Motion-induced colour mixture

1
Motion-induced colour mixture

• Shinya Nishida (1), Junji Watanabe (1, 2),
• Susumu Tachi (2) and Ichiro Kuriki (1)
• (1) NTT Communication Science Laboratories, Japan
• (2) The University of Tokyo, Japan

2
Temporal colour mixture

• Different colours presented closely in time at
  the same retinal location are perceptually mixed.
• Temporal integration improves S/N ratio.
• However, temporal integration based on the
  retinal position is not optimal in our living
  environment, where colours are often attached to
  moving objects.

3
Motion-based colour mixture

• Different colours that stimulate different
  retinal locations, but belong to the same moving
  object, should be mixed.
• Supporting evidence?
• Colour mixture induced in moving slits

4
Colour mixture in moving slits

• When viewed through rapidly moving slits,
  stationary stripes of colour appear to have a
  (tint of) mixed colour of the stripes.

5
Already on the street in Far East!!
6
Tracking eye movement?
Retinal position
Monitor position
Time
Time
7
Apparatus Stimulus
2.75
0.5
2.75
20

• CRS VSG2/5 in Dell Precision 350
• Sony GDM F520 (160Hz, 800 x 600pixels,
  1.5min/pixel at 113cm from the monitor)
• CRS Video Eyetracker toolbox

8
Stimulus in space-time
Frame duration
Exposure duration 200ms (32 monitor refreshes)
Time
Colour width
Slit width
Slit interval
9
Procedures

• 5-scale rating of the degree of colour mixture
• Sample stripes were shown during each response
  period

5 Perfect mixture
4
3 Partial mixture
2
1 No mixture
10
Red/Green Spatiotemporal tuning
Frame duration (ms)
5
JW
4
Rating
3
2
1
0
3
6
9
12
15
Colour width (min)
Slit width Colour width x 2 Red 28 cd/m2 Slit
interval Colour width x 8 Green 84 cd/m2
11
Red/Green Spatiotemporal tuning
Frame duration (ms)
Slit width Colour width x 2 Red 28 cd/m2 Slit
interval Colour width x 8 Green 84 cd/m2
12
No eye tracking
JW Rating 5.0
SN Rating 4.8
Colour width 6.0min Frame duration 6.25ms
13
No change in eye jitter
JW
SN
Error bar1SE
Rating 5.0 1.0
4.8 1.0
14
Blue/Yellow Spatiotemporal tuning
Frame duration (ms)
JW
Slit width Colour width x 2 Blue 15 cd/m2 Slit
interval Colour width x 8 Yellow 112 cd/m2
15
Blue/Yellow Spatiotemporal tuning
Frame duration (ms)
SN
Slit width Colour width x 2 Blue 15 cd/m2 Slit
interval Colour width x 8 Yellow 112 cd/m2
16
Motion or rapid change?

• Stimulus movement induces colour mixture?
• Rapid change (high temporal frequency) lowers
  spatial resolution of the colour system?
• As it lowers spatial resolution of the luminance
  system (Kelly, 1979)

Time
Moving slits
17
Its motion, not rapid change
Time
Frame duration 6.25ms
JW
SN
18
And more ...

• The colour mixture remained to be observed when
  the two colours in the stripes were equiluminant
• An objective test of the perception of mixed
  colour Colour matching
• (Watanabe et al, to be reported at ECVP2004)
• Colour matching to motion-induced colour was
  nearly as accurate as colour matching to
  physically-mixed colour

• Large individual difference
• Fixation stability?
• Ambiguity in event interpretation?

19
Possible mechanisms

• Direction-selective (DS) mechanisms integrate
  colours along motion paths
• DS mechanisms suppress fine (but not coarse)
  non-DS mechanisms

20
Related phenomena

• Binocular colour mixture
• Motion-induced colour spreading (Cicerone et al.,
  1995 Chen Cicerone, 2002)
• Colour decomposition in flash-lag (Nijihawan,
  1997)
• Modulation of chromatic adaptation by target
  motion (Werner, 2004, VSS)
• Spatiotemporal pattern interpolation in
  multi-slit viewing (Ross, 1977 Burr, 1979
  Nishida, in press)

21
Summary

• Colour mixture in moving slits
• Neighboring colours are perceptually mixed when
  they are on the same motion path
• Not an eye movement artifact
• Only for narrow colour stripes rapid motion
• Induced by motion, not by stimulus change

22
Conclusion

• The visual system integrates colour information
  across different samples in space and time when
  they appear to belong to the same moving object.
• Colour mixture is not an early-level phenomenon.
• Colour processing is tightly linked to motion
  processing.

23
Better mixture with narrower slits
Frame duration 6.25ms
2
8
1
4
Time
JW
SN
24
Effects of luminance
Green gt Red gt Background
G R gt B
G R B
Stimulus
Time
Perception
Space
25
Motion-induced reduction of colour mixture
Stimulus
Time
Perception
Space
Moving R/G stripes
Flicker, but R/G are almost mixed

• Consistent with direction-selective
  spatiotemporal integration of colour information