UC San Diego

There are many well-demonstrated and detrimental effects of low-socioeconomic status (SES) on language and cognition by two years of age. Since similar effects are not usually detected during the first year of life, some suggest that early stability in this population is followed by developmental decline. This dissertation was designed to test the hypothesis that early effects of income would be detected if subtle and early-appearing social-cognitive and communicative foundations for language were thoroughly examined. A set of four studies explored this hypothesis and examined related issues pertaining to maternal input and accuracy of maternal report. Participants were an ethnically-diverse group of fifty 12-month-old infants from low-income (n=27) and middle-income (n=23) homes. Study 1 relied on four sources of data (parent report, communication sample, and two behavioral tasks) to measure comprehension vocabulary and gesture use. No differences were detected in the number of words understood or the number of different gestures used by infants, though both groups performed at-chance on the comprehension task. Infants from low-income homes used gestures significantly less often to communicate with the tester. Study 2 measured joint attention and related behaviors via the Early Social-Communication Scales (ESCS; Mundy et al., 2003). No effects of SES were detected, suggesting equivalence in the measured skills. Study 3 validated the results obtained via parent report on the MacArthur-Bates Communicative Development Inventory (CDI; Fenson et al., 1993) in Study 1, by comparing parent report to infant behaviors during tasks. No effects of income or education were detected on the accuracy of parent report. A fourth study explored verbal and nonverbal aspects of mothers' communication during 10 minutes of play with their infants. Mothers with lower income produced fewer words, and mothers with lower education produced significantly more gestures than mothers with higher education, possibly reflecting a greater tendency toward directiveness. A relation was found between maternal input and the number of communicative gestures used by infants. These studies add to our understanding of the effects of a low-SES environment during infancy. I stress the need for longitudinal studies of low- and middle-income infants that may complement the present work