JOURNAL
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
Infants’ Attention
28,
416-423 (1979)
to Intrastimuius
Motion
MARCI R. GIRTON Brown
University
Twenty-four S-week-old infants sucked significantly less when shown a schematic face in which the eye dots oscillated at 4 or 7 cm/set than when shown the same face with the eye dots oscillating at 1 cmisec. When identical moving dots were presented in the absence of the surrounding facial configuration, infants showed the same pattern of response. These results indicate (a) that 5-week-old infants can attend to intrastimulus movement, and (b) that the “externality effect” does not extend to compound visual displays which have moving internal elements.
Since stimulus reception and selective attention are prerequisite to complex information processing and to learning (Cohen & Salapatek, 1975; Hochberg, 1971; Neisser, 1967), much effort has been directed toward discovering the stimulus determinants of infant attention. Recent investigations employing such diverse measures as sucking suppression (Haith, 1966), optokinetic nystagmus (Brazelton, Scholl, & Robey, 1966; Dayton, Jones, Steele, & Rose, 1964), visual fixation (Carpenter, 1974; Volkmann & Dobson, 1976), heart rate change (Gregg, Clifton, & Haith, 1976), and smiling (Sroufe & Waters, 1976) suggest that stimulus motion is especially salient during the first weeks and months of life. This cue may play an important role in the development of attachment by allowing young babies to respond “socially” even before they can respond to people qua people (Bowlby, 1969). Several authors have hypothesized This research is based on a PhD thesis submitted to Brown University, and was conducted while the author was a USPHS Trainee under Training Grant 5T32-MH-14255 to L. P. Lipsitt, Brown University. Several laboratory expenses were made possible by a grant from the William T. Grant Foundation to the Brown University Child Study Center, and preparation of the manuscript was supported by USPHS Grant HD-04756 to E. C. Butterfield, University of Kansas Medical Center. The author thanks B. Reilly for the initial recruitment of maternal cooperation; C. DeLucia, R. Moore, and K. White for technical assistance; M. Forrest and J. Dubuc for facilitating the testing of infants at the Carriage House of the Brown University Child Study Center; and E. R. Siqueland, J. W. Kling, E. C. Butterfield, and T. B. Mustaine for helpful comments on an earlier version of this manuscript. The author is grateful to L. P. Lipsitt for his assistance throughout all phases of this research. Requests for reprints should be sent to the author at the MRRC, University of Kansas Medical Center, 39th and Rainbow, Kansas City, KS 66103. 416 0022~0965/79/060416-08$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
INFANTS' ATTENTION TO MOTION
417
that intrafacial movement enhances the baby’s attention to the caretaker’s face (Brazelton, Koslowski, & Main, 1974; Gibson, 1969; Rheingold, 1961; Robson, 1967; Wolff, 1963), but there is little empirical support for this. Indeed, Milewski (1976) found that, unlike infants 14 to 20 weeks of age, infants 4 to 6 weeks of age show an “externality effect.” That is, they discriminate changes in small shapes only when those shapes are not surrounded by larger, unchanging shapes. Similarly, Salapatek and his co-workers (e.g., Maurer & Salapatek, 1976; Salapatek & Moskovich, 1975) demonstrated that infants 4 to 6 weeks old direct most of their visual fixations toward the external contours of compound forms, while 8- to lo-week-old infants concentrate their visual fixations on the internal elements. The “externality effect” exhibited by infants at 4 to 6 weeks of age approximates the behavior of newborns rather than that of older infants (see Fantz & Miranda, 1975). The evidence that 4- to 6-week-old infants do not attend to stationary intrastimulus elements is suggestive, but does not preclude their attention to intrastimulus elements which move. A recent visual scanning study bears more directly on this issue. Haith, Bergman, and Moore (1977) found that mouth movement enhanced face scanning by 9- to 1 l-week-old infants, but did not affect the percentage of face fixations by 3- to 5-week-old or 7-week-old infants. Furthermore, for all subjects whose data could be analyzed (3- to 5-week-olds’ data were excluded from these analyses because they had so few face fixations), the percentage of face fixations on the mouth was not affected by presence or absence of mouth movements. Yet it may be premature to discount the attentional properties of movement by intrastimulus elements on the basis of these data alone, for several reasons. First, mouth movements were confounded both with auditory stimulation (the mouth moved only when the adult spoke), and also with oscillating movement of the entire adult head. Second, amount of intrastimulus movement was not systematically varied. Finally, the absence of selective fixation does not affirm the absence of selective attention: Infants, like adults (see Kaufman, 1974), may well be capable of nonfocal perception of moving stimuli. Whether or not intrastimulus motion can attract the attention of infants less than 2 months old therefore remains unclear. The measurement of sucking suppression seems a promising way to investigate this problem. Not only has the suppression of ongoing behavior (and a decrease in suppression with continued stimulation) been related to attention (Berlyne, 1960; Bronshtein, Antonova, Kamenetskaya, Luppova, & Sytova, 1958; Sokolov, 1963), but the suppression of nonnutritive sucking in particular has proved useful in the investigation of infant attention to whole-stimulus visual movement (Haith, 1966; Haith, Kessen, & Collins, 1969). Moreover, anecdotal re-
418
MARC1 R. GIRTON
ports indicate that attention to a moving stimulus is commonly accompanied by sucking suppression, even to the extent that a hungry infant will terminate nutritive sucking to watch quietly for several minutes (Gorman, Cogan, & Gellis, 1957; Salzen, 1963). The present study asked whether 5-week-old infants’ attention to a schematic face would increase as the salience (velocity) of its oscillating eye dots increased. It was assumed that decreased sucking indicated increased attention, and that differential responding to faces with differing rates of movement reflected attention to the intrastimulus motion. As a control for the ability of the infants to attend to the moving dots when the dots were not the internal elements of a complex pattern, the eye dots were presented in the absence of the surrounding schematic face on some trials. In addition, all trials with moving stimuli were paired with temporally contiguous trials with identical, but completely stationary, stimuli; it was thus possible to statistically control for the potentially confounding effects of sucking rate fluctuations. METHOD Subjects
Twenty-four full-term clinically normal infants approximately 5 weeks old (12 male and 12 female) participated. Their mean age was 38.3 days (SD = 4.07 days). One male and one female infant were randomly assigned to each of 12 counterbalanced stimulus order conditions. An additional 133 infants were scheduled for testing but were not included because of appointment cancellations (N = 53), fussing (N = 27), sleeping (N = 30), failure to suck on the nipple (N = 21), or experimenter error (N = 2). Apparatus Stimulus equipment. A Medical Systems Corporation Light Stimulator Type 4330/l rear-projected two stimulus eye dots onto a 26.5 x 26.5-cm viewing screen, which was 16 cm away from the infant. The projected dots were 1.5 cm in diameter, 7 cm apart, and each oscillated within a distance of 5 cm at velocities of 1, 4, or 7 crn/sec. In the FACE perimeter condition, a schematic face (approximately 8 x 22.5 cm) on a clear film background was placed directly on the viewing screen. The linewidth of the figure was l-l.5 cm. The two dots projected through, and could be made to oscillate within, the eye outlines. In the NO FACE condition, a clear film without any markings on it was placed on the screen. The dots appeared in the same position and moved in exactly the same manner for both conditions. The FACE and NO FACE visual displays had overall luminances of 2.73 and 2.78 log foot lamberts, respectively, as measured by an SE1 Exposure Meter. The FACE and NO FACE conditions are illustrated in Fig. 1.
INFANTS’
ATTENTION
419
TO MOTION
0
0
FIG. 1. The FACE condition is shown on the left. The FACE outline was placed directly on the viewing screen, and the eye dots were rear-projected onto the screen. The NO FACE condition is shown on the right.
Recording equipment. A sterilized blind nipple was attached to a Grass Instrument pressure transducer by a length of 0.25in. (.64 cm) plastic tubing. Sucking on the nipple produced pressure variations which were recorded by a Grass Model 5 polygraph. These pressure variations were also converted by a Schmitt trigger to discrete responses and recorded on a counter during stimulus presentations, but not during intertrial intervals. Procedure
and Experimental
Design
A week in advance, testing times were scheduled according to the mother’s best estimate of when the baby’s “awake time” would be on the day of the test. Upon arrival at the Brown University Child Study Center the infant’s outer garments were removed and, if necessary, the mother was asked to awaken her infant. As soon as an infant was awake, alert, and not fussing, he or she was offered a sterile blind nipple to suck on, and the sensitivity of the recording apparatus was adjusted. The infant was placed on his or her back in a bassinet, with a support pillow to keep the head from moving. The bassinet was centered under the viewing screen, and a gauze cloth was lowered to keep the experimenter from distracting the infant while observing him or her. Each trial started at the beginning of a sucking burst (defined as at least two sucks within 2 set following an interval of at least 2 set with no sucks) and consisted of 16 set of stimulus presentation. Following every trial, the experimenter recorded the number of sucks during that stimulus and readied the velocity and/or perimeter conditions for the trial to follow. These activities took approximately 5 set to complete. At the beginning of the next sucking burst, a new trial was initiated. This procedure was followed for a total of 36 stimulus presentations, 18 of one perimeter condition (FACE or NO FACE) followed by 18 of the
MARC1 R. GIRTON
420
other. The order of these perimeter blocks was counterbalanced across infants. Within each perimeter block there were three velocity blocks, the order of which was also counterbalanced across infants. Each velocity block consisted of six trials, three with stimulus movement and three without movement. These moving and stationary trials were presented in a predetermined pseudo-random order (three identical stimuli were never presented consecutively) which varied across velocity blocks. RESULTS
The mean sucking rate was calculated for the three moving trials and for the three stationary trials within each velocity block. All analyses were conducted on these data. Preliminary tests ruled out sex as a significant source of variance. Therefore, subsequent analyses collapsed across this factor. Because sucking rate during trials with stimulus movement was considered to be, in part, a function of the infant’s ongoing sucking rate as well as a function of treatment effects, the analysis of covariance design was used to statistically control for fluctuations in sucking rate. Calculation of regression slopes for each cell of the design indicated that the assumption of equal regression slopes could be met. Therefore, an analysis of covariance with repeated measures was used to compare mean sucking rate across velocity and perimeter conditions, with the mean sucking rate for the stationary trials within a given velocity block being used as the covariate for that velocity block. Neither the main effect of perimeter (F (I ,22) = 3.94, p = .060) nor the perimeter x velocity interaction (F (2,415) = 1.07, p = .3.51) reached statistical significance. The highly significant main effect of velocity (F (2,45) = 13.31, p < .OOl) is shown in Table 1. Post hoc Tukey’s (a) tests revealed that infants sucked significantly less when the dots oscillated at 4 cm/set than when the dots oscillated at I cm/set (p < .Ol) and that infants sucked significantly less when the dots oscillated at 7 cm/set than when they oscillated at 1 cm/set (p < .Ol). There was no difference in sucking rate during stimulus velocities of 4 and 7 cm/set.
TABLE MEAN
SUCKS
AS A FUNCTION
1 OF STIMULUS
Covariate Velocity (cm/set) 1 4 7
VELOCITY
Dependent variable
x
Unadjusted 57
Adjusted ?%
17.23 17.13
16.41 13.64 14.13
16.46 13.73 13.99
17.63
INFANTS’
ATTENTION
TO
MOTION
421
DISCUSSION
This experiment investigated whether Sweek-old infants’ attention to a schematic face would increase as the velocity of its oscillating eye dots increased. It was assumed that decreased sucking indicated increased attention. Infants sucked significantly less during trials in which the eye dots oscillated at 4 or 7 cm/set than during trials in which the eye dots oscillated at 1 cm/set, a differential response which clearly indicates more attention to the faces with the faster moving eyes. This empirical demonstration that Sweek-old infants can attend to intrastimulus motion provides indirect support for the hypothesis that intrastimulus motion attracts infants’ attention to faces in everyday life (Brazelton et al., 1974; Gibson, 1969; Rheingold, 1961: Robson, 1967; Wolff, 1963). In the natural environment, intrafacial movement might serve to attract and maintain infants’ attention to faces which are otherwise familiar, or it might attract infants’ attention to faces at an earlier age. These questions deserve direct investigation with real faces. The finding that infants attend to moving internal pattern elements at 5 weeks of age is especially interesting in light of recent reports that 4- to 6-week-olds apparently do not attend to stationary internal pattern elements (Maurer & Salapatek, 1976; Milewski, 1976; Salapatek & Moskovich, 1975). The lack of such an “externality effect” in the present investigation implies that the developmental course of attention to intrastimulus elements may well vary with the dynamics of those elements. This may obtain only for relatively precocious infants, however, since only 23% of the infants brought in for testing in the present study were sufficiently calm and alert to yield useable data. Infants did not suck less during trials in which the dots oscillated at 7 cm/set than during trials in which the dots oscillated at 4 cm/set. This may reflect a floor effect in the sucking suppression measure. Volkmann and Dobson (1976) also found a significant effect of stimulus velocity on the ocular behavior of infants both slightly younger (3 to 5 weeks old) and slightly older (7.5 weeks old) than those in this study, but they did not report any post hoc tests for differences in response to specific velocities. It is generally agreed that a moving stimulus is a more potent recruiter of infant attention than is a stationary one (e.g., Brazelton et al., 1966: Carpenter, 1974; Dayton et al., 1964; Gregg et al., 1976; Haith, 1966). Both the present study and that of Volkmann and Dobson point to stimulus velocity as one potential determiner of the power of the recruitment. Infant response to stimulus velocity was consistent across perimeter conditions, indicating that infants may have attended only to the most salient parts of the face (i.e., the moving eye dots). The fact that the main effect of perimeter approached statistical significance dictates that this interpretation remain tentative, however, and points to the exciting possi-
MARC1 R. GIRTON
422
bility that Sweek-olds may be capable of attending to both the moving and the stationary parts of a compound visual display. A previous study (Haith et al., 1977) reported that the presence of intrastimulus motion in the form of mouth movements did not enhance 3to S-week-olds’ or 7-week-olds’ visual fixations toward a face. Moreover, when Haith et. al. considered only the fixations which were actually on the face, they found that movement did not attract 7-week-olds’ or 9- to 1I-week-olds’ visual fixations toward the mouth (3- to Sweek-olds’ data were excluded from these analyses because they had so few fixations on the face). The fact that Sweek-old infants in the present study clearly did attend to intrastimulus motion raises the interesting question of where the infants were looking. Because movement is a salient peripheral stimulus (see Kaufman, 1974), it is possible that infants were scanning the perimeter of the face (or elsewhere) and processing the movement peripherally. Alternatively, infants may have “locked on” to the moving dots themselves, or fixations may have moved inward from the perimeter as a function of intrastimulus velocity. It might prove fruitful to vary over a wide range the velocity of small moving form(s) within a compound figure and to measure both visual scanning and other indices of attention (such as sucking suppression or heart rate) concurrently. Would these other attentional measures show a sharp increase in attention at the velocity at which visual fixations shifted from the perimeter to the internal moving elements? Most recent research concerned with infant attention to visual stimuli has used stationary displays. Yet the infant watches both people and things moving about in a world which probably appears more dynamic than static. It is time to seriously investigate the infant’s responses to, and actions upon, the dynamic aspects of that world. REFERENCES Berlyne, D. E. Conjict, urousal und curiosir>l. New York: McGraw-Hill, 1960. Bowlby, J. Attachment and loss. Vol. I: Attachment. New York: Basic Books, 1969. Brazelton, T. B., Koslowski, B., & Main, M. The origins of reciprocity: The early motherinfant interaction. In M. Lewis & L. Rosenblum (Eds.), The effect of the infunt on its caretaker. New York: Wiley, 1974. Brazelton. T. B., Scholl, M. L., & Robey, J. S. Visual responses in the newborn. Pediutrics, 1966, 37, 284-290.
Bronshtein, A. I., Antonova, T. G., Kamenetskaya, A. G.. Luppova, N. N., & Sytova, V. A. On the development of the functions of analyzers in infants and some animals at the early stage of ontogenesis. In Problems of evolution ofphysiologicalfunctions. Moscow Academy of Science, 1958. Israel Program for Scientific Translations, 1960, pp. 106-l 16 (U.S. Department of Commerce OTS 60-51066). Bronson, G. The postnatal growth of visual capacity. Child Development, 1974,45,873-890. Carpenter, G. C. Visual regard of moving and stationary faces in early infancy. MerrillPalmer
Quurterly.
1974, 20,
181-194.
Cohen. L. B.. & Salapatek, P. (Eds.), Infant perception: From sensation Vol. 1: Basic visual processes. New York: Academic Press, 1975.
to cognition.
INFANTS’
ATTENTION
TO MOTION
423
Dayton, G. O., Jones, M. H., Steele, B., & Rose, M. Developmental study of coordinated eye movements in the human infant, II: An electro-oculographic study of the fixation reflex in the newborn. Archives of Opthalmology, 1964, 71, 871-875. Fantz, R. L., & Miranda, S. B. Newborn infant attention to form of contour. Child Development.
1975,
46, 224-228.
Gibson, E. J. Principles of perceptual learning and development. New York: AppletonCentury-Crofts, 1969. Gorman, J. J., Cogan, D. G., & Gellis, S. S. An apparatus for grading the visual acuity of infants on the basis of optokinetic nystagmus. Pediatrics, 1957, 19, 1088-1092. Gregg, C., Clifton, R. K., & Haith, M. M. A possible explanation for the frequent failure to find cardiac orienting in the newborn infant. Developmental Psychology. 1976, 12, 75-76. Haith, M. M. The response of the human newborn to visual movement. Journal ofExperimental
Child
Psychology.
1%6,
3, 235-243.
Haith, M. M. Visual competence in early infancy. In R. Held, H. Leibowitz, and H. L. Teuber (Eds.), Handbook of sensory physiology. New York: Springer-Verlag, 1977. Vol. VIII. Haith, M. M., Bergman, T., & Moore, M. J. Eye contact and face scanning in early infancy. Science, 1977, 198, 853-854. Haith, M. M., Kessen, W., & Collins, D. Response of the human infant to level of complexity of intermittent visual movement. Journal of Experimental Child Psychology, 1969, 7, 52-69. Hochberg, J. Perception. I. Color and shape. In J. W. Kling and L. A. Riggs (Eds.), Woodworth and Schlosberg’s Experimental Psychology. New York: Holt, Rinehart & Winston, 1971. Kagan, J. Change and continuity in infancy. New York: Wiley, 1971. Kaufman, L. Sight and mind. New York: Oxford Univ. Press, 1974. Maurer, D., & Salapatek, P. Developmental changes in the scanning of faces by young infants. Child Development, 1976, 47, 523-527. Milewski, A. E. Infants’ discrimination of internal and external pattern elements. Journal of Experimental Child Psychology, 1976, 22, 229-246. Neisser, U. Cognitive psychology. New York: Appleton-Century-Crofts, 1%7. Rheingold, H. The effect of environmental stimulation upon social and exploratory behavior in the human infant. In B. Foss (Ed.), Determinants of infant behavior. London: Methuen, 1961. Robson, K. S. The role of eye-to-eye contact in maternal-infant attachment. Journal ofChild Psychology and Psychiatry, 1967, 8, 13-25. Salapatek, P., & Moscovich, J. Unpublished study. Abstracted by P. Salapatek, Pattern perception in early infancy. In L. B. Cohen & P. Salapatek (Eds.), Infant perception: From sensation to cognition. Vol. I: Basic visuafprocesses. New York: Academic Press, 1975. Salzen, E. A. Visual stimuli eliciting the smiling response in the human infant. Journal of Genetic Psychology, 1963, 102, 51-54. Sokolov, Y. N. Perception and the conditioned reflex. New York: MacMillan. 1963 (translated by S. W. Waydenfeld). Sroufe, L. A., & Waters, E. The ontogenesis of smiling and laughter: A perspective on the organization of development in infancy. Psychological Review, 1976, 83, 173-189. Volkmann, F. C., & Dobson, M. V. Infant responses of ocular fixation to moving visual stimuli. Journal of Experimental Child Psychology, 1976, 22, 86-99. Wolff, P. H. Observations on the early development of smiling. In B. Foss (Ed.), Determinants of infant behavior: II. London: Methuen, 1963. RECEIVED: February 24, 1978; REVISED: January 3, 1979.
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
Infants’ Attention
28,
416-423 (1979)
to Intrastimuius
Motion
MARCI R. GIRTON Brown
University
Twenty-four S-week-old infants sucked significantly less when shown a schematic face in which the eye dots oscillated at 4 or 7 cm/set than when shown the same face with the eye dots oscillating at 1 cmisec. When identical moving dots were presented in the absence of the surrounding facial configuration, infants showed the same pattern of response. These results indicate (a) that 5-week-old infants can attend to intrastimulus movement, and (b) that the “externality effect” does not extend to compound visual displays which have moving internal elements.
Since stimulus reception and selective attention are prerequisite to complex information processing and to learning (Cohen & Salapatek, 1975; Hochberg, 1971; Neisser, 1967), much effort has been directed toward discovering the stimulus determinants of infant attention. Recent investigations employing such diverse measures as sucking suppression (Haith, 1966), optokinetic nystagmus (Brazelton, Scholl, & Robey, 1966; Dayton, Jones, Steele, & Rose, 1964), visual fixation (Carpenter, 1974; Volkmann & Dobson, 1976), heart rate change (Gregg, Clifton, & Haith, 1976), and smiling (Sroufe & Waters, 1976) suggest that stimulus motion is especially salient during the first weeks and months of life. This cue may play an important role in the development of attachment by allowing young babies to respond “socially” even before they can respond to people qua people (Bowlby, 1969). Several authors have hypothesized This research is based on a PhD thesis submitted to Brown University, and was conducted while the author was a USPHS Trainee under Training Grant 5T32-MH-14255 to L. P. Lipsitt, Brown University. Several laboratory expenses were made possible by a grant from the William T. Grant Foundation to the Brown University Child Study Center, and preparation of the manuscript was supported by USPHS Grant HD-04756 to E. C. Butterfield, University of Kansas Medical Center. The author thanks B. Reilly for the initial recruitment of maternal cooperation; C. DeLucia, R. Moore, and K. White for technical assistance; M. Forrest and J. Dubuc for facilitating the testing of infants at the Carriage House of the Brown University Child Study Center; and E. R. Siqueland, J. W. Kling, E. C. Butterfield, and T. B. Mustaine for helpful comments on an earlier version of this manuscript. The author is grateful to L. P. Lipsitt for his assistance throughout all phases of this research. Requests for reprints should be sent to the author at the MRRC, University of Kansas Medical Center, 39th and Rainbow, Kansas City, KS 66103. 416 0022~0965/79/060416-08$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
INFANTS' ATTENTION TO MOTION
417
that intrafacial movement enhances the baby’s attention to the caretaker’s face (Brazelton, Koslowski, & Main, 1974; Gibson, 1969; Rheingold, 1961; Robson, 1967; Wolff, 1963), but there is little empirical support for this. Indeed, Milewski (1976) found that, unlike infants 14 to 20 weeks of age, infants 4 to 6 weeks of age show an “externality effect.” That is, they discriminate changes in small shapes only when those shapes are not surrounded by larger, unchanging shapes. Similarly, Salapatek and his co-workers (e.g., Maurer & Salapatek, 1976; Salapatek & Moskovich, 1975) demonstrated that infants 4 to 6 weeks old direct most of their visual fixations toward the external contours of compound forms, while 8- to lo-week-old infants concentrate their visual fixations on the internal elements. The “externality effect” exhibited by infants at 4 to 6 weeks of age approximates the behavior of newborns rather than that of older infants (see Fantz & Miranda, 1975). The evidence that 4- to 6-week-old infants do not attend to stationary intrastimulus elements is suggestive, but does not preclude their attention to intrastimulus elements which move. A recent visual scanning study bears more directly on this issue. Haith, Bergman, and Moore (1977) found that mouth movement enhanced face scanning by 9- to 1 l-week-old infants, but did not affect the percentage of face fixations by 3- to 5-week-old or 7-week-old infants. Furthermore, for all subjects whose data could be analyzed (3- to 5-week-olds’ data were excluded from these analyses because they had so few face fixations), the percentage of face fixations on the mouth was not affected by presence or absence of mouth movements. Yet it may be premature to discount the attentional properties of movement by intrastimulus elements on the basis of these data alone, for several reasons. First, mouth movements were confounded both with auditory stimulation (the mouth moved only when the adult spoke), and also with oscillating movement of the entire adult head. Second, amount of intrastimulus movement was not systematically varied. Finally, the absence of selective fixation does not affirm the absence of selective attention: Infants, like adults (see Kaufman, 1974), may well be capable of nonfocal perception of moving stimuli. Whether or not intrastimulus motion can attract the attention of infants less than 2 months old therefore remains unclear. The measurement of sucking suppression seems a promising way to investigate this problem. Not only has the suppression of ongoing behavior (and a decrease in suppression with continued stimulation) been related to attention (Berlyne, 1960; Bronshtein, Antonova, Kamenetskaya, Luppova, & Sytova, 1958; Sokolov, 1963), but the suppression of nonnutritive sucking in particular has proved useful in the investigation of infant attention to whole-stimulus visual movement (Haith, 1966; Haith, Kessen, & Collins, 1969). Moreover, anecdotal re-
418
MARC1 R. GIRTON
ports indicate that attention to a moving stimulus is commonly accompanied by sucking suppression, even to the extent that a hungry infant will terminate nutritive sucking to watch quietly for several minutes (Gorman, Cogan, & Gellis, 1957; Salzen, 1963). The present study asked whether 5-week-old infants’ attention to a schematic face would increase as the salience (velocity) of its oscillating eye dots increased. It was assumed that decreased sucking indicated increased attention, and that differential responding to faces with differing rates of movement reflected attention to the intrastimulus motion. As a control for the ability of the infants to attend to the moving dots when the dots were not the internal elements of a complex pattern, the eye dots were presented in the absence of the surrounding schematic face on some trials. In addition, all trials with moving stimuli were paired with temporally contiguous trials with identical, but completely stationary, stimuli; it was thus possible to statistically control for the potentially confounding effects of sucking rate fluctuations. METHOD Subjects
Twenty-four full-term clinically normal infants approximately 5 weeks old (12 male and 12 female) participated. Their mean age was 38.3 days (SD = 4.07 days). One male and one female infant were randomly assigned to each of 12 counterbalanced stimulus order conditions. An additional 133 infants were scheduled for testing but were not included because of appointment cancellations (N = 53), fussing (N = 27), sleeping (N = 30), failure to suck on the nipple (N = 21), or experimenter error (N = 2). Apparatus Stimulus equipment. A Medical Systems Corporation Light Stimulator Type 4330/l rear-projected two stimulus eye dots onto a 26.5 x 26.5-cm viewing screen, which was 16 cm away from the infant. The projected dots were 1.5 cm in diameter, 7 cm apart, and each oscillated within a distance of 5 cm at velocities of 1, 4, or 7 crn/sec. In the FACE perimeter condition, a schematic face (approximately 8 x 22.5 cm) on a clear film background was placed directly on the viewing screen. The linewidth of the figure was l-l.5 cm. The two dots projected through, and could be made to oscillate within, the eye outlines. In the NO FACE condition, a clear film without any markings on it was placed on the screen. The dots appeared in the same position and moved in exactly the same manner for both conditions. The FACE and NO FACE visual displays had overall luminances of 2.73 and 2.78 log foot lamberts, respectively, as measured by an SE1 Exposure Meter. The FACE and NO FACE conditions are illustrated in Fig. 1.
INFANTS’
ATTENTION
419
TO MOTION
0
0
FIG. 1. The FACE condition is shown on the left. The FACE outline was placed directly on the viewing screen, and the eye dots were rear-projected onto the screen. The NO FACE condition is shown on the right.
Recording equipment. A sterilized blind nipple was attached to a Grass Instrument pressure transducer by a length of 0.25in. (.64 cm) plastic tubing. Sucking on the nipple produced pressure variations which were recorded by a Grass Model 5 polygraph. These pressure variations were also converted by a Schmitt trigger to discrete responses and recorded on a counter during stimulus presentations, but not during intertrial intervals. Procedure
and Experimental
Design
A week in advance, testing times were scheduled according to the mother’s best estimate of when the baby’s “awake time” would be on the day of the test. Upon arrival at the Brown University Child Study Center the infant’s outer garments were removed and, if necessary, the mother was asked to awaken her infant. As soon as an infant was awake, alert, and not fussing, he or she was offered a sterile blind nipple to suck on, and the sensitivity of the recording apparatus was adjusted. The infant was placed on his or her back in a bassinet, with a support pillow to keep the head from moving. The bassinet was centered under the viewing screen, and a gauze cloth was lowered to keep the experimenter from distracting the infant while observing him or her. Each trial started at the beginning of a sucking burst (defined as at least two sucks within 2 set following an interval of at least 2 set with no sucks) and consisted of 16 set of stimulus presentation. Following every trial, the experimenter recorded the number of sucks during that stimulus and readied the velocity and/or perimeter conditions for the trial to follow. These activities took approximately 5 set to complete. At the beginning of the next sucking burst, a new trial was initiated. This procedure was followed for a total of 36 stimulus presentations, 18 of one perimeter condition (FACE or NO FACE) followed by 18 of the
MARC1 R. GIRTON
420
other. The order of these perimeter blocks was counterbalanced across infants. Within each perimeter block there were three velocity blocks, the order of which was also counterbalanced across infants. Each velocity block consisted of six trials, three with stimulus movement and three without movement. These moving and stationary trials were presented in a predetermined pseudo-random order (three identical stimuli were never presented consecutively) which varied across velocity blocks. RESULTS
The mean sucking rate was calculated for the three moving trials and for the three stationary trials within each velocity block. All analyses were conducted on these data. Preliminary tests ruled out sex as a significant source of variance. Therefore, subsequent analyses collapsed across this factor. Because sucking rate during trials with stimulus movement was considered to be, in part, a function of the infant’s ongoing sucking rate as well as a function of treatment effects, the analysis of covariance design was used to statistically control for fluctuations in sucking rate. Calculation of regression slopes for each cell of the design indicated that the assumption of equal regression slopes could be met. Therefore, an analysis of covariance with repeated measures was used to compare mean sucking rate across velocity and perimeter conditions, with the mean sucking rate for the stationary trials within a given velocity block being used as the covariate for that velocity block. Neither the main effect of perimeter (F (I ,22) = 3.94, p = .060) nor the perimeter x velocity interaction (F (2,415) = 1.07, p = .3.51) reached statistical significance. The highly significant main effect of velocity (F (2,45) = 13.31, p < .OOl) is shown in Table 1. Post hoc Tukey’s (a) tests revealed that infants sucked significantly less when the dots oscillated at 4 cm/set than when the dots oscillated at I cm/set (p < .Ol) and that infants sucked significantly less when the dots oscillated at 7 cm/set than when they oscillated at 1 cm/set (p < .Ol). There was no difference in sucking rate during stimulus velocities of 4 and 7 cm/set.
TABLE MEAN
SUCKS
AS A FUNCTION
1 OF STIMULUS
Covariate Velocity (cm/set) 1 4 7
VELOCITY
Dependent variable
x
Unadjusted 57
Adjusted ?%
17.23 17.13
16.41 13.64 14.13
16.46 13.73 13.99
17.63
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ATTENTION
TO
MOTION
421
DISCUSSION
This experiment investigated whether Sweek-old infants’ attention to a schematic face would increase as the velocity of its oscillating eye dots increased. It was assumed that decreased sucking indicated increased attention. Infants sucked significantly less during trials in which the eye dots oscillated at 4 or 7 cm/set than during trials in which the eye dots oscillated at 1 cm/set, a differential response which clearly indicates more attention to the faces with the faster moving eyes. This empirical demonstration that Sweek-old infants can attend to intrastimulus motion provides indirect support for the hypothesis that intrastimulus motion attracts infants’ attention to faces in everyday life (Brazelton et al., 1974; Gibson, 1969; Rheingold, 1961: Robson, 1967; Wolff, 1963). In the natural environment, intrafacial movement might serve to attract and maintain infants’ attention to faces which are otherwise familiar, or it might attract infants’ attention to faces at an earlier age. These questions deserve direct investigation with real faces. The finding that infants attend to moving internal pattern elements at 5 weeks of age is especially interesting in light of recent reports that 4- to 6-week-olds apparently do not attend to stationary internal pattern elements (Maurer & Salapatek, 1976; Milewski, 1976; Salapatek & Moskovich, 1975). The lack of such an “externality effect” in the present investigation implies that the developmental course of attention to intrastimulus elements may well vary with the dynamics of those elements. This may obtain only for relatively precocious infants, however, since only 23% of the infants brought in for testing in the present study were sufficiently calm and alert to yield useable data. Infants did not suck less during trials in which the dots oscillated at 7 cm/set than during trials in which the dots oscillated at 4 cm/set. This may reflect a floor effect in the sucking suppression measure. Volkmann and Dobson (1976) also found a significant effect of stimulus velocity on the ocular behavior of infants both slightly younger (3 to 5 weeks old) and slightly older (7.5 weeks old) than those in this study, but they did not report any post hoc tests for differences in response to specific velocities. It is generally agreed that a moving stimulus is a more potent recruiter of infant attention than is a stationary one (e.g., Brazelton et al., 1966: Carpenter, 1974; Dayton et al., 1964; Gregg et al., 1976; Haith, 1966). Both the present study and that of Volkmann and Dobson point to stimulus velocity as one potential determiner of the power of the recruitment. Infant response to stimulus velocity was consistent across perimeter conditions, indicating that infants may have attended only to the most salient parts of the face (i.e., the moving eye dots). The fact that the main effect of perimeter approached statistical significance dictates that this interpretation remain tentative, however, and points to the exciting possi-
MARC1 R. GIRTON
422
bility that Sweek-olds may be capable of attending to both the moving and the stationary parts of a compound visual display. A previous study (Haith et al., 1977) reported that the presence of intrastimulus motion in the form of mouth movements did not enhance 3to S-week-olds’ or 7-week-olds’ visual fixations toward a face. Moreover, when Haith et. al. considered only the fixations which were actually on the face, they found that movement did not attract 7-week-olds’ or 9- to 1I-week-olds’ visual fixations toward the mouth (3- to Sweek-olds’ data were excluded from these analyses because they had so few fixations on the face). The fact that Sweek-old infants in the present study clearly did attend to intrastimulus motion raises the interesting question of where the infants were looking. Because movement is a salient peripheral stimulus (see Kaufman, 1974), it is possible that infants were scanning the perimeter of the face (or elsewhere) and processing the movement peripherally. Alternatively, infants may have “locked on” to the moving dots themselves, or fixations may have moved inward from the perimeter as a function of intrastimulus velocity. It might prove fruitful to vary over a wide range the velocity of small moving form(s) within a compound figure and to measure both visual scanning and other indices of attention (such as sucking suppression or heart rate) concurrently. Would these other attentional measures show a sharp increase in attention at the velocity at which visual fixations shifted from the perimeter to the internal moving elements? Most recent research concerned with infant attention to visual stimuli has used stationary displays. Yet the infant watches both people and things moving about in a world which probably appears more dynamic than static. It is time to seriously investigate the infant’s responses to, and actions upon, the dynamic aspects of that world. REFERENCES Berlyne, D. E. Conjict, urousal und curiosir>l. New York: McGraw-Hill, 1960. Bowlby, J. Attachment and loss. Vol. I: Attachment. New York: Basic Books, 1969. Brazelton, T. B., Koslowski, B., & Main, M. The origins of reciprocity: The early motherinfant interaction. In M. Lewis & L. Rosenblum (Eds.), The effect of the infunt on its caretaker. New York: Wiley, 1974. Brazelton. T. B., Scholl, M. L., & Robey, J. S. Visual responses in the newborn. Pediutrics, 1966, 37, 284-290.
Bronshtein, A. I., Antonova, T. G., Kamenetskaya, A. G.. Luppova, N. N., & Sytova, V. A. On the development of the functions of analyzers in infants and some animals at the early stage of ontogenesis. In Problems of evolution ofphysiologicalfunctions. Moscow Academy of Science, 1958. Israel Program for Scientific Translations, 1960, pp. 106-l 16 (U.S. Department of Commerce OTS 60-51066). Bronson, G. The postnatal growth of visual capacity. Child Development, 1974,45,873-890. Carpenter, G. C. Visual regard of moving and stationary faces in early infancy. MerrillPalmer
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Dayton, G. O., Jones, M. H., Steele, B., & Rose, M. Developmental study of coordinated eye movements in the human infant, II: An electro-oculographic study of the fixation reflex in the newborn. Archives of Opthalmology, 1964, 71, 871-875. Fantz, R. L., & Miranda, S. B. Newborn infant attention to form of contour. Child Development.
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