1) All organisms are born with a set of reflexes (US - UR). These relationships are invariant and biologically based. The behavior elicited by the US is called the unconditioned response (UR).

2) An unconditioned response (reflex behavior) is the behavior elicited by an unconditioned stimulus. Such behavior frequently influences the internal economy of the organism. The form is usually determined by the organism's phylogenetic history.

3) An unconditioned response (reflex behavior) is the behavior elicited by an unconditioned stimulus. Such behavior frequently influences the internal economy of the organism. The form is usually determined by the organism's phylogenetic history.

4) An unlearned response elicited by the presentation of an unconditioned stimulus.

5) A response in which the class of eliciting stimuli has this function without a history of being paired with unconditioned stimuli.