Information Processing Analysis of the Chevreul Pendulum Illusion Randolph D

Journal of Experimental Psychology: Human Perception and Performance 1975, Vol. 1, No. 3, 231-236

Information Processing Analysis of the Chevreul Pendulum Illusion Randolph D. Easton Ronald E. Shor Boston College University of New Hampshire

An information processing investigation was performed to quantify the Chevreul pendulum effect: the tendency of a small pendulum, when suspended from the hand and imaginatively concentrated on, to oscillate seemingly of its own accord. Using a time exposure photographic measure- ment technique, electronically automated visual and auditory imaginal prompts were presented to the subject during imaginal processing tasks. It was found that the pendulum effect was enhanced when vision of actual pendulum oscillations was permitted and visual or auditory spatially oscillating stimuli were present. Visual spatially oscillating stimuli were superior to their auditory counterparts. Results were discussed in terms of ideomotor and visual capture interpretations of signal and imaginal processing.

The construct of ideomotor behavior—the interpretation of the manner in which ex- tendency of thoughts and images of action ternal stimulation and sensory feedback may to become actualized in behavior automat- be involved in the regulation of skilled per- ically—was first brought into the boundaries formance. In other endeavors a renewed of scientific psychology in a series of experi- interest in mental imagery has resulted in ments on alleged spiritualistic phenomena by the development of reliable empirical meth- the French chemist Michel Chevreul (1833, ods to investigate nonverbal representational 1854). Later in the century James (1890) processes (Sheehan, 1972). Finally, mod- succinctly stated the issue by proposing that ern electromyographic techniques have pro- the perceptual image or idea of action initi- vided substantial evidence confirming the ates performance of that action when no ideomotor correlations obtained by early other contradictory idea is present in the behaviorists (McGuigan & Schoonover, mind. The psychological concept of an idea, 1973). Whether or not a motor theory of however, proved not to be respectable within consciousness has validity (Miller, 1969; rigorous behavior theory and the ideomotor Smith, K., 1964, 1969; Smith, S. M., Brown, principle eventually fell into disrepute Teman, & Goodman, 1947), it is evident (Thorndike, 1913; Watson, 1930). that experiments designed to explore the Recent lines of research, however, sug- topography of covert muscle movements that gest the efficacy of the proposed ideomotor are correlated with the symbolic processes principle as a means of exploring certain should help elucidate the nature of imaginal cognitive processes. Greenwald and his representation. This article reports the de- associates (Greenwald, 1970, 1972; Green- velopment of a method aimed at exploring wald & Shulman, 1973) have demonstrated the relations among covert muscle behavior, the utility of the ideomotor principle as an mental imagery, and the perception of external stimulation. This study was supported in part by U. S. The present method uses a pendulum-type National Defense Education Act Title IV Fellow- ship 70-02501 awarded to the first author and by device similar to that used by Chevreul Departmental Science Development Grant GU- which consists of a weighted body suspended 3845 from the National Science Foundation. We by a cord from the fingertips. The pen- wish to thank R. L. Erickson, G. A. Forsyth, and dulum was found to oscillate back and forth J. E. Limber for their helpful comments. Requests for reprints should be sent to Randolph when imaginatively concentrated on, seem- D. Easton, Psychology Department, Boston Col- ingly of its own accord. The actual experi- lege, Chestnut Hill, Massachusetts 02167. ence of seeing the pendulum move is an 231 232 RANDOLPH D. EASTON AND RONALD E. SHOR illusion since an operator does not feel his experiment was designed to substantiate this muscles initiate and maintain the movements, argument empirically. A photographic time when in fact they are the sole agency. exposure technique (described below) was Theoretically, the illusion could arise in one used to compare the magnitude of pendulum of two ways that are not necessarily exclu- oscillations when subjects imagined the pen- sive alternatives. First, the movement could dulum moved back and forth, imagined the indeed occur in an ideomotor way, as an pendulum remained absolutely still, or main- automatic motoric consequence of a central tained as neutral an attitude as possible with neural mechanism's activity, that is, of a regard to pendulum motion. The result kinetic representation or image. Alterna- was that the pendulum moved about 10 tively (or in addition), the subject, in an times as much in the kinetic imagination effort to produce what he has been instructed condition as in the others. The implication to do, namely, to construct a visual imagina- of this finding is that the pendulum can be tion of movement, may initiate pendular held still and that its movements must be movements via small hand movements of the result of psychological processes. Thus, which he is unaware. The literature on a second, more comprehensive experiment visual capture (Gibson, 1933; Nielsen, 1963; was designed to isolate strong parametric Pick, Warren, & Hay, 1969; Rock, 1966; influences of the pendulum motion. Ryan, 1940) indicates that conscious mon- The results of that experiment (Easton & itoring of kinesthetic information is difficult Shor, Note 1) indicated that the extent of in the presence of simultaneous visual in- pendulum motion depended on whether the formation. Thus, without violating the musculature of the entire arm or just the general instruction not to consciously or hand cuffed at the wrist was involved in the deliberately move the pendulum, the subject suspension of the pendulum. When the may do so in an effort to create a kinetic arm was freed, the magnitudes of oscillation image. Such an effect would be quite con- increased except when subjects were re- sistent with the Perky phenomenon which quired to concentrate simultaneously on two indicates that low intensity stimuli may be conceptually antithetical ideas. When sub- confused with an image and that partially jects directed their attention solely to an processed sensory input could trigger a image of movement and were not required seemingly autonomous image (Perky, 1910; to perform cognitive tasks with dual com- Segal, 1972). ponents, resultant pendulum oscillations were The first question asked in previous most extensive, especially when visual and/ experiments designed to quantify the pen- or auditory imaginal prompts were present. dulum effect was whether the pendulum The auditory prompts consisted of the ex- moves simply because the hand cannot be perimenter speaking a back-and-forth ca- held absolutely still. A conceptual analysis dence in the harmonic period of the pen- of the physical principles of the pendulum dulum. The visual prompts consisted of the revealed that all excitatory movements not experimenter moving his hand back and in or near the resonant frequency of the forth beneath the pendulum in its harmonic pendulum would lessen the resonant energy period. The facilitative effect of the verbal of the system (Crandall & Marks, 1963). prompts factor proved to be small and was As only a small portion of natural bodily restricted to specific levels of other factors. movements would be in phase with the In sharp contrast, visual prompts exerted period of the pendulum, the overall effect an overall facilitative influence, suggesting of random movements would be to attenuate the potency of visual stimulation on the the resonant energy. The periodicity of pendulum effect. It was also found that covert responses correlated with subjects' females tended to create more pendulum imagined pendular movement, however, movement than males. should be close to the resonant frequency The experiment to be presented in this of the pendulum, allowing it to act as a report was designed to make the experi- mechanical amplifier. A very simple initial mental method more precise and to explore CHEVREUL PENDULUM ILLUSION 233 ideomotor and visual capture explanations 16-mm movie camera with facility for single-frame of the pendulum effect. Fulfilling these ob- time exposures was positioned to take photographs of the backboard area. The white pendulum held jectives required automating the means of in front of the black backboard permitted time ex- presenting the visual and auditory imaginal posure photographs of the pendulum's side-to-side prompts. Visual stimulation was designed motion with excellent contrast and clarity. which consisted of a vertical white line that Three types of automated imaginal prompts oscillated horizontally on a television moni- were used. The oscillating visual stimulus was a dc voltage sweep generated by an oscillator, dis- tor. Two types of moving auditory stim- played on an oscilloscope, and then videotaped ulation were developed and compared with and played on a 53-cm television monitor. The the visual stimulus. First an ascending- monitor, tipped at a 15° angle away from a vertical descending tone (more concrete than the position, was placed 1 m in front of the subject. The generated vertical white line thus oscillated back-and-forth utterances used previously) horizontally on the television screen 25 cm from was developed. The second auditory stim- side to side. When the occlusion board was not ulus was designed with a direct spatial in place the subject could watch the pendulum and component; a tone appeared to move back at the same time monitor the visual imaginal and forth through space between the sub- prompt in attention. The pendulum and television monitor were not spatially interposed. When the jects' ears. board was in place only the monitor was visible. Also tested was the effectiveness of the The first auditory stimulus was an ascending- imaginal prompts versus no imaginal descending tone (450-850 Hz) presented binaurally prompts under conditions where the subject through earphones. The second auditory stim- could either see or not see the actual pen- ulus involved the dichotic presentation of two amplitude modulated tones (500 Hz). The mod- dulum motion. A visual capture explana- ulation of the tone to one ear was 180° out of tion of the pendulum effect would maintain phase with the modulation of the tone to the that sight of the pendulum is crucial, espe- other ear. The perceived impression was that of cially when no imaginal prompts are present. a single tone moving back and forth laterally in space, between the ears. If sight was occluded no pendulum move- All of the oscillating stimuli were generated ment should result, as the occurrence of sinusoidally and timed to correspond to the exact small hand movements would be unlikely. harmonic period of the pendulum's sinusoidal Since visual information would be absent, motion. The phase relationship between the small hand movements in or near the reson- motion of prompts and the pendulum was not controlled in this experiment. ant frequency of the pendulum would not Timers were arranged to provide a 30-sec only be more easily detected but should not delay interval after the onset of a trial followed occur at all as they could not result in an by a 6-sec single-frame time exposure. The 30- image via visual feedback. The ideomotor sec delay interval allowed time for the pendulum theory, on the other hand, would not hold to overcome inertia and build up to a stable level of motion. The 6-sec time exposure allowed the that visual feedback of pendulum oscilla- pendulum to sweep out about four cycles of tions is necessary. oscillation. As hand movements were uniformly very small during the trial, the picture on the METHOD photographic negative consisted of a shaded isosceles triangle with a curved base, representing Apparatus and materials the area of the pendulum's motion. Protractor The pendulum bob consisted of a silver-colored measurements of the angle of the apex of the 35-mm film canister, 45 mm high by 30 mm in triangle were taken directly from an enlarged diameter with a tapered top, weighted to 86 g. image of the negative frame. Inter- and intra- Attached to the center of its top was a 3 mm (in judge differences were found to be random and diameter) white nylon cord 61 cm long. When within .2° yielding reliability coefficients of .95 in use the pendulum was held in front of a 90 cm and above. high by 60 cm wide black backboard mounted on Subjects were required to wear a heavy leather a 30 cm high pedestal; the subject stood behind glove lined with cotton. This was sufficient to the backdrop, extending the hand holding the pen- sharply reduce or to remove reported awareness dulum over its top, and looked down at the pendu- of tactual feedback. lum against the black top of the pedestal. A removable board was affixed to the top of the Subjects backboard which, when in place, occluded sight Eight male and seven female introductory psy- of the pendulum but not of the visual prompts. A chology students fulfilling requirements at the 234 RANDOLPH D. EASTON AND RONALD E. SHOR

University of New Hampshire served as sub- randomly determined. The eight trials per block jects. represented the crossed levels of the type-of- imaginal-prompt and occlusion factors. Procedure Subjects were run individually. Upon entering RESULTS the experimental room subjects were told that the experimenter was interested in studying imagina- The data were analyzed by means of a tion and concentration. They were informed that three-factor analysis of variance with re- their basic task was simply to hold the pendulum peated measures. No sex differences (main between thumb and forefinger over the backboard, or interactive) emerged in an initial four- and while keeping their eyes on the pendulum, factor analysis. Means for all experimental to imagine that the pendulum moves back and forth. The subjects were asked to refrain from conditions are presented in Table 1. A moving the pendulum deliberately. They were graphic depiction of the significant effects told to keep their head and body relaxed but still. is presented in Figure 1. As can be seen, They were asked, as far as their basic task was the magnitude of pendulum movement was concerned, to try to exclude other thoughts from active processing. The experimenter attempted significantly larger when sight of the actual to maintain a neutral, detached attitude while con- pendulum oscillations was permitted, F(l, ducting the experimental session. 14) = 6.09, p < .05. All three types of Further instructions to subjects indicated that on imaginal prompts significantly facilitated the some trials auxiliary stimuli would be presented in either an auditory or visual mode that could buildup of pendulum motion, F(3, 42) = potentially strengthen their imaginal efforts. They 18.55, p < .001. However, a Newman- were asked to incorporate this information into Keuls comparison indicated that the pres- their imaginal constructions to the extent they ence of the visual stimulus resulted in sig- found it helpful. nificantly larger swings (ps < .01) than About 5 min were then spent in administering a standard set of practice trials to provide warm- either of the auditory stimuli. The latter up and allow the subjects to become familiar with two stimuli did not differ from one another the general task. but were each significantly different from The experimental design consisted of the fac- the no-imaginal-prompt condition (ps < torial combination of three within-subjects factors : a four-level type-of-imaginal-prompt factor .01). In contrast to this objective finding, (no imaginal prompt, ascending-descending tone, postexperimental questioning of the sub- spatial tone, visual prompt), a two-level occlusion jects revealed that 8 of the 15 regarded the factor (pendulum oscillation not visible, pendulum spatial tone as the most subjectively com- oscillations visible), and a three-level blocks-of- trials factor (first, second, and third block of pelling and suggestive of movement. The trials). Three blocks of eight trials each were pattern of results that emerged from an run with the order of trials within each block analysis of just these 8 subjects was not appreciably different from that of the main TABLE 1 analysis. Thus, the spatial component added MEANS OF MAXIMUM ANGLE OF PENDULAR to the auditory stimulus was sufficient to MOTION FOR ALL TREATMENT COMBINATIONS strengthen conscious introspective imagina- Stimulus tion but did not produce as much objective Ascending- effect as a visual-spatial imaginal prompt. descending Spatial Visual Block None tone tone spatial The lack of any interaction among the three factors in this experiment, F(6, 84) Pendulum not visible = .15, is a noteworthy finding. It indicates 1 2.5 3.1 2.7 4.7 that the effect of imaginal prompts was sig- 2 1.9 2.7 3.3 4.7 nificant both when the pendulum was visible 3 2.5 3.3 3.7 4.8 and not visible. Moreover, the rank order Pendulum visible of the facilitative effects of the different prompts remained constant with and with- 1 4.0 4.7 4.9 6.1 out visual feedback. 2 4.1 5.3 5.5 6.5 The blocks-of-trials factor was not sig- 3 4.3 6.0 6.3 6.7 nificant and did not interact with other N - 15. Entries are in degrees. factors. CHEVREUL PENDULUM ILLUSION 235

pendulum visiblr Wy/////i pendulum not visible 6.0

|— • 4.0 1 3.0 m 1 Vs i 'fit y/. % y/,v 2.0 % ^ % I yy no asc-desc spat al visual external tone tone spat al stimulus stimulus stimulus stimulus

FIGURE 1. The effect of imaginal prompts with and without visual feedback of pendulum oscillations. (Asc — ascending, desc = descending.)

DISCUSSION such conditions. This line of reasoning It appears relevant to comment on the would not seem to apply when sight of the subjective quality of the illusory effect of pendulum is prevented, however. Visual the pendulum's motion. The illusion in- capture could not exist and no amount of volves the subjects' failure to notice the actual pendulum movement could fulfill the small muscle movements of the arm and instruction to create an image of movement. hand that set the pendulum into oscillation. Yet, the pendulum moves when sight of The relatively poor monitoring of kinesthetic actual movement is prevented, albeit in an information could be the consequence of an attentuated form. In spite of the attentu- ideomotor process in which muscle move- ation, the relation among the imaginal ments automatically occur as covert accom- prompts prevails and is significant. A rea- paniments of a central nervous system activ- sonable interpretation is that the attenuated ity. On the other hand, the failure to movement occurs in an ideomotor way. detect muscle movements could occur be- One might argue that the imaginal cause simultaneous visual information (sight prompts that were present when the pen- of pendulum oscillations) dominates con- dulum was not visible constituted sufficient scious processing. In this case, hand move- information for intersensory capture to ments could be generated incipiently, result- occur. Even though the phase relation be- ing in a constructed image of movement via tween the motion of the pendulum and visual feedback of pendulum motion. The prompts was not controlled, the perception results from the present study would seem of controlled frequency, sinusoidal move- to indicate that both central and peripheral ment could dominate conscious processing. processing are operating. This indeed may be true and it should When actual pendulum oscillations are caution one against a hasty conclusion that visible, the magnitude of pendulum move- the differences in Figure 1 between movement is larger, presumably because sight of ment of the pendulum with and without pendulum motion easily and directly fulfills sight of pendular oscillations represents the the instructions to construct an imagination contribution of visual capture as an inde- of movement. Further, the phenomenon of pendent influence beyond ideomotor be- visual capture suggests that larger arm and havior. Be that as it may, the pendulum hand movements could .go undetected under did move when sight of the actual pendulum 236 RANDOLPH D. EASTON AND RONALD E. SHOR motion was occluded and when, no imaginal Gibson, J. J. Adaptation, after-effect, and con- prompts were present. That specific contrast in the perception of curved lines. Journal of Experimental Psychology, 1933, 16, 1-31. dition may represent pure ideomotor be- Greenwald, A. G., Sensory feedback mechanisms havior. in performance control: With special reference Consistent with the above discussion is to the ideo-motor mechanism. Psychological the proposal that the facilitative effects of Review, 1970, 77, 73-99. the imaginal prompts are the result of visual Greenwald, A. G. On doing two things at once: Time sharing as a function of ideomotor com- capture and the incorporation of stimulus patibility. Journal of Experimental Psychology, information into imaginal processing. It is 1972, 94, 52-57. known that vision strongly dominates con- Greenwald, A. G., & Shulman, H. G. On doing scious processing while audition does not two things at once: II. Elimination of the psychological refractory period effect. Journal of (Pick et al., 1969). The present finding of Experimental Psychology, 1973, 101, 70-76. a greater facilitative effect for the visual James, W. The principles of psychology (2 vols.). prompt supports this interpretation. New York: Dover, 1950. (Originally pub- One final point is worth noting. The lished, 1890.) ordinal relation among the imaginal prompts McGuigan, F. J., & Schoonover, R. A. (Eds.). The psychophysiology of thinking: Studies of remained the same with and without visual covert processes. New York: Academic Press, feedback. Since the subject also wore a 1973. heavy glove, it seems unlikely that sufficient Miller, N. E. Learning of visceral and glandular conscious information existed in the absence responses. Science, 1969, 163, 434-445. Nielsen, T. I. Volition: A new experimental of visual and tactual feedback to allow the approach. Scandinavian Journal of Psychologv, deliberate production of the obtained small, 1963, 4, 225-230. precisely ordered magnitudes of pendulum Orne, M. T. Demand characteristics and the motion. It would therefore be difficult to concept of quasi-controls. In R. Rosenthal & attribute the results solely to "good subject R. Rosnow (Eds.), Artifact in behavioral research. New York: Academic Press, 1969. roles" (One, 1969). Perky, C. W. An experimental study of imagina- The general conclusion to be drawn from tion. American Journal of Psychology, 1910, the present findings is that the Chevreul 21, 422-452. pendulum effect, though historically con- Pick, H. L., Warren, D. H., & Hay, J. C. Sen- sidered only as a standard test of "sug- sory conflicts in judgments of spatial direction. Perception & Psychophysics; 1969, 6, 203-205. gestibility," is a reliable experiment phe- Rock, I. The nature of perceptual adaptation. nomenon. It appears to be related to New York: Basic Books, 1966. ideomotor theory, visual capture, and the Ryan, T. A. Interrelations of the sensory sys- incorporation of stimulus information into tems in perception. Psychological Bulletin, 1940, 37, 659-698. imagination. Segal, S. J. 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