A conditioned response will not occur for all possible stimuli, indicating that an animal can learn to tell the difference between different stimuli. This is called __________

Which of these is a class of prescription drugs that depress central nervous system activity?

a) opioids b) stimulants c) barbiturates d) hallucinogens

As part of research, Dan is given barbiturates and asked to spend the night in a sleep laboratory where he is carefully monitored. What are researchers likely to notice?

a) He will sleep soundly and will experience an increase in Stage 4 sleep. b) His sleep is not natural in that both REM and Stage 4 are below expected levels. c) He will sleep about two hours more than normal and will have far more REM than normal. d) His sleep will be fitful and unrefreshing, although he will appear to be have slept for many hours.