Development of Intra-Individual Process Metrics in a Serious-Video Game Intervention for ADHD

(1) Background: Attention-deficit/hyperactivity disorder (ADHD) is characterized by persistent difficulties related to inattention, hyperactivity, and impulsivity, which significantly impair daily functioning. The primary objective of this study is to examine the utility of intra-individual metrics as indicators of dynamic cognitive regulation during the intervention with a serious video game (The Secret Trail of Moon, MOON). (2) Methods: Performance data were collected from participants with ADHD enrolled in a randomized clinical trial. Within the MOON group, intra-individual metrics were derived from repeated gameplay sessions of a continuous performance task. For each participant, simple linear regression models were used to estimate the slope of performance across repeated exposures to the task. Slopes were interpreted as indicators of intra-individual change over time. The within-subject standard deviation was also calculated to observe how much a person’s performance fluctuates between sessions. (3) Results: A total of 76 patients with ADHD participated in the clinical trial and were randomized in a 1:1 ratio (MOON: n = 38, 50% and control: n = 38, 50%). The mean performance index of the MOON group (M = 0.88, SD = 0.09) indicates a generally high level of response accuracy, with moderate inter-individual variability across participants. Notably, moderate intra-individual variability (e.g., RT variability, lapse-related indices) was observed, suggesting fluctuations in attentional control despite stable average performance. The absence of linear improvement should not be interpreted as a lack of intervention effect, but rather as evidence of rapid task familiarization and ceiling effects. (4) Conclusions: Intra-individual variability may be a key metric for understanding attentional control in ecological, game-based environments. In this context, performance variability and attentional stability emerge as more sensitive indicators of cognitive regulation than mean-level changes.