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Neural mechanisms of motion perception.

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Presentation on theme: "Neural mechanisms of motion perception."— Presentation transcript:

1 Neural mechanisms of motion perception

2 Exam #2 Review Session Bausch & Lomb 106,
Exam #2 next Thursday 10/19/17 Exam #2 Review Session Bausch & Lomb 106, 5-7PM, 10/17/17

3 V4 V2, Thick stripes MT V3 4B LIP MSTd 4C V1 STS 5, 6 FEF SC LGN
All the different parts of the motion pathway Complex system to most important parts FEF SC LGN Magno P Retina M

4 M (magnocellular) pathway
Retina LGN M P Main Motion Pathway dorsal stream, action pathway, M (magnocellular) pathway where pathway Different names but same motion pathway Starts with the M cells (M cells good at motion)

5 P M Retina M cells respond strongly to rapid changes in intensity, ideal for conveying motion info to the brain. P M LGN M cells are good for transient events M cells are not direction selective -> more sensitive to abrupt changes in temporal events (good sensitivity) P cells are good for sustained responses (poor in motion processing but good spatial resolution -> poor in sensitivity) Motion on the retina

6 P M Retina M cells respond strongly to rapid changes in intensity, ideal for conveying motion info to the brain. P M LGN V1 V1 : motion is detected: complex cells MT MT : “The motion area” where detected motions are “interpreted” V1 motion detection by complex cells (not all V1) -> subset of cells MST: Complex motion processing MST

7 V1 Motion detection Interpretation of motion MT MST 4b 4c M P Retina
LGN MT MST 4b 4c M P Motion detection V1 First stage you detect local motion signals Interpretation of motion

8 LGN MT MST M P Retina V1 V1 : Motion is detected by directionally selective (DS) complex cells (~15%)

9 Motion Detector ~ Reichardt detector
How to detect motion? Cell only fires when there is synchrony Motion Detector ~ Reichardt detector

10 M-cell M-cell DS-cell Delay t M cell (retina and LGN) DS cell at V1
What is the Delay -> model (longer axon, different position, different cell) DS-cell

11 Delay t Coincidence! Neuron signals rightward motion
Signal gets delayed and the two signals excite the DS cell at the same

12 Neuron does not respond to leftward motion
NO Coincidence! The DS cell only responds when the movement causes from the left to right (not right to left) Studied in a beetle (original Reichartd work in Beetle) Neuron does not respond to leftward motion

13 Responds to rightward motion Responds to leftward motion

14 Apparent Motion Flashes but perceivemotion

15 Apparent Motion

16 Delay t Coincidence! Neuron signals rightward motion
Two flashes in the system -> real motion Neuron signals rightward motion

17 How is speed of motion encoded?
Fast motion Slow Separation between M cell Object has to move faster or slower to reach and cause synchrony Delay constants can be different

18 How is speed of motion encoded?
Fast motion Slow motion

19 Motion Detector ~ Reichardt detector
Good response to rightward motion, + Poor response to leftward motion What happens if the direction of motion is slightly different from preferred direction?

20 Directional Tuning Curve Preferred direction of the neuron Up Down
Right Left Preferred direction of the neuron

21 A neuron tuned to another direction
Directional Tuning Curve Up Down Right Left A neuron tuned to another direction

22 Directional Tuning Curve Up Down Right Left Narrowly tuned neuron

23 Directional Tuning Curve Up Down Right Left Broadly tuned neuron

24 Directionally non-selective neuron
Tuning Curve Up Down Right Left ???????? It is not a directionally tuned neuron Directionally non-selective neuron

25 V1 MT MST M P Retina LGN Interim summary How motion detectors work
-How is the direction and the speed of motion encoded -What is directional tuning of a neuron and how is it measured V1

26 V1 P M P M MT MST Retina LGN Interim summary How motion detectors work
-How is the direction and the speed of motion encoded -What is directional tuning of a neuron and how it is measured V1 MT MST

27 More Problems! V1 good for local motion signals
How does the brain perceive complex signals?

28 More Problems! Local motion signals too many motion signals (motion vectors)

29 More Problems!

30 More Problems!

31 More Problems!

32 You perceive global motion not just the local motion

33 V1 MT 10x Detection Interpretation
RF sizes are different at V1 -> MT Detection Interpretation

34

35 Detection (V1) Interpretation (MT)
big snake giant leaf tree trunk Detection (V1) Interpretation (MT) elephant Hindi Parable (3 blind men going into forest) They touch the object -> snake, tree trunk, leaf What is the global thing -> elephant

36 More Ambiguity! Aperture problem Moral:
The response of one neuron is ambiguous. Combination of outputs among many neurons is necessary to resolve the ambiguity. If you only pay attention to the circle, the object looks like it’s going down While the global motion is going to the right Exactly the same motion (need not only the local information but global motion) V1 level

37 More Ambiguity! Aperture problem Moral:
The response of one neuron is ambiguous. Combination of outputs among many neurons is necessary to resolve the ambiguity. Combine information-> MT

38 V1 MT Aperture problem MT integrates information from V1
People still currently working on the topic -> pooling information

39 Component vs. Pattern motion
More Ambiguity! Component vs. Pattern motion = + Component motion Pattern motion Plaid motion Two things at different angles and sum -> global motion (not just the parts)

40 Component vs. Pattern motion
More Ambiguity! Component vs. Pattern motion = + Component motion Pattern motion V1 MT gives you what you perceive V1 gives you bits and pieces MT + =

41 LGN MT MST M P Retina ~ Integration (pooling) of motion signals is necessary to resolve the ambiguities in the responses of V1 neurons ~ Ambiguities include: “Aperture problem” and “Component vs. Pattern motion” ~ Integration occurs in area MT, which has larger receptive fields than V1 ~ What else do we know about area MT? V1

42 Where is MT? Back of the brain Occipital Cortex Front of the brain
Frontal Cortex MT deeply buried in sulcus

43 Where is MT? Back of the brain Occipital Cortex Front of the brain
Frontal Cortex

44 Where is MT? MT Back of the brain Occipital Cortex V1

45 normal motion perception (inability to perceive motion)
Area MT is critical for normal motion perception MT Patient LM Akinetopsia (inability to perceive motion)

46 Directional maps in MT (using optical imaging)
Upward motion MT with preferred direction of motion Neurons that prefer upward motion become more active

47 Directional maps in MT (using optical imaging)
Downward motion

48 A way of manipulating motion strength: correlation
Strong upward motion Weak upward motion Random motion Add noise to motion to make the global motion less obvious

49 Directional maps in MT (using optical imaging)
weak upward motion Monkey signals perception of upward motion

50 Directional maps in MT (using optical imaging)
weak upward motion + microstimulation of “down” neurons Microelectrode Microstimuliation of the downward motion direction (monkey perceives the downward motion) Monkey signals perception of downward motion

51 LGN MT MST M P Retina ~ Integration of motion signals is necessary to resolve the ambiguities in the responses of V1 neurons ~ Ambiguities include: “Aperture problem” and “Component vs. Pattern motion” ~ Integration occurs in area MT, which has larger receptive fields than V1 ~ Without area MT we don’t see motion ~ Stimulation of MT results in the perception of motion V1 Stimulate MT artificially you perceive motion

52 LGN MT MST M P Retina M cells respond strongly to rapid changes in intensity, ideal for conveying motion info to the brain. V1 V1 : Local motion detection by directionally selective (DS) cells (~15%) MT : “The motion area.” Computation of object motion (~90% DS) MST: Complex motion processing. Optic flow.

53 LGN MT MST M P Retina V1 MST: Complex motion processing. Optic flow.

54 Optic flow MT neurons Expansion Contraction Moving toward the object
or the object is moving toward you Moving away from the object or the object is moving away from you

55 Optic flow Expansion Contraction MT neurons

56 Area MST & Optic flow Expansion Contraction MT neurons

57 Area MST & Optic flow 10x MST neurons
Expansion Contraction MT neurons 10x MST neurons

58 LGN MT MST M P Retina M cells respond strongly to rapid changes in intensity, ideal for conveying motion info to the brain. V1 V1 : Local motion detection by directionally selective (DS) cells (~15%) 10x MT : “The motion area.” Computation of object motion (~90% DS) MST: Complex motion processing. Optic flow.

59 Superior Temporal Sulcus (STS)
Other Motion Areas, e.g.: Superior Temporal Sulcus (STS) STS MT There is more to motion perception than just MT/MST Dots create biological motion STS -> biological motion / MT / object area / social perception Stroke in STS? -> Audio of patient (able to tell the dots, relative information of the dots) Object Area

60 Motion-after effect explanation
Expanding Buddha illusion

61 MAE Explanation Up Up Up Before adaptation During adaptation
Down Before adaptation Up Down During adaptation Up Down After adaptation Downward neurons become more active Stop the motion -> down preferred motion got fatigued

62 Accepted MAE definitions
The illusory impression, after prolonged viewing of movement in one direction, that a stationary object is moving in the opposite direction. Blake & Sekuler (2006) Perception. After prolonged inspection of a moving ‘adapting’ stimulus, a static ‘test’ stimulus appears to move in the opposite direction. Anstis, Verstraten & Mather (1998) TICS The motion after-effect (MAE) is a visual illusion experienced after viewing a moving visual stimulus for about a minute and then looking at stationary stimulus. Somebody, Wikipedia 2008 MAE -> prolonged viewing That is not a correct explanation

63 How does MAE timescale compare to
the time-course of neural adaptation? adapting motion (64 ms) probe motion (64 ms later) Rapid adaptation in MT Priebe et al., 2002, J Neurophysiology Neuron’s adapt more rapidly

64 How does MAE timescale compare to
the time-course of neural adaptation? Rapid adaptation in MT Priebe et al., 2002, J Neurophysiology adapting motion (64 ms) probe motion (126 ms later)

65 How does MAE timescale compare to
the time-course of neural adaptation? Rapid adaptation in MT Priebe et al., 2002, J Neurophysiology adapting motion (64 ms) probe motion (256 ms later)

66 Correct identification
Rapidly generated MAE Correct identification of MAE direction Duje’s lab Very brief motion 60 ms people perceive illusion? Motion is too brief to perceive motion -> but after static it looks like it moves the opposite way 58 ms Adapter duration (number of 8.3 ms movie frames) Glasser et al., 2011, PNAS

67 Correct identification
Rapidly generated MAE Correct identification of MAE direction 58 ms Adapter duration (number of 8.3 ms movie frames) Glasser et al., 2011, PNAS

68 Motion responses to static stimuli in MT
MT neurons signaling ADAPTNG motion MT neurons signaling OPPOSITE motion ROC curve 67 ms of motion adaptation Glasser et al., 2011, PNAS

69 Motion responses to static stimuli in MT
MT neurons signaling ADAPTNG motion MT neurons signaling OPPOSITE motion Opposite (red) = illusion Population level 67 ms of motion adaptation Static test stimulus Glasser et al., 2011, PNAS

70 Motion responses to static stimuli in MT
MT neurons signaling ADAPTNG motion MT neurons signaling OPPOSITE motion 67 ms of motion adaptation Static test stimulus Glasser et al., 2011, PNAS

71 Time to change the MAE definition
The illusory impression, after prolonged viewing of movement in one direction, that a stationary object is moving in the opposite direction. Blake & Sekuler (2006) Perception. After prolonged inspection of a moving ‘adapting’ stimulus, a static ‘test’ stimulus appears to move in the opposite direction. Anstis, Verstraten & Mather (1998) TICS The motion after-effect (MAE) is a visual illusion experienced after viewing a moving visual stimulus for about a minute and then looking at stationary stimulus. Somebody, Wikipedia 2008 Previous classical explanations had to be changed

72 Strong will-power can affect motion perception!
LGN MT MST M P Retina V1 Is this the whole story? Feedback -> Motion perception? Whole story? Clockwise? Counterclockwise? Or flip flop Shifts of Attention? (will power) Feed forward pathway -> there exists feedback pathway There is more to the story Strong will-power can affect motion perception!

73 The End

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