Mi-Hyun Choi

Effects of gender, age, and body parameters on the ventricular volume of Korean people

The purpose of this study was to measure the average ventricular volume of normal Koreans (aged in their 20s or 40s) and to analyze the effects of gender, age, and body parameters, such as height and weight on ventricle size. Magnetic resonance brain images were recorded for 118 people in their 20s (58 men, 60 women) and 100 in their 40s (41 men, 59 women). Using automatic and manual segmentation techniques, the volumes of the lateral and the third and fourth ventricles were calculated. To investigate the different and interactive effects of gender and age on ventricular volume, two-way analysis of variance (ANOVA) with gender and age as independent variables was carried out. Multiple regression analysis was used to investigate the effect of body parameters, such as height and weight according to gender on changes in ventricular volume. The average ventricular volume for people in their 20s was 16.2 cm3, and that for people in their 40s was 24.9 cm3. The average ventricular volume for men and women was 22.9 and 18.1 cm3, respectively. The average ventricular volume for men was greater than that for women, and that for people in their 40s was greater than that in their 20s. Enlargement of the ventricles on aging was more markedly observed in men than in women. There was a positive relationship between the body height and ventricular volume for men but not for women. There was no relationship between weight and ventricular volume for either men or women.

A study on the effects of 40% oxygen on addition task performance in three levels of difficulty and physiological signals.

This study investigated the effect of 40% oxygen administration on addition task performance in three levels of difficulty and physiological signals, such as blood oxygen saturation and heart rate. The accuracy rates of the addition tasks were enhanced with 40% oxygen administration compared to 21% oxygen. As the difficulty level increased, the difference in the accuracy rate between 40% and 21% oxygen administration increased. When 40% concentration oxygen was supplied, blood oxygen saturation was increased and heart rate was decreased compared to that with 21% oxygen administration. A positive correlation was found between task performance and oxygen saturation level during the Task3 phase. This result suggests that 40% oxygen administration would lead to increases in addition task performance.

Long-term study of simulator sickness: differences in EEG response due to individual sensitivity.

This study identifies differences in the electroencephalogram (EEG) responses caused by individual sensitivity to simulator sickness. Simulator sickness was investigated by studying the changes in simulator sickness in two different subject groups (sick group and nonsick group). Subjective evaluations using the simulator sickness questionnaire and the EEG response data were gathered every 5 min while the subjects were driving at 60 km/h for 60 min in the driving graphic simulator. The response to every item of the subjective evaluation increased linearly with time; the response level in the sick group was higher than in the nonsick group. The EEG analysis showed that the sick and nonsick groups were statistically significantly different with respect to the parameter θ/total at frontal lobe and parietal lobe.

Cerebral activation and lateralization due to the cognition of a various driving speed difference: An fMRI study

This study investigated the changes of cerebral activation and lateralization due to the cognition of three driving speeds in comparison to a reference driving speed using functional magnetic resonance imaging fMRI. A driving video as a visual stimulation source was recorded with four different driving speeds in a real driving situation. The experiment consisted of three blocks and each block included a one-minute control phase and a one-minute stimulation phase. The activation area and the lateralization index were analyzed by subtracting high speed data from low speed data. Such areas as occipital, parietal and frontal lobes, which is related to visual cognition, high order visual and spatial attention (or vigilance), were activated due to the cognition of various driving speed differences. As the driving speed difference increased, the activation area increased in the areas related to spatial attention (or vigilance), such as the frontal lobe, however, changes of neuronal activation in the occipital and parietal lobes were inconsistent. As the driving speed difference increased, the absolute value of cerebral lateralization decreased. These results may provide some basic data for elucidating the brain-function mechanism related to the cognition of a various driving speed difference based on a realistic visual stimulation.

Effects of three levels of arousal on 3-back working memory task performance

This study investigated how three levels of arousal affected performance of a 3-back working memory task. Ten female and ten male university students participated in this experiment. With pictures selected from a group test, three levels of arousal were induced––i.e., tense, neutral, and relaxed emotions. Each subject was run through the procedure three times, once for each arousal level. The procedure consisted of six phases for each arousal condition: (1) Rest 1 (2 min), (2) Picture 1 (presenting emotion arousing photos for 2 min), (3) 3-back working memory task 1 (2 min), (4) Picture 2 (presenting emotion-arousing photos for 2 min), (5) 3-back working memory task 2 (2 min), and (6) Rest 2 (2 min). The skin conductance level of electrodermal activity was also measured during all phases of the experiment. The accuracy rate of 3-back working memory task performance was the highest at a neutral emotional state, followed by relaxed and then tense emotional states. There were no significant differences in reaction time.

The effects of disruption in attention on driving performance patterns: analysis of jerk-cost function and vehicle control data.

This study analyzes the effects of attention disruption factors, such as sending text messages (STM) and performing searching navigation (SN) on driving performance patterns while actively driving, centering on motion signals. To this end, it analyzes not only data on control of the vehicle including the Anterior-Posterior Coefficient of Variation (APCV), Medial-Lateral Coefficient of Variation (MLCV), and Deviation of Vehicle Speed but also motion data such as the Jerk-Cost function (JC). A total of 55 drivers including 28 males (age: 24.1 ± 1.5, driving experience: 1.8 years ± 1.7 years) and 27 females (age: 23.8 ± 2.6, driving experience: 1.5 ± 1.0) participated in this study. All subjects were instructed to drive at a constant speed (90 km/h) for 2 min while keeping a distance of 30 m from the front car also running at a speed of 90 km/h. They were requested to drive for the first 1 min and then drive only (Driving Only) or conduct tasks while driving for the subsequent 1 min (Driving + STM or Driving + SN). The information on APCV, MLCV, and deviation of speed were delivered by a driving simulator. Furthermore, the motion signal was measured using 4 high-speed infrared cameras and based on the measurement results, JCs in a total of 6 parts including left shoulder (L.shoulder), left elbow (L.elbow), left hand (L.hand), right knee (R.knee), right ankle (R.ankle), and right toe (R.toe) were calculated. Differences among the results of 3 conditions of experiment, Driving Only, Driving + STM, and Driving + SN, were compared and analyzed in terms of APCV, MLCV, Deviation of Vehicle Speed, and JC. APCV and Deviation of Vehicle Speed increased in Driving + SN, rather than in Driving Only. MLCV increased in Driving + STM and Driving + SN, rather than in Driving Only. In the case of most JCs except that of L.hand, the values increased in Driving + SN, compared to Driving Only. This study indicated that JC could be a reliable parameter for the evaluation of driving performance patterns. In addition, it was discovered that additional tasks under driving, such as STM and SN, impaired smoothness or proficiency in driving motion, thereby increasing anterior-posterior and medio-lateral variability and deviation of speed.

Changes in reaction time when using oxygen inhalation during simple visual matching tasks.

This study attempted to identify the effect of inhalation of highly concentrated oxygen on reaction time during simple visual matching tasks. Nine right-handed male graduate students (23.0+/-1.4 years) participated in the study. Two subsets of simple visual matching tasks with similar difficulties were developed. The experiment consisted of visual matching tasks performed under two conditions: normal air (22.1% oxygen) and hyperoxic air (43.2% oxygen). There was a significant decrease in reaction time in the presence of 43.2% oxygen compared with the 22.1% oxygen condition. This result supports the hypothesis that hyperoxic air increase oxygen saturation level in the blood, lead to more available oxygen to the brain, thus increase the ability of cognitive processing.

Development of a simple pressure and heat stimulator for intra- and interdigit functional magnetic resonance imaging

For this study, we developed a simple pressure and heat stimulator that can quantitatively control pressure and provide heat stimulation to intra- and interdigit areas. The developed stimulator consists of a control unit, drive units, and tactors. The control unit controls the stimulation parameters, such as stimulation types, intensity, time, and channel, and transmits a created signal of stimulation to the drive units. The drive units operate pressure and heat tactors in response to commands from the control unit. The pressure and heat tactors can display various stimulation intensities quantitatively, apply stimulation continuously, and adjust the stimulation areas. Additionally, they can easily be attached to and detached from the digits. The developed pressure and heat stimulator is small in total size, easy to install, and inexpensive to manufacture. The new stimulator operated stably in a magnetic resonance imaging (MRI) environment without affecting the obtained images. A preliminary functional magnetic resonance imaging (fMRI) experiment confirmed that differences in activation of somatosensory areas were induced from the pressure and heat stimulation. The developed pressure and heat stimulator is expected to be utilized for future intra- and interdigit fMRI studies on pressure and heat stimulation.

Activation of the limbic system under 30% oxygen during a visuospatial task: An fMRI study

The purpose of this study was to observe activation of the limbic system during the performance of visuospatial tasks under 21% O(2) or 30% O(2). Eight right-handed male college students were selected as subjects for this study. A visuospatial task was presented while brain images were scanned by a 3T fMRI system. The experiment consisted of the following two runs: a visuospatial task under normal air (21% O(2)) and a visuospatial task under hyperoxia (30% O(2)). The accuracy rate on the visuospatial task was enhanced during 30% O(2) compared to 21% O(2). The neural activation areas of the limbic system were similar in the cingulate gyrus, thalamus, limbic lobe and parahippocampal gyrus. Increased neural activation was observed in the cingulate gyrus and thalamus under 30% O(2) compared to 21% O(2). Under 30% O(2), the improvement in visuospatial task performance was related to an increase in neural activation of subcortical structures, such as the thalamus and cingulate gyrus, as well as the cerebral cortex.

Evaluation of the possibility and response characteristics of laser-induced tactile sensation

In this study, we examined the possibility and perceptual response characteristics of tactile sense induced by laser stimulation to the finger with different laser energy densities through human response experiments. 15 healthy adult males and 4 healthy adult females with an age of 22.6±2.2 years were tested. A frequency-doubled Q-switched laser was used with a wavelength of 532 nm and a 5 ns pulse width. The experimental trial spanned a total of 30 s and included a rest phase (19 s), a stimulation phase (7 s), and a response phase (4 s). During the rest phase, subjects kept their fingers comfortable. During the stimulation phase, one of three types of laser energy density (13.5, 16.6, 19.8 mJ/cm(2)) or a sham stimulation was used to irradiate the distal phalanx on the right index finger. During the response phase, the cognitive response to the laser stimulation was recorded by a PC by pressing the response button. The confusion matrix was configured to evaluate the possibility that the tactile sense was caused by the laser. In addition, changes in the response characteristics were observed according to three types of laser energy densities. From the analysis of the confusion matrix, the accuracy and sensitivity were not high. In contrast, precision and specificity were found to be high. Furthermore, there was a strong positive correlation between the laser irradiation and tactile perception, indicating that tactile sense can be induced using a laser in a mid-air manner. In addition, it was found that as the laser energy density increased, the tactile perception possibility also increased.