Processing Speed of Infants with High and Low Communicative Skills

Abstract

Background and rationale. While experimental psychology has focused on the study of processes that determine the individual’s behaviour in specific experimental situations, the studies concerning individual differences have analyzed the stability of observed differences on performance between individuals, in particular those which can be generalized through diverse situations or tasks (Williams et al., J Exp Anal Behav 90:219–231, 2008). Several studies have shown that processing speed is a useful variable to study how age and ability in a specific task affect the performance in more general cognitive tasks such as language (Zheng et al., Psyc Bulletin & Rev 7:113–120, 2000). In studies with infants for example, it is known that younger children are slower to process linguistic stimuli compared with older children while they respond to the same task (Fernald et al. 1998); and that there is a positive relation between vocabulary development and processing speed during the second year of life (Fernald et al., Child Dev 72(4):1003–1015, 2001; Fernald et al., Dev Psychol 42(1):98–116, 2006; Zangl et al., J Cogn Dev 6(2):179–208, 2005).

The present study analyzes the individual differences in processing speed of infants and its relation with the development of communicative skills during the first year of life. Methods. Using the Intermodal Preferential Looking paradigm (IPL), an experimental task was designed whose goal was to determine the time that infants took to look at the target in a word learning task, as well as the relation between processing speed and the vocabulary of the infants measured with the MacArthur Inventory (CD-I). The infants were assigned to one of two groups depending on their performance on the comprehension subscale of the CDI-I Inventory (Group 1: below percentile 25; Group 2: above percentile 75).

Results. Results showed that the infants who scored below percentile 25 on the CDI-I Inventory presented a higher processing time in the experimental task; on the contrary, the group of infants who scored above percentile 75 on the Inventory, showed a lower processing time. In general, the infants above percentile 75 on the comprehension subscale were 11% faster than their peers below percentile 25, in the word learning task.

Discussion. The findings shown here suggest that once age is controlled, differences in the infants’ communicative skills at early ages such as 12 months reflect differences in linguistic skills, such as word learning. Finally, the findings showed here support the study of individual differences in infants’ processing speed in the first year of life in specific experimental tasks.