The neuronal basis of the Pulfrich effect in primate

1
The neuronal basis of the Pulfrich effect in
primate

• Jenny Read
• Bruce Cumming

Laboratory of Sensorimotor Research National Eye
Institute National Institutes of Health Bethesda,
Maryland
2
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

3
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

4
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

5
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

6
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

7
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

8
The Pulfrich effect
Reality Perception

• Illusory perception of a moving object when one
  eyes image is delayed

9
Space-time diagram
space
time

• Moving object

10
Space-time diagram
space
time

• Moving object

11
The Pulfrich effect
space
time

• Moving object.
• A delay is introduced in one eyes image.

12
The Pulfrich effect
left
space
right
time

• Moving object.
• A delay is introduced in one eyes image.

13
The Pulfrich effect
left
space
right
time

• Moving object.
• A delay is introduced in one eyes image.
• The object is perceived as moving in depth.

14
The Pulfrich effect
left
space
right
time

• Moving object.
• A delay is introduced in one eyes image.
• The object is perceived as moving in depth.

15
Classical explanation

• Temporal delay is geometrically equivalent to
  spatial disparity

16
Temporal delay is geometrically equivalent to
spatial disparity

• Temporal delay

space
time
17
Temporal delay is geometrically equivalent to
spatial disparity

• Spatial disparity

space
time
18
Classical explanation

• Temporal delay is geometrically equivalent to
  spatial disparity
• so Pulfrich stimulus activates mechanisms which
  usually process spatial disparity.

19
But the classic explanation doesnt seem to work
for the stroboscopic Pulfrich effect(Lee, 1970)
20
Stroboscopic Pulfrich effect
Flashing stimulus, one eye lagging the other.
space
time
now
21
Stroboscopic Pulfrich effect
Flashing stimulus, one eye lagging the other.
No spatial disparity, purely temporal delay.
space
time
interocular delay
22
Neuronal basis of the Pulfrich effect

• Suggestion (Qian Anderson, 1997)
• this occurs because the stimulus activates cells
  which are sensitive both to direction of motion
  and interocular disparity
• joint encoding of motion and disparity.
• This implies receptive fields which are
  inseparable (tilted) in space and time.

23
Direction-selective cells have receptive fields
which are tilted in space and time
space
time
receptive field
24
Receptive fields tuned to disparity and direction
of motion
space
time
left-eye receptive field
25
Designed to respond to a moving disparate object
space
time
now
26
will also respond to a moving object with zero
disparity but a temporal delay
space
time
now
27
Stroboscopic Pulfrich effect

• No spatial disparity, purely temporal delay.

Stroboscopic stimulus activates tilted RFs.
space
time
now
28
Tilted space-time profiles

• How would a cell with tilted RFs respond as a
  function of spatial disparity and interocular
  delay?

29
left RF
right RF
time
time
space
space
With zero interocular delay, where can we place
point stimuli in order to obtain the maximum
response?
30
left RF
right RF
time
time
space
space
zero interocular delay zero spatial disparity
31
left RF
right RF
time
time
space
space
zero interocular delay zero spatial disparity
32
left RF
right RF
time
time
space
space
left leads right near spatial disparity
33
spatial disparity
interocular delay
left leads right near spatial disparity
34
spatial disparity
interocular delay
time
space
35
left RF
right RF
time
time
space
space
right leads left far spatial disparity
36
spatial disparity
interocular delay
right leads left far spatial disparity
37
spatial disparity
time
38
tilted receptive fields imply tilted interaction
profiles
39
preferred disparity changes with delay
interocular delay
delay
spatial disparity
preferred disparity
40
Anzai, Ohzawa, Freeman 2001
Contour colors
positive values
interocular delay (ms)
negative values
interocular disparity (deg)
41
Neuronal basis of the Pulfrich effect

• Anzai et al. found tilted space-time profiles.
• Concluded that this was the neuronal basis of
  the Pulfrich effect.
• Tilted space-time profiles are expected to be
  direction-selective.

42
Neuronal basis of the Pulfrich effect

• Anzai et al. found tilted space-time profiles.
• Concluded that this was the neuronal basis of the
  Pulfrich effect.
• Tilted space-time profiles are expected to be
  direction-selective.
• The Pulfrich effect is mediated by
• direction-selective cells.

43
What role is played by disparity-selective cells
which are not direction-selective?

• In the cat striate cortex, most cells are
  direction-selective.
• In primate V1, only 25 of cells are
  direction-selective.
• So, is joint encoding of motion and disparity
  less common in primate than cat?

44
dynamic random-dot stereograms
R1
L1
disparity
45
dynamic random-dot stereograms
R1
L1
time
46
dynamic random-dot stereograms
R1
L1
L2
R2
time
47
dynamic random-dot stereograms
L1
L2
L3
time
48
dynamic random-dot stereograms with interocular
delay
L1
L2
L3
time
49
dynamic random-dot stereograms with interocular
delay
L1
L2
R4
L3
time
50
dynamic random-dot stereograms with interocular
delay
L1
correlated
L2
uncorrelated
R4
L3
time
51
ruf092
Interocular delay
40
35
30
0 ms
25
firing rate (spikes/s)
20
15
10
5
-0.2
-0.1
0
0.1
0.2
interocular disparity (deg)
52
ruf092
Interocular delay
40
-42ms
35
-28ms
-14ms
30
0 ms
25
14ms
firing rate (spikes/s)
28ms
20
42ms
15
10
5
-0.2
-0.1
0
0.1
0.2
interocular disparity (deg)
53
some cells have tilted profiles
35
42
30
28
25
14
interocular delay (ms)
20
firing rate (spikes/s)
0
15
-14
10
-28
5
-42
-0.2
-0.1
0
0.1
0.2
interocular disparity (deg)
54
but most are space-time separable.
ruf127
28
70
60
14
interocular delay (ms)
50
firing rate (spikes/s)
0
40
-14
30
-28
20
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
interocular disparity (deg)
55
tilt directional index
55
50
45
40
35
30
25
20
15
10
5
0
0
0.25
0.5
0.75
1
magnitude of tilt directional index (TDI)
56
Frequency of tilted profiles
55
50
45
40
35
30
number of cells
25
20
15
10
5
0
0
0.25
0.5
0.75
1
magnitude of tilt directional index (TDI)
57
Differences in method
Anzai et al.
Present results
Potential for psychophysics
Anesthetized cat
Awake behaving monkey
avoids dependence on linearity assumption
Pulfrich effect depends on horizontal disparity
Reverse correlation
Disparity tuning curves
Disparity applied orthogonal to RF
Disparity applied horizontally
58
Reasons for different results

• Fewer direction-selective cells in monkey
• Hence genuinely fewer tilted profiles.
• We applied disparity horizontally
• Hence tilt might be weaker for cells tuned to
  non-vertical orientations.

59
Frequency of tilted profiles
55
50
45
40
35
30
number of cells
25
20
15
10
5
0
0
0.25
0.5
0.75
1
magnitude of tilt directional index (TDI)
60
Summary Conclusions

• Joint encoding of motion and disparity far less
  common in monkey than in cat striate cortex.
• Appears related to less common direction
  selectivity in the monkey.
• Possible that Pulfrich effect depends solely on
  small population with joint encoding
• Alternatively, joint encoding of motion and
  disparity may not be the sole mechanism
  underlying the Pulfrich effect.
• Currently doing modeling work showing that joint
  encoding not necessary to explain stroboscopic
  Pulfrich effect.