What key aspect differentiates operant conditioning from classical conditioning?

The key aspect that differentiates operant conditioning from classical conditioning is the focus on voluntary behavior modification. In operant conditioning, behaviors are influenced by the consequences that follow them. This means that actions are shaped and maintained through rewards (reinforcements) or punishments, which individuals consciously engage with and respond to in order to either increase or decrease a behavior.

In contrast, classical conditioning involves the association of involuntary responses with neutral stimuli, where a subject learns to associate a conditioned stimulus with an unconditioned stimulus to elicit a conditioned response. This process operates primarily on reflexive or automatic behaviors rather than voluntary actions.

The other answer choices highlight features that are not fundamentally what distinguish operant from classical conditioning. For example, the involvement of unconscious processes better describes classical conditioning, where responses are less about choice and more about automatic reactions. Similarly, the measurement of physiological responses is more relevant to behavioral assessments in various contexts rather than being a definitive characteristic differentiating the two forms of conditioning. Thus, the emphasis on modifying voluntary behaviors through consequences is what distinctly defines operant conditioning.