The Influence Of Emotionally Linked Odors On Motor Reaction

Abstract

Many studies have been investigating the effects of odor on motor actions. However, the effect of odor-induced emotions is less well understood. Arousal and valence, representing fundamental dimensions of emotion, may affect motor reaction differently. PURPOSE: To investigate the influence of odor on reaction time and related muscle activity during elbow flexion when one has a high level of arousal or valence. METHODS: Seven healthy young males (21.7 ± 2.4 yrs) who gave a response of high arousal and negative valence to the odor of ammonia (AMN), and an opposite response to the odor of orange (ORG), were selected as subjects. The subject was quietly seated, wore a plastic mask with a vapored odor-injection pipe, and breathed naturally each of the AMN and ORG odors. A no aroma condition was also included in the test as a control. The subject placed his right arm on the desk while bending the elbow about 90 degrees, and placed his wrist on a load cell secured on the desk. The subject pressed the load cell as quick as possible after hearing a beep sound through a headphone. They repeated the elbow flexion three times with thirty seconds interval. Three trials were performed by each subject for each of the odor conditions. Force signal from the load cell and biceps brachii activity from surface EMG were recorded simultaneously. Force reaction time (FRT), muscle reaction time (MRT), peak force (PF), PF time-of-arrival, and difference between MRT and FRT (mechanical delay time) were evaluated. RESULTS: ANOVA revealed a significant odor effect in the variables of PF (F1,6 = 5.87, P < 0.05) and mechanical delay time (F1,6 = 4.67, P < 0.05). Tukey post-hoc tests revealed that AMN had a higher PF, and a shorter mechanical delay time compared to ORG (p < 0.05, p < 0.05, respectively). CONCLUSIONS: The ammonia odor is linked to arousal, which is strong enough to elevate output of muscle force as well as to facilitate muscle response to flexion of the elbow. Supported by JSPS KAKENHI Grant Number JP 18 K06454.