My experience has been that visual vividness comes and goes with mental fatigue.  When I am well rested, comfortable, and haven&#x27;t spent much time thinking earlier in the same day, I can close my eyes and plainly see detail in childhood toys, places I&#x27;ve traveled, faces, and even illustrations from high school textbooks. When I&#x27;m tired or have spent the whole day thinking intensely, I can barely remember what my roommates faces look like. I suspect that the ability to vividly imagine images is an expensive neural process that becomes much more difficult when the brain is not at peak performance.<p>Curiously, my ability to recall sounds and music does not seem to change with fatigue. Whether I&#x27;m feeling energetic or super tired, I can bring to mind any song I&#x27;m familiar with or hear arbitrary words spoken in the voices of my close friends and family. My suspicion here is that simulating sound is much less expensive and therefore the ability not as easily degraded. That would not be surprising considering the anecdotal point that I can get headaches from too much sunlight but not too much noise (unless it interrupts my sleep).