Motion Perception Chapter 8 Lecture 14 Jonathan Pillow Sensation - - PowerPoint PPT Presentation

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Motion Perception Chapter 8 Lecture 14 Jonathan Pillow Sensation - - PowerPoint PPT Presentation

Dec 11, 2023 259 likes •745 views

Motion Perception Chapter 8 Lecture 14 Jonathan Pillow Sensation & Perception (PSY 345 / NEU 325) Spring 2015 1 countering the depth-from-focus cue 2 Depth Illusions Mller-Lyer Illusion

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Motion Perception Chapter 8

Lecture 14

Jonathan Pillow Sensation & Perception (PSY 345 / NEU 325) Spring 2015

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countering the depth-from-focus cue

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Depth Illusions

Müller-Lyer Illusion

http://www.michaelbach.de/ot/sze_muelue/index.html

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figures are the same size

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“Terror Subterra”

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“Terror Subterra”

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red lines are all the same length

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Depth / Size illusion

  • all 3 cars take up the same space in the image + on your retina!

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Binocular Rivalry

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Two stimuli battle for dominance of the percept

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Strabismus

  • eyes are not aligned,

so different images fall

  • n the fovea
  • If not corrected at an

early age, stereopsis will not develop stereoblindness: inability to use binocular disparity as a depth cue.

Defects in Stereopsis

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  • monocular depth cues
  • binocular depth cues (vergence, disparity)
  • horopter
  • crossed / uncrossed disparities
  • free fusing
  • random dot stereogram
  • stereoscope
  • “correspondence problem”
  • panum’s fusional area
  • strabismus / stereoblindness
  • binocular rivalry (in book)

Chapter 6 Summary:

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Motion Perception Chapter 8

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Main point of this chapter: Motion = Orientation in Space-Time

time space

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which motion is faster?

time space time space

slow fast

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Real vs. Apparent motion

Apparent motion - motion percept that results from rapid display of stationary images in different locations

time space time space

apparent

(movies, flip-books)

“real” Q: why don’t we notice the difference?

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How does the nervous system encode motion? What makes a Motion Receptive Field? Answer: a surprisingly simple neural circuit called a “Reichardt detector”

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Reichardt detector simple summing neuron

delay line

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space time

excitatory inhibitory

Reichardt detector in space-time first RF second RF 2nd neuron has a spatially separated Receptive Field (RF), and a shorter temporal delay

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space time

excitatory inhibitory

Smoother Reichardt detector Like an oriented V1 receptive field, but oriented in space-time!

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space time

excitatory inhibitory

Reichardt detectors respond to real and apparent motion

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Figure 7.3 Constructing a neural circuit for the detection of rightward motion (Part 1)

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Figure 7.3 Constructing a neural circuit for the detection of rightward motion (Part 2)

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Clockwise or Counter-clockwise rotation? (web demo)

Correspondence problem (motion):

  • problem of knowing the correspondence between features in

successive frames (which points in frame 1 are the same objects in frame 2?)

http://sites.sinauer.com/wolfe3e/chap8/correspondenceF.htm

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  • Aperture problem:

when a moving object is viewed through an aperture, the direction of motion may be ambiguous

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  • Aperture problem:

when a moving object is viewed through an aperture, the direction of motion may be ambiguous

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  • Aperture problem:

when a moving object is viewed through an aperture, the direction of motion may be ambiguous

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  • this is a problem because each neuron only sees the scene

through a small aperture (its receptive field!)

  • how can the brain figure out the “global” direction of motion?
  • Aperture problem:

when a moving object is viewed through an aperture, the direction of motion may be ambiguous

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http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm

aperture problem / correspondence problem

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building a global motion detector

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Motion aftereffect (MAE): The illusion of motion that occurs after prolonged exposure to a moving stimulus http://www.michaelbach.de/ot/mot-adapt/index.html

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Motion after-effect

  • Always gives rise to motion in the opposite

direction of the adapting motion

  • Also known as: “waterfall illusion” -

stare at a waterfall; stationary objects will then appear to move upwards.

  • evidence for “opponent channels” in

processing motion

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Computation of Visual Motion Interocular transfer: The transfer of an effect (such as adaptation) from one eye to another

  • MAE: exhibits interocular transfer

What does this tell us about where in the brain motion is computed?

  • Remember: Input from both eyes is combined in area V1
  • Motion seems to be computed in area MT (middle temporal area)

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Interocular transfer: The transfer of an effect (such as adaptation) from one eye to another

  • MAE: exhibits interocular transfer
  • Remember: Input from both eyes is combined in area V1

Q: What does this tell us about where in the brain motion is computed?

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“Motion After-Effect”

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“Motion After-Effect”

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Computation of Visual Motion Newsome and Pare (1988) conducted a study on motion perception in monkeys

  • Trained monkeys to respond to dot motion displays
  • Area MT of the monkeys was lesioned
  • Result: Monkeys needed about ten times as many

dots to correctly identify direction of motion

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  • Optic flow: the local velocity at each point in an image
  • ptic flow field

Q: How do we use motion information to navigate?

  • We experience “optic flow” fields as we move through the

world Example of pilot landing a plane: “Radial expansion”

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Focus of expansion (FOE): point in the center of the horizon from which, when we are in motion, all points in the perspective image seem to emanate

  • one aspect of optic

flow

  • tells the observer

which way they are heading

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Using Motion Information Biological motion: The pattern of movement of all animals

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Biological motion

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non-biological motion

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Eye movements: also give rise to retinal motion.

  • important to distinguish motion due to eye movements

from motion due to moving objects!

two scenarios with same retinal motion eye moves

  • bject moves

time 1 time 2 time 1 time 2

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  • Smooth pursuit - eyes smoothly follow a

moving target

  • Saccade - rapid movement of the eyes that

changes fixation from one location to another

  • Vergence - two eyes move in opposite

directions, as when both eyes turn towards the nose

  • Reflexive - automatic / involuntary (e.g.,

vestibular)

Eye Movements

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Partner up! Smooth pursuit vs. saccadic eye movements in-class experiment

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Saccadic suppression - reduction of visual sensitivity during a saccade

Test it out yourself: Look closely in a mirror and shift your gaze from one eye to the other. You will never see the eyes moving. (But you will see the motion if you watch a friend.)

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How do we discriminate motion due to eye movements vs. object movements? Comparator: compensates for retinal motion due to eye movement

  • receives a copy of the order issued by the motor system to the eyes, and

subtracts the expected motion from the retinal motion

Two scenarios with same retinal motion

  • bject motion = eye motion - retinal motion

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