Perceptualand MotorSkillr, 1991, 73, 79-82. O Perceptual and Motor Skills 1991

INDUCED MOVEMENT-IN-DEPTH AND INDUCED CHANGING-SIZE ELICITED BY A LUMINOUS ROTATING SPIRAL ' A. H. REINHARDT-RUTLAND Univerrily of Ulster at Jordanstown Sttmmary.-Induced movement-in-depth and induced changing-size are idrequently investigated forms of a phenomenon whereby movement is ascribed to a stationary stimulus. The present note concerns qualitative responses to a display designed to elicit both forms. The inducer was a two-arm luminous rotating linear-function spiral, and the stationary stimulus was an annulus concentric with the spiral; it was patterned with concentric luminous circles. Viewing was monocular. Among the findings, induced movement-in-depth was more frequently reported than induced changing-size, despite the lack of veridical movement-in-depth in the display. Possible Lines of explanation are suggested.

Induced movement is the perceived movement of a static stimulus in the opposite direction to adjoining movement (Duncker, 193811929), Most investigations have focused on the linear form of induced movement (Reinhardt-Rutland, 1988). A small number of studies have concerned cases in which the static stimulus appears to move in depth and change in size, first formally identified by Farne (1970). Inducing stimulation has included real movement-in-depth (Farne, 1970) and spiral-rotation (Reinhardt-Rutland, 1983). Also, two displays isolate either induced movement-in-depth (Gogel & Griffin, 1982) or induced size-change (Wade & Swanston, 1984). Despite the relative paucity of research on these forms of induced movement, examples in everyday settings are not unusual. They can be observed on television in stationary subtitles: the inducing stimulation can be a flow-field filmed from a moving vehicle in or opposite the vehicle's direction of motion, or it can entail "zooming" in or out of a stationary scene. Also, these induced movements are likely constituents of the "vista paradox": during forward motion of the observer towards a topographic aperture, distant stationary objects viewed in the aperture may appear to recede and contract (Walker, Rupich, & Powell, 1989; Reinhardt-Rutland, 1990). The present note concerns qualitative observations of a display designed to elicit induced movement-in-depth and induced changing-size. The inducer was a luminous rotating spiral. In particular, it seeks to confirm that induced movement-in-depth tends to be more prominent in the observer's perception than induced changing of size (Farne, 1970). While Farne used an inducer 'Financial assistance was provided by the research committee of the Faculty of Social and Health Sciences at the University of Ulster. Address correspondence to A. H. ReinhardtRutland, Room 17 05, Department of Psychology, Universit of Ulster at Jordanstown, Shore Road. Newtownabley, Co. Antrim, BT37 OQB, Northern h i n d .

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which physically moved in depth, movement-in-depth perceived in the present inducing stimulus was nonveridical.

METHOD The inducing stimulus was a two-arm linear-function spiral. The radius of each arm increased by 8 cm each cycle of rotation to a maximum of 31.5 cm; at the experimental viewing distance, 50 cm, the latter subtended 33.2O. Rotation rate was 30 rpm. The static stimulus consisted of a cardboard annulus concentric with the spiral; its internal radius was 7 cm (8.0') and its external radius was 9 cm (lO.zO). I t was patterned with concentric circles whose radii were 7, 8, and 9 cm. The annulus was supported by transparent Perspex rods 10 mm in front of the spiral. The spiral and circles were coated with luminous paint to a width of 5 mm (spiral) and 3 mm (circles). A static luminous fixation spot was supported 10 mm in front of the spiral's origin. The experiment took place in a light-tight cubicle. Under experimental conditions of total darkness, only the spiral (partidy occluded by the annulus), the three circles, and the fixation spot were visible. Observers were five female and nine male staff and undergraduates of the University of Ulster, aged between 19 and 40 years. All had by self-report normal (11 observers) or corrected-to-normal (3 observers) vision. All were unfamiliar with induced movement and naive as to the purposes of the experiment. Each observer covered the left eye with an eye patch: choice of eye is generally arbitrary since different tests of eye-dominance produce different results (Wade, 1976). The observer fixated the centre of the display, cubicle lights were switched off, and the spiral was set in motion. The observer described how the spiral and-if appropriate-the annulus appeared to move. Care was taken not to influence responding. Each observer viewed during both clockwise and anticlockwise rotation of the spiral; the cubicle was illuminated between trials.

RESULTSAND DISCUSSION As would be predicted, all observers reported perceiving the spiral expand and approach during anticlockwise rotation of the spiral, and all observers reported perceiving the spiral contract and recede during clockwise rotation of the spiral; rotation appeared much less salient (Hershenson, 1987). Three observers noted that they felt themselves to be moving towards or away from the spiral, opposite to its perceived movement-in-depth (linear vection: Dichgans & Brandt, 1978; Reinhardt-Rutland, 1982). All observers reported that the annulus appeared to move in depth. Eight observers reported the annulus as also undergoing two-dimensional sizechange, although each rated the latter as less strong than movement-indepth. The remaining observers reported n o changing size of the annulus. No observer reported the annulus as rotating.

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AU observers reported that ~erceivedmovements of the annulus were opposite to perceived movements of the spiral. Sign tests were applied. The reported directions of perceived movement-in-depth of the annulus were significantly different from chance (p < .0005; N = 14; 2-tailed). For the reported directions of perceived size-change, the result was not significant (p = .79; N = 14; 2-tailed). Consistent with previous evidence (Farne, 1970), induced movement-in-depth is therefore more salient than induced sizechange. In the present case, this occurred despite the lack of real movement-in-depth in the display. The reason for the greater salience of induced movement-in-depth is uncertain: perhaps visual expansion and contraction are more likely to signal an object moving in depth than changing in size, since the rigidity inherent in most objects would make the latter unusual. Similar points apply to apparent movement (Bartley & Miller, 1954). Also, "looming" responses are readdy elicited by two-dimensional visually expanding contours (Schiff, 1965). The results also provide some clues as to possible explanations. Because inducing movement was equal in all radial directions, explanations entailing real or cancelled eye movements (Post & Leibowitz, 1985) or shift in perceived spatial coordinates (Brosgole, 1968) are u d k e l y to contribute to the present results. However, the reports of linear vection by some observers might suggesc that an explanation in such terms is appropriate: an explanation has been proposed linking rotary induced movement with its analogous form of vection (Mapperson & Lovegrove, 1989). Although detailed analysis suggests that this is unlikely (Reinhardt-Rutland, 1991, in press), available evidence does not preclude a link between linear vection and induced movement-in-depth. One final type of explanation that cannot be precluded entails low-level sensory-neural processing of movement information (ReinhardtRutland, 1988). REFERENCES BARTLEY, S. H., & ~ U R J. , W. (1954) Some circumstances surrounding apparent movement in the line of regard. lournal of Psychology, 38, 453-456. BROSGOLE, L. (1968) An analysis of induced motion. Acta Psychologica, 28, 1-44. J., & BRANDT, T. (1978) Visual-vestibular interaction. In R. Held, H. W. Leibowitz, DICHGANS, & H. L. Teuber (Eds.), Handbook of sensory physiology, VIII. Berlin: Springer-Verlag. Pp. 755-804. DUNCKER, K. (1938) ~ b e induzierte r Bewc ong [Concerning induced movement.] In W. D. Ellis (Ed. 8r Trans.), Source book o r ~ e h l psychology. t London: Routledge & Kegan Paul. Pp. 161-172. meprinted from Psychologische Forscbung, 1929, 12, 180-259.1 FARNE,M. (1970) Induced motion in three dimensions. Perceptual and Motor Skills, 30, 426. GOGEL,W. C., & GRIFFIN, B. W. (1982) Spatial induction of illusory motion. Perception, 11, 187-199. HERSHENSON, M. (1987) Visual system responds to rotational and size-change components of complex proximal motion patterns Perception and Psychophysics, 42, 60-64. %PERSON, B., & LOVEGROVE, W. (1989) Stimulus variables affecting induced rotation. Bulletin of the Psychonomic Society, 27, 331-334.

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POST,R. B., & LE~OWITZ, H. W. (1985) A revised analysis of the role of efference in motion perception. Perception, 14, 631-643. REINHARDT-RUTLAND, A. H. (1982) Asymmetry in forward and backward vection. Perceptual and Motor SkilIs, 54, 870. REINHARDT-RUTLAND, A. H. (1983) Induced movement-in-depth: relative location of static stimulus and direction asymmetry. Perceptzral and Motor Skills, 57, 255-258. REINHARDT-RUTLAND, A. H. (1988) Induced movement in the visual modality: an overview. Psychological Bulletin, 103, 57-71. REINHANIT-RUTLAND, A. H. (1990) The vista aradox: is the effect partly explained by induced movement? Perception and ~sychopfysics,47, 95-96. RETNHARDT-RUTLAND, A. H. (1991) Does intermittence in induced rotary movement have any explanatory significance? Perception and Psychopbysics, 49, 579-582. REINF~ARDT-RUTLAND, A. H. (in press) On the salience of che inducer's displacement i n rotary induced movement. Perception. S C ~ FW. , (1965) Perception of impending collision. Psychological Monographs, 49, No. 289 (Whole No. 604). WADE,N. . (1976) On interocular transfer of the movement aftereffect in individuals with an without normal binocular vision. Perception, 5, 113-118. WADE,N. J., & SWANSTON, M. T. (1984) Illusions of size change in dynamic &splays. Perception and Psychopbysics, 3 5 , 286-290. WALKER, J. T., RUPICH,R. C., & POWELL, J. L. (1989) The vista paradox: a natural visual illusion. Perception and Psychopbysics, 45, 43-48.

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Accepted July 9, 1991.

Induced movement-in-depth and induced changing-size elicited by a luminous rotating spiral.

Induced movement-in-depth and induced changing-size are infrequently investigated forms of a phenomenon whereby movement is ascribed to a stationary s...
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