Practice—Not Task Difficulty—Mediated the Focus of Attention Effect on a Speed-Accuracy Tradeoff Task

External focus (attention to the movement effect) has been found effective in motor performance and learning. However, while some investigators have suggested that the effect of attentional focus varies with task difficulty, others reported external focus benefits regardless of difficulty. We hypothesized that attentional focus effects would vary with practice, due to changes in the individual’s processing efficiency. We had three 20-person participant groups (external focus instructions, internal focus instructions, control) practice three difficulty levels of a Fitts reciprocal tapping task over two days. Participants in the external/internal focus groups were instructed to “mentally focus on moving the pen/your hand as fast and accurately as possible,” while control participants were instructed to “mentally focus only on doing your best to achieve the task goal.” We then analyzed the effect of attentional focus by task difficulty at the initial performance (the beginning of the practice) and after learning (the retention/transfer phase), using movement time (MT) and number of error taps (Err) as performance measures. The internal focus group made more errors than the control group only at the retention/transfer phase. We found no error differences between the external and internal focus groups, and there were no MT differences between any groups. Our primary hypothesis about the differential effect of attentional focus by practice was supported. The attentional focus effect on Err differed in the retention/transfer phase from the immediate phase, suggesting that practice mediated the attentional focus effect. We discuss how information theory may supplement understanding of attentional focus interventions in motor skill acquisition.