The intellectual feats just spoken of, unless, indeed, they are referred to some mysterious unconscious mental operations, clearly involve a measure of volitional guidance.

All who dream frequently are occasionally aware on awaking of having greatly exercised their attention on the images presented to them during sleep.

I myself am often able to recall an effort to see beautiful objects, which threatened to disappear from my field of vision, or to catch faint receding tones of preternatural sweetness; and some dreamers allege that they are able to retain a recollection of the feeling of strain connected with such exercise of attention in sleep.
The main function of this voluntary attention in dream-life is seen in the selection of those images which are to pass the threshold of clear consciousness.

I have already spoken of a selective action brought about by the ruling emotion.

In this case, the attention is held captive by the particular feeling of the moment.