US High School Psychology Practice Exam

Stage 1 sleep is the lightest phase of sleep and serves as the transition between wakefulness and deeper sleep. During this stage, a person can be easily awakened and may still be aware of their surroundings, which allows for the possibility of hearing external sounds, such as parts of a lecture, while dozing off. As the brain transitions into the deeper stages of sleep, such as Stage 2 and beyond, the individual's responsiveness to external stimuli decreases significantly, making it less likely that they would hear or process sounds from their environment. Therefore, Stage 1 sleep is characterized by this unique blend of light sleep and awareness, enabling a person to still register sounds even as they transition into sleep.