Effects of similarity grouping on attentional processes in children.

First and fifth graders sorted cards into 2 piles based on the orientation of a T figure. Cards did or did not contain irrelevant information: irrelevant information did or did not contrast in line slope with the target. The position of targets varied within arrays from 1 card to the next. Children at both grade levels sorted more slowly in the presence of contrasting irrelevant information relative to no irrelevant information, but younger children were slowed more that older ones when sorting in the presence of similar irrelevant information relative to contrasting irrelevant information. A second card-sorting experiment examined similar effects in a filtering task in which target position was constant from card to card. Effects were minimal for fifth graders, wheras first graders were slower in the presence of contrasting irrelevant information relative to no irrelevant information, and slower in the presence of similar as compared with contrasting irrelevant information. Processing differences underlying these results are discussed.