Effects of the body position and learning on auditory directional discrimination in a three-D spatial working memory task

Previously, we have investigated the auditory spatial information processing performance of human beings by using a 3D spatial working memory task (3D auditory directional delayed non-matching-to-sample task) and its control apparatus. The previous studies showed that the auditory directional discrimination performance was higher in the upright position (90-degree body position) than in the lying position (0-degree sideways body position). In the present study, in order to analyze this body positional effect more closely, we developed a movable 3D sound stimulator and control apparatus, which can change the body position (angle) between 0 degree (supinely) and 90 degree. Using this equipment, we conducted the 3D spatial working memory task at 0-, 45- and 90-degree body positions. Furthermore, we repeated the identical tasks in 3 sessions for each body position, and examined the changes in auditory directional discrimination performance accompanying the repetition of experiments (learning effect). The results showed that the subjects could easily discriminate whether or not the two stimulus tones came from identical directions in all body positions. The results also showed that the directional discrimination performance gradually became higher from the 0-degree (supine) body position to the 90-degree body position. The directional discrimination performance improved from the beginning to the end of the experiment in each respective body positions, suggesting a learning effect dependent on body position