AP® Psychology · Unit 3 · Topic 3.7
Taste Aversion, One-Trial Learning, and Habituation
Taste aversion is a biologically built-in form of classical conditioning that forms after just one pairing, even with hours between the taste and the sickness. Habituation is the opposite pattern: responding less and less to a repeated, harmless stimulus.
Ordinary classical conditioning needs the neutral stimulus and the unconditioned stimulus to happen close together in time, and it usually takes several pairings before the association sticks. Taste aversion breaks both rules. Eat something unfamiliar, get sick hours later, and the brain still links the taste to the illness after that single pairing, even though nothing else from that day gets blamed. This happens because evolution wired animals to be cautious about food specifically. Any species that waited for repeated poisonings to learn which foods were dangerous wouldn't survive long enough to pass on that trait, so the nervous system is built to form taste-illness links fast and from a single bad experience.
This readiness is called biological preparedness: organisms are predisposed to associate certain stimuli together because doing so helped their ancestors survive. Taste and nausea are a prepared pairing. A tone and a shock, or a light and a puff of air, are not prepared in this way, which is why those associations need the usual close timing and repetition. Preparedness explains why taste aversion looks like it violates the laws of learning when it actually just reveals that those laws have a built-in exception for survival-relevant pairings.
Habituation sits next to conditioning as a simpler, non-associative form of learning. No pairing of stimuli happens at all. An organism just responds less and less to a stimulus that keeps showing up without consequence, because repetition itself teaches that the stimulus can be ignored. A startle response to a loud noise fades after enough harmless repetitions, freeing attention for things that still matter.
Key terms
- Biological preparedness
- An evolved predisposition to learn certain associations, like taste and illness, more easily and quickly than others.
- Taste aversion
- A learned dislike or nausea response to a food, formed after it is paired with illness, often after just one trial.
- One-trial learning
- Forming a lasting association after a single pairing of stimuli, instead of needing repeated exposures.
- Habituation
- A gradual decrease in response to a repeated, harmless stimulus as an organism learns to ignore it.
Watch it explained
- How it worksHow does biological preparedness make some pairings learnable in a single trial?
- How it worksWalk me through a taste aversion forming with hours between the taste and the sickness.
- Common mistakeWhy doesn't the usual rule about the two stimuli being close in time apply here?
- Going furtherWhat happens to a startle response when the same loud noise repeats twenty times?
Check yourself
End of topic.