Physiology of sleep

which the brain is less responsive to external stimuli. We are functionally blind during sleep with no response to visual stimuli and a decreased threshold of response to auditory stimuli. Babies have been exposed to sound of up to 100 dB, which is above the legal limit for ear protection for employees, without waking up. In adults, the process is selective demonstrating continuing cortical function. For example, a sleeping mother is woken by her crying baby but not by other louder noises.