the differentiation of activity in infants' exploration of...

Developmental Psychology1992, Vol. 28, No. 5,851-861

Copyright 1992 by the American Psychological Association, Inc.0012-1649/92/S3.00

The Differentiation of Activity in Infants' Exploration of Objects

Holly A. Ruff, Lisa M. Saltarelli, Mary Capozzoli, and Karen DubinerDepartment of Pediatrics, Albert Einstein College of Medicine

If an activity during manipulative play is exploratory, it should, in contrast to other activity, be useddifferentially for objects that vary in novelty. In a study of 5-month-olds, different definitions ofexploratory mouthing were tested, and results suggested that mouthing followed immediately by alook fulfilled some criteria for an exploratory activity. In the next study of 5- to 11-month-olds,mouthing with looks after and examining, a measure of visual-manipulative inspection, met thecriteria for exploratory activity; other kinds of mouthing and visual-manipulatory activity did not.Exploratory mouthing decreased with age and examining increased. The exploratory function ofmouthing apparently was not due to concurrent manual activity providing haptic information. Theconclusion is that some activities are exploratory and information-gathering and other activities arenonexploratory and serve other functions.

Exploratory behavior in infants of different species has beena topic of investigation for many years (Weisler & McCall,1976). Recently, the manipulative activity of human infants hasbeen scrutinized for evidence that it is intentional and specificto object properties (e.g., Bushnell, Shaw, & Strauss, 1985; E. J.Gibson, 1988; Lockman & McHale, 1989; Palmer, 1989; Ruff,1984). In the course of playing with and manipulating objectsand toys, however, infants engage in many different kinds ofactivities. Only some activities may be exploratory and instru-mental in learning about the object; other activities may not beexploratory at all or may be exploratory at some times and notothers.

One exploratory activity for which there is already consider-able information is visual-manipulative examining. Uzgiris(1967) referred to examining as one among many schematawithin a Piagetian framework; in her words, "in examining,. . . the infant turns it [the object] around, pokes at it, feels itssurface, manipulates its parts while observing the object andthe effect of his manipulations on it" (p. 324). Examining there-fore is focused visual inspection of an object accompanied bymanipulation of the object with the hands. Our previous work(Ruff, 1986) has shown that, when the infant is faced with anovel object, examining has temporal priority over other activi-ties such as mouthing and banging. It also declines dramaticallywith increasing exposure to an object and recovers to novelty.

This research was supported by Grant HD11916 from the NationalInstitute of Child Health and Human Development (NICHD), GrantBNS86-19487 from the National Science Foundation, a Research Sci-entist Development Award to Holly A. Ruff from the National Insti-tute of Mental Health (MH0O652), and postdoctoral fellowships toLisa M. Saltarelli (MH15788 and HD07384). The research was alsofacilitated by Grant HD01799 from NICHD to the R. F. KennedyCenter for Research in Human Development and Mental Retardation.We wish to thank Katharine R. Lawson, Susan A. Rose, and GeraldTurkewitz for their helpful comments on earlier drafts of this article.

Correspondence concerning this article should be addressed toHolly A. Ruff, Room 222, Kennedy Center, Albert Einstein College ofMedicine, 1300 Morris Park Avenue, Bronx, New York 10461.

These are important criteria for determining whether an actionis exploratory (Ruff, 1989).

A major purpose of the present research was to learn moreabout the mouth as an exploratory tool. Unlike examining,which seems to be exclusively exploratory (Ruff, 1989), mouth-ing serves several functions. From the beginning of life, themouth plays a salient role in feeding and need gratification(Rochat, Blass, & Hoffmeyer, 1988). Perhaps, for this reason,infants also find the mouth an important means of comfortingand soothing themselves; very early hand-mouth coordinationmakes such a role possible (Korner & Kraemer, 1970). In addi-tion, the mouth is a potentially important part of the hapticsystem (J. J. Gibson, 1966) and may play a role in infants' acqui-sition of information about objects.

Evidence for such a role comes from several studies. Pecheux,Lepecq, and Salzarulo (1988) conducted a study involving oralfamiliarization with a rigid object inserted into a nipple; duringoral test trials with either the same object or a different rigidobject in the nipple, 2-month-old infants showed more non-rhythmical oral activity with novel than familiar objects. It hasalso been reported that infants from 1 to 12 months (Gibson &Walker, 1984; Gottfried, Rose, & Bridger, 1977; Meltzoff &Borton, 1979) recognize the shape and substance of objects vi-sually when the objects have been previously explored onlyorally.

However, positive results on unimodal and cross-modal tasksdo not answer the question of how mouthing is used duringplay in which all modalities are potentially available. The dis-covery of how whole systems function in different contexts is animportant part of our understanding of behavior and develop-ment; it should not be assumed that infants do acquire informa-tion by mouthing in all situations because they can do so underrestricted conditions. The studies reported here involved ob-serving infants in the context of independent and relatively un-restricted play to see how they spontaneously organize theiractivity, especially mouthing, to serve both exploratory andother functions. Because the novelty of objects is a primarymotivator for activity designed to gather information, it wasexpected that if mouthing is exploratory it would vary systemat-

851

852 RUFF, SALTARELLI, CAPOZZOLI, AND DUBINER

ically with the novelty of objects, that is, decline with increasingfamiliarization and recover to the presentation of novel objects.

The data from previous studies (Ruff, 1984,1986) suggestedthat mouthing might not be exploratory. It did not decline withincreasing exposure to the object, it was not used differentiallyfor different changes in the object, and it tended to occur afterexamining. However, a failure to differentiate among types ofmouthing may have obscured patterns that existed only for par-ticular types of mouthing. In studies of infants younger than 6months, investigators have found it useful to differentiate be-tween sucking and mouthing. Rochat (1983) reported that in-fants from birth to 4 months showed differentiated oral activityand that older infants differentiated nipples of different shapesand types of material with nonrhythmical patterns of mouth-ing, but not with sucking. Along the same lines, Pecheux et al.(1988) found that infants in the first 2 months sucked smoothand nubby spheres equally but showed more nonrhythmicaloral activity with the nubby sphere. In the current research, weexplored distinctions within the category of mouthing thatwould be appropriate for infants of 5 to 12 months.

We report results from two observational studies of infants.The infants in both studies were observed under naturalisticconditions; the data, however, were subjected to specific testsbased on explicit hypotheses about the effect of relative noveltyon exploratory and nonexploratory activity. The first study in-volved 5-month-olds who were expected to show a great deal ofmouthing. This study provided the basis for differentiatingtypes of mouthing by investigating which types declined withincreasing familiarity with the object. The second study was across-sectional investigation of 5- to 11-month-olds, coveringan age range in which the amount of mouthing changes dramati-cally. In addition to providing developmental data about thechanging functions of mouthing over age, the second study al-lowed us to validate the categories of mouthing along with cate-gories of visual-manipulative activity by determining whetherthe categories designated as exploratory recovered when novelobjects were presented.

Study 1

In our search for the best way to characterize and measuremouthing that might be exploratory, we started with a distinc-tion between active mouthing and all other mouthing, a dis-tinction which we had explored briefly in an earlier study(Ruff, 1984). Active mouthing is mouthing in which the mouthis moved over the object or the hands are used to move theobject around in the mouth. It seemed to be a reasonable candi-date for an information-acquiring activity, because it providesthe infant with many changes and transformations in stimula-tion—a good basis for detecting the invariant structural proper-ties of objects (J. J. Gibson, 1966). In addition, we recorded thefrequency with which mouthing episodes were followed imme-diately by a look at the object. The observation of this behaviorin infants certainly gives the impression that the infants arechecking or confirming something that was detected by themouthing that preceded the look, and we have scored the fre-quency of such looks in other studies (e.g., Ruff, 1984).

Method

In this study, 5-month-old infants were presented with three differ-ent objects for periods of free play. The observation of the infants'activities with the objects served as the basis for exploring differenttypes of mouthing and the extent to which each fulfilled the criteria foran exploratory activity. In this study, the major criterion was a decreaseover time as the object became more familiar; that is, exploratory activ-ity was expected to be higher in the beginning of a trial when the objectwas most novel than at the end.

Subjects. The sample of 32 full-term infants (14 girls and 18 boys)was drawn from a population born at the Albert Einstein College ofMedicine. All infants were born within 38 and 42 weeks, had birthweights between 2,500 and 3,800 g, and had no perinatal complica-tions. The infants were seen at a mean age of 22.2 weeks (range =21.3to 23.4 weeks). Two other infants were observed but were too fussy tobe included.

Apparatus. For presentation of objects, we used a narrow table thatcould be adjusted to the infant's height. A SONY Portapak video re-corder and camera were used to record each infant's behavior, and astopwatch was used to time trials. When the videotapes were laterscored for various behaviors, a Rustrak four-channel event recordermoving at 1/8 inch per second was used. The stimulus objects were ablue plastic rattle in the shape of a dumbbell, 10.2 cm in length; a redplastic ring, 10.7 cm in diameter; and a small, colorful rubber doll, 10.7cm in length.

Procedure. The infant was seated on the mother's lap in front of thetable so that objects presented on its surface could be easily graspedand manipulated by the infant. The mother was asked to allow herinfant to play freely with the object and to return it to within theinfant's reach if necessary. Any objects that dropped to the floor wereretrieved by the mother or experimenter. The experimenter, who sat onthe floor in front of the table, presented and removed each object. Theobjects were always presented in the same order for a single trial each.The trial durations varied depending on how long the experimenterjudged the infant to be interested in interacting with the object, up to amaximum of 3 min. Trial durations ranged from 26 to 180 s; 70% of alltrials were more than 150 s.

Dependent measures. From the videotapes we first recorded thefrequency and duration of looking and mouthing. Looking-was scoredwhenever the infant's eyes were directed at the object. Mouthing wasscored whenever the object was in contact with the mouth, lips, ortongue. Interobserver reliabilities for these general measures have al-ways been higher than .90 (Ruff, 1984). Active mouthing was defined asoccurring when the object touched either the inside or outside of themouth and was moved around by the hand or held in place while thelips or tongue moved around the object. The interobserver reliabilityfor this measure was calculated on the basis of two independent ob-servers' total durations of active mouthing for 15 of the infants (r = .97).The duration of other mouthing was obtained by subtracting the dura-tion of active mouthing from total mouthing. Other mouthing in-cluded all other contact between the mouth and object, such as place-holding, gnawing, and sucking. Any one episode of mouthing could becomposed of different proportions of active and other mouthing.

We also recorded the frequency with which the infants looked at theobject immediately after mouthing. The immediacy of the look after iscritical and means that there is no perceived time lapse betweenmouthing and looking; such looks probably occur because the infantsare looking for the object as it is removed from the mouth. If the infantglanced in another direction after mouthing, however briefly, a lookafter was not scored. It was the immediacy of the look that countedhere and not the duration of the look. Interobserver reliability basedon the total number of looks after for 15 infants was very high, .98.

INFANTS' EXPLORATORY ACTIVITY 853

Results

The dependent measures in the analyses to follow are thedurations of active and other mouthing transformed into per-centages of trial time. Averaging over the three objects, the in-fants spent about 27% of trial time looking at the objects (9% to58%) and another 24% mouthing the objects (0% to 55%). Therest of the time was spent mainly in manipulation without look-ing or not attending to the objects at all.

Decline over familiarization. Because the goal was to deter-mine whether active mouthing met the major criterion for ex-ploratory activity, we tested the expected differential effect offamiliarization on the proposed exploratory and nonexplora-tory components of mouthing. The expectation was that activemouthing would decline over time, whereas other mouthingwould not. For these analyses, the data were collapsed over thethree trials. The mean durations of active mouthing and othermouthing for each half of trial were entered into a 2 X 2 (HalvesX Type of Mouthing) analysis of variance (ANOVA). It might beargued that the two types of mouthing are not independent,because the data come from the same trials rather than fromdifferent conditions or sessions, but the proportion of trial timespent in mouthing, as presented earlier, suggests that about 76%of trial time was left in which the duration of either type couldhave varied. In addition, only an ANOVA provides a direct testof the hypothesized interaction between type of mouthing andhalf of trial and, in that sense, is preferable to separate analysesfor the two types. However, there was no main effect of halvesand no interaction between halves and type of mouthing (Fs <1). As can be seen in Table 1, there was literally no change over

Table 1Degree of Decline in Exploratory and Nonexploratory ActivitiesOver Familiarization Period

Measure

Mouthing

Active mouthingMSD

Other mouthingMSD

1st half

12.6*14.6

9.510.0

Mouthing with and without looks after

Proportion of available time (n = 21)Mouthing/look after

MSD

Mouthing/without look afterMSD

Mean duration per episode (n = 15)Mouthing/look after

MSD

Mouthing/without look afterMSD

13.810.4

17.613.5

7.43.6

4.41.9

2nd half

13.212.8

10.99.2

8.38.9

22.213.6

5.72.7

5.13.0

" Percentage of available time averaged over three trials.

time in active mouthing, which is not consistent with activemouthing serving an exploratory function.

Relationship of active mouthing and looks after. As anotherway of assessing the difference between active and othermouthing, we calculated, for each type of mouthing, the pro-portion of episodes that were followed immediately by a look.If active mouthing is exploratory and the infant's attention isfocused on the object during such mouthing, then it seemedreasonable to hypothesize that active mouthing would be fol-lowed by a look more often than other types of mouthing. Forthis test, an episode of mouthing was denned as active if 50% ormore of it had been scored as active. Then, because there weremore active mouthing episodes than other mouthing episodes,a proportion was obtained by dividing the number of episodeswith looks after by the total number of episodes of a particulartype. For those infants who had at least one episode with animmediate look after (n = 21), there was a significantly higherproportion of active episodes (.43) than other episodes (08)followed by an immediate look, t(20) = 5.9, p < .001. Lookingat the relationship of active mouthing and the look after an-other way, 82% of episodes with a look after were designated asactive. If the look after is used to confirm information pickedup during mouthing, then the data are consistent with the hy-pothesis that active mouthing is more exploratory than othermouthing. The immediacy of the look also suggests that theinfant's attention is focused on the object per se and not on itsown activity.

The look after as a marker. In a second analysis, we investi-gated the possibility that the look after could be used as amarker for exploratory mouthing. That is, we took the look asevidence that the mouthing preceding it involved attention tothe object itself and the absence of a look as a lack of suchfocused attention. As in the earlier analysis, 21 infants provideddata; after establishing which of their episodes of mouthingwere followed immediately by a look, we calculated the dura-tion of mouthing with looks after and the duration of mouthingwithout looks after.

The durations for the first and second halves of trial averagedover the three trials were entered into a 2 X 2 (Halves X Type ofMouthing) ANOVA. There was no main effect of halves, butthere was a highly significant interaction between halves andtype of mouthing, F(l, 20) = 14.2, p < .001. As can be seen inTable 1, mouthing with looks after showed a sharp decline, F(l,20) = 12.8, p = .002, a pattern shown by 17 (or 81%) of theinfants; mouthing without looks after tended to increase, F(l,20) = 3.5, p = .07. These data suggest, therefore, that the infantswere less likely to engage in mouthing with looks after as theobject became more familiar; their use of mouthing withoutlooks after did not vary with increasing familiarization (seeTable 1).

A potential rival interpretation of these data is that the lookafter follows mouthing by chance, but, because looking de-clines over time, the probability of a look after declines; there-fore, total duration of mouthing with looks after declines aswell. If this were the case, the use of the look after as a markerfor exploratory mouthing would be unjustified. There are sev-eral ways to test this alternative interpretation. One way is toconsider the total number of "looks" at the object; the upperlimit on the number of "looks after" that can occur in any time

854 RUFR SALTARELLI, CAPOZZOLI, AND DUBINER

segment is the number of mouthing episodes, but the higher theratio of all looks to the number of mouthing episodes, thehigher the probability that an episode of mouthing will be fol-lowed by a look. We therefore calculated the ratios of looks tomouthing episodes for the 19 infants who had at least one lookafter and who also looked at and mouthed the objects in bothhalves of the familiarization trial. The mean ratio for the firsthalf was 1.70, and the mean for the second half was 1.51, anonsignificant difference, J(18) < 1.

Another consideration is the duration of looking; that is, themore time the infant spends looking at the object when notmouthing it, the more likely it is that a look after will occurright after mouthing. The percentage of trial time spent mouth-ing and looking, however, is only about 50%, making this expla-nation unlikely. In addition, among the infants who exhibitlooks after mouthing, the number of looks after is more highlycorrelated to the duration of mouthing (r = .53) than it is to theduration of looking (r = .04).

With an alternative explanation based on a chance relation-ship of the look after to either the frequency or duration oflooking, there would be no reason to expect any systematicchanges in the duration of mouthing episodes over time or anydifference between episodes with and without looks after.Therefore, we examined the mean duration of episodes for bothtypes of mouthing in each half of trial; that is, we divided totalduration of each type of mouthing by the number of episodes ofthat type. For infants who had no episodes of mouthing, a meanduration per episode of 0 would not be meaningful; for thatreason, comparison of the two types of mouthing could notusefully include infants who showed only one type of mouthing(n = 11) or demonstrated it in only one of the halves (n = 6). The2X2 (Halves X Type of Mouthing) ANOVA was therefore donewith 15 subjects and yielded a main effect of type of mouthing,F(l, 14) = 7.5, p = .015; the mean duration per episode ofmouthing with looks after was longer than the mean durationof episodes without looks after. More important, there was asignificant interaction between halves and type of mouthing,F(l, 14) = 6.4, p = .02, with the mean duration of mouthing withlooks after decreasing over time, F(l,l4) = 4.3,p= .06, and themean duration of mouthing without looks after showing nochange, F(l, 14) < 1. These data suggest that there may be some-thing important occurring within the episodes of mouthingwith a look after (see Table 1).

All of these analyses provide evidence against the alternativehypothesis and further confirmation that mouthing with looksafter is exploratory.1 Inspection of the data for individual chil-dren suggested that episodes of mouthing with looks after oc-curred in clusters and were not scattered over the trial. To con-firm our observations statistically, we conducted Wald-Wolfo-witz runs tests (Siegel, 1959) on the data from each of the 21infants. Two-tailed tests were used because, in the data of anyone infant, there could be more or fewer runs than the numberexpected by chance. Seven of the 21 tests revealed significantlyfewer, and therefore longer, runs than expected, ps < .05 to <.001, whereas only one significant result would be expected bychance. In addition, only 4 of the 21 infants had more runs thanexpected, whereas 17 infants had fewer runs than expected (bi-nomial probability = .008). These data suggest that 5-month-old infants' mouthing of objects may be characterized by pe-

riods of concentrated exploration and by a meaningful, not achance, relationship to looking.

Discussion

The main purpose of this study was to elucidate the role ofmouthing in object play of 5-month-old infants. We categorizedmouthing in two different ways to see which system best fit ourcriteria for an exploratory activity. Our first comparison of ac-tive mouthing and other mouthing showed no decline over thefamiliarization periods in either type. On the other hand, activemouthing episodes were followed far more frequently by imme-diate looks, a behavior that we take to indicate that the childdetected something interesting about the object during mouth-ing. We then divided mouthing into the duration of episodesfollowed by looks after and the duration of episodes not fol-lowed by such looks. Duration of mouthing with looks afterdeclined sharply and significantly with increasing familiariza-tion, whereas other mouthing did not change, a difference thatsuggests that mouthing with looks after is truly exploratory andmay involve the intake of information about object characteris-tics. The alternative interpretation—that the total duration ofmouthing with looks after is a function of the duration or fre-quency of looking—does not seem to be viable. In addition, thefact that the look after was more related to active mouthingthan other mouthing is further suggestion that the look after isnot related to mouthing by chance.

It might be argued that any goal-directed activity will declinewhen the child reaches the goal (Bruner, 1973) and, therefore,mouthing that serves functions other than exploration mightalso decline with time. For example, if mouthing is used by anoveraroused infant for soothing, then that mouthing should de-cline along with the infant's arousal; if an individual infant wereanxious or aroused by the unfamiliarity of the experimenterand the setting, that infant might suck on or mouth the objectspresented to reduce the level of anxiety and arousal. However,there is no reason to expect that decrements occurring in suchmouthing would be systematically related to the novelty of theobject. The lack of a significant decline in mouthing withoutlooks after suggests that such mouthing was not related to the

1 Although there was no systematic variation of object characteris-tics, the three objects did vary on a number of dimensions. The mostimportant of these was the complexity of the structure, which variedfrom the ring that was the same at all points, to the rattle whose dumb-bell shape was different in the middle than at the ends and whosesurface was slightly ridged, to the doll that had well-defined body partsincluding hands and feet. The constant order of presentation (rattle,ring, doll) was not the same as the ordering by complexity (ring, rattle,doll). We tested the effect of complexity, because exploratory activityshould, in general, increase as object complexity increases. A 3 x 2(Object x Type of Mouthing) analysis showed a marginal interactionbetween object and type of mouthing, F(2, 40) = 3.0, p < .06. Asexpected, mouthing with looks after was used differentially for thethree objects, F(2,40) = 8.7, p = .001, with the means ordered accord-ing to our judgment of increasing complexity (Ms = 4%, 11 %, and 18%for the ring, rattle, and doll, respectively); mouthing without looksafter was not used differentially (Ms = 19%, 20%, 21%, respectively),F(2,40) < 1. The results are only suggestive but are consistent with ourdesignation of mouthing with looks after as exploratory.


presumed decreasing novelty of the object over the trial. Unfor-tunately, the fixed order of object presentation made it impossi-ble to conduct a direct test of the infants' responses to thepresentation of a novel object.

In summary, the results suggested that mouthing with looksafter may represent the exploratory, or information-gathering,aspect of mouthing objects. The look after, it should be noted, isused here as a marker or a sign that something exploratory ishappening in the mouthing episodes that precede the look. Onthe other hand, the possibility that the infants are visuallychecking information obtained during mouthing also suggestsa coordination between the two modes. We designed the sec-ond study to confirm the results with infants of different agesand to test specifically their responses to the presentation ofexperimentally novel objects.

Study 2

In the second study, we compared exploratory mouthing, asdefined by the look after, with other mouthing in a developmen-tal framework. The age range of 5 to 11 months was chosen tobe representative of the period during which mouthing of ob-jects peaks and then declines (Uzgiris, 1967) as well as to deter-mine whether the role of mouthing in the exploration of objectschanges as the amount of mouthing decreases. Secondarily, wewished to compare visual-manipulative inspection or examin-ing with other types of visual-manipulative activity; althoughexamining has been studied extensively and seems to clearlymeet the criteria for an exploratory activity, there has neverbeen a comparison with other visual-manipulative activity in-volving the object. Including this measure of visual exploratoryactivity also allowed us to determine whether the relative bal-ance of examining and exploratory mouthing changes with age.As noted before, the study was designed to test not only theexpectation of a decline in exploratory activities with familiar-ization, but also the complementary expectation of an increasewith the presentation of novel objects.

Method

Each infant was presented with four objects for periods of familiar-ization. The order in which the objects were presented was counterba-lanced across infants, so that the change from one object to the nextrepresented the presentation of something novel regardless of the na-ture of the particular objects. Each object was markedly different fromthe other three. After the initial period of familiarization, however, thesame object was presented again before the novel object was presented.This acted as a control for the possibility that there would be someincrease in arousal or responsiveness just because of the break in con-tact with the familiar object.

Subjects. The subjects for this study were recruited into four agegroups of 5-, 7-, 9-, and 11 -month-olds. There were 8 infants (4 boys and4 girls) in each age group; the mean ages were 5 months and 10 days(SD = 9.2 days); 7 months and 16 days (SD = 10.0 days); 9 months and 9days (SD = 5.8 days); and 11 months and 11 days (SD = 8.2 days). Thedata from 2 additional infants were not used because of experimentererror or because of the infant's complete lack of attention to the objects.

Experimental objects. There were four pairs of objects that differedfrom each other along several dimensions; within each pair the objectswere very much alike, and each infant saw one object from each pair.2

The pairs were the following: (a) different wooden shapes, both

painted with the same black and white design and both about 2.54 X6.35 cm; (b) orange wooden cubes about 3.81 cm, one ridged and onewith a lacy texture; (c) blue rubber bulbs about 4.57 cm in diameterwith a wooden sphere or a wooden half-cylinder inside; and (d) greenand black cylinders about 6.68 X 1.75 cm, one of which had smallround depressions at one end and the other of which was smooth.

Procedure. Each infant was seen individually in the lab and sat onthe mother's lap at a desk; the session was videotaped with a SONYportable video system. The assignment of each infant to a particularorder of object presentation was determined before the infant arrived;2 infants at each age were assigned to one of four orders (ABCD, BDAC,CADB, or DCBA). For each familiarization period, the chosen objectwas presented until the infant met the criteria for ending a trial or until180 s had elapsed. The criteria were (a) fussing for 5 s, (b) dropping theobject three times with no other engagement with the object in be-tween the drops, and (c) turning away altogether from the test situationfor 5 s. The familiarization trials varied from 50 to 180 s, with a mean of152 s; 64% of the trials lasted the full 180 s. The length of the secondfamiliarization trial was half as long as the original one. The timing ofthe trials was monitored by the experimenter with a stopwatch, and theinterval between trials both within and between problems was only afew seconds. The mothers were asked not to interfere with their infants'activities in any way, although they sometimes helped retrieve droppedobjects. The experimenter stood off to the side of the desk where themother and infant were sitting; she presented the objects and timed thetrials, but otherwise remained as unobtrusive as possible. All objectsexcept the one the infant was given were out of sight.

Dependent measures. All measures were scored from the video-tapes in real time using a computer programmed to serve as an eventrecorder. The coding was done by someone who was not aware of thehypotheses. Looking and the measure of mouthing with and withoutlooks after were recorded in the way described in Study 1; however,duration of looking and the look after were coded at different times. Inaddition, we coded examining, which has been discussed elsewhere indetail (Ruff, 1986,1989; Ruff & Lawson, 1990). Examining reflects theamount of time spent in focused visual inspection of an object; itusually occurs while the infant is also manipulating the object. Al-though any "deliberate" manual activity would be included in examin-ing, the most likely are fingering, turning the object around, and trans-ferring (Ruff & Lawson, 1990); these activities also have been impli-cated in the exploration of particular object characteristics, in contrastto more active, repetitive activities, such as banging (Ruff, 1984). Aserious facial expression, frequently involving knit brows, is importantand suggests that examining is a major way in which infants demon-strate focused attention during play with objects (Ruff, 1986; Ruff &Lawson, 1990). Reliability in scoring examining in infants 6 monthsand older has also been consistently above .90 in several studies withthe same observers (Ruff, 1986). Using the videotapes of 9 infants inthe previous study and two independent observers, we determined thereliability of coding examining in 5-month-olds; interobserver reliabil-ity for the total duration of examining was .87. The duration of examin-ing was subtracted from the duration of total looking to obtain dura-tion of other looking/manipulating; this category includes looking gen-erally accompanied by holding, banging, waving, or dropping theobject.

As before, durations of all activities were converted into percentages

2 These particular pairs of objects were chosen to study infants' re-sponses to unidimensional changes, and originally there were 8 infantsat each age who were presented with the other member of the pair afterthe original familiarization period. There was so little evidence, how-ever, that the infants at any age responded to the discrepancies withinpairs of objects that the data do not warrant further discussion; theseinfants are not part of this report.

856 RUFR SALTARELLI, CAPOZZOLI, AND DUBINER

of available time to correct for the different trial lengths between andwithin individuals.

Results

The percentage of trial time spent looking at the objects didnot change with age (49%, 41%, 47%, and 47% for the 5- to11-month-olds, respectively), whereas the percentage of timespent mouthing peaked at 7 months (11 %, 28%, 18%, and 17% forthe 5- to 11-month-olds, respectively). As in the last study, therewas considerable trial time taken up by activities other thanlooking or mouthing (31% to 40%). The percentages for the5-month-olds differ from those of Study 1, in which the infantsmouthed more and looked less at the objects, probably becausethe objects in Study 1 were larger and easier to grasp.

Decline over familiarization. We first addressed the extentto which exploratory mouthing and examining declined overthe period of familiarization. Figures 1 and 2 show that explor-

EXAMININGPercent Available Time

201—

Trial 1 Trial 2 Trial 3 Trial 4

MOUTHING WITHLOOKS AFTER

16

14

12

10

8

6

4

2

0

Percent of Available Time


MOUTHING WITHOUTLOOKS AFTER


Trial 1 Trial 2

I Familiarization

Trial 3

i Re-Presentation

Trial 4

Figure 1. Patterns of response to familiarization, the re-presentationof familiar objects, and the presentation of novel objects: Contrastbetween mouthing with looks after and mouthing without looks after.

OTHER LOOKING/MANIPULATING



• i Familiarization MM Re-Presentation

Figure 2. Patterns of response to familiarization, the re-presentationof familiar objects, and the presentation of novel objects: Contrastbetween examining and other looking/manipulating.

atory mouthing and examining declined systematically in eachtrial whereas other looking and mouthing showed no system-atic change. For the statistical analysis, percentages of availabletime in first and second halves of each familiarization periodwere averaged over the four trials and entered into a 4 X 2 X 2(Age X Halves X Type of Activity) ANO\A. The important in-teraction between type of mouthing and half was significant,F(l, 28) = 25.6, p < .001, with mouthing with looks after show-ing a highly significant decline, F(l, 28) = 20.7, p < .001, andmouthing without looks after showing a small increase, F(l, 28)= 6.6, p < .02. As can be seen in Table 2, 78% of the infantsshowed the expected decline in mouthing with looks after. Like-wise, the interaction between type of looking and half was sig-nificant, F(l, 28) = 14.4, p < .001, with examining showing asystematic and significant decline, F(l, 28) = 46.1, p < .001,


1

Dec

line

c

00ca

loo

isJ3

5

linin

g

§Xtu

J2

loo

3oJ3

5 wit

c'•s3O

s

|1IIc3O

C

ext

aU.

ft*

BT

c

uT

Rep

.

c

&(2c

fa"

c

next

d

" j .

uT

uT

Age

—; rr,vd wi

<N 00 «-i —

— 00 r<i (N

3"« S2

p —• (NOO3̂ f ) O Os

Os f-

S"2

39.0

15.7

32.9

11.4

vo oovo ©

o o

o\in oo oo i

<N p ^ "0 Ooo r-r n ^ j - v© c«S vd •/•> ON

«6 dn

in r<i

0^ . tO O odoo

oooor '̂vo

•*t •—i oo M oo p vo oo^r in rH •*' — o ON ON

vq • *rn ni

OV Tfod r̂ i

O; p

O\ ON vq —ov ov r-' vo

^t Tt ov inda d -«

QO O\ OOOOo — ——;

a 1

.9 8.3

and other looking showing no change, F(\, 28) < 1. In this case,84% of the infants showed the expected decline in examining.There was an interaction between age and type of looking, F(3,28) = 3.9, p = .02, because examining increased with age andother looking declined.

Recovery to novelty. Figures 1 and 2 also show that there wasno recovery of exploratory mouthing or examining to any re-presentation of the same object and clear recovery of explor-atory mouthing and examining to every presentation of a novelobject. Very different patterns are seen for other looking/mani-pulating and other mouthing. For statistical purposes, the datafrom the re-presentation segments of the first, second, andthird problems were averaged and compared with the averageof the first half of familiarization in the second, third, andfourth problems. The percentages used in this analysis mighthave been affected by the systematic decline in trial lengthfrom the first to the last problem, F(3,84) = 3.7, p = .02, but themean length of the relevant re-presentation segments (74.5 s)and the mean length of the first halves of the relevant familiar-ization periods (76 s) were generally equivalent.

In a 4 X 2 X 2 (Age X Trial: re-presentation vs. first half ofnext familiarization trial X Type of Activity) ANOVA, we founda significant interaction between trial and type of mouthing,F(l, 28) = 9.9, p = .004, with a significant recovery for mouth-ing with looks after, ^(1,28) = 19.5, p < .001, but not for mouth-ing without looks after, F(l, 28) < 1 (see Table 2).3 Again, a solidmajority of the infants (69%) showed the expected recovery inmouthing with looks after. The analysis of looking also showeda significant interaction between type of activity and trial, F(l,28) = 6.2, p = .02, with a significant recovery in examining, F(l,28) = 46.4, p < .001, but not in other looking/manipulating,F(l, 28) = 1.6 (see Table 2). As before, 84% showed the expectedpattern in examining. There was an interaction between ageand trial, F(3,28) = 2.9, p = .05, which stemmed from a greaterincrease of examining with novelty in the two older groups thanin the two younger groups.

Coordination of manual activities with looking and mouthing.The data confirm the exploratory nature of some mouthing andsome simultaneous looking and manipulating. Examining is,by definition, a combination of visual and manual activity. How-ever, mouthing also occurs with simultaneous grasping of theobject. This fact raises the possibility that our observed resultsfor mouthing could have been the result of simultaneous man-ual and oral investigation of the objects. Therefore, it was im-

3 In our earlier study of 5-month-olds, we had noted that there was arelationship between active mouthing and the immediate look after. Inthis study of 5- to 11 -month-olds, active mouthing was also more likelythan other mouthing to be followed by a look after. We conducted a 4 X2 (Age X Type of Episode) ANOVA that included only those infantswho showed both types of mouthing (n = 25); on this basis, 2,0,3, and2 infants were excluded from the four age groups, respectively. Therewas a significant effect of type of episode, F(l, 21) = 6.7, p = .017; themean proportions of episodes followed by a look for active and othermouthing were .47 and .29, respectively. There was, however, no effectof age and no interaction between age and type of episode. Thus, eventhough the number of mouthing episodes declined over age, infants atall ages demonstrated the look after and did so more after active thanother types of mouthing.

858 RUFF SALTARELLI, CAPOZZOLI, AND DUBINER

portant to clarify whether the hands were holding and movingthe object for the mouth to explore or were more directly in-volved in obtaining haptic information. The goal of these analy-ses was to assess the extent to which different manipulativeactivities occurred in the presence of looking and mouthing,which are mutually exclusive activities with the small objects weused.

The manual activities most likely to be seen during examina-tion of an object are (a) fingering, (b) transferring the objectfrom hand to hand, and (c) turning the object around or rotat-ing it (Ruff, 1989). Because these manual actions can also occurduring mouthing of the object, whereas other actions such asbanging cannot, we limited our analyses to these three activi-ties. To the category of fingering, we added squeezing, whichwas more likely to occur with the rubber bulbs (appropriatelyso, because those were the only objects made of an elastic sub-stance). For the analyses in this section, we coded the manualactivities during mouthing and looking from the videotapesand then compared the duration of fingering and squeezing,the duration of rotating, and the frequency of transferring theobject from hand to hand under two conditions: when the in-fants were looking at the objects and when they were mouthingthe objects.4 Our expectation was that the manual actions offingering and transferring would be largely restricted to look-ing, during which they are likely to provide specific and globalhaptic information (Ruff, 1984,1989), but that rotating mightserve to enhance the pick up of oral as well as visual informa-tion.

Because the base durations of looking and mouthing werequite different within infants, the analyses were conducted withthe percentages of time in the relevant condition spent finger-ing and rotating and the rate per second in the case of transfer-ring. As two examples, we divided the total duration of finger-ing that occurred during looking by the total duration of look-ing in that trial and the total number of transfers duringmouthing by the total duration of mouthing. We conducted a4 X 2 (Age X Condition: looking or mouthing) ANOVA withrepeated measures on the second factor for each of the threemanipulative activities. Where appropriate, effects were fol-lowed up with analyses of simple main effects. Although, asbefore, the conditions are part of the same trial, given theamount of manipulation, the data in each condition were notconstrained by the data in the other condition.

Means and standard deviations for both absolute amountsand percentages for each age group are presented in Table 3. Forfingering/squeezing, there was a significant increase with age,F(3,28) = 3.4, p = .03, and a significantly greater percentage offingering/squeezing during looking (M = 5.7%) than duringmouthing (M = 2.0%), F(\, 28) = 11.0, p < .003. The analysis onthe rate of transferring yielded a significant main effect of con-dition. There was a significantly higher rate of transferring dur-ing looking (M = 0.049 per second) than during mouthing (M=0.013 per second), F(l, 28) = 23.6, p < .001. There was, how-ever, only a marginally higher percentage of rotating duringlooking (M= 8.5%) than during mouthing (M= 6.1%), F(l, 28)= 3.2, p < .08. There were no significant interactions betweenage and condition for any of the three dependent variables.

Discussion

Both mouthing with looks after and examining meet the crite-ria of decline with familiarization and recovery to novelty, buttheir nonexploratory counterparts do not. As Figures 1 and 2make clear, the recovery observed could not have been due onlyto the break between the test trial of one problem and thebeginning of the next problem, because re-presentation of thesame object never led to recovery. The differential patterns ofchange with increasing familiarization and presentation of nov-elty confirm and extend the findings of the first study.5

The results of the supplementary analyses confirm the ex-pectation that fingering and transferring are more likely to oc-cur during looking than during mouthing. Rotating or turningthe object around, however, occurs to a greater degree than theother two manipulations during mouthing, perhaps because itprovides the mouth with changing information about the ob-ject.

General Discussion

The data from both studies support our contention that onlysome activity during manipulative play with objects can be con-sidered exploratory The major contribution of this project isthe differentiation of mouthing into subtypes and the demon-stration that only some types fit the criteria for exploratoryactivity. By using the immediate look after as a marker, we wereable to show that duration of mouthing with looks after varies

4 Although the three manipulative activities had previously been re-corded from videotapes of infants in the same age range and by thesame observers, we assessed interrater reliability of the total durationsor frequencies of the activities under the two conditions. These reliabil-ities were based on the data from 2 infants at each age for a givenmanual activity in a given condition. The data represented the dura-tions or frequencies in a given condition summed over all trials of aninfant; the correlation between data sets from the two observers wascalculated with the Pearson product-moment correlation (ns = 8). Forthe duration of fingering/squeezing, the reliability coefficients were.99 and .86 for looking and mouthing, respectively. For the number oftransfers, the equivalent correlations were .98 and .93, respectively. Forduration of rotation, the correlations were .96 and .88. The coefficientsrecalculated with age partialled out were all within .03 of the unad-justed correlations.

5 The possibility that the duration of mouthing with looks aftercould be an artifact of changes in looking was addressed in Study 1. Weagain calculated the ratios of looks to mouthing episodes for everyinfant who mouthed the objects in both halves of the familiarizationtrial; 1, 0, 2, and 2 infants were excluded from the four age groups,respectively, because of a lack of mouthing in one half. The ratios werethen entered into a 4 X 2 (Age X Half) ANOVA. There were no maineffects of age or half and no interaction between age and half. Althoughnot significant, the mean ratio increased from the first to second half(3.0 vs. 3.7). The direction of change is contrary to the alternativeexplanation and therefore strongly suggests that the duration ofmouthing with looks after is not a function of changes in looking overtime. In addition, the number of looks after is related significantlymore to duration of mouthing (83) than to duration of looking (05);the look after therefore does not seem to be related to the generaltendency to look at the object.


Table 3Manipulative Activity During Looking and Mouthing Over Age: Absolute Duration or Frequencyof Activity and Percentage of Available Time Spent in Activity Per Trial

Absolute amount Percentage available time

Age

Looking5 months

MSD

7 monthsMSD

9 monthsMSD

11 monthsMSD

Mouthing5 months

MSD

7 monthsMSD

9 monthsMSD

11 monthsMSD

Finger

1.31.1

3.93.7

6.66.3

7.411.0

0.20.3

1.41.3

1.01.2

0.40.3

Transfer

1.32.0

4.12.0

5.14.7

3.53.7

0.30.7

1.01.13

0.81.3

0.30.4

Rotate

3.84.0

6.95.1

8.28.2

7.58.3

1.32.6

3.50.5

3.03.5

2.42.3

Finger

2.1%1.5

4.9%4.0

7.6%5.3

8.4%8.3

0.3%0.6

3.4%3.7

3.2%4.2

1.2%1.0

Transfer*

0.0150.018

0.0580.031

0.0680.058

0.0530.052

0.0130.024

0.0180.016

0.0150.022

0.0050.007

Rotate

4.8%4.3

10.4%6.9

10.3%10.1

8.8%6.2

3.1%4.6

6.5%4.4

5.9%6.1

8.8%7.9

• For transfer, the transformation is rate per second.

with the novelty of an object; this is not the case for mouthingwithout the look after. Therefore, mouthing with looks after canreasonably be designated "exploratory mouthing." Using thesame criteria, examining proved to be a better example of ex-ploratory behavior than other types of visual-manipulative ac-tivity. Although examining has been studied extensively (Ruff,1986,1989), this study represents the first direct comparison tovisual-manipulative activity that excludes examining (see alsoOakes, Madole, & Cohen, 1991).

The differential decline of activities with exposure and dif-ferential recovery to novelty suggest that examining and explor-atory mouthing are means of gathering information. For thispurpose, exploratory activity may be linked to a more generalsystem of attention; specifically, attention to the object duringexploration may be more intense and require more effort thanattention during other activities. This hypothesis is strength-ened by a study showing that the exploratory activities are lessvulnerable to distraction than are the nonexploratory activities(Saltarelli, Capozzoli, & Ruff, 1990). As another measure ofvariations in state, it might be of value to systematically codefacial expression during both mouthing and visual-manipula-tive activity to determine whether the expression of interest(Izard, 1979) is associated with the exploratory but not the non-exploratory activities. Such an approach might be particularlyhelpful in extending our distinction to activities other thanthose emphasized in this report, for example, banging. The way

in which the infant's activity is related to attention and learningclearly needs more investigation.

The results of Study 2 reveal developmental changes inexploratory behavior over the age range studied. Mouthingpeaks at 7 months and then declines to 11 months. In contrast,the trend is for examining to increase from 5 to 11 months. Ifexploratory mouthing and examining are combined into a gen-eral exploratory score, then the proportion of exploration timedevoted to exploratory mouthing decreases from .61 at 7months to .35 at 11 months, whereas that devoted to examiningincreases from .39 to .65, respectively. These values demon-strate a shift away from mouthing as an exploratory tool andtoward integrated visual and manual inspection. One possiblereason for this shift is that new uses of the mouth, such asarticulated communication, preclude or dominate its formerfunctions. A more important reason, however, may be that thefunction of the mouth in haptic exploration is replaced by amore efficient manual system.

Because this gradual substitution of visual-manual inspec-tion for mouthing would represent an important aspect of earlydevelopment, we suggest a possible history of the two forms ofexploratory activity and the developmental changes observed.Before infants can control their hands well enough to reachaccurately and grasp, they are able to suck on and mouth objectsthat are put into their mouths or that get there through rudimen-tary hand-mouth coordination. The evidence (E. J. Gibson &

860 RUFE SALTARELLI, CAPOZZOLI, AND DUBINER

Walker, 1984; Gottfried et al.; 1977; Meltzoff & Borton, 1979)suggests that the substance and shape of objects can be detectedduring this early mouthing. Infants also spend a good portion oftheir early months looking around, and a multitude of studiesattest to the kinds of information picked up from observedobjects and events. The novelty of an object, whether it is firstdetected by the mouth or the eyes, may therefore arouse a desireto both look at and mouth the object, and the two actions maycompete with one another, particularly as infants become moreadept at taking objects in and out of their mouths. The induc-tion of two actions by the same situation, however, may be animportant mechanism in the development of integrated skills(Fischer, 1980) and might gradually lead the infant to look atthe object after mouthing it in order to confirm or amplify theinformation that was picked up during mouthing. This impliesan integration of two actions in the service of learning moreabout the object.

Mouthing, as a well-practiced haptic system, may dominatein exploratory activity at 5 and 7 months because the visualsystem is, at that point, more engaged than previously in con-trolling the emergent reaching, grasping, and manipulating ofobjects. As the infant becomes more practiced in visuallyguided grasping and manipulating, more attention could bedevoted to the information provided by the hands; the handscould then begin to play a more extensive role in exploratoryactivity. Generally speaking, the hands can serve two functions(J. I Gibson, 1966). Some manual actions are performatory andserve the eyes and possibly the mouth; as the infant turns theobject around during looking and mouthing, the infant is pro-vided with different perspectives of the object, an importantprocess for highlighting the invariant characteristics of the ob-ject. Other manual actions, such as fingering and transferring,are directly exploratory in that they provide the infant withhaptic information about the texture, shape, and substance ofthe objects being handled (Ruff, 1982,1984,1989). With devel-opment, these actions eventually are differentiated and becomespecialized for different object properties (Lederman &Klatzky, 1987).

Our analyses of manipulative activity during mouthing andlooking show that infants are significantly more likely to fingerand transfer objects when they are looking at them than whenthey are mouthing them. Rochat (1989) also found that finger-ing co-occurred with looking more than would be expected bychance, whereas fingering during mouthing was at or belowchance levels. The tendency to manipulate objects while look-ing may be due to a need to visually control manual actions, atleast when the actions are first emerging (Bushnell, 1985; Ruff,1989). Or young infants may be more aroused by the sight of theobject than the feel of it in the mouth, and the increased arousalleads to generally higher activity of the hands. In either case, thefact that looking occurs jointly with some activities that poten-tially provide haptic information again provides a basis for anemerging integration that we see in examining, an activity thatdominates exploration by infants around 9 or 10 months. Thefact that the infant does not seem to integrate the manual andoral methods of gathering haptic information may stem froman undesirable competition, because the mouth and handswould be exploring different parts of the same object simulta-neously. One method—mouthing—drops out as the infant be-

comes a more efficient explorer of objects and the survivingmethod—manual activity associated with vision—provides theinfant with a system in which there is useful redundancy fromtwo modalities and a great deal of flexibility (Lederman &Klatzky, 1989).

These speculations make clear that there is still much to belearned about the development of the components of explor-atory skills and their integration; about the growth of knowl-edge that comes from less and more skilled exploration; andabout the relationship of exploratory activity to the processes ofattention and learning. On the other hand, the other functionsof infants' play with inanimate objects, such as exercise of mo-tor skills, should not be ignored, because nonexploratory activi-ties may also play an important role in development. We hopethat the distinctions explored and validated in these studieswill allow us to refine further our observations and our under-standing of infants as they interact with objects.

References

Bruner, J. S. (1973). Organization of early skilled action. Child Develop-ment, 44,1-H.

Bushnell, E. W (1985). The decline of visual guided reaching duringinfancy. Infant Behavior and Development, 8,139-155.

Bushnell, E. W, Shaw, L., & Strauss, D. (1985). Relationship betweenvisual and tactual exploration by 6-month-olds. Developmental Psy-chology, 21, 591-600.

Fischer, K. W (1980). The theory of cognitive development: The con-trol and construction of hierarchies of skills. Psychological Review,57,477-531.

Gibson, E. J. (1988). Exploratory behavior in the development of per-ceiving, acting and the acquiring of knowledge. Annual Review ofPsychology, 39,1-41.

Gibson, E. J., & Walker, A. S. (1984). Development of knowledge ofvisual-tactual affordances of substance. Child Development, 55,453-460.

Gibson, J. J. (Ed.). (1966). The senses considered as perceptual systems.Boston: Houghton-Mifflin.

Gottfried, A. W, Rose, S. A., & Bridger, W H. (1977). Cross-modaltransfer in human infants. Child Development, 48,118-123.

Izard, C. E. (Ed.). (1979). The maximally discriminative facial codingsystem. Newark, DE: University of Delaware Instructional Re-sources Center.

Korner, A., & Kraemer, H. (1970). Individual differences in spontane-ous oral behavior in neonates. In J. Bosnia (Ed.), Third symposium onoral sensation and perception: The mouth of the infant (pp. 335-346).Springfield, IL: Charles C Thomas.

Lederman, S., & Klatzky, R. L. (1987). Hand movements: A windowinto haptic object recognition. Cognitive Psychology, 19, 342-368.

Lockman, J. X, & McHale, J. P. (1989). Object manipulation in infancy:Developmental and contextual determinants. In J. J. Lockman &N. L. Hazen (Eds.), Action in a social context: Perspectives on earlydevelopment (pp. 129-167). New \&rk: Plenum Press.

Meltzoff, A. N., & Borton, R. W (1979, November). Intermodal match-ing by human neonates. Nature, 282, 403-404.

Oakes, L. M., Madok, K. L., & Cohen, L. B. (1991). Infants' objectexamining: Habituation and categorization. Cognitive Development,6, 377-392.

Palmer, C. (1989). The discriminating nature of infants' exploratoryactions. Developmental Psychology, 25,8*5-893.

Pecheux, M, Lepecq, J, & Salzarulo, P. (1988). Oral activity and explo-ration in 1-2-month-old infants. British Journal of DevelopmentalPsychology, 6, 245-256.


Rochat, P. (1983). Oral touch in young infants: Response to variationsof nipple characteristics in the first month of life. International Jour-nal of Behavioral Development, 6,123-133.

Rochat, P. (1989). Object manipulation and exploration in 2- to 5-month-old infants. Developmental Psychology, 25, 871-884.

Rochat, P., Blass, E. M., & Hoffmeyer, L. B. (1988). Oropharyngealcontrol of hand-mouth coordination in newborn infants. Develop-mental Psychology, 24, 459-463.

Ruff, H. A. (1982). Role of manipulation in infant's responses to invari-ant properties of objects. Developmental Psychology, 18, 682-691.

Ruff, H. A. (1984). Infants' manipulative exploration of objects. Effectsof age and object characteristics. Developmental Psychology, 20,9-20.

Ruff, H. A. (1986). Components of attention during infants' manipula-tive exploration. Child Development, 57,105-114.

Ruff, H. A. (1989). The infants' use of visual and haptic information inthe recognition of objects. Canadian Journal of Psychology, 43, 302-319.

Ruff, H. A., & Lawson, K. R. (1990). The development of sustained,focused attention in young children during free play. DevelopmentalPsychology, 26, 85-93.

Siegel, S. (1959). Non-parametric statistics. New York: McGraw-Hill.Saltarelli, L., Capozzoli, M., &Ruff, H. A. (1990, April). Distractibility

and focused attention in infants. Paper presented at the InternationalConference on Infant Studies, Montreal, Quebec, Canada.

Uzgiris, I. C. (1967). Ordinality in the development of schemas forrelating to objects. In J. Hellmuth (Ed.), Exceptional infant, Vol. 1: Thenormal infant (pp. 317-334). Seattle, WA: Special Child Publica-tions.

Weisler, A., & McCall, R. B. (1976). Exploration and play. AmericanPsychologist, 31, 492-508.

Received September 12,1990Revision received October 4,1991

Accepted October 7,1991 •

Search Opens for Editor of New APA Journal

The Publications and Communications Board has opened nominations for the editorship ofa new journal, Journal of Experimental Psychology: Applied, for the years 1995-2000.Candidates must be members of APA and should be prepared to start receiving manuscriptsearly in 1994 to prepare for issues published in 1995. Please note that the P&C Boardencourages more participation by members of underrepresented groups in the publicationprocess and would particularly welcome such nominees. To nominate candidates, preparea statement of one page or less in support of each candidate. Submit nominations to

Howard E. Egeth, PhDChair, JEP':Applied SearchDepartment of PsychologyJohns Hopkins UniversityCharles & 34th StreetsBaltimore, MD 21218

The Journal of Experimental Psychology: Applied will publish original empirical investi-gations in experimental psychology that bridge practically oriented problems and psycho-logical theory. The journal also will publish research aimed at developing and testing ofmodels of cognitive processing or behavior in applied situations, including laboratory andfield settings. Review articles will be considered for publication if they contributesignificantly to important topics within applied experimental psychology.

Areas of interest include applications of perception, attention, decision making, reasoning,information processing, learning, and performance. Settings may be industrial (such ashuman-computer interface design), academic (such as intelligent computer-aided instruc-tion), or consumer oriented (such as applications of text comprehension theory to thedevelopment or evaluation of product instructions).

First review of nominations will begin December 15,1992.

the differentiation of activity in infants' exploration of...

Documents