Age-related change of the mean level and intraindividual variability of saccadic reaction time performance in persons with intellectual disabilities.

The current study examined age-related change of saccadic reaction time (SRT) in persons with intellectual disabilities (ID). Participants were 29 persons with intellectual disabilities aged between 14 and 34 years whose IQs were between 14 and 70. Participants were divided into Group I (IQ≧35) and Group II (IQ≦34). The mean and the standard deviation of SRT (SRTM and SRTSD, respectively) reduced through adolescence in both groups. This result suggests that the speed and stability of information processing develops during adolescence irrespective of the level of ID. Although SRTM and SRTSD of Group I stabilized after adolescence, those of Group II increased after their thirties. This outcome indicates that persons with severe ID may show signs of the aging process. The results of multiple regression analyses and path analyses indicated that SRTM was influenced by both the speed of information processing and the variability of the response. However, given that the extent of increase of SRTSD in Group II was smaller as compared with that of SRTM, this increase of SRTM after the thirties in Group II appears to be mainly affected by the slowness of information processing.

Effects of age, intelligence and executive control function on saccadic reaction time in persons with intellectual disabilities.

The current research aimed to clarify the influence of age, intelligence and executive control function on the central tendency and intraindividual variability of saccadic reaction time in persons with intellectual disabilities. Participants were 44 persons with intellectual disabilities aged between 13 and 57 years whose IQs were between 14 and 70. Executive control function was evaluated by a test of sustained simple motor action. To elicit saccades, a predictive visually guided saccade paradigm was used. Intelligence and executive control function were significantly associated with saccadic reaction time. The central tendency of saccadic reaction time was negatively correlated with intelligence. The more serious the degree of executive control dysfunction was, the larger the intraindividual variability of saccadic reaction time. It is thought that intelligence and executive control function have relatively independent influences on saccadic reaction time. However, there is a possibility that the increase of intraindividual variability in saccadic reaction time due to the problem of executive control function extends the central tendency of saccadic reaction time.

Age-related trends of interference control in school-age children and young adults in the Stroop color-word test.

In this cross-sectional study, differences in interference control, one component of executive function, were investigated among three age groups, 15 early childhood (7- to 8-yr.-olds), 25 middle childhood (9- to 12-yr.-olds), and 20 young adults (21- to 30-yr.-olds). Participants were administered a computer version of the Stroop color-word test with an oral response; correct responses, response time (RT), and the interference ratio were examined. The data indicated that (1) most of the participants showed no errors in word reading, color-naming, and incongruent color-naming tasks; (2) in word-reading and color-naming tasks, RT for 7- to 8-yr.-olds was longer than that for 9- to 12-yr.-olds, while RT of 9- to 12-yr.-olds and young adults were comparable; (3) in an incongruent color-naming task, RT for 7- to 8-yr.-olds was longer than RT for 9- to 12-yr.-olds, which was longer than RT for young adults; and (4) the interference ratio was higher in 7- to 8-yr.-olds than in 9- to 12-yr.-olds, which was higher than in young adults. These results suggested the difference in interference control between early and middle childhood reported on the go/no-go task and the stop-signal procedure would be observed in the Stroop color-word paradigm as well. The utility of this modified Stroop color-word test for those with intellectual and developmental disabilities was discussed.

Verbal regulation of grip force in preschoolers.

The purpose of this study was to clarify the developmental processes in verbal regulation by preschool children. Participants were 152 typically developing children (74 boys, 78 girls) between 4 and 6 years of age (M = 5.3, SD = .8), and 30 healthy adults (15 men, 15 women) between 19 and 26 years of age (M = 20.8, SD = 1.4). In Exp. 1, the task was to regulate grip force based on quantitative instruction which implies using a scale for regulation. Participants were required to produce a half-grip force of the maximum (Task 1). In Exp. 2, the task was grip-force regulation based on nonquantitative instruction. The participants were asked to respond with a slightly weaker grip force than the maximum (Task 2) and then a further weaker grip force (Task 3) than that used on Task 2. The regulation rates produced the extent of regulation and suggest regulation by quantitative instruction may develop earlier than by nonquantitative instruction. Also, precise grip-force regulation based on the semantic aspect of instruction may be difficult for young children. The developmental changes in the rate of performance especially observed in children of 4 to 6 years indicate that the tendency to use too much grip force disappears during this preschool period. In addition, too little grip force in regulation may reflect the developmental process toward fine grasping movements.

Development of carefulness and quickness observed for a tray-carrying task.

The purpose of this study was to investigate the developmental change in performance of groups of children instructed to behave carefully and quickly in a tray-carrying task. The subjects were 69 nonhandicapped children from a kindergarten, ages 3-4 to 6 years, and 20 adult students who volunteered. Subjects were instructed to carry as fast as they could a tray with a glass of water for 3 m without a spill. The amounts of water spilled and the times taken were measured. The amounts of water spilled were hardly different within groups of children of the same ages or between age groups. But the times were different among groups: the younger ones took longer, and the difference in time between tray-carrying and normal walking was greatest for the youngest group. Children could carry the tray as carefully as adults but could not do so quickly. The nature of the representation of the instruction in relation to the behavior of children and the difference in strategy to guarantee carefulness between children and the adults are discussed.