Competition in early exogenous orienting between 7 and 21 weeks.

Exogenous (stimulus-driven) orienting between 7 and 21 weeks of age was examined in 2 experiments using a display with multiple potential targets of attention. On each trial a small moving probe was used to draw attention to one side of the display or the other. This moving probe appeared simultaneously with 27 static bars. In the first experiment, sensitivity to the moving target was affected significantly by the spatial distribution of these red and green static bars for 14-week-olds but not for 8-week-olds. Sensitivity to the moving target was lower for 14-week-olds when most of the red bars appeared contralaterally to the moving target. This effect replicated a similar effect observed in J. L. Dannemiller (1998). The lack of a contralateral competition effect in Experiment 1 for the 8-week-olds may have occurred because I used a stronger motion stimulus for the younger infants in an attempt to hold the overall performance constant at the 2 ages. A second experiment using a weaker motion stimulus showed that this contralateral competition effect was observable over the entire age range from 7 to 21 weeks of age. Thus as early as 7 weeks of age, sensitivity for a small moving stimulus can be significantly influenced by the simultaneous presence of competing targets of attention in the visual field. Large increases in overall sensitivity were also found across the age range from 7 to 21 weeks. Results are discussed in terms of the development of putative competition mechanisms involved in exogenous orienting. Copyright 2000 Academic Press.