Some psychologists maintain that mental acts such as thinking are not performed in the brain alone, but that one's muscles also participate. It may be said that we think with our muscles in somewhat the same way that we listen to music with our bodies.  You surely are not surprised to be told that you usually listen to music not only with your ears but with your whole body. Few people can listen to music that is more or less familiar without moving their body or more specifically, some part of their body. Often when one listens to a symphonic concert on the radio, he is tempted to direct the orchestra even though he knows there is a competent conductor on the job.  Strange as this behavior. may be, there is a very good reason for it. One cannot derive all possible enjoyment from music unless he participates, so to speak, in its performance. The listener "feels" himself into the music with more or less noticeable motions of his body.  The muscles of the body actually participate in the mental process of thinking 'in the same way, but this participation is less obvious because it is less noticeable.Some psychologists maintain that thinking is ______.