Ch. 8 pt. 1&2

• Akinetopsia, also known as "motion blindness," makes perceiving motion very difficult or impossible
• Causes of Akinetopsia:

  • traumatic brain injury
  • neurodegenerative diseases like Alzheimer's
  • epilepsy
  • hallucinogen persisting perception disorder (HPPD)
• Damage to V5 medial temporal (MT) or Temporo-parieto-occipital junction (TPJ) can result in akinetopsia
• Observers perceive shapes more rapidly and accurately when an object is moving
• Movement serves an organizing function, grouping smaller elements into larger units
• The motion of individual birds can be perceived as the larger unit of the flock, flying in synchrony with each other
• Biological Movement involves the coordination of individual units like arms, legs, and body when a person or animal moves
• An event is a segment of time at a particular location perceived to have a beginning and an end
• Event boundaries mark the end of one event and the beginning of the next
• Perception of movement helps in separating activities into meaningful events
• Event boundaries are more likely to occur with changes in speed or acceleration of movement
• Social cues are often linked to movement
• Heider and Simmel (1944) studied social perception
• Point-Light Walkers: a biological motion stimulus created by placing lights at a number of places on a person's body & having an observed view the moving-light stimulus that results as the person moves in the dark

  • were used to study social interactions and non-social interactions
• Motion perception is essential for navigating through the environment safely, watching and playing sports, and other activities like pouring drinks
• Different types of motion perception include:

  • Real motion
  • Illusory motion (apparent motion)
  • Induced motion
  • Motion aftereffects
  • Comparing real and Apparent motion
• • Real motion involves actual movement
  • Illusory motion does not have actual motion between stimuli
• Induced motion occurs when the motion of one object causes a nearby stationary object to appear to move
• Motion aftereffects happen when viewing a moving stimulus causes a stationary stimulus to appear to move (e.g., waterfall illusion)
• Comparing real and apparent motion can be studied using different displays in an fMRI scanner
• Patients with damage to the FFA experience prosopagnosia, or the inability to recognize faces, underscoring the area's significance in facial perception
• Phenomena associated with perceiving motion, includes:

  • Illusionary Motion
  • Apparent motion (illustrated by the ticker symbol example)
  • Induced Motion (the illusion of the moon moving through clouds)

  These phenomena illustrate how motion perception can be influenced by visual cues and context, leading to misinterpretations of movement in the environment
• 3 Theories of Motion Perception:

  1. Ecological Approach by Gibson
  2. Corollary Discharge Theory
  3. Reichardt Detectors and Neural Mechanisms
• Ecological Approach by Gibson: This theory emphasizes the importance of environmental factors in perception

  • It discusses how motion is perceived through changes in the optic array, with disturbances indicating movement
  • This approach prioritizes external visual information over neural processing in understanding perception
• Corollary Discharge Theory: This theory integrates neural mechanisms, explaining motion perception through the interaction of motor signals and sensory feedback

  • It involves the concept of corollary discharge, where a copy of the motor command is compared with sensory input to distinguish self-induced movements from external motion
  • This theory helps explain why we cannot tickle ourselves and how movement perception is modulated by both motor activity and visual stimuli
• Reichardt Detectors and Neural Mechanisms: This model describes how motion direction is detected by neurons through a process involving the temporal delay and comparison of signals from different visual receptors

  • This mechanism supports the perception of directional movement and is complemented by discussions on neural responses to coherence in motion
  • Highlights neurons' selective response to unified motion in a single direction
• Event Boundary: the point in time when each of these events ends and next one begins

  • can infer different things/meaning of events by interpreting movement(s)
• Real Motion: refers to the actual movement of an object in the physical world
• Illusory Motion: a static image appearing top move due to the cognitive effects of interacting color contrasts, luminance, and geometric shapes within the image

  • (ex. image of the snakes that appear to be turning)
• Apparent Motion: occurs when static images are presented in succession at a certain speed, leading the observer to perceive continuous motion

  • no actual motion between stimuli
  • (ex. movies, television, moving signs)
• Induced Motion: when motion of one object (usually a large one) causes a nearby stationary object (usually smaller) to appear to move

  • (ex. when the moon appears to move through clouds, when it's really the clouds moving)
• Motion Aftereffects: when viewing a moving stimulus causes a stationary stimulus to appear to move

  • occur after prolonged observation of a moving visual stimulus
  • after looking away, the stationary scene appears to move in the opposite direction of the original stimulus
• Ecological Approach to Motion Perception: looking for information in the environment that is useful for perception

  • according to Gibson, information is located not on the retina but "out there" in the environment
• Optic Array: refers to the structured pattern of light rays from the environment that enters the eye and provides visual information about the surrounding world

  • how movement of the observer causes changes in the optic array
• Corollary Discharge Theory: addresses how the brain distinguishes between self-generated and externally generated movements

  • Motor command copy (aka efferent copy) gets sent out to the other brain areas & reaction gets cancelled out
  • However if someone else is doing the action, there's no motor command within your own system to cancel out the reaction
• 3 Signals of Corollary Discharge Theory:

  1. Image Displacement Signal, which occurs when an image moves across the retina
  2. Motor Signal, which is sent from the motor area to the eye muscles cause the eye to move
  3. Corollary Discharge Theory, which is a copy of the motor signal (aka efferent)
• Corollary Discharge Theory:

  (a) Eye follows moving stimuli = CDS = Perceived Motion

  (b) Eye is stationary; stimulus is moving = IMS = Perceived Motion

  (c) Eye moves across stationary scene = CDS & IMS = NO motion
• The Reichardt Detector: a model that explains how motion is detected by the visual system

  • A & B send their signals to an output unit and A goes to delay unit first
  • B releases A from delay unit to meet in output unit
  • As object moves from left (A) to right (B), it activates different stimuli
  • Output unit waits for delay unit & B, to then perceive movement
  • Only in 1 direction
• 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% coherence = all dots are moving independently
  • 100% coherence = all the dots are moving in the same direction
• Delay Unit: it delays the transmission of nerve impulses as they travel from the receptors towards the brain

  • a component of Reichardt Detector proposed to explain how neural firing occurs different directions of movement