Which term describes a simple stimulus–response relation between an antecedent stimulus and the pupil's rapid contraction in bright light?

• A. Punishment
• B. Reinforcer
• C. Reflex
• D. Reactivity

Answer: (C)

This is a reflex. A reflex is an automatic, unlearned stimulus–response connection: a specific cue (bright light) reliably triggers a rapid, involuntary response (pupil constriction). The pupillary light reflex happens quickly through the autonomic nervous system, without any need for learning or reinforcement. Punishment and reinforcer involve consequences that change future behavior, so they don’t describe this immediate, automatic link. Reactivity is a broader idea about how responsive someone is to stimuli, not the exact S–R pairing shown here. So the pupil’s rapid contraction in bright light best fits the term reflex.