Processing speed and working memory in infancy

Two experiments were conducted to examine the relation between processing speed (PS) and working memory (WM) in eighty-two 7-month-old infants in a modification of the Visual Expectation Paradigm (VExP). For both experiments infants saw a center fixation cue followed by a peripheral target in one of four locations (horizontal left, horizontal right, oblique left, and oblique right). Experiment 1 was designed to address PS and whether the Hick paradigm is appropriate for use with infants. Using the Hick paradigm, the experiment asked whether Hick's positive slope function of RT with increasing bits of information would be found in infants. As the number of possible target locations increased from one to four, saccadic RT increased linearly in accord with Hick's finding that increased processing time was required as the number of target locations increased.The purpose of Experiment 2 was to assess WM by determining whether infants could manage more than two cue-target relations, and whether the demand to remember an increasing number of cue-target relations would affect infants' PS. Infants performed better than chance for the one-, two-, and four-cue-target relation conditions. They were also faster and produced more anticipatory saccades with two than four contingency cues. Their reaction times for the two-cue-target relation condition were the same as for the one-cue-target relation condition. However, when the number of cue-target relations increased to four, RT and percent anticipation declined significantly.A comparison of the two experiments revealed that babies benefited from cued conditions through facilitated RT and increased anticipatory saccades except when there were four cue-target relations. These results suggest that babies are sensitive to the number of target locations and the number of cue-target relations, and that an increase in locations or relations to four placed demands on their processing and memory capacity.