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Age changes in perception of verticality and of the longitudinal body axis under body tilt
JOURNAL
Age
OP EXPERIMENTAL
CHILD
PSYCHOLOCY
6,
543-555 (1968)
Changes in Perception of Verticality Longitudinal Body Axis under Body
and Tilt’
of the
SEYMOUR WAPNER Clark University The position of apparent vertical, the apparent location of the longitudinal axis of the body, and their relation were assessed under erect and 30” left and right body tilt in 96 boys and 96 girls ranging in age from 7 to 17 years. It was found: (a) with increase in age, the position of apparent vertical shifts from the side of body tilt to the side opposite tilt; (b) while the apparent location of longitudinal body axis deviates beyond true body tilt in all age groups, after 7 years there is a slight decrease in deviation followed by an accelerated increase after 13 years of age; (c) the angular disparity between apparent vertical and apparent body axis position is relatively small for 7 to 13 year-ok% compared with 15 and 17 year-olds: (d) for both tasks, final adjustment of the rod is relatively close to its position at the beginning of the trial, and this effect, greatest at 7 years, decreases with increase in age. The findings are interpreted as a reflection of an ontogenetic shift toward increasing differentiation between the body spatial reference system and the external spatial reference system.
Beginning with the classic studies by Aubert (1860) a wide variety of facts have been accumulated concerning perception of a main coordinate of the external spatial reference system, viz., perception of verticality (see recent reviews by Bauermeister, 1962, and by Howard and Templeton, 1966; a,lso Gibson, 1952, Witkin et al., 1954, Mann, 1952, Mann and Passey, 1950, Werner and Wapner, 1949, 1952, Wapner and Werner, 1957). Since another reference system-that of body space-also enters into space localization, it is surprising that the earlier literature on space perception contains relatively few studies that have treated perception pertinent to the body reference system (DeLage, 1886; Aubert and DeLage, 1888; Nagel, 1898; Grahe, 1925; Quix and Eijsvogel, 1929). ‘This investigation was supported by Public Health Service Grant MH-00348 from the National Institute of Mental Health. Appreciation is expressed to the Leicester, Massachusetts, Public School System; to J. A. Glick, J. H. McFarland, G. Rand, and P. Werme, who were involved in the extended project of which this study is a small part; and to A. Harvey Baker for constructive criticism of the manuscript. 543
544
SEYMOUR
WAPNER
It is only during the past few years that systematic investigations have been undertaken that treat perception of a main dimension of the body reference system-apparent location of the longitudinal axis of the body-in a manner analogous to the way a main dimension (verticality) of the external reference system has been studied (cf. McFarland, Wapner, and Werner, 1962; Bauermeister, 1964; Bauermeister, Wapner, and Werner, 1963; Bauermeister, Werner, and Wapner, 1964; McFarland and Clarkson, 1966; Bauermeister, Wapner, and Werner, 1966). While the locations of the main dimensions of these two reference systems physically coincide and perceptually approximate each other under normal erect posture, they are differentiable under such conditions as perceptual rearrangement induced by wearing a prism system that rotates the visual field (Rierdan and Wapner, 1966). Moreover, under body tilt, neither the location of the perceived vertical, nor the perceived position of the longitudinal axis of the body coincide with the respective physical locations of these coordinates. Now, it is known that there are striking age changes in the external spatial reference system, as manifest in perception of verticality under 30” body tilt (cf. Witkin et al., 1954; Wapner and Werner, 1957; Comalli, Wapner, and Werner, 1959). Since both body and external reference systems are involved in space localization, a better understanding of the development of such localization requires the simultaneous assessment of verticality and body position. In the present study-which is directed toward accumulating data on this problem by measuring, under 30” body tilt, both perception of verticality and apparent location of the longitudinal body axis-specific age changes are expected on the basis of principles employed by organismic-developmental theory (Werner, 1940, 1957; Wapner and Werner, 1957, 1964; Wapner, 1964; Werner and Kaplan, 1963; Kaplan, 1966). The crucial feature of this approach pertinent to predictions of ontogenetic change is its developmental perspective, which focuses on formal, organizational analysis of progressive changes in a system undergoing transition. More specifically, such system change is treated with reference to the orthogenetic Iaw, which states that with development there is increasing differentiation and hierarchic integration of functions and parts, e.g., self and world. Considering the general proposition that with development there is increasing differentiation between self and world, it is expected that with increase in age there is increasing differentiation between the spatial reference system defined with respect to one’s body and the reference system defined with respect to external space. Given the assumption that under small body tilts the degree of differentiation
AGE
CHANGES
IN
PERCEPTION
545
between the two reference systems is reflected in the angular disparity between apparent verticality and apparent location of the longitudinal body axis, it is expected that the angular disparity will increase with increase in age. This implies, as had already been demonstrated, that under body tilt, with increase in age apparent vertical shifts increasingly opposite the side of body tilt (cf. Wapner and Werner, 1957), and further, that apparent body axis, rotated beyond true body tilt in adults (see McFarland et al., 1962; Bauermeister, 1962, 1964) should be rotated to a lesser degree at earlier stages of development. METHOD
Procedure. S carried out two tasks: (a) Apparent Vertical-adjust a luminous rod in a dark room to a position that appears vertical; and (b) Apparent Body Axis Position-adjust a luminous rod to a position that appears parallel to the longitudinal axis of S’s body. These tasks were carried out under erect body position, as well as 30” left and 30” right body tilt. After presenting the rod at a particular setting (initial starting position), the rod was moved continuously by E according to instructions of S (a) to a position that appeared vertical (verticality task), and (b) to a position that appeared aligned with the longitudinal axis of the body (body axis position task). S was permitted to make fine adjustments in either direction at the very end of the trial until he was satisfied that the rod appeared vertical (lined up with his body). For each task two starting positions (initial placement of the rod at the beginning of a trial) were employed: (a) 30” counterclockwise (CCW) starting position and 30” clockwise (CW) starting position. For verticality the reference location for starting position was true vertical; for apparent body axis position the reference location was the true position of the longitudinal body axis. There were 6 test conditions (3 body positions in combination with 2 starting positions) for the verticality task, and the comparable 6 conditions for the apparent body axis position task. All tests were carried out in a dark room. S was seated in a specially constructed chair with an adjustable head-clamp; the chair could be fixed at the upright as well as tilted 30” to the left and to the right. A luminous rod, 39 inches long and 1 inch wide, was located 7 feet from S. It could be rotated around its midpoint in the fronto-parallel plane and its position was measured by means of a protractor calibrated in half-degrees. Care was taken that all Ss understood the nature of both tasks. This was done by demonstrating what was meant by verticality and what was meant by “lining up” the rod with the longitudinal axis of the body.
546
SEYMOUR
WAPNER
Subjects. One hundred and ninety-two subjects, 16 boys and 16 girls, in each of 6 age groups, were tested. Chronological age and IQ characteristics of the sample are presented in Table 1. IQ’s, obtained from school records, were based on the California Test of Mental Abilities; for the occasional S, when a score on this test was not available, IQ was based on the Otis. Design. The two tasks, verticality and body axis position, were carried out on two different days for any particular S. Half of the males and half of the females within the age groups were test.ed in the sequence verticality followed by body axis position; the remaining subjects were tested in the opposite sequence. Within each of the two tasks, the 6 conditions were randomized. The data were treated by analysis of variance in an independent groups (6 age groups further subdivided for sex), repeated measurements factorially treated (3 body positions in combination with 2 starting positions) design. TABLE
1
&ARACTERISTICS
OF
Age
CAb Mean Sigma IQ
Mean Sigma oN = 192. b Chronological
fh?dPLE’=
groups
I
II
III
IV
V
VI
7:l 0:6
8:ll 0:6
1O:ll 0:5
12: 11 0:7
15:4 0:6
16: 11 0:8
107.3 13.2
108.8 13.5
108.2 8.8
107.6 11.9
107.9 9.1
108.8 11.6
age given
as years:
months.
Measures employ?d. Two measures were employed in separate analyses: (1) Apparent Vertical-location of apparent vertical was measured with respect to objective vertical in degrees, with CW deviations, as viewed by S, designated as +, and CCW deviations designated as - ; (2) Apparent Body Axis Position-location of apparent body axis position was measured with respect to objective body axis position, with deviations of apparent body axis position CW of true body axis position designated by f, and deviations CCW designated by -. In addition, the relation between apparent vertical and apparent body axis position was represented by the angular disparity between these positions, expressed as the apparent body axis position minus position of apparent vertical, ignoring the physical angular difference between true vertical and true position of the longitudinal axis of the body under 36” tilt.
AGE
CHANGES
IN
547
PERCEPTION
RESUL+S
Summaries of the analyses of variance for apparent vertical and apparent body axis position are presented in Table 2. Brief inspection of the table shows that the main expectation of an interaction between age TABLE AGE
CHANQES IN APPARENT BODY AXIS POSITION
2 VERTICAL AND APPARENT UNDER BODY TILT
F-tests
Apparent vertical Source Between Age (4 Sex (G) AXG Pooled indiv. (I)
df 5 1
5 180
Within Body tilt (B) AXB GXB AXGXB
10
Pooled I X B
360
Starting position (S) AXS GXS AXGXS Pooled I X S BXS AXBXS
GXBXS AxGxBxS Pooled I X B X S Total
2 2 10 1
5 1 5 180 2 10
2 10 360 1151
Apparent body axis position
MS
FS
MS
FS
48.15 3.06 17.03 33.21
1.45 .09 .51 -
243.04 12.71 114.25 95.79
2.54O .13 1.19 -
27949.28 648.95 3967.36 84.41 244.37 27946.42 1809.26 333.68 214.52 79.01 3973.08 132.33 17.78 48.14 45.91
114.37b 2.66” 16.23” .34 353.7@ 22.9ob 4.220 2.72” 86.54b 2.88b .39 1.05 -
528.97 272.43 14.02 123.72 45.60 8791.38 576.72 354.00 92.93 44.24 678.88 19.20 17.08 32.30 17.41 49.00
11.60b 5.976 .31 2.71b 198.71b 13.046 8.Oob 2.10 39.00b 1.10 .98 1.86 -
223.39
-
“p < .05. bp < .Ol.
and body tilt axis position. cant findings tasks; finally Apparent
is significant for both apparent vertical and apparent body The specific nature of these age changes as well as signififor other variables is described separately for each of these the relationship between them is considered. verticality. Age changes pertaining to the mean position of
548
SEYMOUR
WAPNER
30'
AGE lh.
GROUP
LEFT TILT
(YEARs:MONTHS)
1. Age changesin location of apparent vertical as a function of body position.
apparent vertical as dependent on body tilt are depicted in Fig. 1. The findings can be briefly stated as follows: there is a general shift of the position of apparent vertical from the side of body tilt to the side opposite body tilt. For both left and right body tilt these changes continue beyond the true vertical with the consequence that the curves of position of apparent vertical for left and right body tilt, pooled for sex, cross over between 13 and 15 years of age. Table 2 also shows that there is a significant triple interaction involving the factors of age, body tilt, and sex .The changes in position of apparent vertical with variation in age and body tilt are similar for males and females with two exceptions: for both sexes, the general changes with age described above hold, but for females the deviations of apparent vertical to the side of body tilt are more extreme in the youngest age group, and the crossover point-shift of apparent vertical from side of body tilt to side opposite-occurs between 15 and 17 years in females as compared with 13 to 15 years in males. Another set of findings pertains to the so-called starting position effect, which is the tendency for the position of apparent vertical to be located closer to the position of the rod at the beginning of a trial. Starting position has an over-all significant effect, and interacts significantly with age, with sex, and with body tilt. As shown in Fig. 2, the starting position ef-
AGE
CHANGES
IN
549
PEBCEPTION
ROD
INITIALLY
30’
CW
....l -......,..,. . *:. .... .... .a.’ .:’
*.a. a. .. ...
” ....
.:. .. .. ..
ccw
I
I
7:l
AGE
2.
:..
.. ROD
INITIALLY
I
t3:l I
Age changes in location rod indicator at beginning of trial. FIO.
-.. *
.:.
:
/’
IO:11 GROUP
30’
CCW
I
I
I
l2:ll
15:4
16:ll
(YEARS:MONTHS)
of apparent
vertical
as a function
of location
of
feet decreases with increase in age, showing a steep gradient up to 12 years, with relatively small changes thereafter. Examination of the means comprising the “starting position X sex” interaction reveals that, overall, the effect of starting position is greater for females than for males. Finally, examination of the mean for the “starting position X body tilt” interaction shows that the apparent vertical is shifted disproportionately CCW under the condition “body left-starting position left” relative to the other test conditions. Apparent body axis position. As will be recalled, in this task the reference position is not a dimension of external space (e.g., objective perpendicularity), but rather a dimension of body space, viz., the longitudinal axis of the body. The task was to use the rod as an indicator of the apparent location of the longitudinal axis of the body by adjusting the rod to a position that appeared to coincide with this axis of the body, and accordingly measurements are taken with respect to it. Age changes pertaining to the apparent position of the body axis, as denendent on body tilt, are presented in Fig. 3. As shown in the graph,
550
SESMOUR
\l’.?PNER
with body tilted 30” from the perpendicular, both left and right, for all age levels the mean apparent location of the body axis tilts beyond the position in which the body axis is actually located. Further, there are striking ontogenetic changes: with age there is a slight decrease in deviation of apparent beyond true location of the body axis followed by an accelerated increase between 13 and 15 years of age. Body tilt also interacts significantly with sex, independent of age, with females showing a greater shift of apparent body axis than the males. CW
; m
+15O
2 t-
+lo”
3o”
L
:
:IA4e
RIGHT
TILT
*... .*.....“’ \ ERECT
*/-
..--
~---------*----------.----
/--
--a_
--a-
--S_
\ 30’ I 7:l
1
AGE
FIQ. 3. Age changes in apparent of body position.
I
I 8:l
IO:11 GROUP
location
I 12:ll
LEFT I 15:4
--_-
‘-8
TILT I 16:ll
(YEARS:MONTHS)
of longitudinal
body axis as a function
The second set of findings, which parallel those that obtained for apparent verticality, deals with starting position. Again for location of body axis, there is an over-all effect of starting position such that apparent location of body axis is relatively close to the position of the rod at the beginning of the trial. In addition to the over-all effect of starting position, there are significant first order interactions involving starting position and the following variables: age, sex, body tilt. As shown in Fig. 4, there is a decrease in effect of starting position with increase in age. As with apparent verticality, there is evidence that the effect of starting position is greater for females than for males, and that the apparent position of the body axis is shifted disproportionately CCW under the condition “body left-starting position left” relative to the other test conditions. The significant triple interaction-age X body tilt X starting position-indicates that the disproportionate shift CCW under “body left-starting position left” is most striking in the youngest group and
AGE
CHANGES
IN
551
PEXKZPTION
ROD
INITIALLY
30’
CW
1s’ * . . . . . .. .
c’..”
,.....
. ..a-
. . . . . . . . . . . . . w.’
**...... ;;;r: ROD
I
I
7:l
8:l AGE
* IO:11
I GROUP
INITIALLY
I
I
12:ll
15:4
30’
CCW
c 16:ll
(YEARS:MONTHS)
Age changes in apparent location of longitudinal of location of rod indicator at beginning of trial. Fro.
. ..a. . . . . . . . . . . . . ...*
4.
body axis as a function
decreases with increase in age, so that it is no longer evident in the oldest two age groups. The relationship between apparent vertical and apparent body axis position. The ontogenetic changes in the relationship between apparent
vertical
and apparent
7:l
location of the longitudinal
8:l AGE
1
1O:ll GROUP
body axis under body
12:ll
15:4
16:ll
(YEARS:MONTHS)
FIQ. 5. Age changes in angular disparity between apparent looation of longitudinal body axis under 30” body tilt.
vertical
and apparent
552
SIGYMOUR
WAPNER
tilt is evident from a comparison of Figs. 1 and 3. These ontogenetic changes are expressed more simply in Fig. 5, which plots the findings in terms of apparent angular disparity, i.e., the deviation of apparent vertical from apparent location of the body axis, ignoring the 30” deviation between true vertical and objective location of body axis. For all age levels, the apparent angular disparity is greater than the objective angular disparity; angular disparity, however, is relatively small in the youngest age group (6.8” for left and 3.4” for right body tilt) and continues to be small through 13 years of age, after which angular disparity increases markedly and reaches a maximum in the oldest age group (approximately 14” for left and right body tilt). DISCUSSION The present analysis advances our understanding of the development of spatiality by taking into account a reciprocal, rather than a one-sided, relationship between object and body perception. This means that the principle of development effective here is formulated in terms of an increase in polarization during ontogenesis between the position of apparent verticality (a main coordinate of the external spatial reference system) and the position of the longitudinal axis of the body (a main coordinate of the body reference system). Angular disparity is introduced as a unitary measure representing the relation between apparent vertical and apparent body position, under the condition of 30” body tilt. The main finding consists in the widening of the difference between the two perceived locations involved, viz., the physical location of the apparent vertical and the physical location of the experienced position of the longitudinal axis of the body. At the youngest age levels the position of apparent vertical and apparent position of the body axis are relatively close as compared with the two oldest age levels. As suggested in an earlier study (Wapner and Werner, 1957)) the relative undifferentiatedness of self and object found in early ontogenesis arises from two diametrically opposed determinants: “stimulus boundedness” and “egocentricity.” ‘( Stimulus boundedness” may be described as change in organismic state in keeping with stimulation, a change reflected in perception. Egocentricity is typically defined as determination of the object world through self as referent (cf. Piaget, 1928; Werner, 1940). Both “stimulus boundedness” and “egocentricity” contribute to a nonstable frame of reference with respect to external space (assessed by the verticality task) and stimulus boundedness contributes to nonstable body space (assessed by the body position task). Since these two processes, by their very nature, affect space localization differentially, it follows that a given response cannot simulta-
AGE
CHANGES
IN
PERCEPTION
553
neously be both purely egocentric and purely stimulus bound. It is possible, however, for the child to show both greater egocentricity and greater stimulus boundedness than the adult. By employing a factorial design, as done here, it is possible to assess each of these tendencies: the closer the location of .apparent vertical or apparent body position to the initial position in which the stimulus was presented the greater the degree of stimulus boundedness (indicated by the interaction “age X starting position” in which body tilts are pooled) ; the closer the location of apparent vertical or apparent body position to true body position the greater the degree of egocentricity (indicated by the interaction “age X body tilt” in which starting positions are pooled). On both apparent vertical and apparent body position tasks, with increase in age there is a progressive decrease in the magnitude of the starting position effect, representing a decline in stimulus boundedness. In keeping with findings by Wapner and Werner (1957), the present study clearly shows that with increase in age the position in which the stimulus is seen as vertical shifts away from the position in which the body is located; it is this increase in the distance between body position and physical location of apparent vertical that reflects the ontogenetic decrease in egocentricity. A similar decrease in egocentricity obtains for the apparent body position task: the child shows a slight overestimation of apparent body position whereas the adult shows a much larger overestimation; or stated another way, with increase in age there is a progressive increase in the distance between true body position and the position in which the stimulus object must be placed to be seen as lined up with the longitudinal axis of the body. It may be noted that with increase in age, the shift of apparent vertical and of apparent body position is opposite in direction ; thus the angular disparity between these two measures is greater at later than at earlier age levels. Independent of the specific interpretation offered, the findings as such have implications for any theory of perceptual development. As observed by Wohlwill (1960) a crucial issue is whether, during the course of development, perception progresses verticality. The findings presented here do not support such a view: for body position the adult makes a larger error than a child; for verticality the adult makes an error in a different direction from the child. REFERENCES H. Eine scheinbare bedeutende Drehung von Objekten bei Neigung des Kopfes nach rechts oder links. Virchow’s Archiv. fuer Pathologiche Anatomie und Physiologic ocnd fuer Kliniwhe Meditin, 1860, 20, 3813%. AUBERT, H., AND DELAQE, Y. Ph&oZogische studien uber die orientierung. Tubingen : Laupp, 1888. AUBERT,
554
SEYMOUR
WAPNER
M. The relation between subjective body space and objective external space under conditions of body tilt. Microfilmed doctoral dissertation, Clark University, 1962. BAUERMEISTER, M. The effect of body tilt on apparent verticality, apparent body position, and their relation. Journal of Experimental Psychology, 1964, 67, 142147. BAUERMEISTER, M., WAPNER, S., AND WERNER, H. Sex differences in the perception of apparent verticality and apparent body position under conditions of body tilt. Journal of Personality, 1963, 31, 394407. BAUERMEISTER, M., WAPNER, S., AND WERNER, H. Method of stimulus presentation and apparent body position under lateral body tilt. Perceptual and Motor Skills, 1967, 24, 43-50. BAUERMEISTER, M., WERNER, H., AND WAPNER, S. The effect of body tilt on tactualkinesthetic perception of verticality. American Journal of Psychology, 1964, ‘77, 451456. COMALLI, P. E., JR., WAPNER, S., AND WERNER, H. Effect, of muscular involvement. on size perception. Perceptual and Motor Skills, 1959,9, 116. , DELAGE, Y. Etudes experimentales sur les illusions statiques et dynamiques de direction pour servir a determiner les functions des canaux semicirculaires de l’oreille interne. Archives de Zoologie Experimentale et General, 1886, 4, 535BAUWMEISTER,
624. GIBSON,
J. J. The relations between visual and postural determinants of the phenomenal vertical. Psychological Review, 1952, 59, 370-375. GRAHE, K. Uber Lageempfindungen und -reflexe beim Menschen. Zeitschrift fiir Hal.+, Nasen-, und Ohrenheilkunde (Berlin), 1925, 12, 640-651. HOWARD, I. P., AND TEMPLETON, W. B. Human spatial orientation. London: Wiley, 1966. KAPLAN, B. Meditations on genesis. Human Development, 1967, 10, 65-87. MANN, C. W. Visual factors in the perception of verticality. Journal of Experimental Psychology, 1952, 44, 460464. MANN, C. W., AND PASSEY, G. E. The perception of the vertical V: Adjustment to the postural vertical as a function of the magnitude of postural tilt, and duration of exposure. Journal of Experimental Psychology, 1950, 41, 10~%113. MCFARLAND, J. H., WAPNER, S., AND WERNER, H. The relation between perceived location of objects and perceived location of one’s own body. Perceptual and Motor Skills, 1962, 15, 331341. MCFARLAND, J. H., AND CLARKSON, F. Perception of orientation: Adaptation to lateral body-tilt. American Journal of Psychology, 1966, 79, 265-271. NAGEL, W. A. Uber das Aubert’sche Phanomen und verwandte Tauschungen uber die vartikale Richtung. Zeitschrift fur Psychologie, 1898, 16, 372-398. PIAGET, J. Judgment and reasoning in the child. London: Routledge and Kegan Paul, 1928. QUIX, F. H., AND EIJSVOGEL, M. H. P. M. Experimente uber die Funkt,ion des Otolithenapparates beim Menschen. Zeitschrift fiir Hal+, Nasen-, und Ohremheilkunde (Berlin), 1929, 23, 68-87. RIERDAN, J., AND WAPNER, S. Experimental study of adaptation to visual rearrangement deriving from an organismic-developmental ceptual and Motor Skills, lQ66, 23, 903-916. WAPNER, S. Some aspects of a research program
approach based
on an
to cognition.
per-
organismic-develop-
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mental approach to cognition: Experiments and theory. Journal of the American Academy of Child Psychiatry, 1964, 3, 193-230. WAPNER, S., AND WERNER, H. Perceptual development. Worcester, Mass.: Clark University Press, 1957. WAPNER, S., AND WERNER, H. An experimental approach to body perception from the organismic-developmental point of view. In S. Wapner and H. Werner (Eds.) The body percept. New York: Random House, 1965. WERNER, H. Comparative psychology of mental development. New York: Harper, 1940; (2nd ed.) Chicago: Follett, 1948; (3rd ed.) New York: International Universities Press, 1957; (4th ed.) New York: Science Editions, 1961. WERNER, H. The concept of development from a comparative and organismic point of view. In D. B. Harris (Ed.), The concept of development: An issue in the study of human behavior. Minneapolis: Univ. of Minnesota Press, 1957. WERNER, H., AND KAPLAN, B. Symbol formation: an organismic developmental approach to language and the expression of thought. New York: Wiley, 1963. WERNER, H., AND WAPNER, S. Sensory-tonic field theory of perception. Journal of Personality, 1949, 18, 88-107. WERNER, H., AND WAPNER, S. Toward a general theory of perception. Psychological Review, 1952, 59, 324-338. WITHIN, H. A., LEWIS, HELEN B., HERTZJIAN, M., MACHOVER, KAREN, MEISSNER, PEARL B., AND WAPNER, S. Personality through perception. New York: Harper, 1954. WOHLWILL, J. F. Developmental studies of perception. Psychological Bulletin, 1960, 57,25O-288.
Age
OP EXPERIMENTAL
CHILD
PSYCHOLOCY
6,
543-555 (1968)
Changes in Perception of Verticality Longitudinal Body Axis under Body
and Tilt’
of the
SEYMOUR WAPNER Clark University The position of apparent vertical, the apparent location of the longitudinal axis of the body, and their relation were assessed under erect and 30” left and right body tilt in 96 boys and 96 girls ranging in age from 7 to 17 years. It was found: (a) with increase in age, the position of apparent vertical shifts from the side of body tilt to the side opposite tilt; (b) while the apparent location of longitudinal body axis deviates beyond true body tilt in all age groups, after 7 years there is a slight decrease in deviation followed by an accelerated increase after 13 years of age; (c) the angular disparity between apparent vertical and apparent body axis position is relatively small for 7 to 13 year-ok% compared with 15 and 17 year-olds: (d) for both tasks, final adjustment of the rod is relatively close to its position at the beginning of the trial, and this effect, greatest at 7 years, decreases with increase in age. The findings are interpreted as a reflection of an ontogenetic shift toward increasing differentiation between the body spatial reference system and the external spatial reference system.
Beginning with the classic studies by Aubert (1860) a wide variety of facts have been accumulated concerning perception of a main coordinate of the external spatial reference system, viz., perception of verticality (see recent reviews by Bauermeister, 1962, and by Howard and Templeton, 1966; a,lso Gibson, 1952, Witkin et al., 1954, Mann, 1952, Mann and Passey, 1950, Werner and Wapner, 1949, 1952, Wapner and Werner, 1957). Since another reference system-that of body space-also enters into space localization, it is surprising that the earlier literature on space perception contains relatively few studies that have treated perception pertinent to the body reference system (DeLage, 1886; Aubert and DeLage, 1888; Nagel, 1898; Grahe, 1925; Quix and Eijsvogel, 1929). ‘This investigation was supported by Public Health Service Grant MH-00348 from the National Institute of Mental Health. Appreciation is expressed to the Leicester, Massachusetts, Public School System; to J. A. Glick, J. H. McFarland, G. Rand, and P. Werme, who were involved in the extended project of which this study is a small part; and to A. Harvey Baker for constructive criticism of the manuscript. 543
544
SEYMOUR
WAPNER
It is only during the past few years that systematic investigations have been undertaken that treat perception of a main dimension of the body reference system-apparent location of the longitudinal axis of the body-in a manner analogous to the way a main dimension (verticality) of the external reference system has been studied (cf. McFarland, Wapner, and Werner, 1962; Bauermeister, 1964; Bauermeister, Wapner, and Werner, 1963; Bauermeister, Werner, and Wapner, 1964; McFarland and Clarkson, 1966; Bauermeister, Wapner, and Werner, 1966). While the locations of the main dimensions of these two reference systems physically coincide and perceptually approximate each other under normal erect posture, they are differentiable under such conditions as perceptual rearrangement induced by wearing a prism system that rotates the visual field (Rierdan and Wapner, 1966). Moreover, under body tilt, neither the location of the perceived vertical, nor the perceived position of the longitudinal axis of the body coincide with the respective physical locations of these coordinates. Now, it is known that there are striking age changes in the external spatial reference system, as manifest in perception of verticality under 30” body tilt (cf. Witkin et al., 1954; Wapner and Werner, 1957; Comalli, Wapner, and Werner, 1959). Since both body and external reference systems are involved in space localization, a better understanding of the development of such localization requires the simultaneous assessment of verticality and body position. In the present study-which is directed toward accumulating data on this problem by measuring, under 30” body tilt, both perception of verticality and apparent location of the longitudinal body axis-specific age changes are expected on the basis of principles employed by organismic-developmental theory (Werner, 1940, 1957; Wapner and Werner, 1957, 1964; Wapner, 1964; Werner and Kaplan, 1963; Kaplan, 1966). The crucial feature of this approach pertinent to predictions of ontogenetic change is its developmental perspective, which focuses on formal, organizational analysis of progressive changes in a system undergoing transition. More specifically, such system change is treated with reference to the orthogenetic Iaw, which states that with development there is increasing differentiation and hierarchic integration of functions and parts, e.g., self and world. Considering the general proposition that with development there is increasing differentiation between self and world, it is expected that with increase in age there is increasing differentiation between the spatial reference system defined with respect to one’s body and the reference system defined with respect to external space. Given the assumption that under small body tilts the degree of differentiation
AGE
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545
between the two reference systems is reflected in the angular disparity between apparent verticality and apparent location of the longitudinal body axis, it is expected that the angular disparity will increase with increase in age. This implies, as had already been demonstrated, that under body tilt, with increase in age apparent vertical shifts increasingly opposite the side of body tilt (cf. Wapner and Werner, 1957), and further, that apparent body axis, rotated beyond true body tilt in adults (see McFarland et al., 1962; Bauermeister, 1962, 1964) should be rotated to a lesser degree at earlier stages of development. METHOD
Procedure. S carried out two tasks: (a) Apparent Vertical-adjust a luminous rod in a dark room to a position that appears vertical; and (b) Apparent Body Axis Position-adjust a luminous rod to a position that appears parallel to the longitudinal axis of S’s body. These tasks were carried out under erect body position, as well as 30” left and 30” right body tilt. After presenting the rod at a particular setting (initial starting position), the rod was moved continuously by E according to instructions of S (a) to a position that appeared vertical (verticality task), and (b) to a position that appeared aligned with the longitudinal axis of the body (body axis position task). S was permitted to make fine adjustments in either direction at the very end of the trial until he was satisfied that the rod appeared vertical (lined up with his body). For each task two starting positions (initial placement of the rod at the beginning of a trial) were employed: (a) 30” counterclockwise (CCW) starting position and 30” clockwise (CW) starting position. For verticality the reference location for starting position was true vertical; for apparent body axis position the reference location was the true position of the longitudinal body axis. There were 6 test conditions (3 body positions in combination with 2 starting positions) for the verticality task, and the comparable 6 conditions for the apparent body axis position task. All tests were carried out in a dark room. S was seated in a specially constructed chair with an adjustable head-clamp; the chair could be fixed at the upright as well as tilted 30” to the left and to the right. A luminous rod, 39 inches long and 1 inch wide, was located 7 feet from S. It could be rotated around its midpoint in the fronto-parallel plane and its position was measured by means of a protractor calibrated in half-degrees. Care was taken that all Ss understood the nature of both tasks. This was done by demonstrating what was meant by verticality and what was meant by “lining up” the rod with the longitudinal axis of the body.
546
SEYMOUR
WAPNER
Subjects. One hundred and ninety-two subjects, 16 boys and 16 girls, in each of 6 age groups, were tested. Chronological age and IQ characteristics of the sample are presented in Table 1. IQ’s, obtained from school records, were based on the California Test of Mental Abilities; for the occasional S, when a score on this test was not available, IQ was based on the Otis. Design. The two tasks, verticality and body axis position, were carried out on two different days for any particular S. Half of the males and half of the females within the age groups were test.ed in the sequence verticality followed by body axis position; the remaining subjects were tested in the opposite sequence. Within each of the two tasks, the 6 conditions were randomized. The data were treated by analysis of variance in an independent groups (6 age groups further subdivided for sex), repeated measurements factorially treated (3 body positions in combination with 2 starting positions) design. TABLE
1
&ARACTERISTICS
OF
Age
CAb Mean Sigma IQ
Mean Sigma oN = 192. b Chronological
fh?dPLE’=
groups
I
II
III
IV
V
VI
7:l 0:6
8:ll 0:6
1O:ll 0:5
12: 11 0:7
15:4 0:6
16: 11 0:8
107.3 13.2
108.8 13.5
108.2 8.8
107.6 11.9
107.9 9.1
108.8 11.6
age given
as years:
months.
Measures employ?d. Two measures were employed in separate analyses: (1) Apparent Vertical-location of apparent vertical was measured with respect to objective vertical in degrees, with CW deviations, as viewed by S, designated as +, and CCW deviations designated as - ; (2) Apparent Body Axis Position-location of apparent body axis position was measured with respect to objective body axis position, with deviations of apparent body axis position CW of true body axis position designated by f, and deviations CCW designated by -. In addition, the relation between apparent vertical and apparent body axis position was represented by the angular disparity between these positions, expressed as the apparent body axis position minus position of apparent vertical, ignoring the physical angular difference between true vertical and true position of the longitudinal axis of the body under 36” tilt.
AGE
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PERCEPTION
RESUL+S
Summaries of the analyses of variance for apparent vertical and apparent body axis position are presented in Table 2. Brief inspection of the table shows that the main expectation of an interaction between age TABLE AGE
CHANQES IN APPARENT BODY AXIS POSITION
2 VERTICAL AND APPARENT UNDER BODY TILT
F-tests
Apparent vertical Source Between Age (4 Sex (G) AXG Pooled indiv. (I)
df 5 1
5 180
Within Body tilt (B) AXB GXB AXGXB
10
Pooled I X B
360
Starting position (S) AXS GXS AXGXS Pooled I X S BXS AXBXS
GXBXS AxGxBxS Pooled I X B X S Total
2 2 10 1
5 1 5 180 2 10
2 10 360 1151
Apparent body axis position
MS
FS
MS
FS
48.15 3.06 17.03 33.21
1.45 .09 .51 -
243.04 12.71 114.25 95.79
2.54O .13 1.19 -
27949.28 648.95 3967.36 84.41 244.37 27946.42 1809.26 333.68 214.52 79.01 3973.08 132.33 17.78 48.14 45.91
114.37b 2.66” 16.23” .34 353.7@ 22.9ob 4.220 2.72” 86.54b 2.88b .39 1.05 -
528.97 272.43 14.02 123.72 45.60 8791.38 576.72 354.00 92.93 44.24 678.88 19.20 17.08 32.30 17.41 49.00
11.60b 5.976 .31 2.71b 198.71b 13.046 8.Oob 2.10 39.00b 1.10 .98 1.86 -
223.39
-
“p < .05. bp < .Ol.
and body tilt axis position. cant findings tasks; finally Apparent
is significant for both apparent vertical and apparent body The specific nature of these age changes as well as signififor other variables is described separately for each of these the relationship between them is considered. verticality. Age changes pertaining to the mean position of
548
SEYMOUR
WAPNER
30'
AGE lh.
GROUP
LEFT TILT
(YEARs:MONTHS)
1. Age changesin location of apparent vertical as a function of body position.
apparent vertical as dependent on body tilt are depicted in Fig. 1. The findings can be briefly stated as follows: there is a general shift of the position of apparent vertical from the side of body tilt to the side opposite body tilt. For both left and right body tilt these changes continue beyond the true vertical with the consequence that the curves of position of apparent vertical for left and right body tilt, pooled for sex, cross over between 13 and 15 years of age. Table 2 also shows that there is a significant triple interaction involving the factors of age, body tilt, and sex .The changes in position of apparent vertical with variation in age and body tilt are similar for males and females with two exceptions: for both sexes, the general changes with age described above hold, but for females the deviations of apparent vertical to the side of body tilt are more extreme in the youngest age group, and the crossover point-shift of apparent vertical from side of body tilt to side opposite-occurs between 15 and 17 years in females as compared with 13 to 15 years in males. Another set of findings pertains to the so-called starting position effect, which is the tendency for the position of apparent vertical to be located closer to the position of the rod at the beginning of a trial. Starting position has an over-all significant effect, and interacts significantly with age, with sex, and with body tilt. As shown in Fig. 2, the starting position ef-
AGE
CHANGES
IN
549
PEBCEPTION
ROD
INITIALLY
30’
CW
....l -......,..,. . *:. .... .... .a.’ .:’
*.a. a. .. ...
” ....
.:. .. .. ..
ccw
I
I
7:l
AGE
2.
:..
.. ROD
INITIALLY
I
t3:l I
Age changes in location rod indicator at beginning of trial. FIO.
-.. *
.:.
:
/’
IO:11 GROUP
30’
CCW
I
I
I
l2:ll
15:4
16:ll
(YEARS:MONTHS)
of apparent
vertical
as a function
of location
of
feet decreases with increase in age, showing a steep gradient up to 12 years, with relatively small changes thereafter. Examination of the means comprising the “starting position X sex” interaction reveals that, overall, the effect of starting position is greater for females than for males. Finally, examination of the mean for the “starting position X body tilt” interaction shows that the apparent vertical is shifted disproportionately CCW under the condition “body left-starting position left” relative to the other test conditions. Apparent body axis position. As will be recalled, in this task the reference position is not a dimension of external space (e.g., objective perpendicularity), but rather a dimension of body space, viz., the longitudinal axis of the body. The task was to use the rod as an indicator of the apparent location of the longitudinal axis of the body by adjusting the rod to a position that appeared to coincide with this axis of the body, and accordingly measurements are taken with respect to it. Age changes pertaining to the apparent position of the body axis, as denendent on body tilt, are presented in Fig. 3. As shown in the graph,
550
SESMOUR
\l’.?PNER
with body tilted 30” from the perpendicular, both left and right, for all age levels the mean apparent location of the body axis tilts beyond the position in which the body axis is actually located. Further, there are striking ontogenetic changes: with age there is a slight decrease in deviation of apparent beyond true location of the body axis followed by an accelerated increase between 13 and 15 years of age. Body tilt also interacts significantly with sex, independent of age, with females showing a greater shift of apparent body axis than the males. CW
; m
+15O
2 t-
+lo”
3o”
L
:
:IA4e
RIGHT
TILT
*... .*.....“’ \ ERECT
*/-
..--
~---------*----------.----
/--
--a_
--a-
--S_
\ 30’ I 7:l
1
AGE
FIQ. 3. Age changes in apparent of body position.
I
I 8:l
IO:11 GROUP
location
I 12:ll
LEFT I 15:4
--_-
‘-8
TILT I 16:ll
(YEARS:MONTHS)
of longitudinal
body axis as a function
The second set of findings, which parallel those that obtained for apparent verticality, deals with starting position. Again for location of body axis, there is an over-all effect of starting position such that apparent location of body axis is relatively close to the position of the rod at the beginning of the trial. In addition to the over-all effect of starting position, there are significant first order interactions involving starting position and the following variables: age, sex, body tilt. As shown in Fig. 4, there is a decrease in effect of starting position with increase in age. As with apparent verticality, there is evidence that the effect of starting position is greater for females than for males, and that the apparent position of the body axis is shifted disproportionately CCW under the condition “body left-starting position left” relative to the other test conditions. The significant triple interaction-age X body tilt X starting position-indicates that the disproportionate shift CCW under “body left-starting position left” is most striking in the youngest group and
AGE
CHANGES
IN
551
PEXKZPTION
ROD
INITIALLY
30’
CW
1s’ * . . . . . .. .
c’..”
,.....
. ..a-
. . . . . . . . . . . . . w.’
**...... ;;;r: ROD
I
I
7:l
8:l AGE
* IO:11
I GROUP
INITIALLY
I
I
12:ll
15:4
30’
CCW
c 16:ll
(YEARS:MONTHS)
Age changes in apparent location of longitudinal of location of rod indicator at beginning of trial. Fro.
. ..a. . . . . . . . . . . . . ...*
4.
body axis as a function
decreases with increase in age, so that it is no longer evident in the oldest two age groups. The relationship between apparent vertical and apparent body axis position. The ontogenetic changes in the relationship between apparent
vertical
and apparent
7:l
location of the longitudinal
8:l AGE
1
1O:ll GROUP
body axis under body
12:ll
15:4
16:ll
(YEARS:MONTHS)
FIQ. 5. Age changes in angular disparity between apparent looation of longitudinal body axis under 30” body tilt.
vertical
and apparent
552
SIGYMOUR
WAPNER
tilt is evident from a comparison of Figs. 1 and 3. These ontogenetic changes are expressed more simply in Fig. 5, which plots the findings in terms of apparent angular disparity, i.e., the deviation of apparent vertical from apparent location of the body axis, ignoring the 30” deviation between true vertical and objective location of body axis. For all age levels, the apparent angular disparity is greater than the objective angular disparity; angular disparity, however, is relatively small in the youngest age group (6.8” for left and 3.4” for right body tilt) and continues to be small through 13 years of age, after which angular disparity increases markedly and reaches a maximum in the oldest age group (approximately 14” for left and right body tilt). DISCUSSION The present analysis advances our understanding of the development of spatiality by taking into account a reciprocal, rather than a one-sided, relationship between object and body perception. This means that the principle of development effective here is formulated in terms of an increase in polarization during ontogenesis between the position of apparent verticality (a main coordinate of the external spatial reference system) and the position of the longitudinal axis of the body (a main coordinate of the body reference system). Angular disparity is introduced as a unitary measure representing the relation between apparent vertical and apparent body position, under the condition of 30” body tilt. The main finding consists in the widening of the difference between the two perceived locations involved, viz., the physical location of the apparent vertical and the physical location of the experienced position of the longitudinal axis of the body. At the youngest age levels the position of apparent vertical and apparent position of the body axis are relatively close as compared with the two oldest age levels. As suggested in an earlier study (Wapner and Werner, 1957)) the relative undifferentiatedness of self and object found in early ontogenesis arises from two diametrically opposed determinants: “stimulus boundedness” and “egocentricity.” ‘( Stimulus boundedness” may be described as change in organismic state in keeping with stimulation, a change reflected in perception. Egocentricity is typically defined as determination of the object world through self as referent (cf. Piaget, 1928; Werner, 1940). Both “stimulus boundedness” and “egocentricity” contribute to a nonstable frame of reference with respect to external space (assessed by the verticality task) and stimulus boundedness contributes to nonstable body space (assessed by the body position task). Since these two processes, by their very nature, affect space localization differentially, it follows that a given response cannot simulta-
AGE
CHANGES
IN
PERCEPTION
553
neously be both purely egocentric and purely stimulus bound. It is possible, however, for the child to show both greater egocentricity and greater stimulus boundedness than the adult. By employing a factorial design, as done here, it is possible to assess each of these tendencies: the closer the location of .apparent vertical or apparent body position to the initial position in which the stimulus was presented the greater the degree of stimulus boundedness (indicated by the interaction “age X starting position” in which body tilts are pooled) ; the closer the location of apparent vertical or apparent body position to true body position the greater the degree of egocentricity (indicated by the interaction “age X body tilt” in which starting positions are pooled). On both apparent vertical and apparent body position tasks, with increase in age there is a progressive decrease in the magnitude of the starting position effect, representing a decline in stimulus boundedness. In keeping with findings by Wapner and Werner (1957), the present study clearly shows that with increase in age the position in which the stimulus is seen as vertical shifts away from the position in which the body is located; it is this increase in the distance between body position and physical location of apparent vertical that reflects the ontogenetic decrease in egocentricity. A similar decrease in egocentricity obtains for the apparent body position task: the child shows a slight overestimation of apparent body position whereas the adult shows a much larger overestimation; or stated another way, with increase in age there is a progressive increase in the distance between true body position and the position in which the stimulus object must be placed to be seen as lined up with the longitudinal axis of the body. It may be noted that with increase in age, the shift of apparent vertical and of apparent body position is opposite in direction ; thus the angular disparity between these two measures is greater at later than at earlier age levels. Independent of the specific interpretation offered, the findings as such have implications for any theory of perceptual development. As observed by Wohlwill (1960) a crucial issue is whether, during the course of development, perception progresses verticality. The findings presented here do not support such a view: for body position the adult makes a larger error than a child; for verticality the adult makes an error in a different direction from the child. REFERENCES H. Eine scheinbare bedeutende Drehung von Objekten bei Neigung des Kopfes nach rechts oder links. Virchow’s Archiv. fuer Pathologiche Anatomie und Physiologic ocnd fuer Kliniwhe Meditin, 1860, 20, 3813%. AUBERT, H., AND DELAQE, Y. Ph&oZogische studien uber die orientierung. Tubingen : Laupp, 1888. AUBERT,
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M. The relation between subjective body space and objective external space under conditions of body tilt. Microfilmed doctoral dissertation, Clark University, 1962. BAUERMEISTER, M. The effect of body tilt on apparent verticality, apparent body position, and their relation. Journal of Experimental Psychology, 1964, 67, 142147. BAUERMEISTER, M., WAPNER, S., AND WERNER, H. Sex differences in the perception of apparent verticality and apparent body position under conditions of body tilt. Journal of Personality, 1963, 31, 394407. BAUERMEISTER, M., WAPNER, S., AND WERNER, H. Method of stimulus presentation and apparent body position under lateral body tilt. Perceptual and Motor Skills, 1967, 24, 43-50. BAUERMEISTER, M., WERNER, H., AND WAPNER, S. The effect of body tilt on tactualkinesthetic perception of verticality. American Journal of Psychology, 1964, ‘77, 451456. COMALLI, P. E., JR., WAPNER, S., AND WERNER, H. Effect, of muscular involvement. on size perception. Perceptual and Motor Skills, 1959,9, 116. , DELAGE, Y. Etudes experimentales sur les illusions statiques et dynamiques de direction pour servir a determiner les functions des canaux semicirculaires de l’oreille interne. Archives de Zoologie Experimentale et General, 1886, 4, 535BAUWMEISTER,
624. GIBSON,
J. J. The relations between visual and postural determinants of the phenomenal vertical. Psychological Review, 1952, 59, 370-375. GRAHE, K. Uber Lageempfindungen und -reflexe beim Menschen. Zeitschrift fiir Hal.+, Nasen-, und Ohrenheilkunde (Berlin), 1925, 12, 640-651. HOWARD, I. P., AND TEMPLETON, W. B. Human spatial orientation. London: Wiley, 1966. KAPLAN, B. Meditations on genesis. Human Development, 1967, 10, 65-87. MANN, C. W. Visual factors in the perception of verticality. Journal of Experimental Psychology, 1952, 44, 460464. MANN, C. W., AND PASSEY, G. E. The perception of the vertical V: Adjustment to the postural vertical as a function of the magnitude of postural tilt, and duration of exposure. Journal of Experimental Psychology, 1950, 41, 10~%113. MCFARLAND, J. H., WAPNER, S., AND WERNER, H. The relation between perceived location of objects and perceived location of one’s own body. Perceptual and Motor Skills, 1962, 15, 331341. MCFARLAND, J. H., AND CLARKSON, F. Perception of orientation: Adaptation to lateral body-tilt. American Journal of Psychology, 1966, 79, 265-271. NAGEL, W. A. Uber das Aubert’sche Phanomen und verwandte Tauschungen uber die vartikale Richtung. Zeitschrift fur Psychologie, 1898, 16, 372-398. PIAGET, J. Judgment and reasoning in the child. London: Routledge and Kegan Paul, 1928. QUIX, F. H., AND EIJSVOGEL, M. H. P. M. Experimente uber die Funkt,ion des Otolithenapparates beim Menschen. Zeitschrift fiir Hal+, Nasen-, und Ohremheilkunde (Berlin), 1929, 23, 68-87. RIERDAN, J., AND WAPNER, S. Experimental study of adaptation to visual rearrangement deriving from an organismic-developmental ceptual and Motor Skills, lQ66, 23, 903-916. WAPNER, S. Some aspects of a research program
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mental approach to cognition: Experiments and theory. Journal of the American Academy of Child Psychiatry, 1964, 3, 193-230. WAPNER, S., AND WERNER, H. Perceptual development. Worcester, Mass.: Clark University Press, 1957. WAPNER, S., AND WERNER, H. An experimental approach to body perception from the organismic-developmental point of view. In S. Wapner and H. Werner (Eds.) The body percept. New York: Random House, 1965. WERNER, H. Comparative psychology of mental development. New York: Harper, 1940; (2nd ed.) Chicago: Follett, 1948; (3rd ed.) New York: International Universities Press, 1957; (4th ed.) New York: Science Editions, 1961. WERNER, H. The concept of development from a comparative and organismic point of view. In D. B. Harris (Ed.), The concept of development: An issue in the study of human behavior. Minneapolis: Univ. of Minnesota Press, 1957. WERNER, H., AND KAPLAN, B. Symbol formation: an organismic developmental approach to language and the expression of thought. New York: Wiley, 1963. WERNER, H., AND WAPNER, S. Sensory-tonic field theory of perception. Journal of Personality, 1949, 18, 88-107. WERNER, H., AND WAPNER, S. Toward a general theory of perception. Psychological Review, 1952, 59, 324-338. WITHIN, H. A., LEWIS, HELEN B., HERTZJIAN, M., MACHOVER, KAREN, MEISSNER, PEARL B., AND WAPNER, S. Personality through perception. New York: Harper, 1954. WOHLWILL, J. F. Developmental studies of perception. Psychological Bulletin, 1960, 57,25O-288.