320 final - ch 8

• Newsome, Britten, and Movshon found that as s coherence between dots direction movement increased

  MT neuron fired more rapidly
• the perception of a point like walker stimulus as a person walks in is an example of

  Structure from motion
• the neurons that seemingly respond to this flow information (optic flow image) have been found in monkeys

  MST (medial superior temporal) area
• motion agnosia


  disability to perceive moving stimulus
• motion perception is very fundamental

  motion is essential for survival

  motion occurs in the peripheral vision

  motion disambiguate 3D structure

  motion creates perceptual organization
• 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
• Structure from motion

  Takes place with point light walkers
• Real motion


  The physical movement of a stimulus
• Illusionary motion


  Perception of motion when there actually is none
• Apparent motion


  Kind of illusory; two stimuli in slightly different locations alternated with correct timing, an observer perceives moving back and forth – displacement of objects
• Induced motion


  Illusory movement of one object that is caused by the movement of another object that is nearby
• 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
• Waterfall illusion


  An aftereffect of movement that occurs after viewing a stimulus moving in one direction, such as a waterfall. Viewing the waterfall makes other objects appear to move in the opposite direction
• Functions of movement perception


  • Survival in the environment
  • Perceiving objects in 3D
  • Perceptual organization
• Motion agnosia


  Damage to cortex resulting in inability to perceive movement, extremely debilitating and dangerous for the patient
• Kinetic depth effect


  Movement of an object's 2D shadow can change into perception of a 3D object – example of structure from motion
• Optic array


  The structured pattern of light created by the presence of objects, surfaces, and textures in the environment
• 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 local disturbance indicates that the object is moving relative to the environment
• Global optic flow


  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
• Corollary discharge theory


  The theory that explains motion perception as being determined both by movement of the image on the retina & by signals that indicate movement of the eyes
• Image displacement signal


  Signal that occurs when an image moves across visual receptors
• Motor Signal


  The signal that is sent to the eye muscles when the observer moves or tries to move his or her eyes
• Corollary discharge signal


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


  Brain structure that receives just one signal – either image displacement or corollary discharge – no movement if receives both signals at the same time
• Reichardt detector


  Consists of 2 neurons A and B which send their signals to an output unit – neural circuit to explain motion perception
• Output unit


  Compares signals received from two or more neurons
• Delay unit


  Proposed to explain how neural firing occurs to different directions of movement. The delay unit delays the transmission of nerve impulses as they travel from the receptors toward the brain
• Middle temporal (MT) area


  Brain region in the temporal lobe that contains many directionally selective neurons. Visual pathway
• As the correlated movement of random dots increased, neurons in MT fired more
• Monkeys with lesions in MT cannot detect motion until coherence is 10-20%
• Transcranial magnetic stimulation (TMS)


  Presenting a strong magnetic field to the head that temporarily disrupts the functioning of a specific area of the brain
• Aperture problem


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


  Motion produced by biological organisms. Most experiments on biological motion have used walking humans with lights attached to their joints and limbs as stimuli
• Motion occurs even in peripheral vision – don't need fovea – Rods for motion perception
• physiological evidence for corollary discharge theory?

  damage to MST leads to perception of movement of stationary environement