A university professor researching sleep disorders occasionally taught class after spending whole nights working in a laboratory. She found lecturing after such nights difficult: she reported that she felt worn out and humorless, and she had difficulty concentrating and finding the appropriate words. After several weeks of lectures, she asked her students to guess which lectures had been given after nights without sleep. Interestingly, very few students were able to correctly identify them. Which one of the following statements is most strongly supported by the information above? ['No one can assess the overall effects of sleep deprivation on a particular person as well as that sleep-deprived person can.', 'University students in a lecture audience tend to be astute observers of human behavior.', 'Occasional sleep deprivation is not as debilitating as extended sleep deprivation.', 'The subjective effects of occasional sleep deprivation are more pronounced than are its effects on overt behavior.']