This article was downloaded by: [Central Michigan University] On: 25 December 2014, At: 02:29 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
The Journal of General Psychology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vgen20
Autokinetic Movement of an Induced Afterimage a
Benjamin Wallace & Katharine Blick Hoyenga
a
a
Western Illinois University , USA Published online: 06 Jul 2010.
To cite this article: Benjamin Wallace & Katharine Blick Hoyenga (1978) Autokinetic Movement of an Induced Afterimage, The Journal of General Psychology, 98:2, 173-178, DOI: 10.1080/00221309.1978.9920870 To link to this article: http://dx.doi.org/10.1080/00221309.1978.9920870
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [Central Michigan University] at 02:29 25 December 2014
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
The Journal of General Psychology, 1978, 98. 173-178.
A U T O K I N E T I C M O V E M E N T OF A N I N D U C E D AFTERIMAGE*' 14'4s t prn
BENJAMIN
III i nois U niz1er.vi t y
WALLACE'A N D
KATHARINE
BLICKHOYENGA
Downloaded by [Central Michigan University] at 02:29 25 December 2014
SUMMARY Thirty-two female Ss participated in a n experiment in which autokinetic movement (AKM) direction change frequency of a n induced afterimage was assessed as a function of stimulus afterimage color (yellow or blue-green) and the presence or absence of eye strain. Afterimage color was found not to affect AKM frequency reports. However, eye strain significantly (p < .002) affected such reports, with the fewest AKM direction changes reported when strain was present. These results were explained in terms of an error signal and noise analysis of AKM.
A.
INTRODUCTION
T h e theory of autokinetic movement (AKM) which has received the most experimental support is outflow theory ( 5 ) . Directionally biased drifts of the eye cause retinal displacement of the light and apparent movement of the light in the direction opposite to the eye drift. T h e brain monitors the efferent signals sent to the eye, including the pursuit-like cancelling responses initiated by movement signals. T h e apparent movement appears to be due to the outflow monitoring of the cancelling response, and the light appears to move in the direction of this monitored cancelling response. Since eye strain increases muscle tension and the number of muscle contractions, eye strain should also increase both the number of efferent impulses going to the eye and the number of small eye movements. If AKM is the result of outflow monitoring of the cancelling response initiated by movement of the light, or what has been referred to as an error signal ( 4 , 8 ) , then imposed strain
* Received in the Editorial Office. Provincetown. .Mii.s;ichucetts. on January 1 . 3 . l 9 7 i . Copyright. 1978, h y The Journal Press. ' This research was supported by ;I Bran1 from the Western Illinois Univer5ity Keswrrh Council awarded to the 5enior author. The recult.. were preyentecl at the 1 ith :\nnu;il R-leetinpof the Psychonomic Society. St. Loui3, Missouri, November. 1976. * Reprint requests should he sent to the tird author at the addrrs.. 5hon.n at the end of this article. 173
Downloaded by [Central Michigan University] at 02:29 25 December 2014
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should decrease the AKM by increasing the total number of efferent impulses or the level of background noise. In other words, detection of any one cancelling response should be made more difficult because of the increase in noise, thereby decreasing AKM as measured by frequency of perceived and reported direction changes, corresponding to the number of efferent impulses actually detected ( 7 ) and attributed to light movement. In a previous experiment (8),eye strain was varied by having an S view the stimulus through prisms. In this manner it was found that prism strength had a significant effect such that increasing eye strain significantly decreased the number of reported direction changes, as predicted. Thus, according to these results, there appear to be two separate sources of variance in the AKM. One is the level of background noise and the other is the error signal or the actual movement of the light source across the retina due to the unmonitored eye movements. When, due to undetected eye drifts, the visual target moves across the retina, this movement causes the central nervous system to initiate a correcting response; this correcting response, in order to produce AKM, must be detected above the background efferent noise level. In this analysis the error signal would be subject to the same factors to which the detection of real movement is subject. Since the velocity threshold for peripheral viewing is greater than for central viewing ( I ) , this would mean that when applied to the error signal for AKM, fewer movements of the light across the retina should be detected in the peripheral retina and thus fewer cancelling responses would be initiated. In fact, it was previously found ( 7 ) that peripheral viewing decreased AKM as measured by number of perceived direction changes. In other previous studies concerned with manipulations of the error signal component of AKM (4,S), small, dim lights foveally observed produced the greatest number of AKM direction changes. Also, displacement of the observed light source from a foveal position interacted with the color of the stimulus (4,7). This latter effect was attributed to the effect of the following variables upon the likelihood of detecting an error signal: the paucity of blue cones in the fovea ( 6 ) , the greater sensitivity of rods to blue-green than to yellow lights ( 3 ) , and the changes in retinal interconnections of rods with dark adaptation ( 2 ) . However, increasing viewing angle from the fovea decreased the effects of size, intensity, and color upon the AKM. Thus, apparently increasing the level of background noise produced by muscle tension or strain decreased the effectiveness of the error signal variables. Previous research (4, 7 , 8), therefore, supports the hypothesized distinction between error signal and noise variables in AKM. The AKM is due directly to the efferent monitoring of a cancelling response initiated by the detection of
Downloaded by [Central Michigan University] at 02:29 25 December 2014
BENJAMIN WALLACE AND KATHARINE HOYENGA
175
movement on the retina, the so-called error signal. The initiation of a cancelling response is affected by the same variables that affect the threshold of real movement: color, intensity, and size, with the greatest AKM seen for small, dim, yellow lights, foveally viewed. The monitoring of the efferent signal for the cancelling response must be accompanied against a background of efferent noise. Increasing the noise by increasing eye strain or eye muscle tension either by retinal or prismatic displacement decreases the AKM (4,7 , 8 ) , and this also decreases the effectiveness of all of the error signal variables: color, size, and intensity. The present experiment proposed to test further the theory that there are two independent sources of input for the AKM: error signal (the initiation of a cancelling response) and noise (the detection of the efferent cancelling response amidst a background of efferent activity). Since error signal variables operate within a system requiring that movement of a perceived image occur on the retina, stabilization of such an image should eliminate error signal effects on AKM. When this is the case and there is no movement of the signal across the retina when the eye is moved, no error signals should be generated to produce correction responses. However, there should still be eye drifts and efferent monitored correction responses, and thus, even a stabilized image should appear to move. One method by which a stabilized image can be investigated is to use an afterimage. And, in fact, as Yasui and Young (9) reported, an afterimage is perceived to move across the retina in parallel with and in the same direction as the slow-phase eye movements induced by rotation. Thus, in the present experiment, an afterimage was employed while varying both error signal and noise variables. Color, as an error signal variable which was previously found to affect AKM of a nonstabilized image (4,7), was expected to have no effect on AKM of a stabilized image. This was predicted to be the case, since with such stabilization, movement of an image across the retina does not occur, eliminating the error signal variable of AKM (4,8). Eye strain, induced by requiring Ss to turn their eyes to the right when viewing the afterimage, should decrease AKM by increasing background noise, just as eye strain decreased AKM of a real image (8).
B. 1.
METHOD Subjects
Thirty-two female volunteers from the introductory psychology classes served as Ss. All of the Ss had normal, uncorrected visual acuity and normal color vision. A female graduate student served as the E .
176
JOURNAL O F GENERAL PSYCHOLOGY
Downloaded by [Central Michigan University] at 02:29 25 December 2014
2.
.-lppavatus
The experiment was conducted in a 5.3 x 10.4 m completely light-proofed room. The stimulus to be observed was produced by a single pulse from an electronic 2000 beam candle power per sec Vivitar, model 2 7 2 , flash unit. The actual size of the flash observed was 6 min visual angle. This was accomplished by totally masking the flash unit so that it would emit light only through the small aperture. In addition, the stimulus was flashed through either a yellow Wratten 9 filter (producing a blue-green negative afterimage) or a blue-green Wratten 44A filter (producing a yellow negative afterimage). Stability of theS’s head during the experiment was maintained with a Bausch and Lomb combination head and chin rest. 3.
Design
A 2 x 2 between3 factorial design was employed. The first factor was the color of the afterimage perceived, either yellow or blue-green. The second factor was eye strain, either present or absent. Eight Ss were randomly assigned to each of the four experimental conditions. 4. Procedure The S s were individually tested after 25 min of dark adaptation with red polaroid goggles outside of the experimental room. The S was then led to a light-proofed room and seated in a chair with a back support and an arm rest upon which was mounted the head and chin rest. The polaroid goggles were then removed and the S was required to place her head in the head and chin support. She was then instructed to gaze in the straight ahead position in space. A single light pulse was then flashed through a six min aperture from a distance of two m. The Vivitar unit producing the flash was mounted on an adjustable stand which could be raised or lowered to allow the light source to be projected from an eye-level position. After the flash each S was instructed to close her eyes. Half of the Ss were also instructed to turn their eyes to the right and to keep them turned as far to the right as possible throughout a two min observation trial. Throughout this period, all Ss were required to give a continuous verbal description of perceived movement and to report any change in the course of the afterimage movement. Even slight direction changes were to be reported--e.g., South to South-Southwest. AnyS failing to report seeing a clear afterimage was removed from the analysis; 13 Ss were so removed and replaced with other Ss.
BENJAMIN WALLACE A N D KATHARINE HOYENGA
Downloaded by [Central Michigan University] at 02:29 25 December 2014
C.
177
RESULTS
An analysis of variance was used to assess the effects of eye strain and stimulus afterimage color on the dependent measure, mean number of direction changes reported. Results showed that eye strain significantly affected direction report frequency [F ( 1 , 28) = 11.99,p < .002]. The mean number of reported direction changes for the eye strain condition was 1.6 (SD = .6), while the number of direction changes for the straight ahead viewing condition (no eye turn) was 3 . 3 ( S D = 1.8). Stimulus afterimage color did not affect AKM direction frequency [F(1 , 28) = .15]. The mean numbers of reported direction changes for the yellow and the blue-green afterimage were 2.3 ( S D = 1.8) and 2 . 5 ( S D = 1.4),respectively. The interaction of the two independent variables was also not significant [F(1, 28) = .01].
D. DISCUSSION The results of the present experiment support the hypothesized distinction between error signal and noise variables in the AKM. Eye strain had a significant effect on the number of direction changes reported since instructing Ss to keep their eyes turned reduced the number of direction changes reported even though the afterimage was still stabilized on the retina. When induced eye turn was present, most of the direction changes were attributed by theS to eye movements due to eye muscle strain and not to any movement of the light across the retina. This effect of AKM is in the same direction as the earlier reported effects of different kinds of strain, such as those induced by peripheral viewing and those induced by foveal viewing with eye turn (4,7 ) . Without eye turn, the afterimage of the present experiment went through a relatively large number of direction changes (compared to other employed AKM conditions), indicating that in this case, where there were fewer efferent signals, movements of the eye were attributed to the light. However, unlike earlier experiments (4, 7 ) , color had no effect on AKM with or without eye strain. Thus, for an image which is stabilized on the retina, there was no error signal component of AKM, and the variability in AKM was due solely to noise variables. The present research confirms earlier theorizing (4)as to the existence of two independent components in AKM. The error signal is initiated by the actual movement of the light across the retina due to the unmonitored eye movements, and this component of AKM is affected by color, size, intensity, and the retinal location of the stimulus (4, 7 , 8). The second component of the AKM is due to background noise or the background level of efferent activity in
178
JOURNAL OF GENERAL PSYCHOLOGY
the nerves to the eye muscles. When the background noise is elevated, AKM decreases because of the difficulty in detecting one particular efferent signal against the background noise, such that most of the movement of the stimulus under high noise conditions is interpreted by the observer as being due to eye movements. As such, the movement of the light across the retina causes an error signal, leading to a correction response. Due to efferent monitoring the observer then perceives the light as having moved.
Downloaded by [Central Michigan University] at 02:29 25 December 2014
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9.
AUBERT,H. Die Bewegungsempfindung. Arch. Ges. Physiol. 1886, 39, 347-370. BARLOW, H. B., FITZHUGH, R.,& KUFFLER,S. W. Change of organization in the receptive fields of the cat’s retina during dark adaptation. J. Physiol., 1957, 3, 338-354. CORNSWEET, T. M. Visual Perception. New York: Academic Press, 1970. HOYENGA, K. B., & WALLACE, B. Effects of stimulus size, intensity, color, and eye strain on autokinetic movement: An error signal and noise analysis. J. Cen. Psychol., 1978, 98, 3 7-46. LEVY,J. Autokinetic illusion: A systematic review of theories, measures and independent variables. Psychol. Bull., 1972, 78, 457-474. WALD,G. Blue blindness in the normal fovea. J . Opt. SOL. Amer., 1967, 57, 1289-1301. WALLACE,B., & HOYENGA,K. B. Outflow theory and autokinetic movements: Color, viewing angle, and dark adaptation. Amer. J . Psychol., 1975, 88, 107-115. -. Prismatically induced eye strain and autokinetic direction frequency. J . Gen. Psychol., 1978, 98, 15-21. YASUI,S., & YOUNG, L. R. Perceived visual motion as effective stimulus to pursuit eye movement system. Science, 1975. 190, 906-908.
Department of Psychology Cleveland State University Cleveland, Ohio 44115
The Journal of General Psychology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vgen20
Autokinetic Movement of an Induced Afterimage a
Benjamin Wallace & Katharine Blick Hoyenga
a
a
Western Illinois University , USA Published online: 06 Jul 2010.
To cite this article: Benjamin Wallace & Katharine Blick Hoyenga (1978) Autokinetic Movement of an Induced Afterimage, The Journal of General Psychology, 98:2, 173-178, DOI: 10.1080/00221309.1978.9920870 To link to this article: http://dx.doi.org/10.1080/00221309.1978.9920870
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [Central Michigan University] at 02:29 25 December 2014
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
The Journal of General Psychology, 1978, 98. 173-178.
A U T O K I N E T I C M O V E M E N T OF A N I N D U C E D AFTERIMAGE*' 14'4s t prn
BENJAMIN
III i nois U niz1er.vi t y
WALLACE'A N D
KATHARINE
BLICKHOYENGA
Downloaded by [Central Michigan University] at 02:29 25 December 2014
SUMMARY Thirty-two female Ss participated in a n experiment in which autokinetic movement (AKM) direction change frequency of a n induced afterimage was assessed as a function of stimulus afterimage color (yellow or blue-green) and the presence or absence of eye strain. Afterimage color was found not to affect AKM frequency reports. However, eye strain significantly (p < .002) affected such reports, with the fewest AKM direction changes reported when strain was present. These results were explained in terms of an error signal and noise analysis of AKM.
A.
INTRODUCTION
T h e theory of autokinetic movement (AKM) which has received the most experimental support is outflow theory ( 5 ) . Directionally biased drifts of the eye cause retinal displacement of the light and apparent movement of the light in the direction opposite to the eye drift. T h e brain monitors the efferent signals sent to the eye, including the pursuit-like cancelling responses initiated by movement signals. T h e apparent movement appears to be due to the outflow monitoring of the cancelling response, and the light appears to move in the direction of this monitored cancelling response. Since eye strain increases muscle tension and the number of muscle contractions, eye strain should also increase both the number of efferent impulses going to the eye and the number of small eye movements. If AKM is the result of outflow monitoring of the cancelling response initiated by movement of the light, or what has been referred to as an error signal ( 4 , 8 ) , then imposed strain
* Received in the Editorial Office. Provincetown. .Mii.s;ichucetts. on January 1 . 3 . l 9 7 i . Copyright. 1978, h y The Journal Press. ' This research was supported by ;I Bran1 from the Western Illinois Univer5ity Keswrrh Council awarded to the 5enior author. The recult.. were preyentecl at the 1 ith :\nnu;il R-leetinpof the Psychonomic Society. St. Loui3, Missouri, November. 1976. * Reprint requests should he sent to the tird author at the addrrs.. 5hon.n at the end of this article. 173
Downloaded by [Central Michigan University] at 02:29 25 December 2014
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JOURNAL O F GENERAL PSYCHOLOGY
should decrease the AKM by increasing the total number of efferent impulses or the level of background noise. In other words, detection of any one cancelling response should be made more difficult because of the increase in noise, thereby decreasing AKM as measured by frequency of perceived and reported direction changes, corresponding to the number of efferent impulses actually detected ( 7 ) and attributed to light movement. In a previous experiment (8),eye strain was varied by having an S view the stimulus through prisms. In this manner it was found that prism strength had a significant effect such that increasing eye strain significantly decreased the number of reported direction changes, as predicted. Thus, according to these results, there appear to be two separate sources of variance in the AKM. One is the level of background noise and the other is the error signal or the actual movement of the light source across the retina due to the unmonitored eye movements. When, due to undetected eye drifts, the visual target moves across the retina, this movement causes the central nervous system to initiate a correcting response; this correcting response, in order to produce AKM, must be detected above the background efferent noise level. In this analysis the error signal would be subject to the same factors to which the detection of real movement is subject. Since the velocity threshold for peripheral viewing is greater than for central viewing ( I ) , this would mean that when applied to the error signal for AKM, fewer movements of the light across the retina should be detected in the peripheral retina and thus fewer cancelling responses would be initiated. In fact, it was previously found ( 7 ) that peripheral viewing decreased AKM as measured by number of perceived direction changes. In other previous studies concerned with manipulations of the error signal component of AKM (4,S), small, dim lights foveally observed produced the greatest number of AKM direction changes. Also, displacement of the observed light source from a foveal position interacted with the color of the stimulus (4,7). This latter effect was attributed to the effect of the following variables upon the likelihood of detecting an error signal: the paucity of blue cones in the fovea ( 6 ) , the greater sensitivity of rods to blue-green than to yellow lights ( 3 ) , and the changes in retinal interconnections of rods with dark adaptation ( 2 ) . However, increasing viewing angle from the fovea decreased the effects of size, intensity, and color upon the AKM. Thus, apparently increasing the level of background noise produced by muscle tension or strain decreased the effectiveness of the error signal variables. Previous research (4, 7 , 8), therefore, supports the hypothesized distinction between error signal and noise variables in AKM. The AKM is due directly to the efferent monitoring of a cancelling response initiated by the detection of
Downloaded by [Central Michigan University] at 02:29 25 December 2014
BENJAMIN WALLACE AND KATHARINE HOYENGA
175
movement on the retina, the so-called error signal. The initiation of a cancelling response is affected by the same variables that affect the threshold of real movement: color, intensity, and size, with the greatest AKM seen for small, dim, yellow lights, foveally viewed. The monitoring of the efferent signal for the cancelling response must be accompanied against a background of efferent noise. Increasing the noise by increasing eye strain or eye muscle tension either by retinal or prismatic displacement decreases the AKM (4,7 , 8 ) , and this also decreases the effectiveness of all of the error signal variables: color, size, and intensity. The present experiment proposed to test further the theory that there are two independent sources of input for the AKM: error signal (the initiation of a cancelling response) and noise (the detection of the efferent cancelling response amidst a background of efferent activity). Since error signal variables operate within a system requiring that movement of a perceived image occur on the retina, stabilization of such an image should eliminate error signal effects on AKM. When this is the case and there is no movement of the signal across the retina when the eye is moved, no error signals should be generated to produce correction responses. However, there should still be eye drifts and efferent monitored correction responses, and thus, even a stabilized image should appear to move. One method by which a stabilized image can be investigated is to use an afterimage. And, in fact, as Yasui and Young (9) reported, an afterimage is perceived to move across the retina in parallel with and in the same direction as the slow-phase eye movements induced by rotation. Thus, in the present experiment, an afterimage was employed while varying both error signal and noise variables. Color, as an error signal variable which was previously found to affect AKM of a nonstabilized image (4,7), was expected to have no effect on AKM of a stabilized image. This was predicted to be the case, since with such stabilization, movement of an image across the retina does not occur, eliminating the error signal variable of AKM (4,8). Eye strain, induced by requiring Ss to turn their eyes to the right when viewing the afterimage, should decrease AKM by increasing background noise, just as eye strain decreased AKM of a real image (8).
B. 1.
METHOD Subjects
Thirty-two female volunteers from the introductory psychology classes served as Ss. All of the Ss had normal, uncorrected visual acuity and normal color vision. A female graduate student served as the E .
176
JOURNAL O F GENERAL PSYCHOLOGY
Downloaded by [Central Michigan University] at 02:29 25 December 2014
2.
.-lppavatus
The experiment was conducted in a 5.3 x 10.4 m completely light-proofed room. The stimulus to be observed was produced by a single pulse from an electronic 2000 beam candle power per sec Vivitar, model 2 7 2 , flash unit. The actual size of the flash observed was 6 min visual angle. This was accomplished by totally masking the flash unit so that it would emit light only through the small aperture. In addition, the stimulus was flashed through either a yellow Wratten 9 filter (producing a blue-green negative afterimage) or a blue-green Wratten 44A filter (producing a yellow negative afterimage). Stability of theS’s head during the experiment was maintained with a Bausch and Lomb combination head and chin rest. 3.
Design
A 2 x 2 between3 factorial design was employed. The first factor was the color of the afterimage perceived, either yellow or blue-green. The second factor was eye strain, either present or absent. Eight Ss were randomly assigned to each of the four experimental conditions. 4. Procedure The S s were individually tested after 25 min of dark adaptation with red polaroid goggles outside of the experimental room. The S was then led to a light-proofed room and seated in a chair with a back support and an arm rest upon which was mounted the head and chin rest. The polaroid goggles were then removed and the S was required to place her head in the head and chin support. She was then instructed to gaze in the straight ahead position in space. A single light pulse was then flashed through a six min aperture from a distance of two m. The Vivitar unit producing the flash was mounted on an adjustable stand which could be raised or lowered to allow the light source to be projected from an eye-level position. After the flash each S was instructed to close her eyes. Half of the Ss were also instructed to turn their eyes to the right and to keep them turned as far to the right as possible throughout a two min observation trial. Throughout this period, all Ss were required to give a continuous verbal description of perceived movement and to report any change in the course of the afterimage movement. Even slight direction changes were to be reported--e.g., South to South-Southwest. AnyS failing to report seeing a clear afterimage was removed from the analysis; 13 Ss were so removed and replaced with other Ss.
BENJAMIN WALLACE A N D KATHARINE HOYENGA
Downloaded by [Central Michigan University] at 02:29 25 December 2014
C.
177
RESULTS
An analysis of variance was used to assess the effects of eye strain and stimulus afterimage color on the dependent measure, mean number of direction changes reported. Results showed that eye strain significantly affected direction report frequency [F ( 1 , 28) = 11.99,p < .002]. The mean number of reported direction changes for the eye strain condition was 1.6 (SD = .6), while the number of direction changes for the straight ahead viewing condition (no eye turn) was 3 . 3 ( S D = 1.8). Stimulus afterimage color did not affect AKM direction frequency [F(1 , 28) = .15]. The mean numbers of reported direction changes for the yellow and the blue-green afterimage were 2.3 ( S D = 1.8) and 2 . 5 ( S D = 1.4),respectively. The interaction of the two independent variables was also not significant [F(1, 28) = .01].
D. DISCUSSION The results of the present experiment support the hypothesized distinction between error signal and noise variables in the AKM. Eye strain had a significant effect on the number of direction changes reported since instructing Ss to keep their eyes turned reduced the number of direction changes reported even though the afterimage was still stabilized on the retina. When induced eye turn was present, most of the direction changes were attributed by theS to eye movements due to eye muscle strain and not to any movement of the light across the retina. This effect of AKM is in the same direction as the earlier reported effects of different kinds of strain, such as those induced by peripheral viewing and those induced by foveal viewing with eye turn (4,7 ) . Without eye turn, the afterimage of the present experiment went through a relatively large number of direction changes (compared to other employed AKM conditions), indicating that in this case, where there were fewer efferent signals, movements of the eye were attributed to the light. However, unlike earlier experiments (4, 7 ) , color had no effect on AKM with or without eye strain. Thus, for an image which is stabilized on the retina, there was no error signal component of AKM, and the variability in AKM was due solely to noise variables. The present research confirms earlier theorizing (4)as to the existence of two independent components in AKM. The error signal is initiated by the actual movement of the light across the retina due to the unmonitored eye movements, and this component of AKM is affected by color, size, intensity, and the retinal location of the stimulus (4, 7 , 8). The second component of the AKM is due to background noise or the background level of efferent activity in
178
JOURNAL OF GENERAL PSYCHOLOGY
the nerves to the eye muscles. When the background noise is elevated, AKM decreases because of the difficulty in detecting one particular efferent signal against the background noise, such that most of the movement of the stimulus under high noise conditions is interpreted by the observer as being due to eye movements. As such, the movement of the light across the retina causes an error signal, leading to a correction response. Due to efferent monitoring the observer then perceives the light as having moved.
Downloaded by [Central Michigan University] at 02:29 25 December 2014
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9.
AUBERT,H. Die Bewegungsempfindung. Arch. Ges. Physiol. 1886, 39, 347-370. BARLOW, H. B., FITZHUGH, R.,& KUFFLER,S. W. Change of organization in the receptive fields of the cat’s retina during dark adaptation. J. Physiol., 1957, 3, 338-354. CORNSWEET, T. M. Visual Perception. New York: Academic Press, 1970. HOYENGA, K. B., & WALLACE, B. Effects of stimulus size, intensity, color, and eye strain on autokinetic movement: An error signal and noise analysis. J. Cen. Psychol., 1978, 98, 3 7-46. LEVY,J. Autokinetic illusion: A systematic review of theories, measures and independent variables. Psychol. Bull., 1972, 78, 457-474. WALD,G. Blue blindness in the normal fovea. J . Opt. SOL. Amer., 1967, 57, 1289-1301. WALLACE,B., & HOYENGA,K. B. Outflow theory and autokinetic movements: Color, viewing angle, and dark adaptation. Amer. J . Psychol., 1975, 88, 107-115. -. Prismatically induced eye strain and autokinetic direction frequency. J . Gen. Psychol., 1978, 98, 15-21. YASUI,S., & YOUNG, L. R. Perceived visual motion as effective stimulus to pursuit eye movement system. Science, 1975. 190, 906-908.
Department of Psychology Cleveland State University Cleveland, Ohio 44115
