Kyle L. Snow

Information processing through the first year of life : a longitudinal study using the visual expectation paradigm

This Monograph uses a developmental function approach to describe age-related change and individual differences in infant information processing during the first year of life. The Visual Expectation Paradigm (VExP) is used to measure speed of information processing, response variability, and expectancy formation. Eye-movement reaction times and anticipatory saccades were gathered from 13 infants assessed monthly from 2 to 9 months and then again at 12 months. Analysis of response patterns demonstrated the applicability of the paradigm throughout the age range studied. Converging operations strongly indicate that the traditional estimate of the minimum time required for infants to initiate a saccade to a peripheral stimulus may be as much as 100 milliseconds (ms) too long. Moreover, the newly estimated minimum of 133 ms does not appear to change during the 2-12-month period. Reanalysis of the present data and past research reveals that the new, shorter minimum reaction time is unlikely to affect findings based on mean reaction time. However, using the traditional minimum reaction time will inflate estimates of percentage anticipation, especially in infants older than 5 months. Group and individual growth curves are described through quantitative models of four variables: reaction time, standard deviation of reaction time, percentage anticipation, and anticipation latency. Developmental change in reaction time was best described by an asymptotic exponential function, and evidence for a local asymptote during infancy is presented. Variability in reaction time was found to decline with age, independent of mean reaction time, and was best described by a polynomial function with linear and quadratic terms. Anticipation showed little lawful change during any portion of the age span, but latency to anticipate declined linearly throughout the first year. Stability of individual differences was strong between consecutive assessments of mean reaction time. For nonconsecutive assessments, stability was found only for the 6-12-month period. Month-to-month stability was inconsistent for reaction-time variability and weak for both anticipation measures. Analyses of individual differences in growth curves were carried out using random regressions for the polynomial models. The only significant individual difference (in growth curves) was found for reaction-time variability. Parameter estimates from the exponential models for reaction time suggested two or three developmental patterns with different exponential trajectories. This finding indicates that the strong form of the exponential growth hypothesis, which states that processing speed develops at the same rate for all individuals, does not hold for the first year of life. In the concluding chapter, Grices Variable Criterion Model (Grice, 1968) is used to integrate three key findings: regular age changes in mean reaction time and variability but no age change in the minimum reaction time. It is argued that the rate of growth of sensory-detection information is developmentally constant during much of the first year but that age changes occur in the level and spread of the distribution of response threshold values. The unique strengths of the paradigm are discussed, and future directions are suggested for further developing the paradigm itself and for using it as a tool to study broad issues in infant cognition.

The Relationships Between Childhood Sexual Abuse, Social Anxiety, and Symptoms of Posttraumatic Stress Disorder in Women

The relationships between childhood sexual abuse, social anxiety, and symptoms of posttraumatic stress disorder were examined in a sample of 313 undergraduate women. Thirty-one percent of the women reported some form of sexual abuse in childhood. Women with a history of sexual abuse reported more symptoms of anxiety, distress in social situations, and posttraumatic stress disorder than other women. Women who experienced attempted or actual intercourse reported more avoidance than women with no history of abuse and women with exposure only, and more PTSD symptoms than all other groups of women. Women who experienced fondling reported more PTSD symptoms than women with no history of abuse. Pressure, age of onset of abuse, abuse by a family friend, and abuse by other perpetrators were all significant abuse characteristics in predicting adult social anxiety. Implications of these results for research and interventions are discussed.