Vision Res. Vol. 32, No. I, pp. 1677171, 1992 Printed in Great Britain. All rights reserved
Copyright
0042-6989/92 $5.00 + 0.00 Q 1992 Pergamon Press plc
Research Note Eye Movements S. H. SEIDMAN,*
During Motion After-effect
R. J. LEIGH,*t$
C. W. THOMAS*
Received 6 February 1991; in revised form 23 May 1991
Using the magnetic search coil technique, we measured torsional eye movements in four male subjects during and after rotation of a visual display around the line of sight. During rotation of the display, subjects developed a torsional nystagmus with slow -phases in the direction of target rotation that had a typical gain of < 0.01. Upon cessation of display motion, subjects experienced a motion after-efSect (MAE) in the direction opposite prior target rotation, which persistedfor > 15sec. During this MAE, slow-phase eye movements of low velocity were in the same direction as the MAE, but did not persist as long as perceptual effects. In separate experiments, horizontal eye movements were recorded during horizontal stimulus motion; during MAE, no eye movements occurred due to stronger fixation mechanisms. We conclude that MAE is not caused by retinal slip of images, but MAE and the accompanying eye movements might be produced by shared or similar mechanisms.
Motion after-effect Human ocular torsion
Magnetic search coil
Eye movement
Optokinetic
nystagmus
(1989) that torsional optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN), although low in gain, do occur when a subject is exposed to a full-field visual stimulus rotating around the line of sight. If OKAN occurs when the target stops, then the retinal slip caused by the OKAN would be in the appropriate direction to cause an apparent reversal of target motion. This would suggest that MAE is, at least in part, due to drift of images on the retina, i.e. “retinal slip”. MAE can also be induced by sustained visual motion in the horizontal plane, but the properties of horizontal fixation and pursuit differ greatly from the torsional case. Our goals, therefore, were to (1) observe eye movements during torsional and horizontal MAE and (2) to determine if MAE was caused by retinal slip following the motion of the target. Some of these findings have been presented in abstract form (Seidman, Thomas, Huebner, Billian & Leigh, 1990).
INTRODUCTION
The motion after-effect (MAE) is an illusory motion perception which follows the viewing of a moving target. After the target stops moving, it appears to move in the opposite direction (Holland, 1965; Wohlgemuth, 1911). This phenomenon, for historical reasons, is also known as the waterfall effect. Eye movements during MAE have not been measured, although there has been speculation as to their presence and effects (Masland, 1969). A popular stimulus for the study of MAE has been a rotating spiral. According to Cavanagh and Favreau (1980), one justification for this particular stimulus has been that rotation of a target around the line of sight involves stimulation of all directions equally, giving rise to the assumption that the eyes do not move during stimulation. This is thought to rule out eye movements as an artifactual cause of the MAE. The eyes, however, are perfectly able to move about the line of sight during this type of stimulation (i.e. torsional, or cyclorotatory eye movements), and therefore the veracity of this assumption requires investigation. It has been shown by Collewijn, Van der Steen, Ferman and Jansen (1985) and by Morrow and Sharpe
METHODS
Four male human subjects, ages 24-43, were studied. All gave informed consent. Two subjects were myopes, one of whom habitually wore contact lenses; none wore corrections during the experiments. Torsional and horizontal rotations of one eye were recorded using a “double-loop” silastic search coil (Skalar, Delft, the Netherlands) and 6 ft field coils (CNC Engineering, Seattle, WA) that employed a rotating field in the horizontal plane and an alternating field in the torsional plane (Seidman & Leigh, 1989). The search coil
*Department of Biomedical Engineering, University Hospitals, Case Western Reserve University and Cleveland Veteran Affairs Medical Center, Cleveland, OH 44106, U.S.A. TDepartments of Neurology, Neuroscience and Otolaryngology, University Hospitals, Case Western Reserve University and Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, U.S.A. fTo whom all correspondence should be addressed at the Department of Neurology, University Hospitals, 2074 Abington Road, Cleveland, OH 44106, U.S.A. 167
IhX
RESEARCH
was precalibrated on a protractor device prior to placement on the subject’s eye. The measurements of eye position were 98.5% linear over an operating range of Ifr20”. The SD of the noise of our coil system was < 1 min arc. The crosstalk artifact on the torsional channel produced by horizontal or vertical rotations was GO.025” torsion per deg of horizontal or vertical movement. Crosstalk of this magnitude did not effect our results. Data were filtered (O-40 Hz) using 4-pole maximally flat filters (Krohn-Hite Corporation, Avon, MA) and digitized at 100 Hz using a 16-bit data acquisition board (Data Translation, Marlborough, MA) installed in an IBM PC-AT computer. Because the torsional eye movements produced by our stimuli were small in magnitude, instantaneous eye velocity was estimated at approx. 75 instances during each trial using an interactive program. This provided a convenient method to view slow-phase direction. Visual targets were generated using an IBM PC-AT with a dedicated board used to create the images. These images were recorded directly on to videotape. A 19” monitor was used to present the stimuli to the subjects. The monitor was placed outside of the magnetic field, and was thus approx. 3 ft from the subject. At this distance, the monitor subtended > 30” of the visual field of the subject, who viewed the display binocularly. Two different groups of stimuli were generated. The first group consisted of circular targets which incorporated 8 or 16 alternating light and dark sectors with a fixation spot in the center, and rotated around the TABLE
NOTF:
line of sight with angular velocities of h0 or 90 deg:sec [Fig. l(A)]. Although this stimulus is not a spiral, MAE is still elicited, and the torsional optokinetic system is stimulated without the presence of complicating linear components. Subjects were requested to fixate upon the center of the rotating display. The second group consisted of 8 or 16 alternating vertical light and dark bars. with a central fixation spot [Fig. l(B)]. These targets moved to the right, and, at the viewing distance of 3 ft. had linear velocities of 6 or 9 deg/sec. Neither the torsional or the horizontal stimuli elicited circularvection (CV) in any subjects. Subjects reported perceptions of motion through use of a continuous potentiometer, which they were asked to rotate at a velocity matching the apparent velocity of the display stimulus. This signal was filtered and digitized in the same manner as the eye position signal. The stationary target was presented on the monitor for a period of 20 sec. At the end of this time period, the target started to move, and continued to do so for 20 sec. The target then stopped moving, but remained visible for a further 60 sec. Data collection began approx. 10 set prior to target movement, and continued for 60 sec. RESULTS Typical responses are shown in Fig. 2, while the responses of all subjects are summarized in Table 1. During rotation of the circular targets, ali subjects 1 Post-movement duration (set)
Target Velocity Subject
Mode
1
T
Sectors
H
T
H
T
H
T
H
T, torsional; H, horizontal; *Not applicable (suppressed tNot measured.
(“isec)
16 16 8 16 16 8 16 16 8 16 16 8 16 16 8
60 90 60 6 9 6 60 90 60 6 9 6 60 90 60
16 16 8 16 16 8 16 16 8
6 9 6 60 90 60 6 9 6
_
Eye movement
Perception 21.0 24.6 233.9 12.6 23.7 27.6 23.3 17.7 18.0 5.9 6.9 6.8 18.7 20.8 16.0
17.2 19.6 26.9 * * * 17.5 12.1 5.6 * * * 6.9 13.2 7.5
t
t
11.8 17.1 24.9
* * 10.0 20.8 11.3 * * *
t t 5.4 5.0 15.0
Gain, optokinetic gain during by fixation, see text).
target
motion
Gain Peak/ steady state 0.01/
Copyright
0042-6989/92 $5.00 + 0.00 Q 1992 Pergamon Press plc
Research Note Eye Movements S. H. SEIDMAN,*
During Motion After-effect
R. J. LEIGH,*t$
C. W. THOMAS*
Received 6 February 1991; in revised form 23 May 1991
Using the magnetic search coil technique, we measured torsional eye movements in four male subjects during and after rotation of a visual display around the line of sight. During rotation of the display, subjects developed a torsional nystagmus with slow -phases in the direction of target rotation that had a typical gain of < 0.01. Upon cessation of display motion, subjects experienced a motion after-efSect (MAE) in the direction opposite prior target rotation, which persistedfor > 15sec. During this MAE, slow-phase eye movements of low velocity were in the same direction as the MAE, but did not persist as long as perceptual effects. In separate experiments, horizontal eye movements were recorded during horizontal stimulus motion; during MAE, no eye movements occurred due to stronger fixation mechanisms. We conclude that MAE is not caused by retinal slip of images, but MAE and the accompanying eye movements might be produced by shared or similar mechanisms.
Motion after-effect Human ocular torsion
Magnetic search coil
Eye movement
Optokinetic
nystagmus
(1989) that torsional optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN), although low in gain, do occur when a subject is exposed to a full-field visual stimulus rotating around the line of sight. If OKAN occurs when the target stops, then the retinal slip caused by the OKAN would be in the appropriate direction to cause an apparent reversal of target motion. This would suggest that MAE is, at least in part, due to drift of images on the retina, i.e. “retinal slip”. MAE can also be induced by sustained visual motion in the horizontal plane, but the properties of horizontal fixation and pursuit differ greatly from the torsional case. Our goals, therefore, were to (1) observe eye movements during torsional and horizontal MAE and (2) to determine if MAE was caused by retinal slip following the motion of the target. Some of these findings have been presented in abstract form (Seidman, Thomas, Huebner, Billian & Leigh, 1990).
INTRODUCTION
The motion after-effect (MAE) is an illusory motion perception which follows the viewing of a moving target. After the target stops moving, it appears to move in the opposite direction (Holland, 1965; Wohlgemuth, 1911). This phenomenon, for historical reasons, is also known as the waterfall effect. Eye movements during MAE have not been measured, although there has been speculation as to their presence and effects (Masland, 1969). A popular stimulus for the study of MAE has been a rotating spiral. According to Cavanagh and Favreau (1980), one justification for this particular stimulus has been that rotation of a target around the line of sight involves stimulation of all directions equally, giving rise to the assumption that the eyes do not move during stimulation. This is thought to rule out eye movements as an artifactual cause of the MAE. The eyes, however, are perfectly able to move about the line of sight during this type of stimulation (i.e. torsional, or cyclorotatory eye movements), and therefore the veracity of this assumption requires investigation. It has been shown by Collewijn, Van der Steen, Ferman and Jansen (1985) and by Morrow and Sharpe
METHODS
Four male human subjects, ages 24-43, were studied. All gave informed consent. Two subjects were myopes, one of whom habitually wore contact lenses; none wore corrections during the experiments. Torsional and horizontal rotations of one eye were recorded using a “double-loop” silastic search coil (Skalar, Delft, the Netherlands) and 6 ft field coils (CNC Engineering, Seattle, WA) that employed a rotating field in the horizontal plane and an alternating field in the torsional plane (Seidman & Leigh, 1989). The search coil
*Department of Biomedical Engineering, University Hospitals, Case Western Reserve University and Cleveland Veteran Affairs Medical Center, Cleveland, OH 44106, U.S.A. TDepartments of Neurology, Neuroscience and Otolaryngology, University Hospitals, Case Western Reserve University and Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, U.S.A. fTo whom all correspondence should be addressed at the Department of Neurology, University Hospitals, 2074 Abington Road, Cleveland, OH 44106, U.S.A. 167
IhX
RESEARCH
was precalibrated on a protractor device prior to placement on the subject’s eye. The measurements of eye position were 98.5% linear over an operating range of Ifr20”. The SD of the noise of our coil system was < 1 min arc. The crosstalk artifact on the torsional channel produced by horizontal or vertical rotations was GO.025” torsion per deg of horizontal or vertical movement. Crosstalk of this magnitude did not effect our results. Data were filtered (O-40 Hz) using 4-pole maximally flat filters (Krohn-Hite Corporation, Avon, MA) and digitized at 100 Hz using a 16-bit data acquisition board (Data Translation, Marlborough, MA) installed in an IBM PC-AT computer. Because the torsional eye movements produced by our stimuli were small in magnitude, instantaneous eye velocity was estimated at approx. 75 instances during each trial using an interactive program. This provided a convenient method to view slow-phase direction. Visual targets were generated using an IBM PC-AT with a dedicated board used to create the images. These images were recorded directly on to videotape. A 19” monitor was used to present the stimuli to the subjects. The monitor was placed outside of the magnetic field, and was thus approx. 3 ft from the subject. At this distance, the monitor subtended > 30” of the visual field of the subject, who viewed the display binocularly. Two different groups of stimuli were generated. The first group consisted of circular targets which incorporated 8 or 16 alternating light and dark sectors with a fixation spot in the center, and rotated around the TABLE
NOTF:
line of sight with angular velocities of h0 or 90 deg:sec [Fig. l(A)]. Although this stimulus is not a spiral, MAE is still elicited, and the torsional optokinetic system is stimulated without the presence of complicating linear components. Subjects were requested to fixate upon the center of the rotating display. The second group consisted of 8 or 16 alternating vertical light and dark bars. with a central fixation spot [Fig. l(B)]. These targets moved to the right, and, at the viewing distance of 3 ft. had linear velocities of 6 or 9 deg/sec. Neither the torsional or the horizontal stimuli elicited circularvection (CV) in any subjects. Subjects reported perceptions of motion through use of a continuous potentiometer, which they were asked to rotate at a velocity matching the apparent velocity of the display stimulus. This signal was filtered and digitized in the same manner as the eye position signal. The stationary target was presented on the monitor for a period of 20 sec. At the end of this time period, the target started to move, and continued to do so for 20 sec. The target then stopped moving, but remained visible for a further 60 sec. Data collection began approx. 10 set prior to target movement, and continued for 60 sec. RESULTS Typical responses are shown in Fig. 2, while the responses of all subjects are summarized in Table 1. During rotation of the circular targets, ali subjects 1 Post-movement duration (set)
Target Velocity Subject
Mode
1
T
Sectors
H
T
H
T
H
T
H
T, torsional; H, horizontal; *Not applicable (suppressed tNot measured.
(“isec)
16 16 8 16 16 8 16 16 8 16 16 8 16 16 8
60 90 60 6 9 6 60 90 60 6 9 6 60 90 60
16 16 8 16 16 8 16 16 8
6 9 6 60 90 60 6 9 6
_
Eye movement
Perception 21.0 24.6 233.9 12.6 23.7 27.6 23.3 17.7 18.0 5.9 6.9 6.8 18.7 20.8 16.0
17.2 19.6 26.9 * * * 17.5 12.1 5.6 * * * 6.9 13.2 7.5
t
t
11.8 17.1 24.9
* * 10.0 20.8 11.3 * * *
t t 5.4 5.0 15.0
Gain, optokinetic gain during by fixation, see text).
target
motion
Gain Peak/ steady state 0.01/
