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Perception and Action > Week 7 Lecture 7 - motion perception > Flashcards

Week 7 Lecture 7 - motion perception Flashcards

1
Q

What is local motion?

A

Motion of individual (local) elements

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2
Q

What is global motion?

A

We can group the motion of many individual elements to perceive a complex pattern of global motion

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3
Q

To process global motion, what do we need?

A

we need to pool information from multiple local motion detectors

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4
Q

What is the motion coherence threshold?

A

minimum proportion of signal dots needed to detect coherent motion

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5
Q

What is humans motion coherence threshold?

A

Humans = 10% (5% when highly practiced)

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6
Q

What does the motion coherence threshold depend on?

A

proportion of signal to noise dots

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7
Q

What size receptive fields do local motion detectors and global motion detectors have?

A

Local motion detectors – small receptive fields
Global motion detectors – large receptive fields

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8
Q

What area of the brain processes motion?

A

area MT = middle temporal

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9
Q

How do we know MT is an important area for motion processing?

A

Single cell recording:
- Nearly all cells in area MT respond to motion – and they have a preferred direction

Artificial Stimulation:
- Salzman et al (1990) – identified cells in monkey area MT that all had same preferred direction
- Artificial stimulation of cells led to motion judgements being biased towards preferred direction

Imaging:
- Tootell et al (1995): fMRI study of the motion after-effect
- When we adapt to motion, then view stationary test, we experience motion in the opposite direction
- Results: MT remains active during period of after-effect (i.e. no direct stimulation, but motion still perceived

Lesions:
- Newsome and Paré (1988) introduced small lesion to monkey MT
- Undamaged coherence thresholds = 5%
- Damaged coherence threshold = 80%

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10
Q

How are different movements created in optic flow?

A
  • Patterns of retinal motion produced when we move
  • Expansion: created by forward translation
  • Contraction: created by backwards translation
  • Horizontal (constant speed): created by eye, head or body rotation
  • Horizontal (parallax): created by lateral (sideways) translation
  • Roll: Created by eye, head or body roll
  • Complex motions: forward translation, head rotation, combined
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11
Q

Smith et al. (2006) comducted an fMRI study to compare 2 cortical sub-regions: MT, MST

Measure response of MT and MST to 5 types of motion:
- Complex
- Expansion
- Rotation (Roll)
- Translation
- Random

What were they interested in?

A

-Interested in the difference in response to optic flow compared to random motion

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12
Q

Smith et al. (2006) comducted an fMRI study to compare 2 cortical sub-regions: MT, MST

Measure response of MT and MST to 5 types of motion:
- Complex
- Expansion
- Rotation (Roll)
- Translation
- Random

What was found?

A
  • The difference in response to optic flow compared to random motion is greater in MST than MT
  • Suggests MST is more specialised for processing optic flow motion than MT
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13
Q

What is optic flow used for?

A

Heading:
- Gibson proposed we use optic flow to tell us where we are heading and to control locomotion

Postural stability:
- Balance relies on vestibular and proprioceptive information but visual information also important
- Optic flow provides information on how our posture is changing

Perception of object motion during self-motion:
- Retinal motion due to 2 sources –>Self motion, Object motion
- Flow-parsing hypothesis

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14
Q

What is the Flow-parsing hypothesis?

A
  • Retinal motion due to self-motion subtracted
  • Remaining motion attributed to object motion
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15
Q

Apart from optic flow, what other information may be used for heading?

A
  • Driving – Land & Lee (1994) showed we don’t look at FOE when driving, we look at other parts of the scene e.g. When on a curved path we look at the tangent
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16
Q

What evidence is there for optic flow’s role in postural stability?

A

The swinging room experiment (Lee & Aronson, 1974):

  • Moving walls and ceiling but floor fixed
  • Simulates the optic flow that would be experienced by a person swaying
  • Participants were 13- 16 month old toddlers
  • When room swings towards toddler it creates pattern of expansion
  • Toddler compensates by swaying backwards
  • When room swings away – toddler sways forwards
  • 26% swayed, 23% staggered and 33% fell over!
  • Adults also found to sway in phase with movements of the room

Conclusion – Optic flow important source of information for balance and can override other sources of balance information

17
Q

What is total optic flow?

A

Total optic flow = Retinal motion (object motion + self motion)

18
Q

What evidence is there for flow parsing?

A

Warren & Rushton (2009):
- an optic flow field influenced the perceived trajectory of a moving object even when the flow was in a different part of the stimulus

  • This provides strong evidence for global processing of optic flow
19
Q

What is biological motion?

A
  • The motion of another person’s body creates a complex pattern of movement
  • Local motion signals need to be integrated to recover the global pattern of motion
  • We appear to be particularly adept at perceiving biological motion
20
Q

What can biological motion provide information about?

A

Biological motion can provide information not only about what someone is doing but also:
- gender
- identity
- affect

21
Q

Grossman & Blake (2001) conducted an fMRI study where participants viewed biological motion vs. scrambled biological motion

What were the results?

A

Area STS (superior temporal sulcus) more active for biological motion compared to scrambled

22
Q

Grossman et al (2005) conducted a TMS experiment where participants viewed biological motion vs scrambled

Noise dots added to make task more difficult

What was the task?

A

Task –is the stimulus biological motion or scrambled?

23
Q

Grossman et al (2005) conducted a TMS experiment where participants viewed biological motion vs scrambled

Noise dots added to make task more difficult

Where was TMS applied?

A

Applied TMS to STS and MT

24
Q

Grossman et al (2005) conducted a TMS experiment where participants viewed biological motion vs scrambled

Noise dots added to make task more difficult

What were the results and conclusion?

A
  • TMS to STS caused significant decrease in ability to distinguish biological motion from scrambled
  • TMS to MT had no effect on biological motion perception
  • Biological motion is a special type of complex motion processed in a specialized area of the brain – area STS

Perception and Action (10 decks)

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