Study on the Psychological States of Olfactory Stimuli Using Electroencephalography and Heart Rate Variability

Abstract

In the modern information society, people are constantly exposed to stress due to complex work environments and various interpersonal relationships. Aromatherapy is attracting attention as one of the methods for relieving stress using aroma. A method to quantitatively evaluate such an effect is necessary to clarify the effect of aroma on the human psychological state. In this study, we propose a method of using two biological indexes, electroencephalogram (EEG) and heart rate variability (HRV), to evaluate human psychological states during the inhalation of aroma. The purpose is to investigate the relationship between biological indexes and the psychological effect of aromas. First, we conducted an aroma presentation experiment using seven different olfactory stimuli while collecting data from EEG and pulse sensors. Next, we extracted the EEG and HRV indexes from the experimental data and analyzed them with respect to the olfactory stimuli. Our study found that olfactory stimuli have a strong effect on psychological states during aroma stimuli and that the human response to olfactory stimuli is immediate but gradually adapts to a more neutral state. The EEG and HRV indexes showed significant differences between aromas and unpleasant odors especially for male participants in their 20-30s, while the delta wave and RMSSD indexes showed potential for generalizing the method to evaluate psychological states influenced by olfactory stimuli across genders and generations. The results suggest the possibility of using EEG and HRV indexes to evaluate psychological states toward olfactory stimuli such as aroma. In addition, we visualized the psychological states affected by the olfactory stimuli on an emotion map, suggesting an appropriate range of EEG frequency bands for evaluating psychological states applied to the olfactory stimuli. The novelty of this research lies in our proposed method to provide a more detailed picture of the psychological responses to olfactory stimuli using the integration of biological indexes and emotion map, which contributes to the areas such as marketing and product design by providing insights into the emotional responses of consumers to different olfactory products.

Keywords: electroencephalography (EEG); heart rate variability (HRV); olfactory stimuli.

Figure A1

Time series plot of delta wave of one participant from the male 20s–30s group. The lines indicate the moving average values of delta wave Y-axis) against the time (X-axis) from the beginning to the end of the experiment. Different colors indicates different experiment conditions (olfactory stimuli or resting as baseline).

Figure A2

Time series plot of delta wave of one participant from the male 40s–50s group. The lines indicate the moving average values of delta wave Y-axis) against the time (X-axis) from the beginning to the end of the experiment. Different colors indicates different experiment conditions (olfactory stimuli or resting as baseline).

Figure A3

Time series plot of delta wave of one participant from the female 20s–30s group. The lines indicate the moving average values of delta wave Y-axis) against the time (X-axis) from the beginning to the end of the experiment. Different colors indicates different experiment conditions (olfactory stimuli or resting as baseline).

Figure A4

Time series plot of delta wave of one participant from the female 40s–50s group. The lines indicate the moving average values of delta wave Y-axis) against the time (X-axis) from the beginning to the end of the experiment. Different colors indicates different experiment conditions (olfactory stimuli or resting as baseline).

Figure 1

Biological sensors used in the experiment: (a) EEG sensor; (b) pulse sensor connected to Arduino board.

Figure 2

Experiment room.

Figure 3

Experimental scene (a) when attaching sensors and (b) during stimulus presentation.

Figure 4

Example of an emotion map using Attention−Meditation as Arousal index and pNN50 as Valence index. The dots with different colors indicate the different olfactory stimuli.

Figure 5

Comparison of changes in Attention−Meditation among stimuli by gender and generation groups divided into the first half (top) and latter half (bottom) of stimulus exposure time. The red lines indicate significant differences between pairs of stimuli.

Figure 6

Comparison of changes in MA Hβ/Hα among stimuli by gender and generation groups divided into the first half (top) and latter half (bottom) of stimulus exposure time. The red lines indicate significant differences between pairs of stimuli.

Figure 7

Comparison of changes in δ wave among stimuli by gender and generation groups divided into the first half (top) and latter half (bottom) of stimulus exposure time. The red lines indicate significant differences between pairs of stimuli.

Figure 8

Comparison of changes in pNN50 among stimuli by gender and generation groups divided into the first half (top) and latter half (bottom) of stimulus exposure time. The red lines indicate significant differences between pairs of stimuli.

Figure 9

Comparison of changes in RMSSD among stimuli by gender and generation groups divided into the first half (top) and latter half (bottom) of stimulus exposure time. The red lines indicate significant differences between pairs of stimuli.

Figure 10

Legend for emotion map.

Figure 11

Emotion maps using pNN50 and Attention−Meditation divided by gender and generation. The left figures show the full-scale emotion maps. The right figures show the zoomed version of the emotion maps on the left for a closer observation of the plots. The dots with different colors indicate the different olfactory stimuli as shown in the legend (Figure 10).

Figure 12

Emotion maps using pNN50 and MA Hβ/Hα divided by gender and generation. The left figures show the full-scale emotion maps. The right figures show the zoomed version of the emotion maps on the left for a closer observation of the plots. The dots with different colors indicate the different olfactory stimuli as shown in the legend (Figure 10).

Figure 13

Emotion maps using pNN50 and δ wave divided by gender and generation. The left figures show the full-scale emotion maps. The right figures show the zoomed version of the emotion maps on the left for a closer observation of the plots. The dots with different colors indicate the different olfactory stimuli as shown in the legend (Figure 10).

Figure 14

Proposed new range of arousal level in an emotion map expanding to low arousal area to visualize psychological states affected by olfactory stimuli. The triangles indicate the olfactory stimuli plotted on emotion map.