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Department of Pediatrics
University of Maryland School of Medicine
737 West Lombard Street
Room 161
Baltimore, MD 21201
E-mail: mblack{at}peds.umaryland.edu
Dear Sir:
We thank Pollitt for his interest and comments regarding our investigation of the effect of micronutrient supplementation on children's development (1).
The first comment made by Pollitt concerned our use of the term "exploration." Exploration refers to infants' use of their senses, motivation, and emerging motor and mental skills to learn about their physical and social environment. Exploration and child development are thought to be interactive, bidirectional processes; exploration enriches infants' developmental skills, and, as infants' mental and motor skills mature, they are capable of more sophisticated exploration.
In our investigation of micronutrient supplementation, we were particularly interested in exploration because it plays an important role in the theory of functional isolation (2), which serves as a possible explanation for the association between nutritional deficiency and delays in children's development. Infants with low rates of exploration may miss opportunities for the physical and social enrichment that advance their developmental skills. If micronutrient supplementation promotes exploration, as we found in our recent investigation (1), it may be an important mechanism in understanding associations between micronutrient deficiency and delays in early child development.
Exploration is often assessed through the observation of infants during play. In our investigation, we observed infants during a warm-up period and during the administration of the Bayley Scales of Infant Development, II (3). We used the "orientation-engagement" factor of the Behavior Rating Scale of the Bayley Scales as an operational definition of exploration because it measures "the child's proclivities toward approaching or avoiding environmental interactions that are task-related or social in nature" (3). For 6–12-mo-old infants, the orientation-engagement factor includes 11 behaviors: social engagement, enthusiasm, persistence in completing tasks, exploration, initiative, interest in materials, energy, positive affect, lack of fearfulness, state of arousal, and stability of state of arousal. Each behavior is assessed by a trained examiner using a 5-point Likert scale after administration of the mental and motor scales of the Bayley Scales. In keeping with the psychometric properties reported for the standardization sample (3) in our investigation, the internal consistency of the orientation-engagement factor exceeded 0.87 during both observations. High scores represent endorsement of the behaviors related to the factor. Thus, a 6–12-mo-old infant with a high score in the orientation-engagement factor was observed to be alert, to be enthusiastic, to be persistent, and to have initiated interactions with materials and people in the testing setting—behaviors that are consistent with exploration in the second 6 mo of life.
The second comment by Pollitt involved the use of the Mental Developmental Index (MDI) of the Bayley Scales of Infant Development, II to examine changes in mental development related to micronutrient supplementation. The MDI represents a complex integration of empirically derived cognitive skills that are based on maturation and other theories of infant development. Although the MDI is probably the most well-standardized, widely used assessment of infant mental development in the world, evidence substantiates the low predictive validity of infant assessments of mental development, such as the MDI, for infants younger than 24 mo to subsequent measures of intelligence (4, 5). The lack of continuity may be partially explained by the multidimensional and rapidly changing aspects of infant mental development and by variations in performance during infancy, variations in tasks used to measure intellectual functioning throughout childhood, and variations in environmental challenges and opportunities that may influence development. Predictability appears to be better when investigators focus on specific cognitive, motivational, or behavioral processes (6).
One might ask why the MDI is so widely used to investigate associations between nutritional supplements and mental development despite its limited predictability. The reasons are many. First, the MDI is a well-standardized, psychometrically strong measure of infant mental development. Because it is an age-normed test, MDI scores can be used to compare the performance of children with that of same-age peers across ages, cultures, and conditions from birth through 42 mo of age. Second, MDI scores are sensitive to deviations in early development associated with environmental and nutritional conditions, such as low birth weight (7). For example, changes in MDI have been reported in response to both iron (8) and zinc (9) supplementation in infants younger than 18 mo. Third, predictability appears to be better among infants with early medical or environmental challenges, such as nutritional deprivation, than among healthy infants (10). Finally, because there is no consensus regarding the mechanisms linking micronutrient deficiency and child development (11), it is not clear what aspects of mental development should be investigated. One alternative is to combine a well-standardized assessment of mental development, such as the MDI, with measures of specific processes thought to be sensitive to the nutritional deficiencies under investigation.
We agree with Pollitt's recommendation to examine how developmental trajectories are related to children's nutrition. As we have shown among children with failure-to-thrive, cognitive development is optimally examined through pathways that begin in the first year of life, extend through at least early school age, and focus on the integration and organization of biological, nutritional, and psychosocial challenges and opportunities (12). Our investigation of changes in motor, mental, and behavioral development from 6 to 12 mo of age related to micronutrient supplementation (1) is a step in that process.
ACKNOWLEDGMENTS
Neither author had a conflict of interest.
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