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Weight perception by newborns of depressed versus non-depressed mothers
Infant Behavior & Development 24 (2001) 305–316
Weight perception by newborns of depressed versus non-depressed mothers Maria Hernandez-Reif*, Tiffany Field, Miguel Diego, Shay Largie Touch Research Institutes, University of Miami School of Medicine, Miami, FL 33101, USA
Abstract A light-weight (2 gms) or heavier-weight (8 gms) object (vial of cotton or pellets, respectively) was placed in the right hand of 50 full-term infants (M age ⫽ 43 hr old) born to depressed (n ⫽ 27) or nondepressed mothers (Mothers’ M age ⫽ 27 yrs old). After the infants habituated to one weight by hand, they were tested with the opposite weight object. The infants of the depressed mothers did not respond to the novel weight, and only 15% of those infants showed hand movements that might have facilitated their perception of the object’s weight (e.g., hand-to-mouth or face, turning/moving of the wrist or hand). In contrast, 78% of the infants of nondepressed mothers showed hand activity that might have facilitated weight perception, and as a group, they held the novel weight longer, suggesting that they had perceived the weight change. © 2002 Elsevier Science Inc. All rights reserved.
1. Introduction Touch is the first sense to develop (Terenghi et al., 1993) and the observation that the fetus responds to a hair stroke to the palm suggests that the fetal hand is sensitive to stimulation (Humphrey, 1970). However, infant researchers argue that perception by the newborn hand may be limited because of motoric constraints (Bushnell & Boudreau, 1998; Morange & Bloch, 1996). For example, hand activity from birth to 3-months is mostly limited to the palmar grasp reflex (or the automatic closing of the fingers when the palm of the newborn hand is stimulated). Grasping may facilitate young infants’ perception of an object’s temperature, substance (that is, whether the object is rigid or elastic) or size. However, grasping alone is not believed to reveal information about an object’s weight, texture or shape, since detection of these properties is believed to involve unsupported holding, rubbing of the
* Corresponding author. E-mail address: [email protected] (M. Hernandez-Reif). 0163-6383/01/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 1 6 3 - 6 3 8 3 ( 0 1 ) 0 0 0 8 1 - 9
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fingers across the stimuli and contour following, respectively (Bushnell & Boudreau, 1991,1998; Lederman & Klatzky, 1987). Although few newborn haptic hand studies exist, at least two studies document what appears to be purposeful hand action by newborns. In these studies recordings were made of the amount of pressure newborns applied with their hands to objects differing in rigidity or texture. In the rigidity study, 2-to 4-day old newborns were found to squeeze hard objects more than soft objects (Rochat, 1987). In the texture study, 3-day-old newborns exerted greater and more frequent pressure on a smooth versus a granular (or rough) tube placed in their hands (Molina & Jouen, 1998). These findings suggest that newborns modulate their grasp according to object properties and that haptically (or by enclosing with the hand) they are sensitive to not only substance but texture information as well. Perhaps the palmar grasp serves to secure the object in the infant’s hand while pressure fluctuations stimulate touch receptors to abstract object information. Although at least the Molina and Jouen (1998) study revealed that newborns grasped smooth and rough textures differently, perhaps perception of finer gradients of texture (e.g., fine vs coarse sand paper) does not occur until later in infancy when infants have greater finger dexterity. Further study is required to determine newborns’ texture perception thresholds and hand behaviors. With respect to weight perception, our literature review revealed two related newborn studies by van der Meer and colleagues. In both studies, when free-hanging weights were attached to newborns’ wrists, the infants applied compensatory forces (that is, moved their hand up and down in the same place). This hand movement might have been sufficient to stimulate joint and stretch receptors and thus detect weight, and, appeared to be purposeful since the arm behavior was evident only if the infants could see their arm (van der Meer, Weel & Lee, 1995; 1996). Although these findings suggest that shortly after birth newborns may be voluntarily moving their arms, they do not reveal whether the newborn’s hand itself is capable of perceiving an object’s weight. Haptic weight studies with older infants reveal mixed findings. In one study, 9- and 12-month olds were presented an object to hold on three 30-sec trials, and, then, on a fourth trial, they were given a lighter or heavier exemplar of the same object (Ruff, 1984). Both age groups showed similar hand movements across the 4 trials, suggesting that they did not perceive the weight change on the last trial (Ruff, 1984). In contrast, in another study, 9- and 12-month-olds presented with varying objects (e.g., toy cars, bells, etc) were found to wave the light and heavy objects differently, suggesting that they perceived weight differences (Palmer, 1989). The mixed weight study findings may be attributed to procedural differences (e.g., length of familiarization trials, stimuli complexity, etc) and perhaps attentional constraints, such as the saliency of the object (Bushnell & Boudreau, 1998). An habituation procedure may be more sensitive than a fixed-trials procedure for familiarizing young infants with objects by hand and for highlighting particular aspects of objects. For example, Streri and her colleagues developed a habituation procedure that involved presenting the same stimulus over successive trials until there was a decline in holding or handling the object, suggesting that the infant had detected the characteristics of the object (Streri, Lhote & Dutilleul, 2000). Following the habituation response, one characteristic of the familiar stimulus was changed. If infants detected the novel aspect of the stimulus, then
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holding time was expected to increase. Using this paradigm, newborns showed a decrease in holding over successive presentations of the same object followed by an increase in holding time when a different shaped object was presented (Streri, Lhote & Dutilleul, 2000). That the neonates perceived changes in an object’s shape suggests that they may be handling and fingering objects, unless some other mechanism underlies their perception of an object’s shape. Studies with older infants revealed mixed findings on infants’ ability to perceive shape (see Bushnell & Boudreau, 1991 for a review). However, those studies did not employ a haptic habituation procedure. If habituation facilitates newborns’ perception of shape, then perhaps haptic weight perception may also be demonstrated in an habituation paradigm. The present study used an habituation paradigm to assess newborns’ perception of an object’s weight. Hand behaviors expected to facilitate weight perception were coded (e.g., transporting hand to face or mouth, and movements that might be related to unsupported holding such as opening and closing the hand and turning the hand or wrist in free space; see procedure section). The present study also compared the hand behaviors and habituation responses of newborns of depressed versus nondepressed mothers. Newborns of depressed mothers show less optimal orientation to animate and inanimate stimuli (Field, 1998) and spend less time in contact with objects (Hart et al., 1999; Hernandez-Reif, Field, Del Pino & Diego, 2000), suggesting that they might display fewer hand behaviors and thus fail to perceive an object’s weight.
2. Method 2.1. Participants Fifty women (M age ⫽ 27 yrs) and their fullterm newborns (M age ⫽ 43 hr old; R ⫽ 13– 84 hr) were recruited from a university hospital. Following informed consent, medical records were checked for the following exclusion criteria: preterm delivery (i.e., ⱕ36 gestational weeks), HIV exposure, medications during pregnancy, mother or infant medical conditions or illnesses (e.g., metabolic disorder), infant Apgar scores less than 7 at one and five minutes, surgery (other than Caesarean) and physical or metabolic anomalies. After meeting exclusion criteria, the women were assessed for current depression with the Center for Epidemiologic Studies Depression Scale (CES-D, see Assessments below). Infants were assigned to a depressed (n ⫽ 27) or a nondepressed group (n ⫽ 23) based on their mothers’ CES-D scores. Infants and mothers did not differ between groups on background and demographic variables (see Table 1). 2.2. Procedure 2.2.1. Stimuli The stimuli were two microcentrifuge plastic vials that were identical in shape, dimensions (4 cm in length ⫻ 1 cm in diameter) and texture. The inside of the vials was painted white to occlude the contents. One vial was stuffed with cotton and weighed 2 gms (light
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Table 1 Demographic data for infants and mothers Variables Maternal variables Age Ethnicity Caucasian Hispanic African American Socioeconomic status (Hollingshead) Middle Lower middle Obstetric complications score* Depression score Infant variables Age (hours) Gender Male Female Postnatal complications score*
Depressed
Non-depressed
27 (5)
26 (7)
7% 41% 52%
4% 39% 57%
p value
2
.34 .25
.20 100% 100 (18) 23 (7)
8% 92% 98 (20) 9 (3)
.37 .001
43 (19)
44 (19)
.48
52% 48% 142 (27)
56% 44% 142 (30)
.24 .54
* Higher score is optimal.
vial) and the other was stuffed with pellets and weighed 8 gms (heavy vial). Five out of five adult raters were able to distinguish the heavy from the light vial within 1–2 s of holding the vial in their right hand. 2.3. Assessments The Center for Epidemiologic Studies Depression Scale (CES-D; Radloff, 1977) is a 20-item self-report questionnaire that assesses depressive symptoms over the past week, including today. The women answered questions reflecting the frequency of symptoms on a Likert scale ranging from 0 (never, rarely), to 1 (sometimes), to 2 (often) to 3 (most of the time). Characteristic items included “I felt sad,” “I had crying spells,” “I could not shake the blues even with the help of family and friends.” CES-D scores range from 0 to 60 with scores equal to or greater than 16 reflecting depressive symptoms and a score under 12 indicating absence of depressive symptoms. Scores between zero to two and 13 to 15 were not used in our study because these are believed to reflect “faking good” and borderline scores, respectively (see Field et al., 1991). The CES-D has been correlated with the Diagnostic Interview Schedule (DIS) (Weissman, Prusoff & Newberry, 1975; Wilcox, Field, Prodomidis & Scafidi, 1998), the Beck Depression Inventory (BDI) (Wilcox et al., 1998) and most recently with frontal EEG alpha asymmetry brain wave patterns noted in depressed adults (Diego, Field & Hernandez-Reif, 2001). 2.4. Weight discrimination task The weight discrimination task consisted of a haptic habituation/dishabituation procedure administered in the newborn’s hospital bassinet. The newborn was first unswaddled, tested
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for the palmar reflex for each hand, and if necessary, roused to a quiet, awake state. Newborns who had just fallen asleep or could not be roused were tested at a later time. To test the palmar reflex, an adult’s index finger was placed into the neonate’s hand and gently pressed on the palmar surface. The palmar grasp was elicited if the neonate’s fingers flexed around the adult’s finger (see Brazelton & Nugent, 1995). Newborns who displayed a weak response or no palmar reflex were not recruited for the study. Newborns who passed the palmar reflex test were placed supine (face up), and the bassinet was tilted upright to a 45-degree angle. In preparation for testing, the newborns’ arms were gently pulled away from the body and freed to move in space. For habituation, the newborns were randomly assigned to receive the light or the heavy vial in their right hand. We chose to place the vial in the newborn’s right hand because the majority of the mothers reported being right handed, and although the literature on manual laterality in newborns is not definitive, it suggests that newborns show a tendency for right handedness (for a review on laterality, see Streri, 1993). An experimenter unaware of the infant’s group assignment (that is, the mother’s depression score) placed the assigned weight vial in the newborn’s right hand, pressing gently into the palm to trigger the enclosing of the hand over the vial. After the infant grasped the vial, the experimenter placed his/her hand (fingers down) under the infant’s elbow to facilitate the newborn’s arm movement in space and inhibit the newborn’s arm from simply resting on his/her body or bassinet. Using a stopwatch, independent observers, unaware of the newborn’s group assignment or the hypothesis of the study, recorded seconds of holding the object for each trial. A trial began when the experimenter placed the vial in the infant’s hand and ended when the infant dropped the vial or accrued 60-s of uninterrupted holding as described in haptic habituation studies by Streri and colleagues (Streri, Lhote & Dutilleul, 2000; Streri & Molina, 1993). The intertrial stimulus interval was 5 s. The dependent measure was seconds of holding on each trial. The first two trials were averaged and served as baseline. Successive trials with the same-weight-vial continued until holding on two consecutive trials was below 50% of baseline (habituation criterion). Because spontaneous recovery has been reported following habituation (Berthental, Haith & Campos, 1983; Streri, Lhote & Dutilleul, 2000), the infants were given two posthabituation trials with the same weight-vial after attaining the 50% criterion. The posthabituation trials were administered after the habituation trials and were followed by two test trials with the novel weight vial (as during the habituation, the intertrial interval was 5 s). Interobserver reliability on when to terminate a trial (dropping the vial or reaching 60 s of holding) was calculated for 26% of the infants and Cohen’s Kappa averaged 1.00 (SD ⫽ 0). Observers also recorded number of trials to reach habituation and the infant’s hand activity while holding the vial across trials. For the latter measure, categories of active and passive hand movements were used comparable to those described in the perception literature (Gibson, 1962; Lederman & Klatzky, 1987; 1990). Specifically, we defined active hand movement as a) opening and closing the hands as if squeezing or pumping the vial in the hand; when observed, this activity involved slight hand opening and closing in rapid succession that rarely led to dropping the object; this behavior has been observed in very young infants (Bushnell & Boudreau, 1998) b) bringing the hand to the face area or near the mouth, perhaps as an attempt to look at or mouth the vial (for safety reasons, newborns were
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never allowed to mouth the small vials) and/or c) turning the hand or wrist back and forth or up and down while holding the object; in the pilot study, this behavior was typically observed only for the hand holding the object. A code of passive (⫹) was recorded if only one of the above behaviors was observed or if the above behaviors occurred for less than half the trials. A passive (-) code was used if a) none of the above behaviors occurred or b) for light holding by a hand that remained partly opened for the duration of the trial. At the end of the session, the infant was assigned a global or summary hand activity score based on the most frequently recorded behavior (A, P⫹, P-). Cohen’s Kappa for hand activity calculated on 26% of the infants averaged 0.90 (SD ⫽ 0.19) between two observers across trials. Summary scores were also calculated for each participant for 1) baseline mean, calculated as average seconds of holding the vials on the first two trials (i.e., Trial 1 ⫹ 2/2), 2) number of trials to reach the habituation criterion, 3) total seconds to reach habituation, 4) average seconds of holding the vials on the two posthabituation trials, 5) average seconds of holding the vials on the two novel test trials and 6) difference score, computed by subtracting score 4 from score 5. A positive difference score indicated longer holding of the vial on the test trials (or a novelty preference), a negative score indicated longer holding of the vial of the posthabituation trials (or a familiarity preference) and a zero indicated no difference in holding for posthabituation vs test trials (or no preference). Similar summary scores have been reported in at least one other haptic habituation study (Steri, Lhote & Dutilleul, 2000).
3. Results Chi. square and t test analyses revealed no group differences on the demographic data (see Table 1). Analyses of variance (ANOVAs) failed to reveal main effects for infant gender, F (1,40) ⫽ 0.27, p ⬎ .10, or type of stimulus (light vs. heavy) presented first, F (1, 40) ⫽ 1.40, p ⬎ .10, suggesting that these variables did not affect infant responding. No significant interactions for these variables were observed (all ps’ ⬎ 0.05). ANOVAs on the habituation trials failed to reveal group differences for seconds of holding at 1) baseline mean, F (1,48) ⫽ 1.74, p ⬎ .05; 2) seconds to reach habituation, F (1,48) ⫽ 0.01, p ⬎ .05; or 3) number of trials to reach habituation, F (1,48) ⫽ 0.49, p ⬎ .05. However, differences were found for seconds of holding on posthabituation trials, F (1,48) ⫽ 5.27, p ⬍ .05, revealing that the infants of the depressed mothers held the vials longer than the infants of the nondepressed mothers on the two trials preceding the test trials (see Table 2). Inspection of the data revealed that the data were skewed and the standard deviations were large. Levene’s test of homogeneity of variances reached significance for the posthabituation trials, F (1,48) ⫽ 12.80, p ⬍ .001 and marginal significance for the difference scores, F (1,48) ⫽ 3.62, p ⫽ .06. To ensure a more powerful test of differences, parametric and nonparametric analyses were conducted. Standard parametric tests revealed that infants of depressed mothers did not differ on seconds of holding for the posthabituation versus novel test trials, t (26) ⫽ 1.48, p ⬎ .10. In contrast, newborns of nondepressed mothers showed greater holding on the novel test trials, t (22) ⫽ 2.95, p ⬍ .01 (see Fig. 1). Wilcoxon signed-rank test confirmed the parametric tests and revealed that 56% (15 out of 27) of the
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Table 2 Mean seconds of holding (standard deviations in parentheses) for infants of depressed versus non-depressed mothers during the habituation weight perception task Variables
Depressed
Non-depressed
Baseline (trials 1 ⫹ 2/2) Sec to habituation Trials to habituation Post-habituation trials (sec) Test trials (sec) Difference (test-posthab) % of infants detecting weight change
26.2 (17.7)a 105.4 (77.7)a 6 (2.7)a 13.5 (12.2)a 18.8 (18.9)a 4.7 (9.5) 56%
20.2 (13.2)a 106.1 (81.8)a 7 (2.2)a 7.1 (10.5)b 15.7 (13.5)a 9.0 (18.3)† 74%‡
Different letter subscripts indicate significantly different means at p ⬍ .05. † Indicates values on that row that differ from chance (zero) at the p ⬍ .05 (one sample t-test). ‡ Indicates values on that row that differ from chance (50%) at the p ⬍ .05 (Wilcoxon signed-rank test).
newborns of the depressed mothers, Z ⫽ 1.02, p ⬎ .10, held the novel weight-vial longer during the test trials than during the posthabituation trials, in contrast to 74% (17 out of 23) of the infants of nondepressed mothers, Z ⫽ 2.51, p ⬍ .05. Thus, overall, the newborns of depressed mothers did not respond to the novel weight object whereas newborns of nondepressed mothers responded to the weight change by greater holding. Chi-square analyses on newborns’ hand activity patterns (A, P⫹, P-) revealed that 85% of the newborns of depressed mothers versus 22% of the neonates of nondepressed mothers showed no or little hand activity (a score of P-) while holding the vial, X2 ⫽ 20.3, p ⬍ .001, (see Table 3). In contrast, 56% infants of nondepressed mothers revealed hand activity for less than 1⁄2 of the trials (P⫹) and 22% for more than 1⁄2 the trials (A) when an object was placed in their hand.
4. Discussion Neonates showed haptic habituation to a small plastic vial placed in their hands. That is, they showed a decline in holding an object over successive presentations. Habituation reflects the ability to abstract stimulus information and recognize the familiar stimulus when it is presented again (McCall & Carriger, 1993). That the newborns in the current study showed haptic habituation supports the view that from birth newborns abstract information or can learn about objects with their hands, irrespective of the palmar grasp reflex. After reaching an habituation criterion, the newborns received two additional trials with the familiar vial followed by two test trials with a heavier or lighter version of the familiar vial (novel weight trials). Newborns of nondepressed mothers held the novel weight longer, suggesting that they perceived the weight change. This is perhaps not surprising in that the newborn hand has been shown to be sensitive to other object properties, such as substance (Rochat, 1987), texture (Molina and Jouen, 1998), and shape (Streri, Lhote & Dutilleul, 2000). Our findings also revealed that the newborns of the depressed mothers failed to display a
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Fig. 1. Seconds of holding on posthabituation and test trials by infants of depressed and non-depressed mothers.
novelty response, suggesting that they did not perceive the novel weight. One reason for this might be that their habituation was a function of motor fatigue rather than haptic learning. That is, perhaps these infants reached the habituation criterion not because they perceived the vial on subsequent presentations as familiar but because they were tired of holding the object. A second explanation might be that they were not sufficiently familiar with the object during habituation. Although on average both groups decreased holding and reached the habituation criterion by the 6th or 7th trial, neonates of the depressed mothers held the objects twice as long on the posthabituation trials compared to the neonates of the nondepressed mothers. This suggests that perhaps the newborns of the depressed mothers were still abstracting information or learning about the object on the 8th and 9th trials. This longer holding may be comparable to longer looking on visual habituation trials, which has been associated with
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Table 3 Hand activity patterns for infants of depressed versus non-depressed mothers (% of infants displaying activity) Hand activity
Groups Depressed
Active (observed for ⁄ of the trials) squeezing (opening & closing hand), bringing object to face or mouth, turning hand or wrist Passive ⫹ (observed for ⬍ than 1⁄2 the trials) showing at least one of the above activities Passive ⫺ showing little or no hand activity
Non-depressed
12
4%
22%
11%
56%
85%
22%
poorer recognition memory (Rose, Feldman & Jankowski, 2001). Longer habituation may also reflect slower learning. Perhaps additional posthabituation trials or a more stringent habituation criterion may benefit some infant groups. The need to develop or improve upon methodologies for testing newborns is imperative to further the study of sensory development and newborn abilities. The null findings for the newborns of depressed mothers suggest that they have difficulty haptically discriminating objects. Why would newborns of depressed mothers have difficulty perceiving objects by touch? At least one other study on newborns of depressed mothers showed that they mouthed objects less (Hernandez-Reif et al., 2000) and a study on one-year-old infants of depressed mothers revealed that they touched and played with objects less (Hart et al., 1999). The findings from these two studies suggest a continuity from the newborn period to one-year of age for infants of depressed mothers in their inattentiveness or lack of motivation to haptically explore or touch objects. Other studies reveal that newborns of depressed mothers orient less well to visual and auditory stimuli (Abrams et al., 1995; Lundy et al., 1999) and show less motor tone, flat affect and lower activity levels (see review by Field, 1998). Moreover, newborns of depressed mothers differ from infants of nondepressed mothers in biochemistry (Field, 1998) and EEG brain wave patterns (Jones et al., 1997; Jones et al., 1998). Taken together, these findings suggest a biological predisposition that may alter how young infants born to depressed mothers perceive and interact with their environment. Clearly, more research is required to determine the impact and intensity of maternal depression effects on infants’ sensory development. That in the present study only 15% of infants of depressed mothers (compared to 78% of infants of nondepressed mothers) showed any hand activity (P⫹ and A combined) when grasping the vial supports the view that they are less active. This lesser activity may reflect less attention to objects placed in their hand or the need for more intense stimuli. Bushnell and Boudreau (1998) have argued that attentional considerations may explain infants’ failure to detect properties of objects, such as weight. If newborns of depressed mothers have higher sensory thresholds they may require more arousing stimuli to respond (Abrams et al., 1995). The nondiscriminatory responses of the newborns of depressed mothers may have related to that the weight difference was not sufficiently salient. A future study might examine the threshold hypothesis and whether more distinct weight differences (e.g., 2 gms vs 20 gms)
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would lead to greater attention and discrimination. A future study might also examine whether attracting the newborns’ attention to the object in their hand (perhaps making the object more visually attractive) enhances exploration and facilitates detection of the weight change. In a recent study, illuminating portions of a display enhanced the performance of 5-month old infants who had previously demonstrated chance responding (Jankowski, Rose & Feldman, 2001). The lesser activity or attentiveness by infants of depressed mothers may be related to their biochemistry (e.g., lowered dopamine levels, dopamine being an activating neurotransmitter). Perhaps the newborns of depressed mothers have central nervous system (CNS) involvement that may impact on attention, exploration and threshold. For example, cocaineexposed newborns show deficits in attention and elevated sensory thresholds that have been linked to CNS involvement and dopamine depletion (Karmel & Gardner, 1996). Interestingly, at birth neonates of depressed mothers show lower dopamine values and more depressive-like symptoms (Lundy et al., 1999), suggesting CNS involvement. If their underlying problem is inattentiveness or an inability to regulate attention, this would explain the null findings in that a fundamental aspect of learning is attending. An infant who is not attentive (or unaware) of an object placed in his/her hands would be unlikely to perceive the properties of the object (Bushnell & Boudreau, 1991). In the same vein, hand activity may be the mechanism by which the newborns of nondepressed mothers perceived the novel weight. Lederman and Klatzky’s (1987; 1993) study on the identification of objects by touch reveals that enclosure and lifting of an object (or unsupported holding) are basic movements for perceiving weight change. In our study, 78% of the newborns of nondepressed mothers at some point in the procedure either lifted the object to their face or mouth area or moved their hand or wrist while holding the object. These activities may have facilitated the weight perception and may reflect their attending to the object in their hand. That so many of the newborns of nondepressed mothers showed patterns suggestive of hand exploration is in itself interesting and counters the view that newborns lack certain exploratory behaviors such as unsupported holding. Future newborn haptic studies are needed to verify these observations. Because less manipulation and exploration of objects have been associated with longerterm cognitive deficits (Ruff, 1984), testing newborn infants’ manipulation of objects by hand, in addition to assessing their mothers’ depression status, might identify “at risk” newborns who may benefit from early intervention. Like preterm infants (Rose, Feldman, & Jankowski, 2001) and cocaine-exposed newborns (Karmel & Gardner, 1996), infants of depressed mothers may show deficits in attention and perception.
Acknowledgments We thank the infants and their mothers who participated in this study. This research was supported by an NIMH Senior Research Scientist Award (MH#00331) and an NIMH Research Grant (MH#46586) to Tiffany Field and funds from Johnson & Johnson to the Touch Research Institutes.
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Rochat, P. (1987). Mouthing and grasping in neonates: evidence for the early detection of what hard or soft substances afford for action. Infant Behavior and Development, 10, 435– 449. Rose, S., Feldman, J., Jankowski, J. (2001). Attention and recognition memory in the 1st year of life: a longitudinal study of preterm and full-term infants. Developmental Psychology, 37, 135–151. Ruff, H. (1984). Infants’ manipulative exploration of objects: effects of age and object characteristics. Developmental Psychology, 20, 9 –20. Ruff, H. (1984). Preterm infants’ manipulative exploration of objects. Child Development, 55, 1166 –1173. Streri, A. (1993). Seeing, reaching, touching. The relations between vision and touch in infancy. Massachusetts: MIT Press. Streri, A., Lhote, M., & Dutilleul, S. (2000). Haptic perception in newborns. Developmental Science, 3, 319 –327. Streri, A., & Molina, M.,(1993). Visual and tactual transfer between objects and pictures in 2-month-old infants. Perception, 22, 1299 –1318. Terenghi, G., Sundaresan, M., Moscoso, G., & Polak, J. M. (1993). Neuropepides and neuronal marker in cutaneous innervation during human doetal development. Journal of Comp Neurology, 22, 595– 603. Van der Meer, A., Van der Weel, F., & Lee, D. (1995). The functional significance of arm movements in neonates. Science, 267, 693– 695. Van der Meer, A., Van der Weel, F., & Lee, D. (1996). Lifting weights in neonates: developing visual control of reaching. Scandinavian Journal of Psychology, 37, 424 – 436. Weissman, M., Prusoff, B., & Newberry, P. (1975). Comparison of the CES-D with standardized depression rating scales at three points in time. Technical Report, Yale University, Contract. ASH 74 –166, NIMH. Wilcox, H., Field, T., Prodomidis, M., & Scafidi, F. (1998). Correlations between the BDI and the CES-D in a sample of adolescent mothers. Adolescence, 33, 565–574.
Weight perception by newborns of depressed versus non-depressed mothers Maria Hernandez-Reif*, Tiffany Field, Miguel Diego, Shay Largie Touch Research Institutes, University of Miami School of Medicine, Miami, FL 33101, USA
Abstract A light-weight (2 gms) or heavier-weight (8 gms) object (vial of cotton or pellets, respectively) was placed in the right hand of 50 full-term infants (M age ⫽ 43 hr old) born to depressed (n ⫽ 27) or nondepressed mothers (Mothers’ M age ⫽ 27 yrs old). After the infants habituated to one weight by hand, they were tested with the opposite weight object. The infants of the depressed mothers did not respond to the novel weight, and only 15% of those infants showed hand movements that might have facilitated their perception of the object’s weight (e.g., hand-to-mouth or face, turning/moving of the wrist or hand). In contrast, 78% of the infants of nondepressed mothers showed hand activity that might have facilitated weight perception, and as a group, they held the novel weight longer, suggesting that they had perceived the weight change. © 2002 Elsevier Science Inc. All rights reserved.
1. Introduction Touch is the first sense to develop (Terenghi et al., 1993) and the observation that the fetus responds to a hair stroke to the palm suggests that the fetal hand is sensitive to stimulation (Humphrey, 1970). However, infant researchers argue that perception by the newborn hand may be limited because of motoric constraints (Bushnell & Boudreau, 1998; Morange & Bloch, 1996). For example, hand activity from birth to 3-months is mostly limited to the palmar grasp reflex (or the automatic closing of the fingers when the palm of the newborn hand is stimulated). Grasping may facilitate young infants’ perception of an object’s temperature, substance (that is, whether the object is rigid or elastic) or size. However, grasping alone is not believed to reveal information about an object’s weight, texture or shape, since detection of these properties is believed to involve unsupported holding, rubbing of the
* Corresponding author. E-mail address: [email protected] (M. Hernandez-Reif). 0163-6383/01/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 1 6 3 - 6 3 8 3 ( 0 1 ) 0 0 0 8 1 - 9
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fingers across the stimuli and contour following, respectively (Bushnell & Boudreau, 1991,1998; Lederman & Klatzky, 1987). Although few newborn haptic hand studies exist, at least two studies document what appears to be purposeful hand action by newborns. In these studies recordings were made of the amount of pressure newborns applied with their hands to objects differing in rigidity or texture. In the rigidity study, 2-to 4-day old newborns were found to squeeze hard objects more than soft objects (Rochat, 1987). In the texture study, 3-day-old newborns exerted greater and more frequent pressure on a smooth versus a granular (or rough) tube placed in their hands (Molina & Jouen, 1998). These findings suggest that newborns modulate their grasp according to object properties and that haptically (or by enclosing with the hand) they are sensitive to not only substance but texture information as well. Perhaps the palmar grasp serves to secure the object in the infant’s hand while pressure fluctuations stimulate touch receptors to abstract object information. Although at least the Molina and Jouen (1998) study revealed that newborns grasped smooth and rough textures differently, perhaps perception of finer gradients of texture (e.g., fine vs coarse sand paper) does not occur until later in infancy when infants have greater finger dexterity. Further study is required to determine newborns’ texture perception thresholds and hand behaviors. With respect to weight perception, our literature review revealed two related newborn studies by van der Meer and colleagues. In both studies, when free-hanging weights were attached to newborns’ wrists, the infants applied compensatory forces (that is, moved their hand up and down in the same place). This hand movement might have been sufficient to stimulate joint and stretch receptors and thus detect weight, and, appeared to be purposeful since the arm behavior was evident only if the infants could see their arm (van der Meer, Weel & Lee, 1995; 1996). Although these findings suggest that shortly after birth newborns may be voluntarily moving their arms, they do not reveal whether the newborn’s hand itself is capable of perceiving an object’s weight. Haptic weight studies with older infants reveal mixed findings. In one study, 9- and 12-month olds were presented an object to hold on three 30-sec trials, and, then, on a fourth trial, they were given a lighter or heavier exemplar of the same object (Ruff, 1984). Both age groups showed similar hand movements across the 4 trials, suggesting that they did not perceive the weight change on the last trial (Ruff, 1984). In contrast, in another study, 9- and 12-month-olds presented with varying objects (e.g., toy cars, bells, etc) were found to wave the light and heavy objects differently, suggesting that they perceived weight differences (Palmer, 1989). The mixed weight study findings may be attributed to procedural differences (e.g., length of familiarization trials, stimuli complexity, etc) and perhaps attentional constraints, such as the saliency of the object (Bushnell & Boudreau, 1998). An habituation procedure may be more sensitive than a fixed-trials procedure for familiarizing young infants with objects by hand and for highlighting particular aspects of objects. For example, Streri and her colleagues developed a habituation procedure that involved presenting the same stimulus over successive trials until there was a decline in holding or handling the object, suggesting that the infant had detected the characteristics of the object (Streri, Lhote & Dutilleul, 2000). Following the habituation response, one characteristic of the familiar stimulus was changed. If infants detected the novel aspect of the stimulus, then
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holding time was expected to increase. Using this paradigm, newborns showed a decrease in holding over successive presentations of the same object followed by an increase in holding time when a different shaped object was presented (Streri, Lhote & Dutilleul, 2000). That the neonates perceived changes in an object’s shape suggests that they may be handling and fingering objects, unless some other mechanism underlies their perception of an object’s shape. Studies with older infants revealed mixed findings on infants’ ability to perceive shape (see Bushnell & Boudreau, 1991 for a review). However, those studies did not employ a haptic habituation procedure. If habituation facilitates newborns’ perception of shape, then perhaps haptic weight perception may also be demonstrated in an habituation paradigm. The present study used an habituation paradigm to assess newborns’ perception of an object’s weight. Hand behaviors expected to facilitate weight perception were coded (e.g., transporting hand to face or mouth, and movements that might be related to unsupported holding such as opening and closing the hand and turning the hand or wrist in free space; see procedure section). The present study also compared the hand behaviors and habituation responses of newborns of depressed versus nondepressed mothers. Newborns of depressed mothers show less optimal orientation to animate and inanimate stimuli (Field, 1998) and spend less time in contact with objects (Hart et al., 1999; Hernandez-Reif, Field, Del Pino & Diego, 2000), suggesting that they might display fewer hand behaviors and thus fail to perceive an object’s weight.
2. Method 2.1. Participants Fifty women (M age ⫽ 27 yrs) and their fullterm newborns (M age ⫽ 43 hr old; R ⫽ 13– 84 hr) were recruited from a university hospital. Following informed consent, medical records were checked for the following exclusion criteria: preterm delivery (i.e., ⱕ36 gestational weeks), HIV exposure, medications during pregnancy, mother or infant medical conditions or illnesses (e.g., metabolic disorder), infant Apgar scores less than 7 at one and five minutes, surgery (other than Caesarean) and physical or metabolic anomalies. After meeting exclusion criteria, the women were assessed for current depression with the Center for Epidemiologic Studies Depression Scale (CES-D, see Assessments below). Infants were assigned to a depressed (n ⫽ 27) or a nondepressed group (n ⫽ 23) based on their mothers’ CES-D scores. Infants and mothers did not differ between groups on background and demographic variables (see Table 1). 2.2. Procedure 2.2.1. Stimuli The stimuli were two microcentrifuge plastic vials that were identical in shape, dimensions (4 cm in length ⫻ 1 cm in diameter) and texture. The inside of the vials was painted white to occlude the contents. One vial was stuffed with cotton and weighed 2 gms (light
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Table 1 Demographic data for infants and mothers Variables Maternal variables Age Ethnicity Caucasian Hispanic African American Socioeconomic status (Hollingshead) Middle Lower middle Obstetric complications score* Depression score Infant variables Age (hours) Gender Male Female Postnatal complications score*
Depressed
Non-depressed
27 (5)
26 (7)
7% 41% 52%
4% 39% 57%
p value
2
.34 .25
.20 100% 100 (18) 23 (7)
8% 92% 98 (20) 9 (3)
.37 .001
43 (19)
44 (19)
.48
52% 48% 142 (27)
56% 44% 142 (30)
.24 .54
* Higher score is optimal.
vial) and the other was stuffed with pellets and weighed 8 gms (heavy vial). Five out of five adult raters were able to distinguish the heavy from the light vial within 1–2 s of holding the vial in their right hand. 2.3. Assessments The Center for Epidemiologic Studies Depression Scale (CES-D; Radloff, 1977) is a 20-item self-report questionnaire that assesses depressive symptoms over the past week, including today. The women answered questions reflecting the frequency of symptoms on a Likert scale ranging from 0 (never, rarely), to 1 (sometimes), to 2 (often) to 3 (most of the time). Characteristic items included “I felt sad,” “I had crying spells,” “I could not shake the blues even with the help of family and friends.” CES-D scores range from 0 to 60 with scores equal to or greater than 16 reflecting depressive symptoms and a score under 12 indicating absence of depressive symptoms. Scores between zero to two and 13 to 15 were not used in our study because these are believed to reflect “faking good” and borderline scores, respectively (see Field et al., 1991). The CES-D has been correlated with the Diagnostic Interview Schedule (DIS) (Weissman, Prusoff & Newberry, 1975; Wilcox, Field, Prodomidis & Scafidi, 1998), the Beck Depression Inventory (BDI) (Wilcox et al., 1998) and most recently with frontal EEG alpha asymmetry brain wave patterns noted in depressed adults (Diego, Field & Hernandez-Reif, 2001). 2.4. Weight discrimination task The weight discrimination task consisted of a haptic habituation/dishabituation procedure administered in the newborn’s hospital bassinet. The newborn was first unswaddled, tested
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for the palmar reflex for each hand, and if necessary, roused to a quiet, awake state. Newborns who had just fallen asleep or could not be roused were tested at a later time. To test the palmar reflex, an adult’s index finger was placed into the neonate’s hand and gently pressed on the palmar surface. The palmar grasp was elicited if the neonate’s fingers flexed around the adult’s finger (see Brazelton & Nugent, 1995). Newborns who displayed a weak response or no palmar reflex were not recruited for the study. Newborns who passed the palmar reflex test were placed supine (face up), and the bassinet was tilted upright to a 45-degree angle. In preparation for testing, the newborns’ arms were gently pulled away from the body and freed to move in space. For habituation, the newborns were randomly assigned to receive the light or the heavy vial in their right hand. We chose to place the vial in the newborn’s right hand because the majority of the mothers reported being right handed, and although the literature on manual laterality in newborns is not definitive, it suggests that newborns show a tendency for right handedness (for a review on laterality, see Streri, 1993). An experimenter unaware of the infant’s group assignment (that is, the mother’s depression score) placed the assigned weight vial in the newborn’s right hand, pressing gently into the palm to trigger the enclosing of the hand over the vial. After the infant grasped the vial, the experimenter placed his/her hand (fingers down) under the infant’s elbow to facilitate the newborn’s arm movement in space and inhibit the newborn’s arm from simply resting on his/her body or bassinet. Using a stopwatch, independent observers, unaware of the newborn’s group assignment or the hypothesis of the study, recorded seconds of holding the object for each trial. A trial began when the experimenter placed the vial in the infant’s hand and ended when the infant dropped the vial or accrued 60-s of uninterrupted holding as described in haptic habituation studies by Streri and colleagues (Streri, Lhote & Dutilleul, 2000; Streri & Molina, 1993). The intertrial stimulus interval was 5 s. The dependent measure was seconds of holding on each trial. The first two trials were averaged and served as baseline. Successive trials with the same-weight-vial continued until holding on two consecutive trials was below 50% of baseline (habituation criterion). Because spontaneous recovery has been reported following habituation (Berthental, Haith & Campos, 1983; Streri, Lhote & Dutilleul, 2000), the infants were given two posthabituation trials with the same weight-vial after attaining the 50% criterion. The posthabituation trials were administered after the habituation trials and were followed by two test trials with the novel weight vial (as during the habituation, the intertrial interval was 5 s). Interobserver reliability on when to terminate a trial (dropping the vial or reaching 60 s of holding) was calculated for 26% of the infants and Cohen’s Kappa averaged 1.00 (SD ⫽ 0). Observers also recorded number of trials to reach habituation and the infant’s hand activity while holding the vial across trials. For the latter measure, categories of active and passive hand movements were used comparable to those described in the perception literature (Gibson, 1962; Lederman & Klatzky, 1987; 1990). Specifically, we defined active hand movement as a) opening and closing the hands as if squeezing or pumping the vial in the hand; when observed, this activity involved slight hand opening and closing in rapid succession that rarely led to dropping the object; this behavior has been observed in very young infants (Bushnell & Boudreau, 1998) b) bringing the hand to the face area or near the mouth, perhaps as an attempt to look at or mouth the vial (for safety reasons, newborns were
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never allowed to mouth the small vials) and/or c) turning the hand or wrist back and forth or up and down while holding the object; in the pilot study, this behavior was typically observed only for the hand holding the object. A code of passive (⫹) was recorded if only one of the above behaviors was observed or if the above behaviors occurred for less than half the trials. A passive (-) code was used if a) none of the above behaviors occurred or b) for light holding by a hand that remained partly opened for the duration of the trial. At the end of the session, the infant was assigned a global or summary hand activity score based on the most frequently recorded behavior (A, P⫹, P-). Cohen’s Kappa for hand activity calculated on 26% of the infants averaged 0.90 (SD ⫽ 0.19) between two observers across trials. Summary scores were also calculated for each participant for 1) baseline mean, calculated as average seconds of holding the vials on the first two trials (i.e., Trial 1 ⫹ 2/2), 2) number of trials to reach the habituation criterion, 3) total seconds to reach habituation, 4) average seconds of holding the vials on the two posthabituation trials, 5) average seconds of holding the vials on the two novel test trials and 6) difference score, computed by subtracting score 4 from score 5. A positive difference score indicated longer holding of the vial on the test trials (or a novelty preference), a negative score indicated longer holding of the vial of the posthabituation trials (or a familiarity preference) and a zero indicated no difference in holding for posthabituation vs test trials (or no preference). Similar summary scores have been reported in at least one other haptic habituation study (Steri, Lhote & Dutilleul, 2000).
3. Results Chi. square and t test analyses revealed no group differences on the demographic data (see Table 1). Analyses of variance (ANOVAs) failed to reveal main effects for infant gender, F (1,40) ⫽ 0.27, p ⬎ .10, or type of stimulus (light vs. heavy) presented first, F (1, 40) ⫽ 1.40, p ⬎ .10, suggesting that these variables did not affect infant responding. No significant interactions for these variables were observed (all ps’ ⬎ 0.05). ANOVAs on the habituation trials failed to reveal group differences for seconds of holding at 1) baseline mean, F (1,48) ⫽ 1.74, p ⬎ .05; 2) seconds to reach habituation, F (1,48) ⫽ 0.01, p ⬎ .05; or 3) number of trials to reach habituation, F (1,48) ⫽ 0.49, p ⬎ .05. However, differences were found for seconds of holding on posthabituation trials, F (1,48) ⫽ 5.27, p ⬍ .05, revealing that the infants of the depressed mothers held the vials longer than the infants of the nondepressed mothers on the two trials preceding the test trials (see Table 2). Inspection of the data revealed that the data were skewed and the standard deviations were large. Levene’s test of homogeneity of variances reached significance for the posthabituation trials, F (1,48) ⫽ 12.80, p ⬍ .001 and marginal significance for the difference scores, F (1,48) ⫽ 3.62, p ⫽ .06. To ensure a more powerful test of differences, parametric and nonparametric analyses were conducted. Standard parametric tests revealed that infants of depressed mothers did not differ on seconds of holding for the posthabituation versus novel test trials, t (26) ⫽ 1.48, p ⬎ .10. In contrast, newborns of nondepressed mothers showed greater holding on the novel test trials, t (22) ⫽ 2.95, p ⬍ .01 (see Fig. 1). Wilcoxon signed-rank test confirmed the parametric tests and revealed that 56% (15 out of 27) of the
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Table 2 Mean seconds of holding (standard deviations in parentheses) for infants of depressed versus non-depressed mothers during the habituation weight perception task Variables
Depressed
Non-depressed
Baseline (trials 1 ⫹ 2/2) Sec to habituation Trials to habituation Post-habituation trials (sec) Test trials (sec) Difference (test-posthab) % of infants detecting weight change
26.2 (17.7)a 105.4 (77.7)a 6 (2.7)a 13.5 (12.2)a 18.8 (18.9)a 4.7 (9.5) 56%
20.2 (13.2)a 106.1 (81.8)a 7 (2.2)a 7.1 (10.5)b 15.7 (13.5)a 9.0 (18.3)† 74%‡
Different letter subscripts indicate significantly different means at p ⬍ .05. † Indicates values on that row that differ from chance (zero) at the p ⬍ .05 (one sample t-test). ‡ Indicates values on that row that differ from chance (50%) at the p ⬍ .05 (Wilcoxon signed-rank test).
newborns of the depressed mothers, Z ⫽ 1.02, p ⬎ .10, held the novel weight-vial longer during the test trials than during the posthabituation trials, in contrast to 74% (17 out of 23) of the infants of nondepressed mothers, Z ⫽ 2.51, p ⬍ .05. Thus, overall, the newborns of depressed mothers did not respond to the novel weight object whereas newborns of nondepressed mothers responded to the weight change by greater holding. Chi-square analyses on newborns’ hand activity patterns (A, P⫹, P-) revealed that 85% of the newborns of depressed mothers versus 22% of the neonates of nondepressed mothers showed no or little hand activity (a score of P-) while holding the vial, X2 ⫽ 20.3, p ⬍ .001, (see Table 3). In contrast, 56% infants of nondepressed mothers revealed hand activity for less than 1⁄2 of the trials (P⫹) and 22% for more than 1⁄2 the trials (A) when an object was placed in their hand.
4. Discussion Neonates showed haptic habituation to a small plastic vial placed in their hands. That is, they showed a decline in holding an object over successive presentations. Habituation reflects the ability to abstract stimulus information and recognize the familiar stimulus when it is presented again (McCall & Carriger, 1993). That the newborns in the current study showed haptic habituation supports the view that from birth newborns abstract information or can learn about objects with their hands, irrespective of the palmar grasp reflex. After reaching an habituation criterion, the newborns received two additional trials with the familiar vial followed by two test trials with a heavier or lighter version of the familiar vial (novel weight trials). Newborns of nondepressed mothers held the novel weight longer, suggesting that they perceived the weight change. This is perhaps not surprising in that the newborn hand has been shown to be sensitive to other object properties, such as substance (Rochat, 1987), texture (Molina and Jouen, 1998), and shape (Streri, Lhote & Dutilleul, 2000). Our findings also revealed that the newborns of the depressed mothers failed to display a
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Fig. 1. Seconds of holding on posthabituation and test trials by infants of depressed and non-depressed mothers.
novelty response, suggesting that they did not perceive the novel weight. One reason for this might be that their habituation was a function of motor fatigue rather than haptic learning. That is, perhaps these infants reached the habituation criterion not because they perceived the vial on subsequent presentations as familiar but because they were tired of holding the object. A second explanation might be that they were not sufficiently familiar with the object during habituation. Although on average both groups decreased holding and reached the habituation criterion by the 6th or 7th trial, neonates of the depressed mothers held the objects twice as long on the posthabituation trials compared to the neonates of the nondepressed mothers. This suggests that perhaps the newborns of the depressed mothers were still abstracting information or learning about the object on the 8th and 9th trials. This longer holding may be comparable to longer looking on visual habituation trials, which has been associated with
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Table 3 Hand activity patterns for infants of depressed versus non-depressed mothers (% of infants displaying activity) Hand activity
Groups Depressed
Active (observed for ⁄ of the trials) squeezing (opening & closing hand), bringing object to face or mouth, turning hand or wrist Passive ⫹ (observed for ⬍ than 1⁄2 the trials) showing at least one of the above activities Passive ⫺ showing little or no hand activity
Non-depressed
12
4%
22%
11%
56%
85%
22%
poorer recognition memory (Rose, Feldman & Jankowski, 2001). Longer habituation may also reflect slower learning. Perhaps additional posthabituation trials or a more stringent habituation criterion may benefit some infant groups. The need to develop or improve upon methodologies for testing newborns is imperative to further the study of sensory development and newborn abilities. The null findings for the newborns of depressed mothers suggest that they have difficulty haptically discriminating objects. Why would newborns of depressed mothers have difficulty perceiving objects by touch? At least one other study on newborns of depressed mothers showed that they mouthed objects less (Hernandez-Reif et al., 2000) and a study on one-year-old infants of depressed mothers revealed that they touched and played with objects less (Hart et al., 1999). The findings from these two studies suggest a continuity from the newborn period to one-year of age for infants of depressed mothers in their inattentiveness or lack of motivation to haptically explore or touch objects. Other studies reveal that newborns of depressed mothers orient less well to visual and auditory stimuli (Abrams et al., 1995; Lundy et al., 1999) and show less motor tone, flat affect and lower activity levels (see review by Field, 1998). Moreover, newborns of depressed mothers differ from infants of nondepressed mothers in biochemistry (Field, 1998) and EEG brain wave patterns (Jones et al., 1997; Jones et al., 1998). Taken together, these findings suggest a biological predisposition that may alter how young infants born to depressed mothers perceive and interact with their environment. Clearly, more research is required to determine the impact and intensity of maternal depression effects on infants’ sensory development. That in the present study only 15% of infants of depressed mothers (compared to 78% of infants of nondepressed mothers) showed any hand activity (P⫹ and A combined) when grasping the vial supports the view that they are less active. This lesser activity may reflect less attention to objects placed in their hand or the need for more intense stimuli. Bushnell and Boudreau (1998) have argued that attentional considerations may explain infants’ failure to detect properties of objects, such as weight. If newborns of depressed mothers have higher sensory thresholds they may require more arousing stimuli to respond (Abrams et al., 1995). The nondiscriminatory responses of the newborns of depressed mothers may have related to that the weight difference was not sufficiently salient. A future study might examine the threshold hypothesis and whether more distinct weight differences (e.g., 2 gms vs 20 gms)
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would lead to greater attention and discrimination. A future study might also examine whether attracting the newborns’ attention to the object in their hand (perhaps making the object more visually attractive) enhances exploration and facilitates detection of the weight change. In a recent study, illuminating portions of a display enhanced the performance of 5-month old infants who had previously demonstrated chance responding (Jankowski, Rose & Feldman, 2001). The lesser activity or attentiveness by infants of depressed mothers may be related to their biochemistry (e.g., lowered dopamine levels, dopamine being an activating neurotransmitter). Perhaps the newborns of depressed mothers have central nervous system (CNS) involvement that may impact on attention, exploration and threshold. For example, cocaineexposed newborns show deficits in attention and elevated sensory thresholds that have been linked to CNS involvement and dopamine depletion (Karmel & Gardner, 1996). Interestingly, at birth neonates of depressed mothers show lower dopamine values and more depressive-like symptoms (Lundy et al., 1999), suggesting CNS involvement. If their underlying problem is inattentiveness or an inability to regulate attention, this would explain the null findings in that a fundamental aspect of learning is attending. An infant who is not attentive (or unaware) of an object placed in his/her hands would be unlikely to perceive the properties of the object (Bushnell & Boudreau, 1991). In the same vein, hand activity may be the mechanism by which the newborns of nondepressed mothers perceived the novel weight. Lederman and Klatzky’s (1987; 1993) study on the identification of objects by touch reveals that enclosure and lifting of an object (or unsupported holding) are basic movements for perceiving weight change. In our study, 78% of the newborns of nondepressed mothers at some point in the procedure either lifted the object to their face or mouth area or moved their hand or wrist while holding the object. These activities may have facilitated the weight perception and may reflect their attending to the object in their hand. That so many of the newborns of nondepressed mothers showed patterns suggestive of hand exploration is in itself interesting and counters the view that newborns lack certain exploratory behaviors such as unsupported holding. Future newborn haptic studies are needed to verify these observations. Because less manipulation and exploration of objects have been associated with longerterm cognitive deficits (Ruff, 1984), testing newborn infants’ manipulation of objects by hand, in addition to assessing their mothers’ depression status, might identify “at risk” newborns who may benefit from early intervention. Like preterm infants (Rose, Feldman, & Jankowski, 2001) and cocaine-exposed newborns (Karmel & Gardner, 1996), infants of depressed mothers may show deficits in attention and perception.
Acknowledgments We thank the infants and their mothers who participated in this study. This research was supported by an NIMH Senior Research Scientist Award (MH#00331) and an NIMH Research Grant (MH#46586) to Tiffany Field and funds from Johnson & Johnson to the Touch Research Institutes.
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