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Lecture 15

PSYC 361 Lecture 15: lecture15

Course Code
PSYC 361
Catharine Winstanley

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Schedules of reinforcement
Rules for how often and when reinforcers are delivered. Using lever pressing for sugar pellets as
an example:
Ratio schedules key factor is ratio between number of responses made to earn a single reward
Fixed ratio (FRn): response is reinforced every n times it occurs ie under FR2, rat must press lever
twice to receive one food pellet
Variable ratio (VRn): variable number of responses must be made before reinforcement occurs,
but on average the number of response = n ie under VR5, animals must make an average of 5
responses to get a food pellet. Some trials this will be 2, some it will be 7. (gambling). Actually
harder to extinguish this kind of reinforcement, because individual expects non-outcomes as
Fixed Interval (Fin) the first response made n seconds after reinforcement delivery is reinforced
Variable interval (Vin) variable amount of time when the reinforcement is introduced again. One
does not know when the reinforcement will happen again, but within a mean range. Best way for
keeping conditioned responses even if lacking reinforcements
Theories of rewards as reinforcers
Rewards are often called reinforcers because a response followed by a reward strengthens the
association between them
Response theories - Skinner
Skinner: "any stimulus which increases probability of preceding response is a reinforcer
Can describe or explain many situation, but not all. Just because a stimulus decreases the
probability of responding does not necessarily mean it is a weaker reinforcer. Dose response
curve. Animals prefer a certain amount of cocaine (experience of the drug).
Response theories - Premack
Premack principle: reinforcing event is viewed as a response rather than being stimulus-driven/
Whether a reinforcer is effective depends on the response required to get the reinforcer. If
response. A occurs with a higher probability than response B, then A can act as a reinforcer for B.
The experience is what drives behaviour and not the outcome.
Even though it is now accepted that hedonic stimulus properties actually model behavioural
responding a lot better, the Premack Principle is still used in educational settings eg. Maths comes
before art.
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