Simultaneous attention in the two visual hemifields and interhemispheric integration: a developmental study on 20- to 26-month-old infants.

Simultaneous attention in the two visual fields was studied in 20-, 24- and 26-month-old infants. The stimuli were pairs of simple geometrical elements. The two elements were presented simultaneously either to one visual hemifield (unilateral presentation), on the right or left side of a central fixation point, or across the two visual fields (bilateral presentation), with one component on each side of the fixation point. The task was an operant conditioning task with two conditions. In the Position condition, subjects had to decide whether the two components were horizontally aligned or not. In the Shape condition, they had to decide whether the shapes of the two components were identical or not. The results show that even the youngest group of subjects was able to reach the learning criterion in the unilateral presentation condition, whereas reaching the learning criterion in the bilateral condition becomes possible only at the age of about 24 months. No differences in the subjects' performances were found to exist between the Position and Shape conditions. It is concluded that simultaneous attention to the two visual fields and the production of a unified response emerge very late in development at about the age of 24 months.