BAND-PASS, LOW-PASS, AND HIGH PASS TUNING
TO MOTION IN DEPTH
Martin Lages, Erich W. Graf, & Alexander Dolia
Department of Psychology, University of Glasgow
INTRODUCTION
RESULTS
We used the Pulfrich effect to investigate motion-in-depth perception.
Sensitivity to interocular phase difference was measured in four
observers who judged direction of motion in depth.
Discrimination thresholds in terms of interocular phase difference were
transformed into horizontal disparity, temporal delay, and velocity difference
to compare spatial and temporal tuning on theses scales.
Actual path of
pendulum bob
Time (t)
4
Neutral
density filter
3
0.4
20
0.3
0.2
10
0.1
EG
1 c/deg
2 c/deg
3 c/deg
4 c/deg
140
120
100
80
60
40
20
0
0.5
1
2
1.5
2
2.5
3
3.5
0
4.5
4
0
0
0.5
1
Temporal Frequency (Hz)
Dt
d
Right Eye
30
0.5
0
1
Left Eye
0.6
40
Disparity Threshold (arcsec)
5
0.7
160
1 c/deg
2 c/deg
3 c/deg
4 c/deg
EG
0
RE
-1
LE
0
1
Space (x)
Fig. 1. Illustration of Pulfrich effect in top view. Space-time plot of
sinusoidal motion with phase lag between the left and right eye.
500
EG
1 c/deg
2 c/deg
3 c/deg
4 c/deg
400
300
200
100
0
0
0.5
1
1.5
2
2.5
3
3.5
4
PROCEDURE. On each trial Ss converged on a fixation cross flanked
by nonius lines before the stimulus was presented. After each
presentation Ss were asked to indicate direction of motion in depth
(CW or CCW when viewed from above). No feedback was given.
E-MAIL: m.lages@psy.gla.ac.uk
ACKNOWLEDGEMENTS
supported by EPSRC and NSF-IRFP
4
4.5
4
4.5
1 c/deg
2 c/deg
3 c/deg
4 c/deg
50
40
30
20
10
0
0.5
1
1.5
2
2.5
3
3.5
Temporal Frequency (Hz)
2
ML
100
1.5
80
60
1
40
0.5
1 c/deg
2 c/deg
3 c/deg
4 c/deg
0
0.5
1
1.5
2
2.5
3
3.5
4
20
0
4.5
600
ML
500
400
300
200
1 c/deg
2 c/deg
3 c/deg
4 c/deg
100
0
0
0.5
1
600
ML
1 c/deg
2 c/deg
3 c/deg
4 c/deg
500
400
300
200
100
0
0
0.5
1
1.5
2
2.5
3
3.5
Temporal Frequency (Hz)
1.5
2
2.5
3
3.5
4
4.5
4
4.5
Temporal Frequency (Hz)
Velocity Difference Threshold (deg/s)
Interocular Delay Threshold (msec)
Temporal Frequency (Hz)
OBSERVERS. Four experienced observers took part.
3.5
Temporal frequency tuning of disparity and phase difference thresholds are
band-pass relatively independent of spatial frequency content whereas tuning
of temporal delay and velocity difference thresholds are high-pass and lowpass, respectively.
0
DESIGN. Direction of motion (left and right) and interocular phase
difference (-p/4 to +p/4) was systematically varied across trials in
randomly intermixed order. Temporal frequency (0.25 to 5 Hz) and
spatial frequency (1 to 4 c/deg) were manipulated in a series of
sessions.
3
EG
60
0
4.5
Binocular Disparity Threshold (arcsec)
STIMULI. Stimuli were presented to the left and right eye on a
calibrated CRT flat screen with a refresh rate of 120 Hz, mean
luminance of 34 cd/sqm and 10% Michelson contrast in a split-screen
Wheatstone configuration. The vertically oriented sine-wave gratings
oscillated sinusoidally for 1 sec in a Gaussian envelope.
2.5
Fig. 2. Discrimination thresholds (rad, arcsec, msec and deg/s) of Observer
EG plotted against temporal frequency (Hz).
Interocular Phase Threshold (rad)
We reproduced the Pulfrich effect with sinusoidal gratings. Phasesensitivity of the binocular motion system was measured by
systematically varying interocular phase difference.
2
70
Temporal Frequency (Hz)
EXPERIMENT
1.5
Temporal Frequency (Hz)
Velocity Difference Threshold (deg/s)
6
sin(t+f) sin(t)
Interocular Delay Threshold (msec)
Apparent path of
pendulum bob
Interocular Phase Threshold (rad)
0.8
4
4.5
250
ML
1 c/deg
2 c/deg
3 c/deg
4 c/deg
200
150
100
50
0
0
0.5
1
1.5
2
2.5
3
3.5
Temporal Frequency (Hz)
Fig. 3. Discrimination thresholds (rad, arcsec, msec and deg/s) of
Observer ML plotted against temporal frequency (Hz).
CONCLUSION
These results support the idea that perception of motion in depth is based
on a system that integrates motion and disparity rather than temporal
delay or velocity difference.