Glossary of Terms

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Glossary of Terms

Acclimate -To become accustomed to a different climate, environment, or circumstances through gradual exposure the situation. Acclimation is often used to help a subject overcome anxiety or fear associated with a particular set of circumstances. There is no reinforcement specifically associated with acclimation. See Habituation.

            Allow the dog to freely go into and come out of his crate.

Animal Welfare The literature suggest several definitions as this is a very difficult term to define in a single way.

  • The degree to which an animal can cope with challenges in its environment as determined by a combination of veterinary health measures and measures of psychological well-being (AZA Animal Welfare Committee).
  • Relates to an animal’s affective state:  what it feels. Good welfare thus means experiencing positive emotional states and negligible suffering, while poor welfare entails severe or prolonged states of mental suffering (Mason, 1993, 2009). Welfare also refers to how an animal is coping with the environment in which it lives.
  • The state of an animal as it attempts to cope with its environments (Fraser and Broom, 1990).

Autonomic Conditioning - Operant conditioning technique for controlling autonomic responses (blood pressure, intestinal contractions, et cetera) that are normally not under the organism’s control.

Aversion - A dislike or desire to avoid something.

Aversive Conditioning – Refers to the conditioning procedures that use escape, avoidance and punishment to motivate behavioral responses.

- B -

Baiting - A training technique in which the presentation of a reward, typically food, (or something desirable) is used to elicit a particular behavioral response. The reward is presented prior to the subject making a move to perform the correct behavioral response; therefore subject makes the correct move to acquire the reward. Also called Bribing or Luring.

The trainer throws a meal worms into the induction chamber to encourage the tamarin to enter.

Behavioral Management – A proactive method of managing animal behavior that involves the use of Positive Reinforcement Training and Environmental Enrichment as the technical elements, and facility design, operational considerations, and the animal’s social environment as the support elements. Assessment and problem solving are integral to the process (Desmond, 1993).

Behavioral Chain - A group of behaviors performed in a specific order, which is defined as a unit. See Chain.

Behavioral Drift - A change or stray from the norm in standard of response. The result of drift over a period of time is Deviation.

Behaviorism - School of psychology that relies on objective observation of overt behavior.

Behavior Modification - The differential reinforcement of successive approximations leading to a targeted behavioral pattern.

Bridging Stimulus - A stimulus that pinpoints the precise moment of a desired response, and bridges the gap between that point and when the organism may receive further reward. A stimulus that signals the delivery of a reinforcer. Often called a secondary or conditioned reinforcer because it acquires its effectiveness through a history of being paired with primary reinforcement.

- C -

Capturing Behavior - Involves reinforcing a behavior when it occurs. Although there are some behaviors that can only be trained by capturing, capturing behavior as a primary means of training doesn’t provide the animal with the strong learning history that’s associated with Shaping. A problem with capturing is that when regression occurs, there are no small steps to be retraced, therefore waiting for behavior to be offered again is the trainer’s best option. This can be time consuming and frustrating if the animal doesn’t offer the behavior. Another disadvantage of capturing compared to shaping is that there’s no opportunity to “learn to learn” and no generalization.

The sea lion vocalizes; the trainer reinforces that behavior.

Chain - Two or more behaviors linked together as a single unit. One behavior produces the conditions that make the next behavior possible. The stimulus linking the behaviors together serves as both as a conditioned reinforcer, maintaining the topography and frequency of the behaviors produced, and as the stimuli setting the occasion for the following behaviors. A series of behaviors that are linked by stimuli that act both as conditioned reinforcers and discriminative stimuli.

Chaining - The process of learning a sequence of behaviors that proceed semi-automatically in a determinate order; the previous response provides the stimulus for the succeeding behavior and the succeeding behavior reinforces the behavior that precedes it.

Classical Conditioning - A form of conditioning in which stimuli associated with naturally meaningful stimuli tend to become substitutes for the stimuli themselves and to elicit similar responses. The response is elicited reflexively; the organism exercises no control in the situation and the organism’s action produces no change in its environment. The bridge is conditioned in this manner.

Blow a whistle; offer a bit of food. Repeat this over and over and the animal will anticipate the food upon hearing the whistle.

Collaborative Training - Socialization training technique in which individuals must work together towards a common goal. Their collaborative efforts are reinforced. Such collaborative training results in the strengthening of social ties and can create social bonds (Whittaker, 2005).

Two monkeys are trained to pick up a heavy object and place it in a bucket. They will be reinforced for working together.

Conditioned Aversive Stimulus - An event that is initially neutral but has acquired aversive properties by virtue of being paired with aversive events or with a signal that no reinforcement will be coming.

The word “no”. An animal is told the word “no” in a loud voice that is startling to the animal. The word “no” could also be accompanied by an aversive event such as striking the animal or turning the hose on the animal. Thus, the meaningless word “no” becomes associated with another unpleasant event.

Conditioned Punisher - An initially neutral stimulus that through pairing with aversives, is used to decrease the frequency or occurrence of a behavior.

The word “no” is associated with an aversive event, such as a water hose being sprayed at an animal, until the word “no” can be used to decrease a behavior without use of the hose.

Conditioned Reinforcer - A previously neutral stimulus that has gained value as a reinforcer because it has been repeatedly associated with a primary reinforcer. See Secondary Reinforcer.

Whistle, clicker, “good”

Conditioned Response (CR) - A new or modified response that is elicited only by a given stimulus after conditioning has occurred. In classical conditioning, a response that develops to the conditioned stimulus after a number of pairings of the conditioned stimulus with an unconditioned stimulus. The conditioned response is similar to the unconditioned response.

Conditioned Stimulus (CS) - A stimulus that has the property of producing a response through pairing or association. In classical conditioning, a stimulus with which the unconditioned stimulus is paired; as a result of the pairing, the CS comes to elicit a response similar to the original response to the unconditioned stimulus (US).

Conditioning - A change in the frequency and form of a behavior due to the influences of the environment. It can be brought about by the application of reinforcers or punishers.

Cooperative Feeding - Socialization training technique where the dominant individual is specifically reinforced for allowing the subordinate to have access to a desired resource (e.g. food, enrichment, attention from trainer).

Cue - A signal that will elicit a specific behavior or reflex as a result of a learned association. See Conditioned Stimulus and Positive Discriminative Stimulus.

- D -

Desensitization - The lessening or disappearance of a response accomplished by the paring of a positive reinforcer with the presentation of the stimulus. Typically used to “train out” fear to a stimulus, and typically done by presenting smalls steps leading to the final behavioral objective, which each small step paired heavily with a positive reinforcer.

Differential Reinforcement (aka selective reinforcement) - The selective or differential reinforcement of one aspect of a behavior or behavioral pattern to the exclusion of other aspects.

Monkey is reinforced for responding quicker when called to trainer.

Differential Reinforcement of Incompatible Behavior (DRI) - The delivery of a reinforcer following a response that is incompatible with an undesirable behavior. The effect is to increase the frequency of the incompatible response and to decrease the frequency of the undesired target response. See Incompatible Behavior.

Differential Reinforcement of Other Behavior (DRO) - The delivery of a reinforcer after the performance of any behavior except a particular (usually undesirable) one. The DRO schedule specifies the performance that is not to be reinforced, rather than the one that is. The result is a decrease in the frequency of the particular performance that is undesirable.

Spitting chimp is given attention every time it does not spit.

Discriminative Stimulus (SD) - In conditioning, the stimulus to which responses are positively reinforced. A stimulus which consistently elicits a particular response because it has been positively reinforced.

Distress - The condition or state of excessive and inescapable stress. A state in which an animal, unable to adapt to one or more stressors, is no longer successfully coping with its environment and its well-being is compromised. Generally, a state of distress develops over a relatively long period of time; however, short, intense stressor(s) can also compromise animal well-being and induce acute distress. Thus, an animal may be in distress even if it appears to recover rapidly after the removal of the stressor or the conclusion of the procedure (NRC, 2008).

Most definitions characterize distress as an aversive, negative state in which coping and adaptation processes fail to return an organism to physiological and/or psychological homeostasis (Carstens and Moberg 2000; Moberg 1987; NRC 1992). Progression into the maladaptive state may be due to a severe or prolonged stressor or multiple cumulative stressful insults with deleterious effects on the animal’s welfare. Distress can follow both acute and chronic stress, provided that the body’s biological functions are sufficiently altered and its coping mechanisms overwhelmed (Moberg 2000).

- E -

Escape or Escape Behavior - The relationship between a performance and an aversive stimulus in which the performance terminates the aversive stimulus. The actual behavior that terminates an aversive stimulus. Not to be confused with Avoidance, where the aversive stimulus does not occur at all as long as the avoidance performance continues to postpone it.

Escape Learning - Conditioning technique in which the subject learns to escape or terminate an unpleasant stimulus. The process of learning to emit a behavior in order to escape an aversive event in progress. Also known as Negative Reinforcement Training.

Eustress – is a term coined by endocrinologist Hans Selye which is defined in the model of Richard Lazarus (1974) as stress that is healthy, or gives one a feeling of fulfillment or other positive feelings. Eustress is a process of exploring potential gains.

Environmental Enrichment – A dynamic process for enhancing animal environments within the context of the animals’ behavioral biology and natural history. Environmental changes are made with the goal of increasing the animal’s behavioral choices and drawing out their species-appropriate behaviors, thus enhancing animal welfare (1999 AZA Behavior Scientific Advisory Group).

Experimental Extinction - The specific procedure of presenting the conditioned stimulus unaccompanied by the usual reinforcement; also the decrease in a conditioned response that results from that procedure.

Extinction - In psychology, the gradual disappearance of learned behavior when the reinforcement is removed. In classical conditioning, removal of the unconditioned stimulus causes extinction; in operant conditioning, removal of the stimulus that causes the emitted response to persist causes extinction.

Chimp has been reinforced with attention for spitting at people. ALL attention is withheld whenever the chimp spits.

Extinction Burst - An increase in responses or performance that is brought about by the withdrawal of reinforcement. Extinction bursts occur just prior to the decline of behavior (due to lack of reinforcement) prior to extinction.

Spitting chimp spits more frequently and with greater volume of water as he tries hard to get the reinforcement (attention from people).

- F -

Free Contact - A situation in which the animal and the trainer occupy the same space.

- G -

Generalization - The process whereby an organism responds similarly to stimuli which resemble one another. Reinforcement of a specific behavior increases the frequency of similar behaviors.

The rhino is trained to touch his hip to a target, then his shoulder to a target; each successive body part is easier for him to learn because the concept of touching the target is generalized.

- H -

Habituation - A method of eliminating unconditioned responses through repeat exposures. The ability to escape or avoid the aversive stimulus is not an option and nothing the subject does affects the stimulus. Not associated with any kind of reinforcement. The process of gradually getting an animal used to a situation which it normally avoids by prolonged exposure.

See also Acclimation.

Placing the squeeze cage near the animal’s home cage so he can become acclimated to its proximity and appearance

- I -

Incompatible Behavior - A trained behavior that cannot occur or is physically impossible for an animal to perform at the same time as another (usually undesirable) behavior. Typically used to prevent or eliminate undesirable behaviors.

When training a chimpanzee for abdominal ultrasound, the chimp is trained to place his hands and feet in a particular location or on targets. This is incompatible with grabbing the ultrasound wand during training and the exam.

- J –

Jackpot or Bonus ‑ A reward that is much bigger than normal reinforcer, and comes as a surprise to subject.

The macaw opens wings fully for the first time during a training session; he is given 3 large Brazil nuts instead of the usual single, shelled peanut.

- L -

Latency - The time between a discriminative stimulus (SD) and the organism’s response to it (the performance of a behavior).

Law of Effect - The concept that an organism will tend to repeat and learn behavior that has a satisfying or reinforcing outcome; behaviors that cause pain or discomfort will not be repeated or learned.

Learned Helplessness – Has been used by experimental psychologists to describe a loss of responsiveness to stimuli after prolonged exposures in which animal cannot escape an aversive stimuli or gain satisfaction in obtaining a desirable one (Overmier, 2002). "The crux of learned helplessness is that when one's efforts at control repeatedly fail, not only does one cease trying to cause that particular outcome (helplessness), but one may also actually fail to exert control in some new situation in which control is possible." (Fiske & Taylor, 2008). Some have considered learned helplessness as an adaptive process, but Webster (2005) suggests rather than adaptive, it is a state of psychological exhaustion; the animal has given up or is hopeless.

Learning - A relatively permanent change in response patterns which occurs as a result of reinforcement or punishment; behavior that has been modified as a result of an organism’s experience.

- M -

Magnitude of Reinforcement - Refers to the size, strength, or duration of a reward following a behavior.

An animal performs a well-established behavior and receives a piece of carrot. The same animal does a difficult, new behavior in the presence of a more dominant animal, and receives a large piece of banana (more preferred than carrot). The magnitude of reinforcement for the more difficult situation is greater.

Marking Up - A technique that requires an animal to station before the trainer enters its enclosure. See Station.

Modeling - Involves physically moving the subject into the correct position or behavior. The trainer must physically contact the animal and push him/her into place. This technique has fewer advantages than disadvantages. One advantage is that that animal may learn to relax and allow the trainer to move him/her into position. The disadvantages include:

  • Pushing an animal may cause it to resist being forced into the position.
  • It is likely that very little learning about the actual behavior happens during the modeling phase.
  • Modeling can take a long time before the animal understands that he is supposed to make the movement on his own.

Motivation - The non-stimulus variables controlling behavior; the general name for the fact that an organism’s acts are partly determined in direction and strength by its own nature and/or internal state.

- N -                                                         

Negative - To remove from the environment.

Negative Discriminative Stimulus (Ss) - In operant conditioning, the stimulus to which responses are not reinforced or are negatively reinforced; also known as a stimulus delta.

Negative Punishment - A form of punishment in which the subject’s opportunity to gain rewards is removed with the intent of reducing or eliminating the frequency of an undesired behavior. Removing the situation in which an organism can get reinforcement. See Time Out.

Negative Reinforcer - An aversive stimulus whose withdrawal increases the probability that the response will persist.

Seat belt buzzer, squeeze cage wall moving, hose, any threatening event

Negative Reinforcement - Following an action or response by the removal of an unpleasant stimulus, no matter how mild, that the subject wants to avoid. Negative reinforcement has occurred when the frequency of a behavior increases in order to avoid the onset of, or to terminate an aversive stimulus. Not to be confused with Punishment.

Turn hose towards monkey while saying “shift”; the hose is turned off as soon as the monkey walks from cage A to B.

Neutral Stimulus - Any stimulus that has no effect on behavior before conditioning.

- O -

Observational Learning - is a type of learning that occurs as a function of observing, retaining, and replicating novel behavior or the end product of a behavior executed by others. Two primary types of observational learning should be noted: 1) emulation involves copying an end product rather than the exact behaviors required to achieve that end product; and 2) imitation involves copying the exact actions of another (Hopper, 2010; Lambeth, pers. comm). Observational learning does not require that the behavior exhibited by the model is duplicated. For example, the learner may observe an unwanted behavior and the subsequent consequences, and would therefore learn to refrain from that behavior (Riopelle, A.J. (1960).

Operant - Operating or producing an effect or effects on the environment.

Operant Behavior - Emitted behavior that is controlled by its consequences.

Operant Conditioning - Operant conditioning is based on the premise that all behavior is determined by its consequences. It is a type of learning in which the probability of a behavior recurring is increased or decreased by the consequences that follow. This includes positive reinforcement, negative reinforcement, and punishment.

- P -

Pleasure-Pain Principle -The principle that organisms are motivated to seek pleasure and avoid pain.

Positive - To add to the environment.

Positive Discriminative Stimulus (SD) - In conditioning, the stimulus to which responses are positively reinforced. A stimulus which consistently elicits a particular response because it has been positively reinforced.

Positive Punishment - In operant conditioning, the addition of an aversive stimulus—something the organism seeks to avoid—to the organism’s environment following a response, thereby decreasing the frequency of that response.

A chimpanzee throws feces on a person, and the person turns the hot water hose on the chimpanzee to discourage repeating the behavior.

Positive Reinforcer - In operant conditioning, a stimulus whose presentation increases the probability that the response leading to it will persist.

Food, juice, social play, grooming

Positive Reinforcement - Following an action or response by giving something the subject wants, thereby increasing the likelihood of the action or behavior occurring again. Positive reinforcement has occurred when the frequency of a behavior increases in order to obtain the reward.

A chimp responds to a cue correctly by sitting when asked to, and is given with a piece of apple and a sip of juice.

Premack Principle - A principle that states that of any pair of responses or activities in which an individual freely engages, the more frequent one will reinforce the less frequent one.

Primary Reinforcer - An unconditioned reinforcer. Anything of intrinsic value to an organism and one that satisfies a biological need.

Examples are food, water, sex, and social needs.

Principle of Symmetry - The concept that individuals tend to react in the same way that they are acted upon; for example, matching aggression with aggression.

Protected Contact -The trainer remains physically separated from the animal.

Punisher – The “things” (typically painful or aversive), that when presented to a subject, decrease or eliminate the likelihood of a behavior being repeated.

Punishment – A process. The application or presentation of a punisher. A process that occurs over time and decreases the likelihood of a behavior being repeated.

- R -

Ratio Schedule of Reinforcement – Schedule of reinforcement based on the number of correct behavioral responses.

Regression - A return to an earlier mental or behavioral level or to an earlier stage of learning. An organism is said to have regressed when its previously conditioned behavior has dropped back to a lower stage of development.

Reinforcement – A process. The application or presentation of a reinforcer. A process that occurs over time and increases the likelihood of a behavior being repeated.

Reinforcer – Anything (rewarding or aversive) that when presented to a subject, increase the likelihood of a behavior recurring.

Remote Training - A training situation in which an attempt is made to remove the human element from the picture. No relationship or trust between the animal and the trainer can be developed during this type of training.

Repertoire - A set of behaviors characteristic of a species or individual. In training, a set of behavioral responses that are under stimulus control.

Respondent Behavior - Behavior that is elicited or automatically controlled by antecedent stimuli. Reflexes are respondents because their performance automatically follows certain stimuli. The connection between unconditioned respondents and antecedent events that control them is unlearned. Respondents may come under the control of otherwise neutral stimuli through classical conditioning. Respondent behavior is not produced willingly.

Response - An identifiable unit of behavior.

Reward - A satisfaction-yielding stimulus or stimulus object that is obtained upon the successful performance of a task.

- S -

Satiation - Satiation occurs when a normally positive stimulus is repeatedly offered until it loses its reinforcing properties.

Schedule of Reinforcement - Refers to the conditions under which reinforcement is delivered. Continuous and variable reinforcement schedules are most important to animal training.

            Continuous Schedule - A schedule of reinforcement in which each correct response is                      followed by a primary reinforcer.

                 Every time the tortoise touches the target, he receives a bite of sweet potato.

            Variable-Interval Schedule - A schedule of reinforcement in which reinforcement is delivered             after a period of time that is random and varied. Reinforcement is independent of correct                     responses. A variable interval schedule produces a uniform rate of responding and is useful               in providing a benchmark to test the effects of various factors such as reward size on                         behavioral performance.

                  Gorilla receives food reinforcer after 10 seconds, 1 minute, 5 minutes, 45 seconds, etc. or                   at random time intervals during a training session

             Variable-Ratio Schedule - A schedule of reinforcement in which reinforcement is delivered                after a random and variable number of non-reinforced but correct responses. A schedule in                which reinforcement occurs irregularly after a number of responses. Similar to Variable-                      Interval, but based on responses rather than a time frame.

                   Gorilla receives food reinforcer after every other, 3rd, 5th, 10th, 4th, 7th, 2nd, etc. correct                        response.

             Fixed-Interval Schedule - A schedule of reinforcement in which organisms are reinforced                  for the first correct response that occurs after a fixed period of time has elapsed since the                  previous reinforced response. This schedule of reinforcement produces a scalloped                            response curve and is a poor motivator.

                  The crocodile works for 5 minutes during a training session and is reinforced every 30                         seconds.

            Fixed-Ratio Schedule - A schedule of reinforcement in which the organism is reinforced                     after a set number of non-reinforced correct responses.

                  The crocodile is reinforced after every 5th correct behavioral response.

Secondary - A quality that an organism responds to because its perception has been conditioned or learned.

Secondary Reinforcer - A stimulus that gains value when associated with primary reinforcers. A secondary reinforcer initially has no rewarding properties but because of its association with other desired or primary reinforcers, gains reinforcement value. Also known as a Conditioned Reinforcer.

Sensitization - The intensifying of an organism’s response to stimuli that does not ordinarily produce such strong reactions.

Shaping - A technique for achieving a final behavior by reinforcing successive approximations or small steps leading towards the desired response. See Successive Approximation.

Social Learning - A process through which information is transmitted between individuals, and down generations, by a process of learning, rather than inherited genetically (Hopper, 2010). Social learning refers to learning that is influenced by observation of, or interaction with, another animal (typically a conspecific) or its products (Box, 1984; Galef, 1988). Social learning includes imitation, emulation, contagion, local enhancement and stimulus enhancement (Hopper, 2010).

Socialization Training - Positive reinforcement training whose purpose is to increase species typical levels of affiliative behaviors, reduce agonism, and ultimately strengthen social bonds. Also teaches socially incompetent individuals appropriate social behaviors.

Station (noun) – A position or location an animal is trained to find and remain by; the station is designated by a trainer.

Station (verb) – The act of an animal moving to and remaining at a particular position or location as designated by the trainer. Also see Marking Up.

Stereotypic Behavior – Unvarying, repetitive behavior patterns that have no obvious goal or function. Sometimes included are stereotypies that are not non-repetitive, such as abnormal posturing (Mason, 1993). Mason (2009) has suggested a new definition that centers on the mechanisms underlying repetition: that stereotypic behaviors are repetitive behaviors induced by frustration, repeated attempts to cope, and/or CNS dysfunction.

Stimulus - Any environmental condition that an organism can detect. The organism must be able to perceive the stimulus.

Stimulus Control - The condition when a behavior is consistently performed in the presence of a particular stimulus (SD), and without the presentation of other behavioral responses.

Stimulus Delta - See Negative Discriminative Stimulus.

Stress – The state when an animal encounters adverse physiological or emotional conditions which cause a disturbance of its normal physiological or mental equilibrium (Manser, 1992). Stress encompasses all possible extra-individual events capable of evoking a broad spectrum of intra-individual responses mediated by a complex filter labeled individual differences. There are three aspects of stress:  the stressors, the individual differences, and the stress reactions. (Ladewig et al, 1993).

Successive Approximation -The small steps that make up the complete behavior in the Shaping Process.  See Shaping.

Superstitious Behavior - An undesired behavior that is unrelated to the desired behavior, but is associated with it. The superstitious behavior has been accidentally reinforced, and thus becomes fixed in the subject's mind as necessary for reinforcement. Trainer is often unaware that this is being reinforced.

A chimp is bridged for making the initial movement of a turn, she inadvertently shakes her head at the same time. On the next response she once again shakes her head as she begins the turn, and is again reinforced. The chimp now views the behavior of “turn” as including the head shaking.

- T -

Tactile Reinforcer - Any reinforcer discernible by touch.

Target (noun) - A point of reference that the animal moves towards. This can be a physical prop, and used to elicit gross and fine movements, or communicate the animal should hold a position or location.

Target (verb) - An animal’s action to touch a designated reference point. The process of stimulating an animal to touch a particular spot or object.

Team-Based Contingency - A group contingency in which members earn reinforcers on the basis of the performance of the group.

Terminal Response - The final pattern of behavior that an organism is expected to demonstrate after the completion of shaping procedures.

Threshold - The point at which a stimulus is just strong enough to be perceived or produce a response. The magnitude or strength of a stimulus which is just sufficient to elicit a respondent behavior or emit an operant behavior.

Time Out - A form of punishment in which the subject’s opportunity to gain rewards is removed for a brief period of time with the intent of reducing or eliminating the frequency of an undesired behavior. See Negative Punishment.

During training session, the hyena continues to break from position. On third time, trainer immediately picks up treats and walks short distance away, stopping with back turned toward animal. After 2 minutes, and when hyena is back in position waiting, trainer returns and begins sessions again

Training ‑ Teaching animals by using specific stimuli to achieve a desired response or behavior.

- U -

Unconditioned Reflex - A response that is emitted on exposure to a stimulus without previous conditioning.

Unconditioned Reinforcer - See Primary Reinforcer.

Unconditioned Response (UR) - In classical conditioning, an unlearned and innate response to an unconditioned stimulus. A response that is elicited by an unconditioned stimulus without prior learning.

Unconditioned Stimulus (US) - In classical conditioning, a stimulus that elicits an unlearned and innate response (UR). Any stimulus possessing the capacity to elicit reactions from organisms in the absence of prior conditioning.

 

References

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Desmond, T. (1994). Behavioral Management:  An Integrated Approach to Animal Care. In:  AZA Annual Conference Proceedings. Presented at the AZA Annual Conference in Toronto, Canada, 1994.

Duncan, I. J. H.; Rushen, J.; and Lawrence, A. R. (1993). Conclusions and implications for animal welfare. In:  Stereotypic Animal Behaviour:  Fundamentals and Applications to Welfare. Eds. Lawrence, A. and Rushen, J., CAB International, Wallingford, Oxon, UK.

Fiske, S T, & Taylor, S E (2008). Social Cognition: From Brains to Culture. McGraw-Hill

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Hopper, L. M. (2008). ‘Ghost’ experiments and the dissection of social learning in humans and animals. In: Biological Reviews (2010), Cambridge Philosophical Society.

Ladewig, J., DePasille, A.M., Rushen, J., Schouten, W., Terlouw, E.M.C. and von Borell, E. (1993). Stress and the physiological correlates of stereotypic behaviour. In: Stereotypic Behaviour. Eds. A.B. Lawrence and J. Rushen. CAB International, Wallingford, Oxon, UK.

Laule G, Whittaker M. (2000). Protected contact: beyond the barrier. In:  AZA Annual Conference Proceedings. Paper presented at the AZA annual conf, Orlando, FL, September.

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Mason, G. (2009). Stereotypic Animal Behavior:  Fundamentals and Applications to Welfare. CAB International, Wallingford, Oxon.

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National Research Council (US) Committee on Recognition and Alleviation of Distress in Laboratory Animals. Recognition and Alleviation of Distress in Laboratory Animals. Washington (DC): National Academies Press (US); 2008.

Riopelle, A. J. (1960). Observational learning of a position habit by monkeys. In: Journal of Comparative and Physiological Psychology, 53, 426-428.

Webster, John. (2005). Animal Welfare: Limping Towards Eden. Universities Federation for Animal Welfare (UFAW). Blackwell Publishing.

Whittaker, M. (2005). Managing Monkey Behavior:  Advancing the Social Management of Old World Monkeys. In: AZA Annual Conference Proceedings.