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Received Jan 16, 2018; Revised Mar 27, 2018; Accepted Apr 24, 2018
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1. Introduction
Previous studies revealed a link between the left and right cerebral hemispheres and depression, providing a better understanding of the neuropathology of depression. Liotti and Tucker’s results of a side-by-side simple response task showed that the left visual field response is impaired in healthy people with a depressive mood and in mild unipolar depressive patients, while the right visual field of healthy people with a depressive mood and in mild unipolar depressive patients did not show a slow response time for the viewing material [1]. A related EEG study in emotion recognition tasks also found that higher right frontal activity was associated with negative emotions and higher left frontal activity was associated with positive emotions [2]. When the healthy subjects were induced to experience negative emotions, the alpha power of the right frontal lobe was more inhibited than the left frontal lobe was, whereas in cases of positive emotions, the asymmetry of alpha power in the relevant region showed opposite results. These findings indicate that individuals with higher right frontal lobe activity have stronger negative emotions than individuals with higher left frontal lobe activity have [3–5]. The above findings discuss the relationship between the left and right hemispheres and emotions. The right frontal activity is enhanced in depressive patients or healthy subjects who were induced to experience depressive emotions.
There are also differences in information processing between the left hemisphere and the right hemisphere. The information processing of the left hemisphere is characterized by sequence, analysis, and logic; the information processed by the right hemisphere is parallel, holistic, and intuitive [6]. Based on the differences between left and right brain information processing, many experiments were designed to determine the characteristics of different hemispheric cognitive functions. The tachistoscopic visual half-field technique [7] and the dichotic listening technique [8] have been used to examine the effects of each hemisphere in visual and auditory processing. Bruder et al. used dichotic listening and visual half-field tasks to detect the perceptual asymmetry of depressive patients. The...