Jeffery J. Jankowski

Attention and Recognition Memory in the 1st Year of Life: A Longitudinal Study of Preterm and Full-Term Infants.

Several aspects of visual attention and their implications for recognition memory were examined in a longitudinal sample of full-term and preterm (birth weight < 1,750 g) infants seen at 5, 7, and 12 months of age. At all 3 ages, full-terms had shorter look durations, faster shift rates, less off-task behavior, and higher novelty scores than preterms. Both groups followed similar developmental trajectories, with older infants having shorter looks and more shifts. Infants were consistent in attentional style across problems of the same type, across problems that used different types of stimuli (faces and patterns), and across the familiarization and test phases of this paired-comparison design; there was also modest cross-age stability. Shorter looks and higher shift rates during familiarization were related to better recognition memory, with shift rate adding to prediction independently of either peak or mean look. These findings underscore the importance of attention to infant information processing.

Processing Speed in the 1st Year of Life: A Longitudinal Study of Preterm and Full-Term Infants

Processing speed was assessed at 5, 7, and 12 months in full-term and preterm infants (birth-weight < 1,750 g). Speed was gauged directly in a new task by presenting infants with a series of paired faces, one that remained the same across trials and one that changed; trials continued until infants showed a consistent novelty preference. At all ages, preterms required about 20% more trials and 30% more time than full-terms to reach criterion. Among preterms, slower processing was associated with greater medical risk (e.g., respiratory distress syndrome). Developmental trajectories for speed (and attention) were similar for both groups. Thus, the deficits in processing speed previously found for preterms in childhood are already present in the 1st year of life.

Modeling a cascade of effects: the role of speed and executive functioning in preterm/full-term differences in academic achievement.

This study identified deficits in executive functioning in pre-adolescent preterms and modeled their role, along with processing speed, in explaining preterm/full-term differences in reading and mathematics. Preterms (< 1750 g) showed deficits at 11 years on a battery of tasks tapping the three basic executive functions identified by Miyake - updating/working memory, inhibition, and shifting. Confirmatory factor analysis showed that these executive functions, though correlated, were distinct from one another and from processing speed, which later proved to account for much of the intercorrelation among executive functions. In the best-fitting structural equation model, the negative effects of prematurity on achievement were completely mediated by the three executive functions and speed in a cascade of effects: prematurity → slower processing speed → poorer executive functioning (working memory) → lower achievement in math and reading.

A Cognitive Approach to the Development of Early Language

A controversial issue in the field of language development is whether language emergence and growth is dependent solely on processes specifically tied to language or could also depend on basic cognitive processes that affect all aspects of cognitive competence (domain-general processes). The present article examines this issue using a large battery of infant information-processing measures of memory, representational competence, processing speed, and attention, many of which have been shown to predict general cognition in a cohort of full-terms and preterms. Results showed that various aspects of infant memory and representational competence (a) related to language at both 12 and 36 months, (b) predicted similarly for the two groups, and (c) predicted 36-month language, independently of birth status, 12-month language, and the 12-month Bayley Mental Development Index. Additionally, the results established predictive validity for the MacArthur 12-month language measure. These findings support a domain-general view of language.

Very Low Prenatal Exposure to Lead and Mental Development of Children in Infancy and Early Childhood: Krakow Prospective Cohort Study

Background: The primary purpose of the study was to establish a possible association between very low levels of prenatal exposure to lead and mental development of children at 12, 24 and 36 months of age. Methods: The study sample consisted of 444 children born to mothers who attended ambulatory prenatal clinics in Krakow inner city in the first and second trimesters of pregnancy. We assessed exposure to lead by the cord blood lead measurements, and mental development in infancy and early childhood using the Bayley Mental Development Index (MDI). The relationship between prenatal lead exposure and MDI scores at each follow-up period was evaluated with linear multivariate regression. To test the overall effect of maternal exposure to lead during pregnancy on the Bayley test scores at 12, 24 and 36 months of age, we used the generalized estimating equations (GEE) longitudinal panel model as well. Results: The median lead level in cord blood was 1.23 μg/dl, in the range of 0.44–6.90 μg/dl. An adverse effect of prenatal lead exposure (log-transformed lead concentrations) on MDI scores at 12 months of age was of border significance (β = –5.42, 95% CI: –11.19 to 0.35). Subsequent testing of children at 24 months of age showed a significant inverse association of mental function and lead exposure (β = –7.65, 95% CI: –14.68 to –0.62). A significant deficit in cognitive function due to prenatal lead exposure was also confirmed at 36 months of age (β = –6.72, 95% CI: –12.5 to –0.89). The GEE panel model showed that the average deficit in the cognitive development attributable to lead exposure over 3 years was also significant (β = –6.62, 95% CI: –1.52 to –1.72). Mental function scores of girls were better than boys, and the effect of maternal education remained strongly significant in relation to mental function of 3-year-olds. Conclusion: The results of the study demonstrate that the neurotoxic impact of very low levels of prenatal lead exposure (below 5 μg/dl) may occur in infants and very young children, and suggest a revision of established health guidelines for prenatal lead exposure criteria.

GENDER SPECIFIC DIFFERENCES IN NEURODEVELOPMENTAL EFFECTS OF PRENATAL EXPOSURE TO VERY LOW-LEAD LEVELS: THE PROSPECTIVE COHORT STUDY IN THREE-YEAR OLDS

UNLABELLED The primary purpose of this study was to assess the relationship between very low-level of prenatal lead exposure measured in the cord blood (<5 microg/dL) and possible gender-specific cognitive deficits in the course of the first three years of life. The accumulated lead dose in infants over the pregnancy period was measured by the cord blood lead level (BLL) and cognitive deficits were assessed by the Bayley Mental Development Index (MDI). The study sample consisted of 457 children born to non-smoking women living in the inner city and the outlying residential areas of Krakow. The relationship between prenatal lead exposure and MDI scores measured at 12, 24 and 36 months of age and adjusted to a set of important covariates (gender of child, maternal education, parity, breastfeeding, prenatal and postnatal environmental tobacco smoke) was evaluated with linear multivariate regression, and the Generalized Estimating Equations (GEE) longitudinal panel model. The median of lead level in cord blood was 1.21 microg/dL with the range of values from 0.44 to 4.60 microg/dL. Neither prenatal BLL (dichotomized by median) nor other covariates affected MDI score at 12 months of age. Subsequent testing of children at 24 months of age showed a borderline significant inverse association of lead exposure and mental function (beta coefficient=-2.42, 95%CI: -4.90 to 0.03), but the interaction term (BLL x male gender) was not significant. At 36 months, prenatal lead exposure was inversely and significantly associated with cognitive function in boys (Spearman correlation coefficient=-0.239, p=0.0007) but not girls (r=-0.058, p=0.432) and the interaction between BLL and male gender was significant (beta coefficient=-4.46; 95%CI: -8.28 to -0.63). Adjusted estimates of MDI deficit in boys at 36 months confirmed very strong negative impact of prenatal lead exposure (BLL>1.67 microg/dL) compared with the lowest quartile of exposure (beta coefficient=-6.2, p=0.002), but the effect in girls was insignificant (beta coefficient=-0.74, p=0.720). The average deficit of cognitive function in the total sample over the first three years of life (GEE model) associated with higher prenatal lead exposure was also significant (beta coefficient=-3.00; 95%CI: -5.22 to -0.70). Beside prenatal lead exposure, presence of older siblings at home and prenatal environmental tobacco smoke had a negative impact on MDI score. Better maternal education showed a strong beneficial effect on the cognitive development of children. CONCLUSION the study suggests that there might be no threshold for lead toxicity in children and provides evidence that 3-year old boys are more susceptible than girls to prenatal very low lead exposure. The results of the study should persuade policy makers to consider gender-related susceptibility to lead and possibly to other toxic hazards in setting environmental protection guidelines. To determine whether the cognitive deficit documented in this study persists to older ages, the follow-up of the children over the next several years is to be carried out.

Visual Short-Term Memory in the First Year of Life: Capacity and Recency Effects.

A span task was developed to assess the amount of information infants could hold in short-term memory. In this task, infants were presented with up to 4 items in succession and then tested for recognition by successively pairing each item with a novel one. A large sample of full-terms and low-birth-weight preterms (< 1,750 g) was tested longitudinally, at 5, 7, and 12 months of age. Results were similar for both groups: (a) Longer spans were more difficult, especially at the 2 younger ages; (b) memory capacity increased over the 1st year of life--whereas less than 25% of the sample could hold as many as 3-4 items in mind at once at the younger ages, nearly half could do so by 12 months of age; (c) there was a marked recency effect (greater memory for the final item) for spans of 3 and 4 at all ages; and (d) there were modest cross-age correlations, indicating that individual differences in memory capacity showed some stability from age to age.

Modifying the distribution of attention in infants

In three experiments, the distribution and malleability of infant visual attention were studied in 5-month-olds (N = 72) while they inspected large geometric designs. In Experiment 1, we established that infants maintained their distribution of attention from a pretest to a familiarization phase. We also replicated and extended our previous findings that infants who examined targets with briefer, more numerous looks and shifts-short lookers-had novelty scores above chance, whereas long lookers demonstrated chance responding. In Experiment 2, different portions of the display were successively illuminated with red light. This manipulation induced long lookers to scan like short lookers during familiarization; they then showed novelty scores well above chance. A third experiment ruled out the simple presence of a red light as the source of this effect. In sum, then, these results suggest that the distribution of attention is malleable, and that a broader distribution of attention, as reflected in briefer and more numerous looks and shifts, can improve processing.

A longitudinal study of visual expectation and reaction time in the first year of life.

Developmental change and stability of visual expectation and reaction times (RT) were examined at 5, 7, and 12 months in a longitudinal sample of term and preterm infants (birthweight <1,750 g). Using the traditional 200-ms cut-point to separate anticipatory from reactive saccades, RTs (and their standard deviations) declined markedly over age, whereas anticipations increased. Those infants who had faster RTs were more likely to anticipate upcoming events and were more attentive (fewer trials off-task and less response variability). Crossage stability was modest for most measures from 5 to 7 and 7 to 12 months, but rarely significant from 5 to 12 months. When the cut-point was lowered to 150 ms (to accommodate recent concerns that the higher cut-point may misclassify some true RTs as anticipations), the age-related increase in anticipations disappeared. Thus, although the results indicate marked increases in processing speed with age, evidence for increasing anticipations is equivocal. Findings were similar for preterm and term infants.

Infant visual recognition memory: independent contributions of speed and attention.

Relations between infant visual recognition memory and later cognition have fueled interest in identifying the underlying cognitive components of this important infant ability. The present large-scale study examined three promising factors in this regard--processing speed, short-term memory capacity, and attention. Two of these factors, attention and processing speed (but, surprisingly, not short-term memory capacity), were related to visual recognition memory: Infants who showed better attention (shorter looks and more shifts) and faster processing had better recognition memory. The contributions of attention and processing speed were independent of one another and were similar at all ages studied--5, 7, and 12 months. Taken together, attention and speed accounted for 6%-9% of the variance in visual recognition memory, leaving a considerable, but not unexpected, portion of the variance unexplained.