Perceptual and Motor Skills, 1979,48, 943-950. @ Perceptual and Motor Skills 1979
EFFECT OF EYE MOVEMENT O N PERCEPTION OF FLICKER T A D A H l K O FUKUDA
Broadcasting Science Research Laboratories of Nippon Hoso Kyokaz7
Summary.-With 3 experienced subjects CFF during eye movements was higher than that obtained by fixing a line of sight. CFF increased with a moving line of sight. W i t h additional subjects CFF during eye movements was related ro various factors such as target size and conditions of eye movement. More thorough study is required.
Generally the effect of eye movement or stimulus movement is a reduction in visual sensitivity (Brooks & Holden, 1973). It has also been reported that no loss in sensitivity occurs if smooth tracking eye movements are involved (Start, 1969), and with very similar background there is little loss in sensitivity (Volkmann, et al., 1968). In any case, however, there is some loss in sensitivity. W e should note that a loss in sensitivity is observed when spatial stimulation is employed but not when temporal stimulation is employed. Usually our line of sight is not fixed but always moving, and most of the visual information is supposed to be obtained during eye movements. In the present study, we examined the effect of eye movement on perceiving temporal stimulation, i.e., flickering target. The experiment had two parts. In the first, the critical fusion frequency was measured, fixing a line of sight to a stationary point and presenting a flicker stimulus in the fovea and 40' nasal in the periphery. In the second part, a moving target was employed to lead a line of sight, and the effect of eye movement on the CFF was measured.
METHOD A schematic diagram of the experiment is shown in Fig. 1. A subject was seated on a chair with a head rest. The left eye was covered with an eye patch. The subject looked at a fixation point and observed a test stimulus with the right eye without an artificial pupil. The stimulus light was presented on a circular aperture of a light-diffusing sphere mounted behind a background screen which is a large hemisphere with radius of 90 cm. A halogen lamp was used as the light source for the flicker stimulus. The light was sinusoidally modulated by an optical unit and led into the light-diffusing sphere through a light guide. The modulation ratio was kept constant on 100%. The average light intensity was varied using neutral density filters. The inner surface of the hemisphere had a matte white finish. It was uniformly illuminated with 8 Tungsten lamps attached to its edge. A laser spot reflected by a mirror galvanometer was used as a fixation point and a moving 'Or Japan Broadcasting Corporation, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157, Japan.
T. FUKUDA
FIG. 1. A schematic diagram of the experiment target. It was projected on a background screen at a predetermined distance from a flicker stimulus. The viewing distance to both fixation point and test stimulus was 90 an. The method of adjustment was employed for subjective judgment, and the flicker frequency was gradually reduced from fusion to a point at which the subject just perceived the test stimulus as flickering or increased from flickering to a point at which she just perceived it as fused. The CFF value was indicated by a frequency counter on which the operating button was pushed by the subject. Experiments were made mainly on three individuals, two of them were female, aged 2 3 yr. and the other was male aged 32 yr. with no known visual defects. N o corrective lenses were required. They were experienced in such experiments. Another 10 observers were employed to confirm the results. In the first part a line of sight was fixed to a stationary fixation point. CFF was measured at the fovea and a position located 40" from the fovea along the horizontal plane on the nasal retina. In the second part the mirror gal-
EYE MOVEMENT IN FLICKER PERCEPTION
945
vanometer was driven by a sine wave signal from a signal generator so that the moving target moved sinusoidally along the horizontal plane on the same level as the flicker stimulus. The relation between a test field and a stationary fixation point or a moving target is illustrated in Fig. 2. Each subject was instructed to follow the moving target with her line of sight. The amplitudes of the sinusoidal motion were chosen in 1" and 8" in visual angle (peak to peak), and the frequencies were 0.2, 0.5, and 1.0 Hz for each amplitude. The CFF determination was made near the fovea and the position located 40" from the fovea along the horizontal plane on the nasal retina. Both the average luminance of the stimulus target and the background luminance were fixed on 30 cd/m2. The target size varied between 4/4" and 2".
Central Vision A
g s
B J
M
Peripheral Vision
s
M
FIG. 2. The presentation of a moving target to lead a line of sight and a stationary fixation point. Symbols TF, S, and M indicate a test field (flickering stimulus), a stationary fixation point and a moving target, respectively.
RESULTSA N D DISCUSSION Two examples of resula obtained by fixing a line of sight in the first part and those obtained during the eye movements in the second part are illustrated in Fig. 3 in order to allow a direct comparison. These results are obtained under the condition of eye movement whose amplitude is 8" and whose frequency is 0.5 Hz. The upper example shows the CFF in peripheral vision and the lower one shows the CFF in central vision. In each case four plots with the standard deviation at each point indicate the CFF during the eye movements, and dashed line indicates the CFF obtained by fixing a line of sight. As shown in this figure the CFF value obtained during the eye movements is far higher than that obtained by fixing a line of sight in each case. This tendency is commonly noted for the four observers and is also confirmed for another 10 observers without exception. The statistical difference among observers is also small except for Observer ISS in central vision. Furthermore, the increase in the CFF is also confirmed when the line of sight moves not only horizontally but also vertically.
T. FUKUDA C F F Hr
[
0 Peripheral Visbn 0 - 1 (40' U---I RU=UI r.
,
Observers FKD IKI
.
CFF during the eyes move
oHB
Standard deviation
-------__----
_.---
CFF during the eyes are fixed
d-
01
--- ..
'
1/4O
/+----
I
I
Target
I
I
1/2O
lo
,
,
2"
Sire 0 Central Wsion 0
Target
Sire
FIG. 3. Mean crirical flicker frequencies for four observers obtained under the conditions in which a line of sight is fixed to a stationary point (dashed line) and it moves sinusoidally along the horizontal plane ( 4 plots in each point). Borh the average luminance of the stimulus target and the background are fixed o n 30 cd/m2, and the CFF value for 40" nasal (upper) and fovea (lower) are measured.
EYE MOVEMENT I N FLICKER PERCEPTION
--
CFF Hz
0" 4 0 ~ ) M o v i n g Target
+
60
- +40
20
-
OoO)~ i x e dTarget
1.OHz
-
l0
Target Size CFF Hz 70
-
10
-
0-
0.2Hz
1/40 1/20
- 8' lo 2 O Target
Size
FIG. 4. Mean critical flicker frequencies for three observers obtained under the conditions in which a line of sight is fixed to a stationary point and it moves sinusoidally along the horizontal plane. Both the average luminance of the stimulus target and the background are fixed on 30 cd/mS, and the CFF values for the fovea and 40" nasal are measured. The three groups of curves shown on the upper half depict results obtained when the amplitude of the eye movement was lo. and in the three groups on the lower half the amplitude of 8" (peak to peak in visual angle). The full marks indicate the CFF obtained by fixing a line of sight, and the open marks indicate the CFF obtained during eye movement. Circular marks are data for the fovea and square marks for the periphery.
In Fig. 4 the results of various conditions are shown. The three groups of curves in the upper half depict the results obtained when the amplitude of the eye movement was 1' and in the three groups on the lower half with an amplitude of 8'. The frequency of the sinusoidal motion was chosen in 0.2, 0.5, and 1.0 Hz for each amplitude. The open circles indicate the CFF in foveal vision, open squares the CFF in peripheral vision during the eye movements, and full circles the CFF obtained by fixing a line of sight to a point 40' deviation along the horizontal plane. Each plot is the mean of 10 measurements for three observers. As Fig. 4 shows, when a line of sight is fixed, a linear relation holds well between the CFF value and the logarithm of the target size not only in the fovea but also in the periphery. Also, the CFF value obtained in the fovea is higher than that obtained in the periphery in each case. On the other hand, the CFF is higher during the eye movements than when a line of sight is fixed. The CFF value in the periphery is generally lower than that in the fovea when a target size is small (less than 2' at least) as shown in the results for the first part; however, this result suggests the possibility that such a tendency is reversed depending upon the conditions of the eye movement even when the target size is small; for example, the conditions of the eye movement whose amplitude is 1' and whose frequency is 0.5 Hz, the CFF value in the periphery is higher than that in the fovea. The effect of eye movement on perception of flicker varies depending upon the target size and the conditions of eye movement. It is also suggested that CFF becomes maximum at a certain value of the amplitude or speed of eye movement. In Fig. 5 the relation between the CFF during the eye movements and the average angular velocity of eye movement is shown. This is reconstructed from the data shown in Fig. 4. The data for the target size of 2' are given as open circles, those of 1' as filled circles, those of 1/2' as open triangles and those of x0 as filled triangles. The data for foveal vision are given as solid lines and those for peripheral vision as dashed lines. As shown in Fig. 5, the CFF during the eye movements is maximal when the average angular velocity of a line of sight is 16' per second in the fovea and also in the periphery, and regardless of the target size. The effect of target size on the determination of CFF during eye movements is greater in the periphery than in the fovea. An increase in size of test field enlarges the number of retinal elements stimulated and the CFF value also increases with it. The retinal area is scanned by a test field with a certain area projected on the retina during the eye movements. Thus the retinal area stimulated is also enlarged. It seems profitable to suppose that the increase in the CFF value during the eye movements is associated with the enlargement of the retinal area stimulated. But we have to direct our attention to the fact that the CFF is determined not by the total
EYE MOVEMENT IN FLICKER PERCEPTION
CFF Hz Target Size
,, --------- ------&' 20 *-,,.. A-------k'I 10 -
-.
30
“TA
##
&
&
)-""""
,,,-
0
0.8
--. --A
4..
.*
I
I
I
2
4
6.4
Angular Velocity
I
I
16
32
O/ssec.
FIG. 5. The relation between the average angular velocity of a moving target (or a line of sight) and the value of CFF. The solid lines indicate CFF for the fovea and the dashed lines for the periphery. The open circles indicate the data for 2" field, full circles for lo, open triangles for and full triangles for
so,
area of the retina stimulated but by that portion of the retina stimulated which is capable of the best temporal resolution (Roerig, 1959). Accordingly, it seems more profitable to understand the enlargement of the portion of the retina with best resolution is one of the sources of the increase in the CFF value. Comparing the CFF value for a test field with the same area as the scanned area by a moving test field on the retina with those obtained during the eye movements, the former was less than the latter. From this result, another factor caused by the eye movement should be required to explain the increase in the CFF during the eye movements. They might be involved in both photochemical process in the receptor cells of the retina and the transmission of the pulse train to the central nervous system. Further, it appears that increases in the CFF are also closely related to components of the eye movement, i.e., smooth pursuit and saccadic eye movement. Therefore, a more thorough investigation of the increase in the CFF value during eye movements and origin seems highly desirable. REFERENCES
BROOKS, B.,
&
HOLDEN, A. L. Suppression of visual signals by rapid image displace-
950
T. FUKUDA
ment in the pigeon retina: a possible mechanism for "saccadic suppression." Vision Research, 1973, 13, 1387-1390. ROEHRIG.W. C. The influence of the portion of the retina stimulated on the retinal flicker fusion threshold. Journal o f Psychology. 1959, 48, 57-63. STARR,A., ANGEL,R., & YATES,H. Visual suppression during smooch following and saccadic eye movements. Vision Research, 1969, 9, 195-197. VOLKMANN,F. C., SCHICK, A. M. L., & RTGCS,L. A. Time course of visual inhibition during voluntary saccade. Journal o f the Optical Society o f America, 1968, 58,
562-569.
Accepted April 10, 1979.
EFFECT OF EYE MOVEMENT O N PERCEPTION OF FLICKER T A D A H l K O FUKUDA
Broadcasting Science Research Laboratories of Nippon Hoso Kyokaz7
Summary.-With 3 experienced subjects CFF during eye movements was higher than that obtained by fixing a line of sight. CFF increased with a moving line of sight. W i t h additional subjects CFF during eye movements was related ro various factors such as target size and conditions of eye movement. More thorough study is required.
Generally the effect of eye movement or stimulus movement is a reduction in visual sensitivity (Brooks & Holden, 1973). It has also been reported that no loss in sensitivity occurs if smooth tracking eye movements are involved (Start, 1969), and with very similar background there is little loss in sensitivity (Volkmann, et al., 1968). In any case, however, there is some loss in sensitivity. W e should note that a loss in sensitivity is observed when spatial stimulation is employed but not when temporal stimulation is employed. Usually our line of sight is not fixed but always moving, and most of the visual information is supposed to be obtained during eye movements. In the present study, we examined the effect of eye movement on perceiving temporal stimulation, i.e., flickering target. The experiment had two parts. In the first, the critical fusion frequency was measured, fixing a line of sight to a stationary point and presenting a flicker stimulus in the fovea and 40' nasal in the periphery. In the second part, a moving target was employed to lead a line of sight, and the effect of eye movement on the CFF was measured.
METHOD A schematic diagram of the experiment is shown in Fig. 1. A subject was seated on a chair with a head rest. The left eye was covered with an eye patch. The subject looked at a fixation point and observed a test stimulus with the right eye without an artificial pupil. The stimulus light was presented on a circular aperture of a light-diffusing sphere mounted behind a background screen which is a large hemisphere with radius of 90 cm. A halogen lamp was used as the light source for the flicker stimulus. The light was sinusoidally modulated by an optical unit and led into the light-diffusing sphere through a light guide. The modulation ratio was kept constant on 100%. The average light intensity was varied using neutral density filters. The inner surface of the hemisphere had a matte white finish. It was uniformly illuminated with 8 Tungsten lamps attached to its edge. A laser spot reflected by a mirror galvanometer was used as a fixation point and a moving 'Or Japan Broadcasting Corporation, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157, Japan.
T. FUKUDA
FIG. 1. A schematic diagram of the experiment target. It was projected on a background screen at a predetermined distance from a flicker stimulus. The viewing distance to both fixation point and test stimulus was 90 an. The method of adjustment was employed for subjective judgment, and the flicker frequency was gradually reduced from fusion to a point at which the subject just perceived the test stimulus as flickering or increased from flickering to a point at which she just perceived it as fused. The CFF value was indicated by a frequency counter on which the operating button was pushed by the subject. Experiments were made mainly on three individuals, two of them were female, aged 2 3 yr. and the other was male aged 32 yr. with no known visual defects. N o corrective lenses were required. They were experienced in such experiments. Another 10 observers were employed to confirm the results. In the first part a line of sight was fixed to a stationary fixation point. CFF was measured at the fovea and a position located 40" from the fovea along the horizontal plane on the nasal retina. In the second part the mirror gal-
EYE MOVEMENT IN FLICKER PERCEPTION
945
vanometer was driven by a sine wave signal from a signal generator so that the moving target moved sinusoidally along the horizontal plane on the same level as the flicker stimulus. The relation between a test field and a stationary fixation point or a moving target is illustrated in Fig. 2. Each subject was instructed to follow the moving target with her line of sight. The amplitudes of the sinusoidal motion were chosen in 1" and 8" in visual angle (peak to peak), and the frequencies were 0.2, 0.5, and 1.0 Hz for each amplitude. The CFF determination was made near the fovea and the position located 40" from the fovea along the horizontal plane on the nasal retina. Both the average luminance of the stimulus target and the background luminance were fixed on 30 cd/m2. The target size varied between 4/4" and 2".
Central Vision A
g s
B J
M
Peripheral Vision
s
M
FIG. 2. The presentation of a moving target to lead a line of sight and a stationary fixation point. Symbols TF, S, and M indicate a test field (flickering stimulus), a stationary fixation point and a moving target, respectively.
RESULTSA N D DISCUSSION Two examples of resula obtained by fixing a line of sight in the first part and those obtained during the eye movements in the second part are illustrated in Fig. 3 in order to allow a direct comparison. These results are obtained under the condition of eye movement whose amplitude is 8" and whose frequency is 0.5 Hz. The upper example shows the CFF in peripheral vision and the lower one shows the CFF in central vision. In each case four plots with the standard deviation at each point indicate the CFF during the eye movements, and dashed line indicates the CFF obtained by fixing a line of sight. As shown in this figure the CFF value obtained during the eye movements is far higher than that obtained by fixing a line of sight in each case. This tendency is commonly noted for the four observers and is also confirmed for another 10 observers without exception. The statistical difference among observers is also small except for Observer ISS in central vision. Furthermore, the increase in the CFF is also confirmed when the line of sight moves not only horizontally but also vertically.
T. FUKUDA C F F Hr
[
0 Peripheral Visbn 0 - 1 (40' U---I RU=UI r.
,
Observers FKD IKI
.
CFF during the eyes move
oHB
Standard deviation
-------__----
_.---
CFF during the eyes are fixed
d-
01
--- ..
'
1/4O
/+----
I
I
Target
I
I
1/2O
lo
,
,
2"
Sire 0 Central Wsion 0
Target
Sire
FIG. 3. Mean crirical flicker frequencies for four observers obtained under the conditions in which a line of sight is fixed to a stationary point (dashed line) and it moves sinusoidally along the horizontal plane ( 4 plots in each point). Borh the average luminance of the stimulus target and the background are fixed o n 30 cd/m2, and the CFF value for 40" nasal (upper) and fovea (lower) are measured.
EYE MOVEMENT I N FLICKER PERCEPTION
--
CFF Hz
0" 4 0 ~ ) M o v i n g Target
+
60
- +40
20
-
OoO)~ i x e dTarget
1.OHz
-
l0
Target Size CFF Hz 70
-
10
-
0-
0.2Hz
1/40 1/20
- 8' lo 2 O Target
Size
FIG. 4. Mean critical flicker frequencies for three observers obtained under the conditions in which a line of sight is fixed to a stationary point and it moves sinusoidally along the horizontal plane. Both the average luminance of the stimulus target and the background are fixed on 30 cd/mS, and the CFF values for the fovea and 40" nasal are measured. The three groups of curves shown on the upper half depict results obtained when the amplitude of the eye movement was lo. and in the three groups on the lower half the amplitude of 8" (peak to peak in visual angle). The full marks indicate the CFF obtained by fixing a line of sight, and the open marks indicate the CFF obtained during eye movement. Circular marks are data for the fovea and square marks for the periphery.
In Fig. 4 the results of various conditions are shown. The three groups of curves in the upper half depict the results obtained when the amplitude of the eye movement was 1' and in the three groups on the lower half with an amplitude of 8'. The frequency of the sinusoidal motion was chosen in 0.2, 0.5, and 1.0 Hz for each amplitude. The open circles indicate the CFF in foveal vision, open squares the CFF in peripheral vision during the eye movements, and full circles the CFF obtained by fixing a line of sight to a point 40' deviation along the horizontal plane. Each plot is the mean of 10 measurements for three observers. As Fig. 4 shows, when a line of sight is fixed, a linear relation holds well between the CFF value and the logarithm of the target size not only in the fovea but also in the periphery. Also, the CFF value obtained in the fovea is higher than that obtained in the periphery in each case. On the other hand, the CFF is higher during the eye movements than when a line of sight is fixed. The CFF value in the periphery is generally lower than that in the fovea when a target size is small (less than 2' at least) as shown in the results for the first part; however, this result suggests the possibility that such a tendency is reversed depending upon the conditions of the eye movement even when the target size is small; for example, the conditions of the eye movement whose amplitude is 1' and whose frequency is 0.5 Hz, the CFF value in the periphery is higher than that in the fovea. The effect of eye movement on perception of flicker varies depending upon the target size and the conditions of eye movement. It is also suggested that CFF becomes maximum at a certain value of the amplitude or speed of eye movement. In Fig. 5 the relation between the CFF during the eye movements and the average angular velocity of eye movement is shown. This is reconstructed from the data shown in Fig. 4. The data for the target size of 2' are given as open circles, those of 1' as filled circles, those of 1/2' as open triangles and those of x0 as filled triangles. The data for foveal vision are given as solid lines and those for peripheral vision as dashed lines. As shown in Fig. 5, the CFF during the eye movements is maximal when the average angular velocity of a line of sight is 16' per second in the fovea and also in the periphery, and regardless of the target size. The effect of target size on the determination of CFF during eye movements is greater in the periphery than in the fovea. An increase in size of test field enlarges the number of retinal elements stimulated and the CFF value also increases with it. The retinal area is scanned by a test field with a certain area projected on the retina during the eye movements. Thus the retinal area stimulated is also enlarged. It seems profitable to suppose that the increase in the CFF value during the eye movements is associated with the enlargement of the retinal area stimulated. But we have to direct our attention to the fact that the CFF is determined not by the total
EYE MOVEMENT IN FLICKER PERCEPTION
CFF Hz Target Size
,, --------- ------&' 20 *-,,.. A-------k'I 10 -
-.
30
“TA
##
&
&
)-""""
,,,-
0
0.8
--. --A
4..
.*
I
I
I
2
4
6.4
Angular Velocity
I
I
16
32
O/ssec.
FIG. 5. The relation between the average angular velocity of a moving target (or a line of sight) and the value of CFF. The solid lines indicate CFF for the fovea and the dashed lines for the periphery. The open circles indicate the data for 2" field, full circles for lo, open triangles for and full triangles for
so,
area of the retina stimulated but by that portion of the retina stimulated which is capable of the best temporal resolution (Roerig, 1959). Accordingly, it seems more profitable to understand the enlargement of the portion of the retina with best resolution is one of the sources of the increase in the CFF value. Comparing the CFF value for a test field with the same area as the scanned area by a moving test field on the retina with those obtained during the eye movements, the former was less than the latter. From this result, another factor caused by the eye movement should be required to explain the increase in the CFF during the eye movements. They might be involved in both photochemical process in the receptor cells of the retina and the transmission of the pulse train to the central nervous system. Further, it appears that increases in the CFF are also closely related to components of the eye movement, i.e., smooth pursuit and saccadic eye movement. Therefore, a more thorough investigation of the increase in the CFF value during eye movements and origin seems highly desirable. REFERENCES
BROOKS, B.,
&
HOLDEN, A. L. Suppression of visual signals by rapid image displace-
950
T. FUKUDA
ment in the pigeon retina: a possible mechanism for "saccadic suppression." Vision Research, 1973, 13, 1387-1390. ROEHRIG.W. C. The influence of the portion of the retina stimulated on the retinal flicker fusion threshold. Journal o f Psychology. 1959, 48, 57-63. STARR,A., ANGEL,R., & YATES,H. Visual suppression during smooch following and saccadic eye movements. Vision Research, 1969, 9, 195-197. VOLKMANN,F. C., SCHICK, A. M. L., & RTGCS,L. A. Time course of visual inhibition during voluntary saccade. Journal o f the Optical Society o f America, 1968, 58,
562-569.
Accepted April 10, 1979.
