Color contrast, luminance contrast and competition within exogenous orienting in 3.5-month-old infants

Exogenous (stimulus driven) orienting shows evidence of competition in earl y infancy. The infant's tendency to detect and orient to a small moving sti mulus is affected significantly by the colors and spatial distribution of o ther static stimuli in the visual field. In previous work infants consisten tly showed lower detection of the moving stimulus when the side of the fiel d contralateral to this stimulus contained mostly red bars on a white backg round. The competition in this case was much stronger than when the contral ateral field contained mostly green bars. In this experiment we tested the hypothesis that the strength of this competition effect is determined prima rily by the color contrasts of the static bars. We found partial support fo r this hypothesis. The contralateral competition was abolished when the col or contrasts of the red and green bars were made more equal by presenting t hem on yellow backgrounds. This elimination of contralateral competition on ly occurred, however, when there was substantial luminance contrast also pr esent between these bars and their backgrounds. The competition effect pers isted when the luminance contrast was reduced to near zero leaving primaril y color contrast. We also found evidence that this competition effect can b e produced only by luminance contrast, although the effect was significant only in one of the two experiments. Infants had a difficult time detecting movement when the moving stimulus was defined primarily by color rather tha n by luminance contrast. These experiments tell us about how different basi c features like color, contrast, and movement are weighted in the initial s election of targets of attention.