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 lim- ited maternal perceptions of their infants’ capacities, but were not associated with analgesic medication during labor.

infants attrition low engagement experiments free-play risk factors

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

experiment. The more demanding the experi-

mental task, for example in the length of sustained attention required of the infant, the

more likelihood there is of subject loss. Signif- icant rates of attrition persist despite infancy researchers having developed the necessary

expertise in the design of laboratory environ- ments, 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 ISSN 0163-6383 Copyright 0 1998 ABLEX Publishing Corporation All rights of reproduction in any form reserved.

556 INFANT BEHAVIOR & DEVELOPMENT Vol. 21, No. 4, 1998

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 diffi-

culties (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 thir- teen months. It has been suggested that levels

of infants’ engagement in cognitive tasks have

correlates in a range of maternal factors

including mothers’ perceptions of their

infants’ cognitive and affective capacities and

their behavior with their infants (Wachs & Smitherman, 1985).

The capacity to engage with another per-

son, or with some other contingently respon-

sive ‘object’ (as in an infant-control experiment) involves both the ability to main-

tain 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 intensi- ties 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

development of primary intersubjective under-

standing (Trevarthen, 1993) and the experi-

ence of ‘relatedness’ with another (Hobson,

1993). Relatively stable differences in young

infants’ capacities to maintain this sort of rela-

tion with another agent might be one source of

the variation found in their behavior in experi-

ments 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) sug-

gested that such differences between infants

may be connected with qualities of the rela-

tionship between mother and infant, particu-

larly with the mother’s projective

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 attrib-

uted more ‘person’ qualities to their infants,

having also identified with their infants in this

way during the early months of their preg-

nancy.

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 responsive-

ness they experience with the mother. In addi-

tion, experiences of the birth are likely still to

be affecting both mother and infant. Interfer-

ence 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 out- lined, as exemplified by the accumulating evi-

dence on the effects of post-natal depression

on mothers’ and infants’ behavior in the short

and long term (Murray, 1992; Murray, Kemp-

ton, 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 557

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

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 complica- tion 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

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 Popula- tion 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 unclassi-

fied (member of armed forces).

Procedures

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 sig- nal amplifier connected to a standard non-ven- tilated 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


similar technique has also been used with digi- tized 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.

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.

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 giv- ing it a name. They were asked about the details of labor and delivery, and asked to

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%). Demo- graphic details and a pregnancy, delivery and post-partum medical history were also taken.

Video Records and Coding

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

1. eyes closed, loss of limb, body, neck tone.

2. eyes closed but retains limb, body, neck tone.

3. eyes partly or wholly open, no attention to screen or elsewhere

4. attention fixed on edge of screen or other visual feature/shifting attention

5. attention 20% to stimulus display / 80% elsewhere



8. 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. Reli- ability coefficients for independent blind cod-


ers using this scale on a 10% random sample

of both the free-play and experiment video recordings were 85% or greater.

Measures

Number of Trials Completed

An individual trial was treated as ‘non-

completed’ 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 crite-

rion 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 col- lapsed into two categories: completion (all tri-

als 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.

Engagement 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.

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-

tion between four and six months of pregnancy.

Mothers’ Perceptions of their lnfan ts’

Emotional 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 cate- gorisation reflected a natural division in mother’s responses.

Mothers’ Perceptions of their Infants’

Feelings for Them

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’ 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

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


during labor in contrast to the other two main categories). All mothers in the normal vaginal

delivery with medication group received intra- muscular injection of meptazinol during labor

for general analgesia. The epidural anesthesia used was bupivacaine, administered by cathe- ter 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 medica-

tion 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 preg-

nancy, 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

= .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 preg-

nancy complications, nor were any trends evi-

dent. Infants who had experienced an illness

since their birth, or who were described by

their mothers as crying a lot or otherwise diffi-

cult 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’ per-

formance was approximately evenly distrib-

uted 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’ capaci-

ties 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 com-

pleted a mean of 5.8 trials (SD = 3.2), Mann-

Whitney U = 94.5, p = .0006. Caesareatiepi-

dural 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 signifi-

cance, Mann-Whitney U = 136, p = .092 (see Table 2).

Infants who were described by their moth-

ers as only capable of experiencing primitive emotions completed a mean of 6 trials (SD = 3.3) while those described as capable of expe-

riencing more complex emotions completed a

mean of 8.7 trials (SD = 2.7), Mann-Whitney U = 118, p = Xl054 (see Table 3).


TABLE 1 Number of trials completed and engagement scores for infants in non-medicated,

medicated and caesarean/epidural labor categories

n Trials Completed

Engagement (Experiment)

Engagement (Free-play)

No medication

M SD

9.06 2.58

5.40 2.30

4.32 1.85

General analgesic

M SD

6.50 3.06

4.97 1.72

4.00 .70

Caesareadepidural

M SD P

4.44 2.83 .0004

6.23 1.59 ns

4.00 .a3 ns

TABLE 2 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 P

n Trials Completed 7.93 3.71 6.64 3.06 ns

Engagement (Experiment) 6.32 1.47 4.91 2.07 .017

Engagement (Free-play) 4.92 1.63 3.53 .Vl .OOl

TABLE 3 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

n Trials Completed 6.04 3.30 8.67 2.68 .005

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 right- censored 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-

562 INFANT BEHAVIOR & DEVELOPMENT Vol. 21, No. 4,1998

TABLE 4

Number of trials completed and engagement scores for infants attributed with loving

feelings towards their mothers and infants attributed with ambivalent or negative feelings

n Trials Completed

Engagement (Experiment)

Engagement (Free-play)

Ambivalent/negative love

M SD M SD P

6.39 3.46 8.69 2.66 .025

5.03 2.21 6.16 1.28 ns

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/non- completion, 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

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

P 1 -

‘E .-

; .8 No medication

S S .6 -

E F .4 - 6

c!! .P ‘r ra, .2-

General analgesia

g:: go

CaesarearVepidural

cl.c o- I 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.


2 l-

‘iz ‘5 E .8 - I ul

Early identification 5 .6 -

z 5 E .4 -

.G .g None/late

tzal .2- gg

a’.5 o- I I I I 1 I I I I I I

0 1 2 3 4 5 6 7 8 9 10

Trial number

FIGURE 2 Attrition of infants whose mothers identified with them early in pregnancy and infants where identific- aion was late or lacking.

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

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

2 l-

.e ‘iii

.8 -

E 2

Complex

v) 2 .6 -

I 3 E .4 -

e5 5 .E .2- Primitive

g ::

LE.: o- I I I I I I I I I I I

0 1 2 3 4 5 6 7 8 9 10

Trial number

FIGURE 3 Attrition of infants attributed with complex emotions by mothers and infants attributed with primitive emotions.


0 .G .f

E 2

Love

0-J

5 .6 -

E 5 $

.4 - Ambivalent

=E .P ‘C negative

ra, .2- ;:

r5.G o- I I I I I I I 1 I I I

01234567 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 covari- ates in a proportional hazards multiple regres- sion analysis, with the hazard rate for the no-

medication 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 Mantel- Cox x2 (1,42) = 6.5, p = .Ol, Caesareadepidu- ral 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

Risk factors for Attrition 565

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 free- play 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. Sec- ond, 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 llZday- olds 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

566 INFANT BEHAVIOR & DEVELOPMENT Vol. 21, No. 4,1998

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-month-

old infants’ levels of performance in a non-

social 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 vari-

ations in infants’ attention in experiments are

not simply due to randomly distributed state

changes but may indicate enduring differ-

ences. 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 num-

bers 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 atten-

tion to and engage with another agent, and

another process to do with the infant sustain-

ing 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

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


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 free-

play 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 medica-

tion 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-

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 sen-

sitive 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 pro-

cesses involved prospective longitudinal

research would seem to be the most appropri-

ate design, starting early in pregnancy and fol-

lowing through to several months post-

partum, with particular attention to maternal

variables.

While no associations (direct or indirect)

were found between infants’ behavioral differ-

ences 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 foe-

tus 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 rela-

tively 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 medica-

tion 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


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 wish- ing 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 correspond- ing 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-

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 Uni- versity Research Committee. Sincere thanks to Linda Corlett for general assistance, conduct of interviews and coding; Matthew Stratfold and Ben Hawkridge for computer program- ming 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.

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