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Survival in the Environment Movement Perception

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Predators use movement of prey as a primary means of location in hunting.

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Attentional Capture Movement Perception

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Motion attracts attention to the moving object. If prey remains motionless, it is less likely to be noticed.

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Akinetopsia Movement Perception

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Blindness to motion. - Difficulties in pouring tea. - Difficulties in social interactions. - Sudden appearances of objects potentially life-threatening.

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Functions of Movement Perception

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- Motion helps us understand gestures and activities. - Motion perception is essential for navigating in the environment. - Motion attracts attention. Movement helps perceptual organization. - Helps disambiguate the "inverse projection problem".

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Real Motion

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An object is physically moving.

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Apparent Movement Illusory Motion

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Stationary stimuli are presented in slightly different locations. Basis of movement in movies and TV.

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Induced Motion

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Movement of one object results in the perception of movement in another object.

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Motion Aftereffect

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View a moving stimulus for 30 to 60 seconds causes a stationary stimulus to appear to move. Movement appears to occur in the opposite direction from the original movement. The waterfall illusion is an example of this.

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Larsen et. al Comparison of Apparent and Real Motion

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Participant is scanned by an fMRI while viewing three different 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. Results: - Control condition - each dot activated a separate area of visual cortex. - Apparent and real motion - activate visual cortex representing the space between the dots, both sets of stimuli were similar. The perception of motion in both cases is related to the same brain mechanism.

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An object moves, and the observer is stationary.

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Movement creates an image that moves on the observer's retina. Motion perception is more than a stimulus crossing the retina.

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An object moves, and the observer follows the object with his or her eyes.

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Movement is tracked so that the image is stationary on the retina. Motion perception is more than a stimulus crossing the retina.

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An observer moves through a stationary environment.

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Image of environment moves across the retina but environment is perceived as stationary Motion perception is more than a stimulus crossing the retina.

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Fovea

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Focus

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Retina (peripheral)

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Non-focus

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Ecological Approach - J.J. Gibson Motion Perception: Information in the Environment

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Information is directly available in the environment for perception. Look as an object moves past.

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Optic Array

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Whole picture. Structure created by surfaces, textures, and contours. Change as the observer moves through the environment. Accounts for self movement and environmental movement.

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Local Disturbance in the Optic Array

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Objects relative to background such that it is covered and uncovered. When anything changes in optic array. Perceiving motion.

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Global Optic Flow

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Information for movement that occurs when all elements in a scene move. Indicates that it is the observer that is moving and not the scene. Overall movement of optic array.

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Follow a Moving Object Motion Perception: Information in the Environment

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- As Maria follows Jeremy with her eyes. - Though Jeremy's image is stationary on the retina, there is local disturbance in the optic array. - Jeremy still covers and uncovers parts of the array.

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Look Around the Room Motion Perception: Information in the Environment

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As Maria scans the room: everything moves at once. Global optic flow.

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Reichardt Detectors Motion Perception: Information in the Environment

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Neurons that fire to movement in one direction. Inhibition and excitation changes can code it movement. Can only explain detection of image moving across retina situation.

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Corollary Dishcharge

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Signals from the retinal and the eye muscles.

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Image Displacement Signal (IDS) Corollary Discharge Theory Motion Perception: Retina Eye Information

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Movement of image stimulating receptors across the retina. Movement perception depends on these three signals.

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Motor Signal (MS) Corollary Discharge Theory Motion Perception: Retina Eye Information

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Signal sent to eyes to move eye muscles.

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Corollary Discharge Signal (CDS)

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Split from the motor signal.

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Comparator

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

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Corollary discharge signal (CDS) OR image displacement signal (IDS). Corollary Discharge Theory Motion Perception: Retina Eye Information

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Movement is perceived when comparator receives input from

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Movement is not perceived when comparator receives input from: Corollary Discharge Theory Motion Perception: Retina Eye Information

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Both corollary discharge and image displacement signals at the same time.

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Behavioral Evidence for Corollary Discharge Theory Demonstrations

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Eliminating the IDS with an afterimage. Seeing motion by pushing on the eyelid.

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Physiological Evidence for Corollary Discharge Theory

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Damage to the MST in humans leads to perception of movement of stationary environment with movement of eyes; Experienced vertigo. Yes = IDS, but due to damage; no = CDS

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Real-Movement Neurons Physiological Evidence for Corollary Discharge Theory

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Found in monkeys that respond only when a stimulus moves and do not respond when eyes moved.

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Neurons on the striate cortex Motion Perception in the Brain

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Respond to movement of ends of objects.

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Middle Temporal sensitive to motion Motion Perception in the Brain

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Evidence for this has been found in the MT cortex of monkeys.

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Firing and Coherence Experiment by Newsome et. al Motion Perception in the Brain *KNOW THIS STUDY!!*

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Coherence to indicate the degree to which the dots move in the same direction; coherence of movement of dot patterns was varied. Monkeys were taught to judge direction of dot movement and measurements were taken from MT neurons. Results: Showed that as coherence of dot movement increased: the firing of MT neurons increases, and the judgment of movement accuracy increases.

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Lesioning Experiment by Newsome & Paré Motion Perception in the Brain

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Normal monkeys can detect motion with coherence of 1 or 2%. Monkeys with lesions in MT cortex cannot detect motion until the coherence is 10-20% Further evidence linking the firing of MT neurons to the perception of the direction of motion.

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Microstimulation Experiment Movshon & Newsome Motion Perception in the Brain

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Electrically stimulate neurons in the MT cortex. - Monkey was trained to indicate direction of fields of moving dots. - - Neurons in MT cortex that respond to specific direction were activated. - Experimenter used micrositmulation to activate different direction sensitive neurons. - Monkey shifted judgment to the artificially stimulated direction. *Direction perception matched stimulated MT cells not the actual direction of the stimuli.*

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Complex Cortical Cells Motion from a Single Neuron's POV

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Respond preferentially to an oriented bar moving in a specific direction.

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MT and MST Cortex

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Respond to motion.

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Response of a single directionally selective neuron

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Does not provide sufficient information to indicate the direction of movement.

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Aperture Problem

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Observation of a small portion of a larger stimulus leads to misleading information about direction of movement. Activity of a single complex cell does not provide accurate information about direction of movement.

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Biological Motion Perceptual Organization

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Movement of person or other living organism.

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Point-Like Walker Stimulus

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Biological motion made by placing lights on the joints of a person.

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Structure-from-Motion

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Takes place with point light walkers.

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Neurological studies show biological motion is

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Processed by STS and FFA.

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Solving the aperture problem

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MT pools responses of many V1 neurons (transform info.)

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Grossman et. al Motion and the Human Body

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- Participants viewed point-light stimulus for activities. - Task was to determine whether motion was biological or scrambled. - Noise was added to dots so they can only achieve a 71% accuracy. - Transcranial magnetic stimulation applied to STS caused a decrease in ability to detect biological motion.

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Implied Motion

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Still pictures that depict an action that involves motion.

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Representational Momentum

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Observers show that the implied motion is carried out in the observer's mind.

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Stimulus used by Freyd

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Frozen pictures remembered in the anticipated state.

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Kourtzi & Kanwisher

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fMRI response was measured in the MT and MST to pictures with: Implied motion, no-implied motion, at rest, houses. Results: Showed areas of brain responsible for motion fire in response to pictures of implied motion.

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Event Event Perception

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A segment of time at a particular location with a beginning and an end.

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Event Boundary Event Perception

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The point where one event ends and another begins.

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Connection between events to motion perception

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Events almost always involve motion. Changes in the nature of motion are often associated with event boundaries.

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the MT neuron fired more rapidly.

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Newsome, Britten, and Movshon found that as the coherence between the dots' direction of movement increased

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the "time-forward" condition.

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Freyd (1983) presented two pictures sequentially that implied motion, such as a person jumping off a low wall. In the "same" condition, the second picture was identical to the first; in the "time-forward" condition, the second picture was the jumper closer to the ground; and in the "time-backward condition, the jumper was further from the ground. The observer's task was to respond whether or not the two pictures were the "same" or "different." The response time was longest for

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similar when viewing apparent motion and real motion.

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Larsen et al. (2006) showed that the activation of brain areas is

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person when the point-light walker is moving.

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A "point-light walker" wears lights on different body locations. When viewed in a dark room, an observer would perceive a(n)

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decreased the person's ability to perceive biological motion.

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Presenting transcranial magnetic stimulation to the area of the STS in humans

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apparent movement

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Our ability to perceive movement when reading "message boards" used in advertising, is based on

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movement, because there is a CDS, but not an IDS.

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Percy is injected with a drug that paralyzes his eye muscles. When he is instructed to try to move his eye when looking a stationary scene, he perceives

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the comparator receives the corollary discharge signal alone or image displacement signal alone.

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According to Corollary Discharge Theory, movement is perceived when

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being motionless reduces both the attention-attracting effect of motion, and the chance that the cat will see the mouse against the background.

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A mouse "freezes" when it sees a cat nearby. This assists the mouse's survival because

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a stimulus; the eye

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Real-motion neurons found in the monkey cortex fire when _____ moves, but do not fire when _____ moves.

HSP – Chapter 8 – Perceiving Motion – Flashcards

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