In the present study, the ROCF test was initially conducted involving 30 healthy young individuals, in a quiet environment as Experiment 1 to examine variations in the score among different methods to memorize the figure. In such an environment, no significant differences were observed in the score between the copying and outer speech groups, which suggested the possibility of some of the former groups having used outer speech in a voice too low to be heard or moving their lips without vocalization, achieving the same effect as outer speech, and consequently leading to the absence of differences from the outer speech group. On the other hand, the score markedly varied between the mouthpiece and copying or outer speech groups. As lip movements were suppressed in the former case, the unconscious use of outer speech was also prevented, possibly leading to poor results. Based on these findings, it may be possible to enhance the effects of rehabilitation in a clinical setting by promoting patients’ memorization using outer speech to vocalize the contents of training.