Evaluation of physical and emotional responses to vibrotactile stimulation of the forearm in young adults, the elderly, and transradial amputees

• VS was applied on the forearm in young, elderly, and amputee adults.
• We evaluated the SR to VS and verified whether VS on the forearm evoked displeasure.
• All subjects' responses to the lateral site were higher than those to the medial site.
• Several subjects expressed displeasure.
• The emotional responses differed according to sex, age, or amputation.

Vibrotactile stimulation (VS) is widely used in the biomedical and biomechanics fields. Most studies have attempted to verify the effects and/or function of VS, but few studies have evaluated emotional response (ER) to VS, although emotions play a critical role in human behavior. This study aimed to evaluate the subjective response (SR) to VS in young, elderly, and amputee adults and to verify whether VS on the forearm evokes displeasure. Twenty-four young adults (YM: male 13, YF: female 11), 31 elderly subjects (EM: male 15, EF: female 16), and 19 transradial amputees (AM: male 11, AF: female 8) participated. Eight equally spaced vibration motors were attached around the circumference of the forearm (channels 1–4 on the lateral site and channels 5–8 on the medial site) and were located 25% of the proximal forearm. Vibration stimuli with frequencies ranging from 37 Hz to 258 Hz were applied. An SR 10-level test and ER (displeasure or not) test were performed. In all 3 groups, SRs to the lateral site were higher than those to the medial site (YM group, p < 0.001; YF group, p = 0.002; EM group, p < 0.001; EF group, p = 0.031; AM group, p < 0.001; AF group, p = 0.021). Additionally, SRs were saturated at certain frequencies (YM group, 149 Hz; YF and EM groups, 198 Hz; EF and AM groups, 120 Hz; AF group, 176 Hz). Several subjects (YM group, 7; YF group, 4; EM group, 2; EF group, 6; AM group, 3; AF group, 1) expressed displeasure, and ERs were different according to sex, age, or amputation. As a result, the lateral site was more sensitive to VS than the medial site, regardless of sex, age, or amputation. Furthermore, VS may evoke displeasure.