A clinician is evaluating a patient with erectile disorder. To determine whether physical factors are responsible for the condition, the clinician should measure:

A) performance anxiety.
B) masturbatory arousal.
C) spectator role.
D) nocturnal penile tumescence.

Nocturnal Penile Tumescence

The phenomenon of penile erection during sleep, often occurring during rapid eye movement (REM) sleep.

Masturbatory Arousal

Sexual excitement and stimulation achieved through self-touch or masturbation.

Spectator Role

A position taken by an individual who observes an event or situation without directly participating or influencing its outcome, often used in contexts of social interaction and psychological behavior.