Meditation has two distinct meanings. One meaning of meditation refers to a psychological centering device such as mantra recitation, focus on the breath, mindfulness, or a visual focus. Psychological centering devices help one feel more relaxed and centered. The other meaning of meditation is the experience of complete mental silence. Traditionally, the purpose of centering devices is to achieve complete mental silence. Although the dual meanings of meditation have been documented since at least 1977, most studies involving meditation focus on centering devices and ignore the question of whether participants experience complete mental silence.
Remarkably, the experience of complete mental silence is practically unstudied in psychology. I believe that the experience of mental silence is more common than reference works on positive psychology suggest.-Joshua Pritikin
I recently participated in Joshua's survey on the subjective passage of time and mental silence. I found it thought provoking and enjoyed going through it. You might enjoy it too. Take a look: http://tiny.cc/q2qmfw