Risk factors for infant attrition and low engagement in experiments and free-play

RISK FACTORS FOR INFANT ATTRITION AND LOW ENGAGEMENT IN EXPERIMENTS AND FREE-PLAY

John Oates The Open

University

at Milton

Keynes

Forty-three 2-month-old infants participated with their mothers in a laboratory study of factors associated with variations in infants’ attrition and levels of attention/engagement in a cognitive-perceptual experiment, and in free-play with their mothers. Increased risk of attrition from the experiment was strongly associated with analgesic medication having been administered during labor and with more restricted maternal perceptions of infants’ capacities. Attrition rates and levels of engagement varied independently, showing different patterns of association with explanatory variables. Infants’ levels of engagement in the experiment and in free-play were correlated across settings and low levels were associated with a lack of maternal identification with the foetus during early pregnancy and more limited maternal perceptions of their infants’ capacities, but were not associated with analgesic medication during labor.

infants

attrition

low engagement

INTRODUCTION To obtain usable and meaningful data in perceptual-cognitive experiments it is essential to ensure infants’ attention to and engagement with the experimental task. Rates of attrition in infant experiments commonly run at 50% or higher because infants fail to attend or their attention tails off before completion of the

experiments

free-play

risk factors

experiment. The more demanding the experimental task, for example in the length of sustained attention required of the infant, the more likelihood there is of subject loss. Significant rates of attrition persist despite infancy researchers having developed the necessary expertise in the design of laboratory environments, the procedures for participant recruitment, reception and handling, as well as the

l John Oates, Centre for Human Development and Learning, School of Education, Open University, Walton Hall, Milton Keynes MK7 6AA Great Britain; Tel: 01908-652395; Fax: 01908-654111; e-mail: [email protected].

INFANT BEHAVIOR & DEVELOPMENT 21 (4), 1998, pp. 555-570 Copyright 0 1998 ABLEX Publishing Corporation

ISSN 0163-6383 All rights of reproduction in any form reserved.

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detailed design of the experimental tasks and sensitivity to infant state when starting trials. Previous exploratory studies have suggested that attrition may be systematically related to infant variables such as temperament (Wachs & Smitherman, 1985), discrimination ability, cardiac deceleration and recovery (Lewis & Johnson, 1971), looking times (Richardson & McCluskey, 1983), sex (DeLoache, Rissman, & Cohen, 1978) and developmental level and incidence of adjustment and behavioural difficulties (Bathurst & Gottfried, 1987), although this latter study was of infants aged 12 months and older. Analyses of the characteristics of a large sample of ‘non-completing’ 4-month-old infants in a simple habituation task (Bell, Bell, & Yeung, 1994) have shown that failure to complete has short-term stability and that it is also associated with non-completion at thirteen months. It has been suggested that levels of infants’ engagement in cognitive tasks have correlates in a range of maternal factors perceptions of their including mothers’ infants’ cognitive and affective capacities and their behavior with their infants (Wachs & Smitherman, 1985). The capacity to engage with another person, or with some other contingently respon(as in an infant-control sive ‘object’ experiment) involves both the ability to maintain attention towards the object and also the ability to sustain contingent interchange with it (Beebe & Stem, 1977). Observation of infants participating in experiments and natural social exchanges suggests that the two abilities are to some extent independent, in that while some infants may consistently show generally intense concentration and other infants may show generally reduced intensities of attention, the length of time for which they typically sustain an engagement episode does not appear to be related to the intensity of their engagement. Sustained episodes of mutual, close engagement between an infant and another person, during which each is the object of the other’s attention, and each individual’s behavior is contingent on the other’s, are widely considered to be important for the

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development of primary intersubjective understanding (Trevarthen, 1993) and the experience of ‘relatedness’ with another (Hobson, 1993). Relatively stable differences in young infants’ capacities to maintain this sort of relation with another agent might be one source of the variation found in their behavior in experiments and also a significant factor in their early social development. A pilot study of 21 infants’ behavior in an operant conditioning experiment and in natural interaction with their mothers (Oates & Corlett, 1992) suggested that such differences between infants may be connected with qualities of the relationship between mother and infant, particuwith the mother’s projective larly identification with her infant, both before and after the birth. This pilot study found that mothers whose infants engaged well with the experiment and completed trials tended to have more elaborated models of their infants’ cognitive and emotional abilities and attributed more ‘person’ qualities to their infants, having also identified with their infants in this way during the early months of their pregnancy. For infants in the first 2-3 months after birth, variations in their propensity to engage may be partly constitutional (viz. the fretful, irritable, hard to soothe infant) and in part arise from varied amounts and qualities of periods of sustained contingent responsiveness they experience with the mother. In addition, experiences of the birth are likely still to be affecting both mother and infant. Interference with the infant’s and mother’s capacities to sustain contingent relations might lead to a delay in the infant’s development of a more general capacity to engage in the way outlined, as exemplified by the accumulating evidence on the effects of post-natal depression on mothers’ and infants’ behavior in the short and long term (Murray, 1992; Murray, Kempton, Woolgar, & Hooper, 1993; Field, 1995). Thus a closer examination of subject loss has the potential also to shed light on more general developmental processes.

Risk Factors for Attrition

The study reported here set out to explore further the factors associated with variations in young infants’ engagement with an habituation task. It was hypothesized that there would be cross-context consistency in infants’ levels of engagement, and observations of infant behavior in a free-play episode were carried out to provide the comparison context. It was also hypothesized that associations would be found between levels of infants’ engagement and mother’s reports of their feelings towards the foetus during pregnancy, their experiences during labor and their models of their infants’ cognitive and emotional capacities. METHOD

557

Non-Hispanic White and one was Asian. Two mothers had left school with no qualifications; 20 had O-levels only; 5 had A-level qualifications; 13 had higher or further education qualifications up to undergraduate degree level and three had postgraduate qualifications. According to the British Standard Occupational Classification (Office of Population Censuses and Surveys, 1991), using the male head of household as the reference person, seven cases were classified as I (professional), 13 as II (managerial and technical), seven as IIIN (skilled occupation; non-manual), 10 as HIM (skilled occupation; manual) and four as V (unskilled occupation). One was unemployed and one was unclassified (member of armed forces).

Procedures Mother-infant pairs were recruited with the assistance of health visitors in the Milton Keynes Community NHS Trust catchment area. At their first home visit, a few days after the birth of an infant, health visitors gave mothers an information sheet on the research project, an invitation to participate and a reply-paid postcard. These were only given to mothers of infants born at full term without illness or other disorder that might have interfered with their participation in the study. The mean age of the mothers at the time of testing was 30 years (SD = 5) and the mean age of the infants was 56 days (SD = 17). 23 infants were female (M = 56 days; SD = 20) and 20 were male (M = 57 days; SD = 14.8). Twenty-two were firstborns and 21 were second or subsequent births. Forty-two were born in Milton Keynes General Hospital; one was born at home. Labor and delivery were uncomplicated for 32 of the infants; in 11 cases there had been some form of complication during labor. Five deliveries were by caesarean section; two of these were elective. Twenty-four mothers had received some form of medication during labor; 19 received none. Mothers had a range of socio-economic and educational backgrounds, approximating to a stratified community sample. Forty-two were

All data collection was carried out in a laboratory on the university campus. For the habituation experiment, infants were seated on their mothers’ laps at the same height as and approximately 60 cm from a stimulus display screen. Mothers were asked not to attend to the screen display, nor to intervene in any other way with their infants’ behavior during the experiment, other than to replace the pacifier if it fell out of their infant’s mouth.

Habituation

Experiment

The habituation experiment was controlled by a Mac IIsi computer. Infant sucking was sensed through a pressure transducer and signal amplifier connected to a standard non-ventilated pacifier by a 2 metre flexible plastic tube. Stimuli were displayed on a standard 14” color monitor and the accompanying sound through a pair of loudspeakers. Prior to this study, the feasibility had been established of extending a method previously developed by other researchers for speech perception experiments (the HAS procedure; e.g., Jusczyk, 1985) to the use of visual/sound stimuli as reinforcers in an operant conditioning habituation/dishabituation paradigm (Oates, 1991). A

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similar technique has also been used with digitized color photographs (Walton, Bower, & Bower, 1992). The computer program allowed infants to control stimulus presentation by sucking on the pressure-sensing pacifier. For the experiment that formed the basis of this study, color video recordings of three female actors speaking a standard phrase (‘What are you doing?‘) with three different emotional expressions (happy, neutral and concerned) were prepared as 1 s digital video files. The experimental design gave each infant the opportunity to control the presentation of a series of ten of these stimuli, each stimulus being available during a 45 s trial. On the completion of each trial, a new trial began when the next high-amplitude suck was detected. Thus a complete run of 10 trials had a total duration of approximately 7.5 min.

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describe their infants’ capacities for experiencing different emotions, including their infants’ feelings towards them, and to name the emotions they felt their infant experienced. They were also asked whether they perceived their infants as crying a lot or were felt to be otherwise difficult to manage. Transcripts of the interview recordings were coded using sets of category elements which had been developed in the previous pilot study and were further refined during the initial stages of the coding process. Reliability of the coding was assessed by a second coder blind to the details of the study, who coded a 10% random sample of interview tapes. Reliability coefficients averaged 89% (range 74-100%). Demographic details and a pregnancy, delivery and post-partum medical history were also taken. Video Records and Coding

Free-Play Episode For the ‘free-play’ episode, mothers were given a standard set of toys (red ring from Bayley test, two Lego rattles which could be fitted together and a 24 cm wooden doll) and asked to ‘play with your baby as you would at home.’ Mothers sat in a comfortable chair alongside a low table on which the toys were placed. One of the experimenters sat quietly in a corner of the room throughout, while the other left the room and returned after 5 min. The entire episode was video-recorded.

The video recordings of each infants’ behavior in the experiment were coded on an S-point engagement scale for each 45 s trial: 1. 2. 3. 4. 5.

Structured

Interview

with Mothers

A tape-recorded interview was conducted with each mother using a structured schedule to gather information on her experiences during pregnancy, labor and delivery, and her relationship with and perceptions of her infant around the time of the lab visit. Mothers were asked specifically to say at what point during pregnancy they first started to think about their foetus as a real person, for example by talking to it, imagining its personality or giving it a name. They were asked about the details of labor and delivery, and asked to

6. 7. 8.

eyes closed, loss of limb, body, neck tone. eyes closed but retains limb, body, neck tone. eyes partly or wholly open, no attention to screen or elsewhere attention fixed on edge of screen or other visual feature/shifting attention attention 20% to stimulus display / 80% elsewhere attention 50% to stimulus display / 50% elsewhere attention 80% to stimulus display / 20% elsewhere sustained visual fixation of screen and video image

The 5-min free-play episodes were coded by observers blind to the experimental hypotheses and participant details in 45 s time samples using the same engagement scale, for visual engagement of infant with mother. Reliability coefficients for independent blind cod-

Risk Factors for Attrition

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ers using this scale on a 10% random sample of both the free-play and experiment video recordings were 85% or greater.

tion between nancy.

Mothers’

Measures Number

Emotional

of Trials Completed

An individual trial was treated as ‘noncompleted’ if an infant fully disengaged, e.g., by falling fully asleep, rejecting the pacifier, or fretting/crying sufficiently for the mother or experimenter to intervene and terminate the experiment during the trial. This is the criterion used by Richardson and McCluskey (1983). Trials in which the infant was drowsy or otherwise disengaged for only part of the trial were treated as ‘completed.’ For some of the statistical analyses this measure was collapsed into two categories: completion (all trials completed) and non-completion (fewer than ten trials completed).

Engagement

Mean

(Experiment)

The mean level of engagement, coded from the video recordings of each experiment run, using the above scale, for the trials completed.

Mean

(Free-Play)

The mean level of engagement, coded from the free-play video recordings using the above scale for 45 s consecutive samples covering the whole 5 min episode.

Perceptions

of preg-

of their lnfan ts’

Capacities

Mothers’ descriptions of their infants’ capacities for experiencing different emotional states were coded into two groups; one in which infants were described as only experiencing primitive, positive and negative states, and one in which the infants were described as experiencing a more complex and wider range of differentiated emotional states. This categorisation reflected a natural division in mother’s responses.

Mothers’ Feelings

Perceptions for Them

of their Infants’

Mothers’ responses to this part of the interview were coded into two groups; one in which mothers reported that their infants felt love for them and one in which mothers reported that their infants’ feelings towards them were either ambivalent or predominantly negative.

Mothers’ Engagement

four and six months

Perceptions

of infant

Crying

Mothers’ reports on how often their infants cried were coded as ‘cries often’ or ‘does not cry often.’ (‘Cries often’ was usually associated with the mother reporting that her infant’s crying troubled her to varying degrees.)

Type of Labor/Delivery Mothers’

Identification

with Foetus

Mothers were coded into two groups: those who reported an identification with their foetus early in pregnancy (within the first three months) and those who had not experienced such identification at all or only in last two months of the pregnancy. This grouping reflected a natural division in the sample, with no mothers reporting the onset of identifica-

The type of labor/delivery experienced by mothers was coded as: normal vaginal delivery with no analgesic medication during labor; normal vaginal delivery with analgesic medication during labor; or caesarean/epidural delivery (this latter category was grouped because of small numbers in the two sub-categories and the relative similarity of them in terms of the amount of medical intervention

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during labor in contrast to the other two main categories). All mothers in the normal vaginal delivery with medication group received intramuscular injection of meptazinol during labor for general analgesia. The epidural anesthesia used was bupivacaine, administered by catheter or by injection for C-section.

RESULTS

Completion

Rates

The first dependent measure examined was a dichotomous classification of cases into those where infants completed the entire experiment (‘completers’) and those who failed to do so (‘non-completers’). Significant associations with completion were found for type of labor, maternal identification with the foetus and mothers’ accounts of their infants’ capacities for experiencing emotions. Of the 20 infants who completed the full experiment, 25% (5) of their mothers had received medication during labor. Of the 23 who did not complete, 82% (19) of their mothers had been given medication; x2 (1, N = 42) = 14.4, p = .OOOl. When the medication group was split into caesarearJepidura1 anesthesia and general analgesic groups, it was found that only one of the nine infants of the caesarean/epidural group had completed, while 25% (5) of the 16 infants whose mothers were given general analgesics completed. For the 14 mothers who had identified with their foetus early in pregnancy, 7 1% (10) of their infants completed full runs of the experiment, while for the 28 mothers who had not identified in this way, had experienced negative feelings towards their foetus or only identified late in pregnancy, only 32% (9) of their infants completed; x2 (1, N = 41) = 5.8, p = .015. Mothers of completers more often described their infants as experiencing a complex range of emotions rather than simply primitive positive/negative states; x2 (1, N = 42) = 8.2, p = .004. Completers were also more likely to be described as feeling love for their mothers x2 (1, N = 40) = 6, p

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= .014. No significant associations were found between completion and sex or age of infant, mothers’ age, parity, educational level or socio-economic status, length of labor or pregnancy complications, nor were any trends evident. Infants who had experienced an illness since their birth, or who were described by their mothers as crying a lot or otherwise difficult to manage were no less likely to complete, nor were any trends evident.

Attrition:

Number

of Trials Completed

Twenty infants completed all ten trials of the experiment; the remaining 23 infants’ performance was approximately evenly distributed between one and 9 trials completed (M = 7.14, SD = 3.29). For trials 1-9, the numbers of infants who completed up to and including that trial but then failed to continue were as follows: 2,2,1,4,0,3,3,6,2. The number of trials completed was associated with labor type and mothers’ descriptions of their infants’ capacities for emotional experience. Infants whose mothers had received no medication during labor completed a mean of 9.1 trials (SD = 2.6) while ‘medicated’ mothers’ infants completed a mean of 5.8 trials (SD = 3.2), MannWhitney U = 94.5, p = .0006. Caesareatiepidural type birth was associated with a mean of 4.4 trials completed (SD = 2.8) and other labor analgesia with a mean of 6.5 trials (SD = 3.1), Kruskall-Wallis (2, N = 41) H = 13.8, p = .0004 (see Table 1). Although there was a trend for more trials to be completed by infants whose mothers had identified positively with the foetus early in pregnancy, this effect failed to reach significance, Mann-Whitney U = 136, p = .092 (see Table 2). Infants who were described by their mothers as only capable of experiencing primitive emotions completed a mean of 6 trials (SD = 3.3) while those described as capable of experiencing more complex emotions completed a mean of 8.7 trials (SD = 2.7), Mann-Whitney U = 118, p = Xl054 (see Table 3).

Risk Factors for Attrition

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TABLE1 Number of trials completed and engagement scores for infants in non-medicated, medicated and caesarean/epidural labor categories No medication

General analgesic

Caesareadepidural

M

SD

M

SD

M

SD

P

n Trials Completed

9.06

2.58

6.50

3.06

4.44

2.83

.0004

Engagement (Experiment)

5.40

2.30

4.97

1.72

6.23

1.59

ns

Engagement (Free-play)

4.32

1.85

4.00

.70

4.00

.a3

ns

TABLE2 Number of trials completed and engagement scores for infants whose mothers identified with their foetus early in pregnancy, and infants whose mothers had late or no identification Early identification

None/late

M

SD

M

SD

n Trials Completed

7.93

Engagement (Experiment)

6.32

3.71

6.64

3.06

ns

1.47

4.91

2.07

.017

Engagement (Free-play)

4.92

1.63

3.53

.Vl

.OOl

P

TABLE3 Number of trials completed and engagement scores for infants attributed with primitive emotions by their mothers and infants attributed with complex emotions Primitive

Complex

M

SD

M

SD

P .005

n Trials Completed

6.04

3.30

8.67

2.68

Engagement (Experiment)

5.33

1 .vo

5.51

2.13

ns

Engagement (Free-play)

3.76

1.16

4.30

1.51

ns

Infants whom mothers described as having loving feelings for them completed a mean of 8.7 trials (SD = 2.7) whereas those described as having ambivalent or predominantly negative feelings for their mother only completed a mean of 6.4 trials (SD = 3.5), Mann-Whitney U = 107, p = .025 (see Table 4). As the length of each trial in the experiment was fixed at 45 s, it was possible to apply a survival analysis to the data using number of last trial completed as a discrete

time measure. This allowed an assessment of the effects of factors associated with differences in the progressive attrition rates over the trial series. Observations of infants who completed all ten trials were treated as rightcensored data since these infants might have continued for a further (unknown) period had the experiment not been terminated at the end of the tenth trial. The risk of attrition from the infants remaining in the experiment in each of the trial periods was approxi-

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TABLE 4 Number

of trials completed

and engagement

scores for infants attributed

feelings towards their mothers and infants attributed

with ambivalent

love

Ambivalent/negative

M

with loving

or negative feelings

SD

M

SD

P

n Trials Completed

6.39

3.46

8.69

2.66

.025

Engagement (Experiment)

5.03

2.21

6.16

1.28

ns

Engagement (Free-play)

3.88

1.52

4.31

.93

ns

mately equal across the trials, indicating a constant hazard function and allowing the application of Cox’s proportional hazards model (Cox & Oakes, 1984). This analysis confirmed the effects of labor type and identification with foetus on completion/noncompletion, and associations of completion/ non-completion with the mothers’ descriptions of their infants’ emotional capacities. As suggested by the pattern of findings given above, the strongest effect was related to type of labor. Figure 1 shows the effect of labor type across the time-span of the experiment, with higher attrition associated with infants whose mothers received medication during labor (both caesarean/epidural and

P

general analgesics) apparent from the first trial onwards. In the caesarean/epidural group, all infants had dropped out by the end of the sixth trial, while in the general analgesic group 60% had dropped out by the end of the tenth and final trial, compared to 20% for the no medication group. These differences were statistically significant: logrank Mantel-Cox x2 (1,42) = 28.3, p < .OOOl. The association between maternal identification early in pregnancy and a reduced attrition rate is evident only from trial four onwards (see Figure 2). This difference in risk was, nevertheless, significant: logrank Mantel-Cox x2 (1,41) = 4.1, p = .043. Differences in survival were also

1 -

‘E .-

No medication

;

.8

S S

.6 -

E 6 F

.4 -

c!! .P ‘r ra, g:: go cl.c

General analgesia .2CaesarearVepidural oI

I

I

I

I

I

1

I

I

I

I

0

1

2

3

4

5

6

7

8

9

10

Trial number FIGURE 1 Attrition

of infants from experiment

for different types of labor.

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Risk Factors for Attrition

2

l-

‘iz ‘5 E

.8 -

I ul 5

.6 -

z 5 E

.4 -

Early identification

None/late

.G .g tzal gg

.2-

a’.5

oI

I

I

I

0

1

2

3

1 4

I

I

I

I

I

I

5

6

7

8

9

10

Trial number FIGURE2 Attrition of infants whose mothers identified with them early in pregnancy and infants where identificaion was late or lacking.

those for infants whose mothers attributed them with capacities for a wider range of differentiated feelings. For mothers who described their infants as feeling love towards them, attrition was consistently lower from trial three onwards, compared with infants whose mothers saw them as

significantly associated with differences in the ways that mothers described their infants’ capacities for emotional experience: logrank Mantel-Cox x2 (1,42) = 8, p = .005. Figure 3 contrasts the attrition rates for infants whose mothers described them as only capable of simple, primitive emotional experience with

2

l-

.e ‘iii E 2 v) 2

.8

I 3 E

.4 -

e5 5 .E

.2-

-

Complex

.6 -

Primitive

g :: LE.:

oI

I

I

I

I

I

I

I

I

I

I

0

1

2

3

4

5

6

7

8

9

10

Trial number FIGURE3 Attrition of infants attributed with complex emotions by mothers and infants attributed with primitive emotions.

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0 .G .f E

Love

2 0-J 5 E 5 $ =E .P ‘C ra, ;: r5.G

.6 .4 -

Ambivalent negative

.2oI

I

I

I

I

I

I

01234567

1

I

I

I

8

9

10

Trial number FIGURE 4 Attrition

of infants perceived by mothers as loving them and infants whose mothers perceived ambiva-

lent or negative feelings.

having more ambivalent, often negative feelings: logrank Mantel-Cox x2(1, 40) = 5.26, p = .022 (see Figure 4). These four factors were entered as covariates in a proportional hazards multiple regression analysis, with the hazard rate for the nomedication group as baseline. Only type of labor contributed significantly to the fit of the model: baseline (no medication group) logrank Mantel-Cox x2 (1, 42) = 11.5, p = .003, general analgesic group logrank MantelCox x2 (1,42) = 6.5, p = .Ol, Caesareadepidural logrank Mantel-Cox x2 (1, 42) = 11.5, p = .0007. Model coefficients for the latter groups suggest approximately two-fold and two and a half-fold increases above baseline risk of attrition for the two types of medicated labor: general analgesics coefficient = 1.8; Caesarean/ epidural coefficient = 2.5.

Engagement

Levels

The mean level of engagement across all trials completed was 5.4 (SD = 2) for the whole sample. In the free-play episode, infants’ levels of engagement were lower, with a mean of 4 (SD=1.3). A series of r-tests was

performed to identify possible effects of group differences on the mean levels of infant engagement in the trials completed, for entry into a factorial ANOVA. Significant effects were found for age of infant, maternal identification with foetus and whether or not the mother was breast-feeding her infant. Higher average levels of engagement were found for older infants t( 1, 38) = -4.74, p < .OOOl, infants whose mothers had identified with them early in pregnancy t( 1, 37) = 2.20, p = .017 (see Table 2) and breast-fed infants t(1,37) = -1.73, p = .046. A three-factor ANOVA examining these effects showed no significant interaction effects and post-hoc tests confirmed the t-test results for infants older than the sample mean age showing higher levels of engagement and infants whose mothers had identified with them early in pregnancy also showing higher levels. Method of feeding failed to reach significance in this analysis; F( 1,37) = 2.42, p = .13. There were no associations between infants’ engagement levels and length or type of labor, mothers ’ age, parity, socio-economic status, educational level, or pregnancy complications, nor were any trends evident. The correlation between infant age and average level of

565

Risk factors for Attrition

engagement was moderate: Pearson’s r = 561, p < .OOOl. Inspection of the scatter plot showed that there was reduced variability in engagement level for infants older than 60 days. There was also a moderate correlation, Pearson’s r = .601, p c .OOOl, between the infants’ levels of engagement during the experiment and their levels of engagement with their mothers during the free-play episode. While the trend for older infants to show higher engagement in the free-play episode just failed to reach significance when assessed by a correlation analysis (Pearson’s r = .31,p = .061), a r-test comparison between infants younger than the sample mean and older infants was borderline significant: t( 1,36) = -1.64, p = .0547. As was found for engagement with the experiment, infants whose mothers described a clear identification with their foetus early in pregnancy also showed notably higher average levels of engagement during free-play than infants of mothers who had not identified in this way; t(1. 35) = 3.30, p = .OOl (see Table 2). While a t-test for breast-fed infants showing higher levels of engagement in free-play was non-significant, t( 1,34) = -.498, p = .3 1, a two-factor ANOVA of identification and method of feeding on engagement during freeplay showed significant main effects of each factor (identification F(1, 30) = 18.9, p < .OOOl, feeding method F( 1, 30) = 4.45, p = .043) and a significant interaction F(1, 30) = 5.3, p = .028, such that infants who were breast-fed and whose mothers had identified with them early in pregnancy showed 2 points higher mean levels of engagement in free-play than bottle-fed infants from the same group. This difference associated with method of feeding was not apparent in the group of infants whose mothers had not identified with them early in pregnancy.

DISCUSSION The principal results of this study were, first, that two aspects of infants’ engagement, their capacity to sustain attention, and their level of engagement, were found to have different

associations with explanatory variables, and that these two aspects appear to be relatively independent (uncorrelated). Because of the strong associations with other variables, neither attrition from the experiment nor low levels of engagement in the task can be explained simply by fluctuations in infants’ states. Second, that individual differences in these two aspects are consistent across a social setting (engaging in free-play with the mother) and a non-social setting (engaging with the experiment). Three sources of explanation for the individual differences found have been identified: the administration of analgesic medication during labor, mothers’ identification with their foetuses during pregnancy and mothers’ models of their infants’ capacities.

Age of Infant Infant age explained a significant amount of the variation in engagement levels in the experiment and in free-play, but infant age was not related to rates of attrition from the experiment. While Wachs and Smitherman (1985) found no general age-related differences in completion rates for infants across the range 77-196 days of age, Richardson and McCluskey (1983) found 70-day-old infants less likely to complete than either llZdayolds or 168-day-olds. DeLoache et al. (1978) found that female infants of average age 112 days were less likely than males to complete, and Wachs and Smitherman (1985) found that female infants (range 77-196 days of age) who failed to complete all trials also tended to complete fewer trials than the male non-completers. In the present study, which included younger infants than the studies referred to above, there was no overall increase with age in full completion rates nor in the number of trials completed, nor was infant sex linked to any of the dependent measures.

Social and Non-Social

Engagement

The correlation found between infants’ engagement levels in the experiment and in

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free-play supports the hypothesis that a single underlying factor influences behavior in both settings. Dunham and Dunham (1990) have reported an equivalent finding that 3-monthold infants’ levels of performance in a nonsocial contingency experiment similar to that used in this study are positively correlated with their levels of social interaction with their mothers in a free-play episode also similar to that employed in this study. The finding that prenatal and perinatal factors appear to be related to infants’ engagement levels in both settings also supports the hypothesis that variations in infants’ attention in experiments are not simply due to randomly distributed state changes but may indicate enduring differences. This is in accord with Bell’s findings of stability in non-completion (Bell et al., 1994) and is also supported by the finding in the present study that completion rates and numbers of trials completed were no higher for older infants in the sample. However, the older infants were more likely to show higher levels of engagement with both the experiment and the mother in free-play, suggesting a possible developmental trend for this aspect of infants’ attention. The finding that infants’ persistence in sustaining engagement was associated with different factors from those associated with their levels of engagement suggests that these are two partially independent components of an infant’s propensity to engage in contingent interaction with another agent, as does the lack of any correlation between engagement levels and number of trials completed. These results taken together support the hypothesis that two separate processes are operating which require differing explanations; one process to do with how well an infant is able to direct their attention to and engage with another agent, and another process to do with the infant sustaining the level of engagement attained, which may have a developmental component. The first process may be more involved with infants’ sensitivity and orienting to contingent and information-rich stimuli and events, while

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the latter may have more to do with cognitive engagement and resistance to distraction.

Labor Medication and Ma ternal Models of the Infant The most striking findings from the present study are the strong effects associated with mothers’ type of labor and their identification with their foetus early in pregnancy, particularly on infants’ ability to sustain interaction. The results also consistently show infants’ levels of engagement being associated with measures that describe aspects of mothers’ relationships with their infants. Several of the findings indicate that low engagement is associated with a mother having a relatively impoverished model of their infant’s abilities, particularly in respect of their cognitions and capacities for emotional aspects of interpersonal relating. Emory, Schlackman, and Fiano (1996), in a study of 42 infants, found that neonatal responsiveness was significantly lower in a labor medication group, and Lester, Als, and Brazelton (1982), in a study of 54 neonates, found that labor medication was associated with depressed Brazelton NBAS cluster scores up to 10 days post-par-turn. The latter authors noted interactions with other factors including length of labor and parity: neither of these were found to be significant in the present study. Murray, Dolby, Nation, and Thomas (1981), with data from 60 infants, found similar effects on NBAS scores up to five days post-partum, although these effects were largely absent by one month post-partum. However, some associations between medication and aspects of mothers’ interactions with and perceptions of their infants were still evident at one month post-partum. Of particular note in this latter study is that mothers in the non-medicated group were found at one month post-partum to be generally more positive and responsive towards their infants and engaged in more eye-contact during feeding, findings consonant with those from the present study. Similarly, in a study of 97

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infants, Hollenbeck, Gewirtz, Sebris, and Scanlon (1984) found that labor medication was associated with depressed interaction behaviours with the infant for both mothers and fathers. It should be noted that, in the present study, infants who had experienced a period of illness since the birth did not show any less propensity to engage in either freeplay or the experiment. In part this may have been because these illnesses were generally minor (colds and minor stomach upsets). It is also of note that infants who were reported to ‘cry a lot’ by their mothers were no less likely to engage or complete. It is possible that these infants received as much or more attention from their mothers as more settled infants, which would explain this negative finding if the amount of attention from the mother is one contributory factor to an infant’s capacity for engagement. However, neither the findings noted above of other studies of the effects of labor medication nor the results of the present study resolve the question of the extent to which personality factors in the mother may predispose her to particular attitudes towards medication during labor and delivery, and hence influence the choices she makes. In the hospital in which the births in the present study took place, mothers played a role in deciding whether they should receive medication, the type of medication and at what point during labor it was given. Such self-selection into different treatment groups makes it problematic to clearly identify effects and their directions from group comparisons. It seems plausible that a mother who identifies strongly with her foetus early in pregnancy is likely to have more concern for the effect of the birthing experience on her infant, and also on their developing relationship. There is an attitude that a ‘natural birth’ (i.e., without medication) is more conducive to ‘bonding’, and a mother with this attitude is also likely to value engagement and interaction with her infant more highly. Similarly, a mother with this attitudinal stance is probably more likely to be able to tolerate higher levels of discom-

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fort and pain during labor and also to attribute greater capacities for emotional experience to her infant. In contrast, a mother who may be less concerned for her infant both during and after pregnancy may also be more concerned with herself and hence more anxious and sensitive to pain, making her more likely to choose an assisted labor. In this study, the assessment of a mother’s identification with her foetus during pregnancy was retrospective. While there is no particular reason to expect a particular systematic bias in retrospective reporting of this aspect, to clarify the processes involved prospective longitudinal research would seem to be the most appropriate design, starting early in pregnancy and following through to several months postpartum, with particular attention to maternal variables. While no associations (direct or indirect) were found between infants’ behavioral differences and mothers’ socio-economic status, educational level, or parity, this study does provide evidence that one important variable may be the extent to which a mother is able to establish a positive identification with her foetus early in pregnancy. The results show a lack of early identification being associated with a mother’s later disposition towards the use of analgesics during labor and also with a relatively impoverished model of her infant’s capacities for thinking and relating at 2-3 months of age. Given a pre-existing weak identification that predisposes a mother to a medicated labor and may also reduce her motivation to engage with her infant, the direct physiological effects of labor medication might contribute to a further reduction in positive, contingent interaction with her infant in the period following the birth; a concrete example of what Lester et al. (1982) called ‘synergistic effects.’ This may be a partial explanation of the large group differences observed in this study in infants’ behavior and mother-infant interaction at two months of age. Reductions in the amounts of an infant’s

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experience of periods of sustained attention and engagement with the mother may delay the development of the more general capacity to engage.

lmplica tions This study suggests that researchers wishing to use habituation experiments with young infants to examine hypotheses involving factors that overlap with or might covary with those identified in this study should consider seriously the biasing effects of failing to gain data from a significant proportion of infants recruited. This group of infants is likely to be different in important respects from the group of infants who engage with and complete experiments. Where the factors identified in this study are not relevant to the experimental hypotheses, significant reductions in ‘subject loss’ with young infants could be achieved most effectively by screening out infants whose mothers received medication during labor. The study also provides evidence that variation in infants’ engagement in experiments and the likelihood of attrition are associated with differences in mothers’ perinatal experiences, their models of their infants and aspects of their interpersonal relationships. Further, the results suggest that the extent to which a mother experiences an identification with her developing foetus early in pregnancy may serve as an indicator for these variations. The relative difficulties many young infants have in initiating and sustaining engagement in experiments were also evident in corresponding restrictions in their interactions with their mothers, suggesting that the underlying capacity may be context-general. The set of associations found is consistent with results from other studies of differences in infant behavior associated with the administration of medication during labor. However, the self-selection of treatment samples makes the interpretation of directions of effects from such data problematic. The magnitudes of the effects found, and the prevalence of the use of general anal-

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gesia in obstetrics suggest that further research is needed to examine and clarify those factors in mothers which predispose towards the use of medication during labor, and to develop a better understanding of the longer-term effects on mother-infant relationships and infant development. Acknowledgments: This research was supported by grants from the Economic and Social Research Council of Great Britain (grant ROO0234331) and from the Open University Research Committee. Sincere thanks to Linda Corlett for general assistance, conduct of interviews and coding; Matthew Stratfold and Ben Hawkridge for computer programming assistance; Ian Robertson and Rachel Reynolds for reliability coding; Peter Hobson and John Morton for consultations; the Milton Keynes Community NHS Trust and health visitors for help with recruitment; and the mothers and infants for their participation.

REFERENCES Bathurst, K., & Gottfried, A. W. (1987). Untestable subjects in child development research: developmental implications. Child Development, 58, 1144-1153.

Beebe, B., & Stem, D. N. (1977). Engagement-disengagement and early object experiences. In N. Freedman & S. Grand (Eds.), Communicative structures and psychic structures: A psychoanalytic interpretation of communication (pp. 3555). New York: Plenum Press. Bell, C., Bell, I?, & Yeung, R. (1994, June). The baby and the bathwater revisited: completion and non completion in habituation tasks. Poster

presented at the Ninth International Conference on Infant Studies, Paris, France. COX,D. R., & Oakes, D. (1984). Analysis of survival data. New York: Chapman and Hall. DeLoache, J. S., Rissman, M. W., & Cohen, L. B. (1978). An investigation of the attention-getting process in infants. Infant Behavior and Development, 1, 11-25. Dunham, P., & Dunham, F. (1990). Effects of mother-infant social interactions on infants’ subsequent contingency task performance. Child Development,

61, 785-793.

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569

Emory, E. K., S&la&man, L. J., & Fiano, K. (1996). Drug-hormone interactions on neurobehavioral responses in human neonates. Infant Behavior & Development,

19, 213-220.

Field, T. (1995). Infants of depressed mothers. Infant Behavior & Development, 18, 1-13. Hobson, R. I? (1993). Autism and the development of mind. Hove: Lawrence Erlbaum. Hollenbeck, A. R., Gewirtz, J. L., Sebris, S. L., & Scanlon, J. W. (1984). Labor and delivery medication influences parent-infant interaction in the first post-partum month. Infant Behavior & Development,

7,201-209.

Jusczyk, P W. (1985). The high amplitude sucking procedure as a methodological tool in speech perception research. In G. Gottlieb & N. A. Krasnegor (Eds.), Measurement of audition ana’ vision in thefirst year of postnatal life: A methodological overview (pp. 195-222). Norwood, NJ: Ablex. Lester, B. M., Als, H., & Brazelton, T. B. (1982). Regional obstetric anesthesia and newborn behavior: a reanalysis toward synergistic effects. Child Development, 53, 687-692.

Lewis, M., & Johnson, N. (1971). What’s thrown out with the bath water: a baby? Child Development, 42, 1053-1055.

Murray, A. D., Dolby, R. M., Nation, R. L., & Thomas, D. B. (1981). Effects of epidural anesthesia on newborns and their mothers. Child Development, 52, 71-82.

Murray, L. (1992). The impact of postnatal depression on infant development. Journal of Child

infants and its relation to infant gender and cognitive development. Journal of Child Psychology and Psychiatry, 34, 1083-l 102.

Oates, J. (1991, September). Information processing in infants. Paper presented at the British Psychological Society Annual Developmental Section Conference, Cambridge, England. Oates, J., & Corlett, L. (1992, July). Infant learning and infant-mother relationships. Paper presented at the meeting of the British Infancy Research Group, Exeter, England. Richardson, G. A., & McCluskey, K. A. (1983). Subject loss in infancy research: How biasing is it? Infant Behavior & Development, 6, 235-239. Office of Population Censuses and Surveys. (1991). Standard Occupational Classification: Vol. 3. Social Classifications and Coding Methodology. HMSO: London. Trevarthen, C. (1993). The functions of emotions in early infant communication and development. In J. Nadel & L. Camaioni (Eds.), New perspectives in early communicative development (pp. 49-81). London: Routledge. Wachs, T. D., & Smitherman, C. H. (1985). Infant temperament and subject loss in a habituation procedure. Child Development, 56, 861-867. Walton, G., Bower, N. J. A., & Bower, T. G. R. (1992). Recognition of familiar faces by newborns. Infant Behavior and Development, 15, 265-269.

Psychology and Psychiatry, 33, 543-561.

Murray, L., Kempton, C., Woolgar, M., & Hooper, R. (1993). Depressed mothers’ speech to their

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