%- direction is easy to detect)
what happens when the MT cortex is lesioned
there must be a higher coherence for monkeys to detect the direction of movement
what happens when the MT cortex is deactivated using TMS?
participants experienced a form of akinetopsia
Transcranial magnetic stimulation (TMS)
a method that temporarily disrupts the normal functioning of neurons by placing a magnetic coil above the skull to create a strong magnetic field. A series of electromagnetic pulses are then presented and if the behaviour is disrupted by the pulses, the disrupted area is involved in the behaviour
what happens when the MT cortex is stimulated using microstimulation?
the perception of direction is shifted (ex. If neurons activated by downward motion are stimulated, the participant judges the original right motion as being downward and to the right)
microstimulation
a method where neural activity is enhanced by lowering a small wire electrode into the cortex and passing a weak electrical charge through the tip of the electrode. The weak shock stimulates neurons near the tip, causing them to fire.
Medial superior temporal (MST) area
involved in processing optic flow, locating moving objects, and reaching for moving objects
biological motion
the self-produced motion of a person or other living organism
implied motion
a situation in which a still picture depicts an action involving motion
do areas of the brain that respond to motion respond to implied motion?
yes
akinetopsia is also called
motion blindess
what types of diseases lead to akinetopsia
Often occurs following traumatic brain injury, neurodegenerative diseases such as Alzheimer’s, Epilepsy, hallucinogen perception disorder (HPPD)
brain damage in what areas cause akinetopsia?
Caused by damage to V5 medial temporal (MT) & temporo-parieto-occipital junction (TPJ), which are located along the dorsal stream
patient LM
Suffered from akinetopsia after a bilateral brain hemorrhage
patient SM
Couldn’t detect fear following bilateral amygdala damage
Leaf-tail gecko & pygmy sea horse
difficult to detect because they camouflage, but once they start moving, you can detect it
when do we perceive movement most accurately
when an object is moving
what is one of the most important functions of movement?
it serves an organizing function, which groups smaller elements into larger units
when do we perceive movement?
when there’s real or illusionary movement
what’s a famous example of apparent movement?
the phi phenomenon
phi phenomenon
apparent motion that is observed if two nearby optical stimuli are presented in alternation with a relatively high frequency
what happens according to the corollary discharge theory if the eye follows a moving stimulus?
the corollary discharge signal is activated and movement is perceived
what happens according to the corollary discharge theory if the eye is stationary but a stimulus is moving?
the image displacement signal is activated and movement is perceived
what happens according to the corollary discharge theory if the eye moves across a stationary scene?
both the image displacement signal and the corollary discharge signal are activated and movement is not perceived
