AP Syllabus focus:
‘Behavior can be shaped through reinforcement, but biological tendencies may limit learning through instinctive drift.’
Operant learning can build complex behaviours by rewarding small steps toward a goal.
Labeled photograph of a cumulative recorder used to produce cumulative response records in operant research. The device exemplifies how operant behavior is quantified continuously over time rather than summarized as a single score. Linking shaping to this measurement logic highlights why reinforcement that is immediate and contingent produces clearer, more reliable changes in recorded response patterns. Source
However, inherited action patterns can compete with trained responses, placing natural limits on what reinforcement can reliably produce.
Shaping: building behaviour with reinforcement
Core idea
Shaping: An operant conditioning procedure that reinforces successive approximations of a target behaviour, gradually requiring closer matches to the goal response.
Shaping is used when the target behaviour is unlikely to occur spontaneously. Instead of waiting for the full behaviour, the trainer creates a pathway of manageable steps that the learner can perform and be reinforced for.
Successive approximations in practice
Specify the terminal behaviour in observable, measurable terms (what counts as “done”).
Assess the starting point (what the organism already does that is closest to the goal).
Select an effective reinforcer and ensure it is available immediately after the desired response.
Reinforce the first approximation (a small action that moves in the right direction).
Raise the criterion gradually:
stop reinforcing the earlier approximation
reinforce only a closer approximation
repeat until the terminal behaviour occurs reliably
Minimise errors and frustration by increasing difficulty in small increments and keeping reinforcement frequent early on.
Fade extra cues (e.g., prompts or trainer presence) so the behaviour occurs under the intended natural conditions.
Why reinforcement timing matters
Reinforcement is most effective when it is immediate and contingent (delivered because of the response).
Delayed or inconsistent reinforcement can strengthen unintended behaviours, especially when approximations are ambiguous.
Instinctive drift: biological constraints on shaping
What instinctive drift means
Instinctive drift: The tendency for conditioned behaviours to be disrupted or replaced by species-typical, innate behaviours, even when the conditioned behaviour has been reinforced.
Shaping assumes behaviour is highly flexible, but organisms bring evolved predispositions to learning situations. Under certain conditions, these predispositions “pull” behaviour away from the trained response and back toward instinctive patterns.
How instinctive drift interferes with learning
Competing responses: An instinctive action (e.g., food-related handling behaviours) competes with the trained response for the same situation or reinforcer.
Misbehavior despite reinforcement: Even when the trained response has a reinforcement history, the organism may revert to innate sequences that are biologically linked to the goal (e.g., foraging routines).
Limits on trainability: Some behaviours are difficult to shape because they conflict with natural movement patterns, defensive reactions, or fixed action tendencies.
A classic demonstration comes from animal training research (e.g., the Brelands), where animals began performing instinctive food-related behaviours that undermined the reinforced task.
Implications for designing shaping programs
Choose behaviours that fit the species’ natural repertoire (responses that are easy for that organism to emit).
Match reinforcers to the behaviour: some reinforcers (especially food) can evoke instinctive handling or foraging behaviours that compete with the target response.
Adjust the shaping steps so approximations do not accidentally strengthen an instinctive chain.
Reinforce an incompatible alternative when drift appears (strengthen a response that cannot occur at the same time as the instinctive behaviour).
Recognise realistic limits: if drift is strong and persistent, the most effective “fix” may be changing the target behaviour rather than increasing effort or reinforcement.
FAQ
Trainers often begin by reinforcing any movement toward the goal, or by arranging the environment so a tiny approximation is likely to occur.
Food can activate evolved feeding sequences (approach, grab, manipulate), which may compete with the trained response for control of behaviour.
No. The organism may have learned the contingency, but innate tendencies can still override performance in that context.
Not always. It can often be reduced by choosing species-appropriate targets, altering reinforcers, and reinforcing incompatible responses.
In principle, yes: biologically prepared responses (e.g., strong approach/avoid patterns) can compete with trained habits, limiting how far reinforcement can reshape behaviour.
Practice Questions
Define shaping and outline how reinforcement is used in shaping to produce a new behaviour. (3 marks)
1 mark: Accurate definition of shaping (reinforcing successive approximations towards a target behaviour).
1 mark: Reinforcement is given for early/partial steps that resemble the target.
1 mark: Criteria are gradually raised so only closer approximations are reinforced.
Explain instinctive drift and discuss how it can limit a shaping programme. Include one relevant example and one way a trainer could respond. (6 marks)
1 mark: Defines instinctive drift (learned behaviour replaced/disrupted by innate species-typical behaviour).
1 mark: Links drift to biological predispositions/constraints on learning.
1 mark: Explains interference (competing responses reduce reliability of the shaped behaviour).
1 mark: Provides a relevant example (e.g., animals reverting to food-handling/foraging behaviours during a trained task).
1 mark: Provides a practical response (e.g., change reinforcer, reinforce incompatible behaviour, redesign steps/target).
1 mark: Clear application to shaping (shows why reinforcement alone may not overcome drift).
