week 7 - motion perception Flashcards
akinetopsia
blindness to motion
Heider and Simmel experiment (animated shapes)
- subjects watched a film of animated shapes that acted as characters and interacted with each other
- subjects were then asked to describe what was occurring
What were the results of the Heider and Simmel experiment?
despite not being people, subjects were able to create stories explaining the actions of the different objects and even gave them human like characteristics/personalities
attentional capture
- motion attracts attention to the moving object
- ex.) waving arm to attract the attention of someone across the room
real motion
object is physically moving
illusory motion
Arises when an observer looks at an object for a long period of time and looks at a stationary stimulus. The stationery stimulus then appears to be moving
apparent motion
- stationary stimuli are presented in slightly different locations
- basis of movement in moves and TV
apparent movement experiment
- Experiment containing two light sources in slightly different locations. One light turns on, followed by a period of darkness, and then the other light turns on
- One would perceive that a single light is moving from on area to the other
induced motion
- movement of one object results in the perception of movement in another object
- ex.) movement of clouds creates the illusion that the moon is moving
motion aftereffect experiment
- Observer looks at movement of object for 30-60 seconds
- Observer then looks at stationary object
- Movement appears to occur in the opposite direction from original movement
Larsen experiment (light dots)
- participants scanned by fMRI while viewing 3 displays
- control condition: two dots in different positions are flashed simultaneously
- real motion: a small dot is moved back and forth
- apparent motion: dots are flashed so they appear to move
What were the results of the Larsen experiment?
- two areas are overlapping, they activate the same different neural regions
- control condition: each dot activated a separate area of the visual cortex
- apparent and real motion: activation of visual cortex from both sets of stimuli was similar; thus the perception of motion in both cases is related to the same brain mechanism
an object moves and the observer is stationary…
movement creates an image that moves on the observer’s retina
an object moves and the observer follows the object with their eyes…
movement is tracked so that the image is stationary on the retina
an observer moves through a stationary environment…
image of environment moves across retina but environment is perceived as stationary
motion perception
information in the environment
ecological approach (gibson)
- information is directly available in the environment for perception
- ex.) optic array
optic array
structure created by surfaces, textures, and contours which change as the observer moves through the environment
local disturbance in the optic array
objects relative to background such that is covered and uncovered
global optic flow
- overall movement of optic array
- indicates that the observer is moving and not the environment
reichardt detectors
- neurons that fire to movement in one direction
- excitation and inhibition are arranged so that movement in one direction creates inhibition that eliminates neural responding
describe the movement of reichardt detectors inhibiting neural response
- A is excited by light
- A excites E
- E inhibits F
- light excites B but it is too late to excite
- neural response is eliminated
describe the movement of reichardt detectors exciting neural response
- Receptor D is excited by light
- D activates H
- neural response is activated
- Light reaches receptor C
- C excites G and attempts to inhibit H but it has already been excited
corollary discharge theory
movement perception depends on 3 signals: 1. image displacement signal 2. motor signal 3. corollary discharge signal
image displacement signal
movement of image stimulating receptors across the retina
motor signal
signal sent to eyes to move muscles
corollary discharge signal
split from motor signal; copy of motor signal sent to different area of brain
What are the physiological evidence for the corollary discharge theory?
- damage to medial superior temporal area in humans lead to perception of movement of stationary environment with the movement of eyes
- real-movement neurons found in monkeys that respond only when a stimulus moves and do not respond when eyes move
Newsome experiment (firing and dot coherence)
- coherence of movement of dot patterns was varied
- monkeys were taught to judge direction of dot movements and measurements were taken from MT neurons
What were the results of the Newsome experiment?
as coherence of dot movement increased, so did the firing of the MT neurons and the judgment of movement accuracy
Newsome and Pare (monkey lesioning)
- normal monkeys can detect motion with coherence of 1 or 2%
- monkeys with lesions in MT cortex cannot detect motion until coherence is 10-20%
Movshon and Newsome (microstimulation)
- monkey trained to indicate direction of moving dots
- neurons inMT cortex that respond to specific direction were activated
- microstimulation of different direction sensitive neurons
What were the results of Movshon and Newsome?
monkey shifted judgment to the artificially stimulated direction
complex cortical cell
respond preferentially to an oriented bar moving in a specific direction
aperture problem
observation of small portion of larger stimulus leads to misleading information about direction of movement
biological motion
movement of person or other living organism
Grossman and Blake experiment (point-light)
- Participants viewed point-light stimuli for activities
- Task was to determine whether motion was biological or scrambled
Noise was added to dots so they could only achieve 71% accuracy
What occurred in the Grossman and Blake experiment when TMS was applied to STS?
- Transcranial magnetic stimulation applied to STS caused a decrease in ability to detect biological motion
- Suggests that STS is helpful for perceiving biological motion
implied motion
still pictures that depict an action that involves motion
jumping over wall (implied motion)
- We have difficulty differentiating two still motion pictures going forward in time because our brain automatically perceives the motion occurring
- However, it is much easier to detect the still motion picture going backwards
representational momentum
observers show that the implied motion is carried out in the observer’s mind
Kourtzi and Kanwisher experiment
fMRI response was measured in MT and MST to pictures with
- Implied motion
- No-implied motion
- At rest
- Houses
What were the results of the Kourtzi and Kanwisher experiment?
Results showed areas of brain responsible for motion fire in response to pictures of implied motion
