Neonatal perception of spatial relationships

INFANT

BEHAVIOR

AND

DEVELOPMENT

8, 15-23

(1985)

Neonatal Perception of Spatial Relationships* SUE E.G. ANTELL University of Maryland-Baltimore County

ALBERT J.CARON George WashingtonUniversity Alert healthy neonates (average age, 61 h) were able to discriminate in spatial relationships between two simple geometric forms as habituation of visual fixation to a constant positional arrangement absolute location, and recovery of fixation to a navel arrangement habituated absolute location. Such recovery suggests that newborns, infants, ore able to extract invariant relational information against change. neonatal

habituation

neonatol

perception

spatial

a difference evidenced by across varying in a previously like older a backdrop of

relations

Human beings perceive an organized world in which objects and events are related to each other and are understood in the context of those relations. But what of the origins of this capacity? Do young infants also perceive a coherent world, or do they see a Jamesian confusion that dissipates only gradually over time? A contemporary version of this debate centers on whether young infants have direct access to the relationships between things or whether access is mediated by cognitive structures that emerge after prolonged experience. Thus, J. Gibson (1966, 1979) argues that the perceptual system is attuned at birth to relational information that remains invariant against a backdrop of change. By contrast, Piaget (1952) contends that young infants perceive fleeting, unconnected images until well into the second year when abstract schemes for construing simple percepts are formed. Investigation of the perceptual capacities of newborns may be expected to shed light on this issue. However, while infants as young as 2 to 4 months have been shown to detect a number of holistic/relational properties of stimuli (Caron & Caron, 1982; Milewski, 1979; Schwartz & Day, 1979; Vurpillot, Ruel, & Castrec, 1977), the evidence in the crucial neonatal period is less firm. A few exploratory investigations suggest that newborns may indeed be sensitive to structural aspects of the environment. Ante11 and Keating (1983), for example, demonstrated that infants during the first week of life can ab* This paper is based in part on a doctoral dissertation submitted by the first author to the graduate faculty of the University of Maryland Baltimore County. The authors wish to thank J. K. Felix, M.D., and Kathleen Stevens, M.D., of Sinai Hospital of Baltimore for their assistance in arranging access to subjects. We would also like to acknowledge Stanley Feldstein and Daniel Keating of the University of Maryland Baltimore County, and Rose Myers and Rose Caron of the Infant Research Laboratory for their thoughtful comments on an earlier draft. Computer time for this project was donated by the Computer Science Center, UMBC. Research assistants were Cindy Brason and Antoni Shefchek. Requests for reprints may be directed to either author at the Infant Research Laboratory, 10620 Georgia Avenue, Silver Spring, MD 20902.

16

ANTELL

AND

CARON

stract small-set numerosity (two vs. three elements) from visual arrays across changes in contour density. Additionally, it has been reported that neonates can discriminate various facial expressions modeled by a single adult (Field, Woodson, Greenberg, & Cohen, 1982) as well as different intonations of the same voice (Mehler, Bertoncini,.& Barriere, 1978). On the other hand, acknowledged methodological shortcomings (confounding effects of brightness, potential tester bias, etc.) limit the conclusiveness of these findings. Moreover, evidence that 6-week-olds respond to absolute rather than relational aspects of some stimuli (Cohen & Younger, 1984) further cloud the issue. The present research represents a direct test of neonatal ability to perceive relational information. Specifically, it examines whether newborns can detect an invariant spatial relationship across changes in the absolute locus of an array. The study differs from previously cited neonatal work in two important respects. First, unlike experiments which involve human attributes (and hence might be influenced by special sensitivity to social stimuli), it uses simple geometric forms which are presumably devoid of learned or intrinsic value. It should be pointed out, however, that while the forms are of limited ecological significance, the relationship between them (relative position) is not. Second, potentially confounding effects of brightness and contour density, which often contaminate visual research with infants, have been strictly controlled. METHOD Subjects

Subjects for this research were 40 healthy, alert human newborns (M age = 61.5 hr; SD = 32.25 hr) born on the obstetrical service of a major metropolitan hospital and whose parents had given consent for the procedure. All infants in the nursery were evaluated on a number of characteristics, and consents were solicited from the parents of all those infants who satisfied the following criteria: gestational age, 38-42 weeks; weight greater than 2,720 g; Cesarean section for maternal cause only; Apgar scores at least 7/9; no gestational illness in mother; no general anesthesia; bilirubin less than 7 mg/dl on day 1, 10 mg/dl on day 2, and 12 mg/dl thereafter without phototherapy; no obvious congenital illness or abnormality. The 40 infants included in the study were randomly selected from the population of infants who satisfied these criteria and whose parents had given consent. Subjects were randomly assigned to each of three conditions in the main experiment and to an additional control condition (10 infants per condition) with the restriction that each cell contain equal numbers of male and female infants. Seventeen additional babies were dropped from the study because they were unable to maintain state long enough to complete the procedure. stimuli The stimuli for the main experiment (see Fig. 1) consisted of 15 x 15 cm white cards on which were embossed a black 2.54-cm cross and square in a specific

NEONATAL

PERCEPTION

Habituation

EC,

Posthabituation

mmm

cc

m

+ + El 0 H q: n

0

Figure 1. Stimuli for the moin experiment. used in the experiment01 conditions. Rows trol condition subjects. Half of the control other half sow the cards in row 4.

17

n +

Rows 1 and 2 represent 3 and 4 are the figures subjects saw the cards

the figures shown to conin row 3, the

spatial relationship (square above cross or cross above square). The shapes were separated by 1.27 cm of white space. Subjects were habituated to three exemplars of these elements which varied the absolute location of the entire array with reference to the horizontal perimeters of the cards but which maintained the spatial relation between the individual elements. At test, subjects saw a fourth card which presented the same elements in a previously habituated absolute location, but with the relation between the elements reversed. Because only the position of the elements was changed any obtained discrimination could not be due to a difference in brightness. Stimuli for the additional control group (Fig. 2) consisted of 15 x 15 cm white cards on which the cross and square appeared either separated by white space or with contiguous borders. The primary purpose of this control was to determine whether infants perceived the experimental stimuli as composed of two distinct elements or some single element. Indeed, if the two elements were perceived as a unitary figure, then two alternative explanations could be argued. On the one hand, the infants could have detected a single figure which changed in orientation (detection of nonrelational spatial information), or a single figure which was simply replaced by a novel figure at test (nonspatial nonrelational). If either were the case, then the interpretation of the findings as relational would not be legitimate. Consequently, we wanted to determine whether our subjects could at least detect the gap between the two figures. Infants in this condition were habituated to a single exemplar that was either separated or contiguous and were then tested with a figure which maintained the spatial relationship but altered the border separation.

18

ANTELL

Figure posure

AND

2. Stimulus orroys for the orientation to either of the two sets of stimuli

CARON

control group. (OCI or OC,).

Subjects

received

ex-

Procedures Upon arrival in the nursery, the first author evaluated all subjects for state. Since the experiment required infants to be awake and alert, those subjects who were found spontaneously in the quiet alert state were tested immediately. Active awake or crying infants were quieted prior to the start of testing. Asleep subjects were gently awakened, and the desired state induced if possible. Subjects were then taken into a testing room adjacent to the nursery where those who needed restraining were swaddled, and all infants were placed on their right sides in their own hospital bassinet. All infants were offered a pacifier at the start of testing; all but 6 infants accepted and used it during testing. While there is concern that pacifiers may affect visual processing (Bruner, 1973), they have nevertheless been found useful in maintaining state, orientation to stimulus, and concentration in very young infants (Ante11 & Keating, 1983; Bruner, 1973; Haith, 1980; Mendelson & Haith, 1975). Those infants who did not accept the pacifier were randomly distributed across the stimulus conditions. Once settled in the bassinet, the subjects were manually oriented toward a white foamboard screen which shielded them from nonexperimental visual stimuli and which was fitted with white brackets to hold the stimulus cards. The screen was located 17-19 cm from the infant’s eyes (Haynes, White, & Held, 1965). A trial began when the investigator dropped the first stimulus card into the bracket, and an observer who was blind to experimental condition and criterion of habituation noted the reflection of the stimulus on the infant’s pupils. The observers reported that the stimulus was reflected only as a dark field on a white background so that they could not tell what stimulus was exposed on any trial. Each trial continued for a maximum of 40 s, or until the infant was off target for 2 or more s. Following an intertrial interval of 5-10 s, the next card in the series was inserted. If necessary, alertness during the inter-

NEONATAL

PERCEPTION

19

trial interval was maintained by vestibular stimulation (raising the infant to a sitting position and then lowering him/her back onto the side) or with gentle patting. Infants who could not be realerted with these maneuvers were dropped from the study (N= 17). Infants in the main experiment (N= 30) continued to be exposed to the three habituation stimuli until they met’a criterion of three successive trials in which they exhibited a decline in looking of at least 8 s from the mean time of fixation on the first three trials. This criterion is a variation of the one reported by Friedman (1972a, 1972b) as having the greatest empirical utility in habituation research with neonates and was used successfully by Ante11 and Keating (1983) as well. After meeting criterion, the 20 infants in two of the conditions (EC,, EC,; 10 per group) were exposed for two trials to a novel card which transposed the spatial relation between the elements but which maintained a previously habituated absolute location (in the vertical center of the stimulus card). To control for the possibility of spontaneous increases in fixation following habituation, a third group of 10 infants (CC) continued to see the center exemplar of the previously habituated spatial relation at test (also for two trials). Finally, the 10 infants in the orientation control (OC) group, who had been habituated to a single cross/square array in which elements appeared either separated (N= 5) or contiguous (N= 5), were given two test trials in which the border separation alone was altered. All other manipulations for this group were essentially the same as in the main experiment. Timing of visual fixation in all conditions was accomplished by the naive observer using a digital stopwatch with readout of .Ol s. Written recording of fixation and computation of criteria was accomplished on line by the principal investigator. Interrater reliability determined for 30 randomly selected trials yielded an intraclass reliability coefficient (r,) of .92. RESULTS The design for the main experiment consisted of a 3 (Condition) x (Gender) x (Habituation/Test) mixed model analysis of variance (ANOVA) with the first two variables between subjects and the last within subjects. The major dependent variables were mean time of visual fixation for the last two habituation trials and the two test trials, respectively (see Table 1). As predicted, the main analysis revealed a significant Condition x Habituation/Test interaction, F (1,24) = 9.148, p < .OOl , which indicated that infants in the two experimental groups looked longer at the test arrays than at tht ‘&St two habituation arrays [habituation M= 13.25 [EC,), 12.96 (E(L); test M= 23.65 (EC,), 28.05 (EC,) 1. By contrast, looking continued to decline in the control group (habituation M= 9.05; test M= 5.13). Planned comparisons on the interaction confirmed that both experimental groups differed significantly from the control group at test, Fcomp, (1,18) =49.14, p< .OOl; Fcompl (1,18) = 3 1.34, p < .OOl . Post-hoc comparisons of the three groups revealed no significant differences in looking duration during the last two habituation trials.

ANTELL

20

AND

TABLE Means

Condition EC, M SD

and

Standard

Deviations

Last

2 Habituation

CARON

1

of Looking Trials

Time

(h

s) by Condition 2 Posthabituation

13.25 3.95

23.65

M

12.96

SD

6.26

28.05 11.42

Trials

a.90

EC,

cc M

SD oc, M SD oc, M SD

9.05 5.41

5.13

11.09 4.33

26.18 13.71

7.96 9.10

17.05 6.97

4.22

As a further check on the comparability of the three groups during habituation, the number of trials to criterion, mean trial length, and total time spent in habituation were analyzed in individual ANOVAs. No differences were found for any of these parameters of looking behavior. Backward habituationrecovery curves for the three groups are shown in Fig. 3. The analysis of the data from the fourth group (OC) consisted of a 2 (Habituation/Test) x (Gender) mixed model ANOVA with the first variable within subjects and the second, between subjects. The dependent variable was again mean time of fixation on the last two habituation trials and the two test trials, respectively. There was a significant main effect for habituation/test, indicating that infants looked longer at the novel border arrangement than at the habituated arrangement, F(1,18) = 14.29, pt7< .Ol. It appears, then, that infants perceived separated elements differently from fused elements, a finding that is at least consistent with the hypothesis that the gap between the cross and square had been perceived in the main experiment (see Table 1). Finally, to determine whether infants in the main experiment were sensitive to variations in absolute location of the three habituation exemplars, the number of trials to criterion during habituation was compared for infants in the three main conditions (where absolute location varied) with those in the OC, condition (where absolute location was held constant). A one-way ANOVA revealed that infants who were exposed to three locations took significantly more trials to habituate than did infants who were exposed to a single exemplar, thus supporting the assumption that infants had discriminated changes in absolute location, F(3,31) = 2.95, p < .05 (log-transformed scores). Mean trials to criterion were 10.1 (SD=5.3) in EC,; 13.3 (SD=8.03) in EC,; 13.8 (SD= 8.16) in CC; and 6.0 (SD= .7) in OC,.

NEONATAL

21

PERCEPTION .---.-.-.-.-

EC, EC2 cc

\

Figure 3. Trial by trial looking time experiment. T is the final hobituotion

for

each of the three trial; T+ 1 and T+2

conditions ore the

in the main test trials.

DISCUSSION

The present results indicate that newborn infants are capable of detecting an invariant spatial relation between two elements and of using that information to discriminate a novel arrangement of the same elements. The findings cannot be attributed to discrimination of change in absolute location of the components, since they appeared at test in a location that had been occupied during some portion of the habituation phase. Nor is it likely, based on the findings in the orientation control condition, that infants had perceived a single feature changing in orientation (rather than two figures changing in relationship) or simply as novel figures. The specific intent of the OC manipulation was to demonstrate that infants had in fact detected the separation between the cross and square. This conclusion seems warranted, even though change in border separation was confounded with other changes (most notably, in overall form, amount of contour, size, and absolute location of the cross and square). For one thing, discrimination of contour length and form would each necessarily involve detection of the change in the gap between components. Second, although there was a slight change in absolute location of both elements (the top figure was moved .635 cm down and the bottom, .635 cm up), it is reasonable to assume that the more compelling change was that of border separation. With regard, finally, to size, there is evidence that change in size is much less salient for young infants than change in other features such as shape and orientation (Caron, Caron, & Carlson, 1978). If it can be concluded that our subjects had,detected the separation between square and cross, then, given that 3-month-olds have been shown to perceive separated objects as discrete and the same objects when contiguous as unitary (Bower, 1977; Prather & Spelke, 1982), it is possible that the cross and square had been encoded as discrete elements in relationship. In view of the limited objectives of the study, a number of broader questions remain unanswered. First, we cannot be certain about the generality of

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ANTELL

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the findings. Would they, for example, apply to other dimensions (the horizontal or diagonal), or to other fixed distances, or sizes of figures? Second, the question of how abstractly infants had encoded the relation remains to be resolved. Could they have generalized responding to new absolute distances between the components or to the cross and square when rotated 45 “? Finally, we can only speculate about possible mechanisms that might have mediated perception of the present relationship. According to a Gestaltist view, relational properties of stimuli are directly apprehended. Gibson (1966, 1979), too believes that invariant relations are extracted whole from the optical flux. However, other explanations cannot be ruled out. For example, sequential scanning models of relational encoding previously proposed for adults (Norton & Stark, 1971) and in computer simulations of infant perception (Willatts, 1977) might conceivably apply here. According to such a scheme, the infant would have encoded the habituation stimuli as repeated sequences of “cross, downward eye movement, square” and “square, downward eye movement, blank space.” At test, the control infants encounter the same, but the experimental subjects encounter two novel sequences, “square, downward eye movement, cross” and “cross, downward. eye movement, blank space.” A model of this sort has some affinity with the rules of information search for newborns recently advanced by Haith (1980). A last comment is in order regarding the apparent discrepancy between the present findings and those indicating that slightly older infants (6 weeks) seem to encode absolute rather than relative aspects of experience (Cohen & Younger, 1984). One possibility is that relational processing abilities present in rudimentary form at birth may drop out at a subsequent point and reappear later in stable and complex form (Bower, 1977). Alternatively, the discrepancy may be due to procedural differences between the respective experiments. It is worth noting in this regard that in the Cohen and Younger study, which was concerned with the ability of infants to detect angular relations, an invariant angle size was not exposed across variations in orientation, but instead infants were shown the same angle in a single unchanging orientation. The fact that under these circumstances infants appear to have encoded an absolute feature (orientation of the line segments) implies only that this feature was initially more prominent than the relational figure (angle size). It does not speak to the issue of whether they might have detected an invariant angular relation under conditions of changing orientation. Overall, the demonstration that neonates are sensitive to relative location is consistent with the view that the world of the newborn is more organized and more objective than previously suspected. The results further imply that the gap between perceiving and knowing is not as formidable as initially envisioned within the Piagetian frame. REFERENCES Antell, S.. & Keating, D. (1983). Perception of numerical invariance in neonates. Child Development,

54, 695-702.

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PERCEPTION

Bower, T. G. R. (1977). A primer of infani development. San Francisco: Freeman. Bruner, J. (1973). Pacifier produced visual buffering in human infants. Developmental biology,

Psycho-

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Field, T., Woodson, R., Greenberg, R., & Cohen, D. (1982). Discrimination and imitation of facial expressions by neonates. Science, 218, 179-181. Friedman, S. (1972a). Habituation and recovery of visual responses in the alert human newborn. Journal

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Psychology,

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Friedman, S. (1972b). Newborn visual attention to repeated exposure of redundant vs. “novel” targets. Perception and Psychophysics, 12. 291-292. Gibson, J. J. (1966). Thesensesconsideredaspercep/ualsysrems. Boston, MA: Houghton-Mifflin. Gibson, J. J. (1979). An ecologicalapproach to visualperception. Boston, MA: Houghton-Mifflin. Haith, M. (1980). Rules that babies look by. Hillsdale, NJ: Erlbaum. Haynes, H., White, B., & Held, R. (1965). Visual accommodation in human infants. Science, 148, 528-530. Mehler, J., Bertoncini, J., & Barriere, M. (1978). Infant recognition of mother’s voice. Perception.

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Mendelson, M., & Haith, M. (1975). The relation between nonnutritive sucking and visual information processing in the human newborn. Child Developmenr, 46, 1026-1029. Milewski, A. (1979). Visual discrimination and detection of configural invariance in 3-month infants. Developmental Psychology, IS, 357-363. Norton, D., & Stark, L. (1971). Scanpaths in eye movements during pattern perception. Science, 171, 308-311. Piaget, J. (1952). The origins of infelligence in children. New York: International Universities Press. Prather, P., & Spelke, E. (1982, March). Perception of adjacenl andpartially occluded objects by fhree-month-old infanfs. Paper presented at the International Conference on Infant Studies, Austin, TX. Schwartz, M., & Day, R. (1979). Visual shape perception in early infancy. Monographs of the Society for Research in Child Development, 44, (7, Serial No. 182). Vurpillot, E., Ruel, J., & Castrec, A. (1977). L’organisation perceptive chez el nourrison: Response au toot ou a ses elements. Bullefin de Psychologie, 327, 396-405. Willatts, P. (1977). Two visual systems in infancy: A computer model of their integration and development. Bulletin of the Brirish Psychological Society, 30, 88. 24 August

1983;

Revised

9 August

1984

n