Visual search and the N2pc in children

Abstract

While there is growing understanding of visual selective attention in children, some aspects such as selection in the presence of distractors are not well understood. Adult studies suggest that when presented with a visual search task, an enhanced negativity is seen beginning around 200 ms (the N2pc) that reflects selection of a target item among distractors. However, it is not known if similar selective attention-related activity is seen in children during visual search. This study was designed to investigate the presence of the N2pc in children. Nineteen children (ages 9-12 years) and 21 adults (ages 18-22 years) completed a visual search task in which they were asked to attend to a fixation surrounded by both a target and a distractor stimulus. Three types of displays were analyzed at parietal electrodes P7 and P8; lateral target/lateral distractor, lateral target/midline distractor, and midline target/lateral distractor. Both adults and children showed a significant increased negativity contralateral compared to ipsilateral to the target (reflected in the N2pc) in both displays with a lateral target while no such effect was seen in displays with a midline target. This suggests that children also utilized additional resources to select a target item when distractors are present. These findings demonstrate that the N2pc can be used as a marker of attentional object selection in children.

Fig. 1

Stimulus display for the task when the target color is red

Fig. 2

Event-related potentials (ERPs) elicited in the 600-ms interval after search array onset at posterior electrode sites P7/8 in adults (left column) and children (right column). (a) ERPs for search arrays containing a midline target and lateral distractor, (b) lateral target and midline distractor, and (c) lateral target and lateral distractor

Fig. 3

Difference waves at posterior electrode sites P7/8 in adults (left column) and children (right column) in the 600-ms interval after search array onset