Fitts' law-based identification of motor development stages for the upper limb: proof of concept in three age groups

Psychomotor development, including fine motor skills, progresses throughout childhood and stabilizes in adulthood. This process is closely tied to neurological maturation, with "reaching and pointing tasks" considered fundamental upper limb functions. According to Fitts' law, movement time (MT) depends on the task's index of difficulty (ID). From an Information Theory perspective, throughput (TP) reflects processing speed in reaching tasks, while error rate (ER) quantifies incorrect selections. As motor control improves, TP is expected to increase and ER to decrease, indicating greater efficiency and coordination. This study aimed to compare TP and ER across three age groups to assess motor control evolution.

Sixty participants were divided into three groups: children (5-6 years), adolescents (14-15 years), and adults (21-24 years). All participants performed a 2D reaching task on a tablet using their dominant hand, in accordance with the International Organization for Standardization (ISO) 9241-411 standard. Each participant completed 23 trials under four IDs, varying target size and distance. TP and ER were calculated and the data were statistically analyzed using an analysis of variance (ANOVA) and post-hoc tests to identify differences between groups.

TP and ER showed significant differences across age groups. Children (5-6 years) had the lowest TP (3.84 ± 0.95 bits/s) and the highest ER (17.07 ± 8.15%). Adolescents (14-15 years) demonstrated higher TP (5.88 ± 0.64 bits/s) and lower ER (5.06 ± 3.13%), while adults (21-24 years) exhibited the highest TP (6.46 ± 1.05 bits/s) and a slightly higher ER (6.81 ± 5.07%) than adolescents. A one-way ANOVA confirmed a significant effect of age on TP (F_2,57 = 47.18, p < 0.001, $$ = 0.623) and ER (F_2,57 = 22.1, p < 0.001, $$ = 0.437). Post-hoc comparisons revealed that children had significantly lower TP and higher ER than both adolescents and adults (p < 0.001). Additionally, adolescents showed significantly lower TP than adults (p < 0.05). However, no significant differences in ER were found between adolescents and adults.

The results indicate that TP and ER, derived from Fitts' law, effectively capture age-related differences in motor control across different developmental stages. These findings align with typical neuromotor development. Children show the lowest performance in both speed and accuracy, with adults outperforming both children and adolescents in processing speed, and adolescents demonstrating similar accuracy compared to adults. These metrics show potential for clinical and research applications, particularly in evaluating motor impairments or tracking rehabilitation progress in neurological conditions and advancing motor development research. Future studies should explore its use in clinical populations and across various age ranges to enhance assessment and intervention strategies.