Learning, Memory and Forgetting

Reinforcement schedules

A reinforcement schedule is a rule that specifies which occurrences of a behaviour are followed by reinforcement and when. Schedules differ on two dimensions: the criterion may be a number of responses (ratio) or an amount of elapsed time (interval), and that criterion may be fixed (constant) or variable (changing around an average).

• Fixed-ratio (FR-n) reinforces every nth response, as in piecework pay. It produces a high rate of responding with a brief pause after each reinforcer.
• Variable-ratio (VR-n) reinforces after an unpredictable number of responses averaging n. It produces steady, high rates of responding that are very resistant to extinction.
• Fixed-interval (FI-t) reinforces the first response after a constant period of t seconds. Responding is low just after reinforcement and rises toward the end of the interval, giving a scalloped pattern.
• Variable-interval (VI-t) reinforces the first response after a period that varies around a mean of t. It produces a steady, moderate rate of responding with few pauses.

The key contrast is that ratio schedules depend on counting responses, whereas interval schedules depend on time, so responding faster does not bring reinforcement sooner on an interval schedule. A schedule described as 'varying time' is a variable-interval schedule.

Matching the names to their definitions is a common exam task: fixed ratio means a fixed number of responses, fixed interval means a constant time, variable ratio means an unpredictable number of responses, and variable interval means a varying time before reinforcement.

Classical conditioning acquisition

Acquisition is the initial phase of classical conditioning, in which a neutral stimulus repeatedly presented just before an unconditioned stimulus comes to elicit a conditioned response. When the strength of the conditioned response is plotted against the number of paired trials, the result is an acquisition curve.

The typical acquisition curve is negatively accelerated. The largest gains occur on the first few trials, and each later trial adds less, because the response approaches its asymptote, or maximum level. The rate of learning is therefore higher on early trials than on later ones. It does not increase in proportion to the number of trials, and it does not rise faster toward the end of training.

• Asymptote — the maximum level of conditioned responding that training can reach.
• Negatively accelerated — a curve that rises steeply and then flattens.

Several theories try to explain why conditioning occurs. Pavlov's account, stimulus substitution, holds that the conditioned stimulus comes to substitute for the unconditioned stimulus. The Rescorla-Wagner model is an associative account. Cognitive accounts emphasise information and expectation: the conditioned stimulus signals that the unconditioned stimulus is coming, and the organism learns that expectation. Spontaneous recovery and stimulus generalization, by contrast, are phenomena that conditioning produces. They describe what is observed and are not explanations of how learning occurs.

Memory stores: sensory, short-term, long-term

The multistore model describes memory as three stages through which information passes in sequence. Each store differs in capacity and duration.

• Sensory memory is a very brief copy of incoming stimulation. Iconic memory is its visual form and lasts only a fraction of a second, roughly a quarter to half a second. Echoic memory is its auditory form and lasts a few seconds. Iconic memory is therefore a subtype of sensory memory, not of short-term or semantic memory.
• Short-term memory holds a limited amount of information, about seven items on average according to Miller's classic estimate. It keeps information for roughly 15 to 30 seconds without rehearsal. It holds information briefly while the information is being actively used, which is why it overlaps with working memory.
• Long-term memory has very large capacity and stores information for long periods. Transfer depends on rehearsal and encoding.

Attention determines which sensory information moves into short-term memory, and rehearsal and encoding move information onward into long-term memory. Duration and capacity must be kept separate. Echoic memory lasts longer than iconic memory, but the question of duration does not tell us anything about capacity.

Learning theories and cognitive imitation

Classic learning theories were developed by different psychologists, and each is associated with a particular type of learning.

• Classical (respondent) conditioning, studied by Ivan Pavlov, describes how a neutral stimulus acquires the power to elicit a response through repeated pairing with an effective stimulus.
• Trial-and-error learning and the law of effect, associated with E. L. Thorndike, describe how responses followed by satisfying consequences are strengthened.
• Instrumental (operant) conditioning, developed by B. F. Skinner, describes how behaviour is shaped and maintained by its consequences. Skinner is the psychologist linked to this form of learning.
• Insightful learning, studied by W. Köhler in chimpanzees, describes a solution that appears suddenly after the relations among elements of a problem are perceived.

Cognitive imitation is the learning of an abstract rule or sequence from watching a model, rather than copying its exact motor movements. An observer that reproduces the order of a model's actions and then applies that order to a new arrangement has acquired the rule, not merely the movements. This is different from classical imitation, which copies the specific motor actions, and from social imitation, a broad term for copying others within a group.

Example: a child watches an adult sort blocks by colour, then sorts a new set of blocks with a different layout in the same order of steps. The child has learned the rule and has not just memorised the positions.

Types of amnesia

Amnesia is a loss of memory, and its types are named according to the period of time that is affected.

• Retrograde amnesia is the loss of memories for events that occurred before a trauma, brain injury or illness. The person may remember how to behave but not what happened before the injury.
• Anterograde amnesia is the inability to form new long-term memories after the onset of the injury, while older memories may remain intact. The classic case is H.M., who lost the ability to form new declarative memories after surgery on the medial temporal lobes.
• Infantile amnesia is the lack of accessible memories from early childhood.
• Posthypnotic amnesia is the forgetting of material after a hypnotic session.

A quick test for the type is to ask whether the gap lies before or after the event. Retrograde amnesia looks backward in time, and anterograde amnesia looks forward.

Memory failures (seven sins)

Daniel Schacter described seven ways in which memory fails. Three are omissions, in which a memory is not retrieved when wanted, and four are commissions, in which an unwanted memory is retrieved or a memory is distorted.

• Transience — the decline of accessibility over time, so that a memory becomes weaker as the time since encoding grows.
• Absent-mindedness — forgetting caused by lapses of attention during encoding or retrieval, such as forgetting where one put the keys.
• Blocking — a memory that is temporarily unavailable because of interference from another memory, as in the tip-of-the-tongue state.
• Misattribution — confusion about the source of a memory, so that a fact learned from one source is credited to another.
• Suggestibility — memories that are implanted or distorted by leading questions or suggestions.
• Bias — memories that are reconstructed to fit present beliefs or moods.
• Persistence — the inability to forget unwanted memories, such as traumatic events, that repeatedly intrude.

The seven sins are a useful classification, so learn each name with its defining feature.

Positive and negative reinforcement

Reinforcement is any consequence that increases the future frequency of a behaviour. It is classified by whether a stimulus is added or removed.