4.3. Different Effects of Olfactory, Visual and Olfactory–Visual Stimuli on Human Physiological Indexes
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In this study, it was found that the changes in the physiological indicators differed considerably among the different stimulation methods. These significant differences were recorded in both the autonomic nervous system (SC) and the central nervous system (α and β brainwaves).From the perspective of SC, the SC values significantly increased under the olfactory–visual stimulus method, and this increase was significantly higher than that of the single olfactory stimulus method. It can be speculated that the olfactory–visual stimulus method caused a surge in the sympathetic nerve activity in the human ANS, which had a cumulative effect. This may mean that people become subconsciously (not subject to subjective consciousness) sympathetically excited when they smell and view garden plants, and this degree of excitement is much higher than when they purely smell or view these plants. Song found that forest-related olfactory–visual stimuli had cumulative effects on parasympathetic activity [In this study, in terms of CNS indicators and, in particular, the changes in α and β brainwaves caused by the Osmanthus fragrance, the olfactory–visual stimulus group recorded increases that fell between those of the olfactory and visual groups. Therefore, it can be concluded that the degree of activity of the human CNS when subjected to an olfactory–visual stimulus falls between that when subjected to a pure smell stimulus and a pure visual stimulus, a compromise effect. This indicates that the degree of the stability, relaxation and refreshing effects on the brain levels dominated by the subjective will when people smell Osmanthus and watch an Osmanthus landscape at the same time may fall between the degrees for pure sight and for pure smell. Research in the domain of neuroscience suggests that visual processing has a potential causal effect on olfactory perception [In this study, based on the above analysis, it can be determined that when the subjects were stimulated by Osmanthus-related olfactory–visual stimuli, they became very excited and subconsciously happy (ANS control), while such excitement was inhibited in their subjective consciousness (CNS control). As the ‘effect of images on olfaction’ is still poorly understood [