Reward Given for Behavior to Happen Again

3.i. INTRODUCTION

In everyday use the discussion "reward" describes an result that produces a pleasant or positive affective experience. Amongst beliefs scientists, reward is often used to describe an outcome that increases the probability or rate of a behavior when the consequence is contingent on the behavior. In this usage reward is a synonym of reinforcement. At best these common usages create ambiguity. At worst the ii meanings of advantage are conflated, leading to the supposition that reinforcement is always the result of positive affect produced by rewarding events. Although reward certainly influences behavior, its influence is non as straightforward every bit is oftentimes assumed, nor is reward the merely reinforcement procedure that tin influence behavior.

In the present analysis, "reinforcement" is the term used to describe any process that promotes learning: a change in behavior equally the consequence of experience. The effect (or stimulus) that initiates the process is called the reinforcer. Since both the reinforcer and its behavioral effects are observable and can be fully described, this can be taken as an operational definition. However, this definition is uninformative with respect to the processes that underlie the behavioral furnishings of reinforcement and tends to obscure the fact that there are several such effects, all of which result in behavioral change. This chapter discusses evidence for the beingness and independent function of iii reinforcement processes.

3.2. Iii REINFORCEMENT PROCESSES

Reinforcers are events that elicit several types of responses without prior experience. They are unremarkably grouped into two broad types based on one grade of these responses. Reinforcers that elicit arroyo responses are usually called positive; reinforcers that elicit withdrawal are chosen aversive or negative. These attributions are based on the assumption that arroyo-eliciting reinforcers also elicit some array of internal perturbations that constitute a pleasant or rewarding experience, and that withdrawal-eliciting reinforcers produce an aversive experience. Although these internal affective responses cannot be directly observed, their existence can be inferred from behavior in certain situations, making them a 2nd type of response elicited by reinforcers. In add-on to producing approach or withdrawal and advantage or aversion, both positive and negative reinforcers also produce a third type of internal response that strengthens, or modulates, memories. Each of these three kinds of responses (approach/withdrawal, reward/disfavor, and retentiveness modulation) is a reinforcement process because each affects learning, albeit in dissimilar means. The three processes are illustrated in Figure 3.1a.

FIGURE 3.1

The iii unconditioned (a) and conditioned (b) reinforcement processes.

An of import feature of the responses elicited past reinforcers is that they are all field of study to Pavlovian conditioning (Pavlov 1927). In Pavlovian terms the reinforcer is an unconditioned stimulus (United states of america) and the responses information technology evokes are unconditioned responses (URs). Neutral stimuli present when such responses occur acquire the property of evoking very like responses, thereby condign conditioned stimuli (CS) that evoke conditioned responses (CRs). These CSs part as conditioned reinforcers with effects similar to those produced past the USs that generated them, so there are three kinds of conditioned reinforcement that parallel the three kinds of reinforcement (see Effigy 3.1b). Importantly, the conditioned reinforcers part in the absenteeism of the reinforcers.

Following a more than detailed clarification of the 3 reinforcement processes, the main content of this chapter reviews evidence from specific learning situations, showing how the beingness of each of these rewarding processes can be deduced.

iii.2.1. Approach/Westwardithdrawal

Certain naturally occurring stimuli such as nutrient, h2o, or a sexual partner tin elicit observable, unlearned approach responses; other events that cause injury or fear of injury arm-twist withdrawal responses (Craig 1918; Maier and Schnierla 1964). Similar responses are elicited by CSs in rewarding (Kesner 1992; Schroeder and Packard 2004; White and Hiroi 1993; Koob 1992) and aversive (Fendt and Fanselow 1999; Davis 1990) situations. In the present assay the approach and withdrawal (motor) responses are independent of the rewarding and aversive (melancholia) responses that usually accompany them. This assertion is primarily based on information showing that the two types of responses are impaired by lesions to different parts of the brain (Corbit and Balleine 2005; Balleine, Killcross, and Dickinson 2003; Dayan and Balleine 2002). These studies will non be reviewed here although they are addressed in other capacity in Part III of this book.

three.2.ii. Affective States

Reward and aversion are internal affective states elicited by reinforcing events (Young 1959; Glickman and Schiff 1967; White 1989; Cabanac 1992). When melancholia states are considered independently of other reinforcement processes that may or may not accompany them, ii things almost them get clear. First, they must exist consciously experienced in order to influence behavior (one of the basic ideas of affective neuroscience: Burgdorf and Panksepp 2006; Panksepp 1998). This differentiates affective states from the other reinforcement processes of approach/withdrawal and memory modulation, which function unconsciously. 2nd, the mere feel of an affective land has no influence on behavior. An melancholia state affects behavior simply when an individual learns what to practice to maintain or re-initiate a state of affairs that the private likes and wants, or what behavior leads to the termination of a state the private does non like.

This kind of learning is necessarily a cerebral process that results in the representation of a contingent, or predictive, human relationship between behavior and its consequences. This human relationship has been described using the term expectancy (Tolman 1932), in the sense that an individual learns what behaviors or other events lead to a rewarding event. The behaviors are not fixed in form but remain oriented towards the desired change in affective state. This procedure has also been called instrumental learning (Thorndike 1933b) or operant conditioning (Skinner 1963). More recently, the term action-outcome learning has been used to depict learning about affective states (Everitt and Robbins 2005). This theme is taken up in greater particular in Chapter 13.

Activity-outcome learning also occurs with artificially produced rewards such every bit electric stimulation of certain brain areas (Olds 1956) or injection of an addictive drug (Weeks 1962; Pickens and Thompson 1968; Pickens and Harris 1968). Since these events lack external reference points, they may produce a disorganized increase or decrease in activity. Little can be inferred from such diffuse behavioral changes. Organized behavior that tin be the footing of inferences about internal reward processing appears only when some form of action-outcome learning nigh the behaviors required to obtain the reward has occurred (White 1996). This illustrates the full general point that in non-verbal animals there is no way to infer the being of an affective state without activity-outcome learning involving the reinforcer that produces the state.

3.2.3. Memory Modulation

Retentivity modulation is a general procedure whereby central (McGaugh 2000; McGaugh and Petrinovitch 1965) and peripheral (Gold 1995; McGaugh and Gold 1989) processes initiated by reinforcers human activity in the brain to strengthen the neural representations of memories acquired effectually the same time as the reinforcer occurs. The effect has been demonstrated using a diversity of memory tasks, from inhibitory abstention in rats (Gold, McCarty, and Sternberg 1982; McGaugh 1988) to verbal learning in humans (Gold 1992; Watson and Craft 2004). Memory modulation is content-free: its occurrence does non involve learning anything nigh the reinforcer that modulates the representation of a retentiveness. Appropriately, neither the arroyo/withdrawal nor the affective properties of a reinforcer are involved in its modulatory action. Both rewarding and aversive reinforcers modulate memories (Huston, Mueller, and Mondadori 1977). As described beneath, the modulatory action of reinforcers is inferred from experiments designed to eliminate the possibility that either the affective or approach processes can influence the learned behavior.

3.3. ANALYSIS OF REINFORCER Deportment IN LEARNING TASKS

iii.three.1. Instrumental Learning

Instrumental learning occurs when an individual acquires a new behavior that leads to a positive reinforcer (or avoids a negative reinforcer). Yet, in many learning tasks that fit the operational definition of instrumental learning, it is difficult to be sure which reinforcement process produced the behavioral change. This trouble can be illustrated by examining how a nutrient reinforcer acts to increase the running speed of a hungry rat over trials in which a rat is placed at i end of the runway and the food is at the other end.

I possibility is that running speed increases because the food reinforcer modulates (strengthens) a stimulus-response (S-R) association between the stimuli in the runway and the running response. An effect of this kind will exist described beneath in the department on win-stay learning.

Some other possibility is that the stimuli in the rail become CS that elicit conditioned approach responses which increase running speed. A mechanism very similar to this was proposed by Spence and Lippit (1946) as a modification of Hull'due south (1943) original S-R learning theory. An example will be described below in the department on conditioned cue preference (CCP) learning.

Finally, it is possible that the change in behavior is due to the acquisition of a neural representation of an activeness-outcome clan (Everitt and Robbins 2005). Since consuming the food leads to a rewarding state, the rat may run faster because it learns that this behavior will lead to that state as soon as information technology reaches the end of the runway.

What kind of evidence would permit us to conclude that beliefs is due to action-outcome learning? The partial reinforcement extinction effect (Skinner 1938; Capaldi 1966) is an experimental paradigm that was used past Tolman (1948) for this purpose. Two groups of rats were trained to run down a runway for food. 1 grouping found food at the end on every trial; the other institute food on merely 50% of the trials. Afterward running speeds increased to similar levels in both groups, the food was eliminated completely for both groups and their extinction rates were compared. Results indicated that the grouping reinforced on fifty% of the trials took significantly longer to extinguish than the group reinforced on 100% of the trials.

Both the modulation of South-R associations and conditioned approach are based on the promotion of specific behaviors by the reinforcer, leading to the prediction that resistance to extinction should be stronger in the 100% group because the response was reinforced twice every bit many times as in the 50% grouping. However, the behavior observed does not support these predictions.

Instead, the rats' beliefs is consequent with the idea that the 100% rats learned to await nutrient on every trial while the 50% rats learned to look food on only some of the trials. Therefore, fewer trials with no food were required to disconfirm the expectancy of the 100% rats than were required to disconfirm the l% rats' expectancies. This interpretation suggests that the rats' beliefs was determined by learned information (or knowledge) about the rewarding consequences of running down the alley (an action-event association). This information maps the relationships among the stimuli, one or more possible responses, and events, such as eating food, that atomic number 82 to a rewarding state. Rather than promoting a specific behavior, the learned information contributes to determining behavior based on current weather. Some authors have emphasized the flexibility of the behavior produced by this blazon of learning about reinforcers (Eichenbaum 1996).

Bar pressing for a reinforcer, possibly the most-used form of instrumental learning, is equally subject to influence by all iii reinforcement processes. 1 of the virtually popular methods for studying the effects of addictive drugs in animals is the self-administration paradigm in which rats press a bar to evangelize doses of a drug to themselves through implanted intravenous catheters. It is oftentimes claimed that the similarities between instrumental bar pressing and human drug self-assistants brand bar pressing a good model of addiction. However, given bear witness that addictive drugs initiate the same array of reinforcement processes as naturally occurring reinforcers (White 1996), the difficulty of disambiguating these processes using an instrumental learning paradigm such as bar pressing raises the issue of whether instrumental learning is the all-time mode to study the underlying processes of addiction. The apply of reinforcement schedules such equally progressive ratio (due east.1000., Roberts, Loh and Vickers. 1989) may help to sort out the processes, but it is arguable that other methods such as the CCP paradigm (see below) have revealed more than near the reinforcing actions of drugs such as morphine than accept self-administration studies (Jaeger and van der Kooy 1996; Bechara, Martin, Pridgar and van der Kooy. 1993; White, Chai, and Hamdani 2005).

Although the partial reinforcement extinction effect and other paradigms, such equally advantage contrast (McGaugh et al. 1995; Salinas and McGaugh 1996; Kesner and Gilbert 2007), are consistent with the idea that action-outcome learning is a major influence on behavior in the conditions of those experiments, they practice not rule out the possibility that the other processes discussed besides influence behavior in these and other learning situations. The following word focuses on an analysis of reinforcer actions in several learning paradigms: the CCP, postal service-training administration of reinforcers, and win-stay learning on the radial maze. In each case the goal is to deduce which of the three reinforcer processes produces the learned behaviors observed.

These are all paradigms for studying behavior in rats. It seems a off-white assumption that the same processes apply to humans, although the interaction among them and with learned behaviors is undoubtedly more complex. The discussion is near completely confined to the behavioral level of analysis and does not attempt to draw in detail prove from studies using lesions, brain stimulation, or drugs, all of which contribute to understanding the physiological bases of reinforcement. All the same, it is of import to note that the interpretation of physiological and neuroscientific information hinges on the way in which the psychological processes of reinforcement are understood to role, and therefore this analysis is intended as a contribution to that understanding.

three.3.2. Conditioned Cue Preference

This learning task (too known as conditioned place preference) uses an appliance with two discriminable compartments and an area that connects them. Rats are confined in the two compartments on alternating days. 1 compartment always contains a reinforcer (east.g., food); the other is ever empty. Afterward several such training trials the rats are placed into the connecting area and immune to move freely between the two compartments, neither of which contains food. Rats choose to spend more time in their nutrient-paired compartments than in their unpaired compartments (Spyraki, Fibiger, and Phillips 1982; Everitt et al. 1991; White and McDonald 1993), an outcome known equally the conditioned cue preference because information technology indicates that the cues in the reinforcer-paired compartment have caused conditioned stimulus backdrop. Addictive drugs also produce CCPs (Reicher and Holman 1977; Sherman et al. 1980; Mucha et al. 1982; Phillips, Spyraki, and Fibiger 1982; Tzschentke 1998, 2007).

In this task the reinforcer promotes a learned beliefs: a preference for the stimuli in the reinforcer-paired compartment. Because the assignment of the reinforcer to the two compartments is counterbalanced, the preference cannot exist attributed to any URs to the stimuli in either 1. Since the rats are always confined in their reinforcer-paired compartments during training, they never have an opportunity to acquire the response of entering them from the connecting area, nor are they always required to perform any other new behavior to obtain the reinforcer, eliminating the possibility that an Southward-R association could be formed. This means that the preference cannot exist due to instrumental learning most how to obtain the food reward.

The remaining possibility is that the preference is solely due to the CS backdrop acquired by the distinctive stimuli in the reinforcer-paired compartment during the training trials. During the test trial a CS in the paired compartment could elicit ii different CRs in the absence of the reinforcer (US) (see Figure three.1). One is a conditioned approach response from the point in the apparatus at which the rat tin see the stimuli in the paired compartment. The other is conditioned reward, experienced when the rat has entered the compartment, resulting in action-result learning during the examination trial (in contrast to the impossibility of such learning during the training trial when the rat is confined in the compartment with the reinforcer). Both of these CRs would increment the rat's tendency to enter and remain in the reinforcer-paired compartment, resulting in the observed preference. The CCP procedure and the influence of these CRs are illustrated in Figure 3.2, and the effect of the two CRs on behavior is discussed in more detail here.

FIGURE three.two

Illustration of two conditioned responses that could produce conditioned cue preference. Rats are trained by placing them into one compartment with a reinforcer (e.g., nutrient, drug injection) and into the other compartment with no reinforcer an equal number (more...)

3.iii.2.i. Conditioned Arroyo

Conditioned arroyo behaviors have been demonstrated in a prototype chosen autoshaping, first developed as a method of grooming pigeons to peck at a disc on a cage wall when the disc was lit. The standard method was to "shape" the pigeon's beliefs by manually reinforcing successively closer approximations of the birds' responses until they pecked at the disc on their ain. Dark-brown and Jenkins (1968) attempted to eliminate experimenter interest in shaping by simply illuminating the disc and providing admission to the nutrient when the illumination went off, regardless of what responses the pigeon made or did not make while the disc was lit. Subsequently a mean of about 50 such paired presentations the pigeons responded reliably to the light by pecking the disc, even though the reinforcement was non contingent on those responses. The pigeons had shaped themselves, hence "autoshaping." The sequence of events in the autoshaping paradigm is illustrated in Effigy 3.3.

FIGURE 3.three

Autoshaping paradigm. (a) Initial training: CS (lit disc) is followed by access to food (US). Response to food (UR) may or may non occur (foursquare brackets). (b) Autoshaped response: gradually the bird begins pecking the lit disc (the CR) reliably. Response (more...)

The increment in responding was attributed to Pavlovian conditioning (Gamzu and Williams 1971; Jenkins and Moore 1973). The conditioning process involved the transfer of a response (pecking) elicited past the food (the Us) to the illuminated disc (the CS) due to the contiguity of the two stimuli.

One problem with this interpretation is that giving access to the reinforcer immediately after the disc light went off reinforced any responses made while information technology was on. Information technology could therefore be argued that the increase in responding was due to accidental response reinforcement without invoking Pavlovian conditioning. Testify supporting the conditioning interpretation was obtained with a paradigm chosen reinforcer omission (Williams and Williams 1969), in which a response to the lit disc cancelled the admission to the food that usually followed, completely eliminating response reinforcement (see Figure iii.three). Pigeons did not acquire the response in the reinforcer omission condition, just if they were trained on autoshaping kickoff and then switched to reinforcer omission they maintained a higher charge per unit of responding than birds trained in a command condition, such equally random presentations of CS and US or CS presentations with no US at all. This supports the idea that increased responding to the CS observed in autoshaping is due to Pavlovian workout in which the response elicited by the reinforcer is transferred to the CS.

A conditioned approach response (see Effigy 3.1) similar to the one that is acquired in the autoshaping procedure (see Figure 3.2) tin explicate the preference for the food-paired environment seen in the CCP paradigm. Exposure to the stimuli in that environment together with a reinforcer could result in a transfer of the arroyo response (UR) elicited by the food (U.s.) to the environmental stimuli (CS). On the test trial the CS in the food-paired environs elicit the conditioned approach response (CR) resulting in a preference for that surround.

iii.3.two.2. Conditioned Advantage

In addition to producing conditioned approach, pairing the stimuli in the food-paired environment volition also result in conditioned reward (come across Effigy three.1). If the stimuli in the reinforcer-paired environment learn conditioned rewarding backdrop during the grooming trials, a rat moving freely during the test trial would experience conditioned reward when information technology entered the reinforcer-paired environs (meet Figure three.2). This experience might induce the rat to remain in the environment but, perhaps more importantly, the rat would larn that inbound the surroundings from the connecting surface area leads to a rewarding experience. This is action-outcome learning virtually the conditioned rewarding stimuli and is another way Pavlovian conditioning tin can produce a CCP.

This explanation of how the CCP tin can exist produced by conditioned reward is an appetitive learning awarding of Mowrer'southward (Mowrer 1947; McAllister et al. 1986) two-factor theory of avoidance learning. Co-ordinate to this thought, when rats are shocked on one side of an appliance with two distinct compartments they larn conditioned aversive responses to the stimuli on the side where the daze is given. These CRs make the shock side of the apparatus aversive even if the shock is not given. When the rats run to the other (no-shock) side of the apparatus they learn how to escape from the aversive conditioned cues, an instance of instrumental learning.

As already mentioned, addictive drugs also produce CCPs, and information technology is usually assumed that they do and so because of their rewarding effects. However, it is also possible that conditioned approach responses to initially neutral stimuli are caused when the stimuli are paired with the effects of an addictive drug in a CCP or other paradigm. Although this upshot is under investigation (Ito, Robbins, and Everitt 2004; Di Ciano and Everitt 2003; White, Chai, and Hamdani 2005), there is at present no articulate evidence that drug-induced CCPs can be produced by conditioned arroyo responses.

3.iii.3. Post-Training Administration of Reinforcers

Retentiveness modulation (McGaugh 1966, 2000) is a reinforcement procedure that improves, or strengthens, memory for an event or response. The reinforcer must be contemporaneous with the acquisition of the memory, but does not have to be related to it in whatever other manner. A pop instance of this effect is the observation that near everyone can retrieve where they were and what they were doing when they starting time heard about the destruction of the World Trade Middle in New York on September 11, 2001 (Ferre 2006; Davidson, Cook, and Glisky 2006). This emotional (reinforcing) experience was presumably unrelated to the retentivity it strengthened in near of united states of america but nevertheless acted to attune our diverse individual memories.

The basis of this effect is the phenomenon of retentiveness consolidation, outset demonstrated past Muller and Pilzecker (1900), who showed that memory for a list of words was disrupted when a second list was learned a short time after the first one, merely not when the second listing was learned some time later. This suggested that the neural representation of the retentiveness of the first list was relatively delicate immediately after it was learned, merely became more robust with the passage of time (see McGaugh 1966 for review and discussion). This generalization has since been confirmed for a wide variety of memory tasks using a similarly large number of dissimilar post-learning events, including caput trauma (Dana 1894; Russell and Nathan 1946) and electroconvulsive shock (Zubin and Barrera 1941; Duncan 1949). Other modulatory events better rather than disrupt recall when they occur around the time of acquisition, but accept no result hours later on. The earliest demonstrations of memory improvement used stimulant drugs such as strychnine and amphetamine (Breen and McGaugh 1961; Westbrook and McGaugh 1964; Krivanek and McGaugh 1969). These observations led to the notion that modulatory events accelerate consolidation by strengthening the representation of the retentivity (Bloch 1970).

A study past Huston, Mondadori, and Waser (1974) illustrates evidence supporting the merits that the memory modulation process is contained of the melancholia value of the reinforcer. Hungry mice were shocked when they stepped downward from a platform (encounter Figure iii.4). When tested the next day, the shocked mice remained on the platform longer than unshocked controls. This behavior was probably due to activeness-result learning: the mice recalled the aversive experience produced past the shock when they stepped off the platform and contradistinct their behavior accordingly; although it could also take been due to conditioned withdrawal (freezing).

FIGURE 3.4

Post-training reinforcement effects of food reward on conditioned withdrawal. Hungry rats were placed on the platform and shocked when they stepped down onto the grid flooring. Rats in the mail-training reinforcement grouping were and then placed in a separate (more...)

In a subsequent phase of the written report by Huston et al., one grouping of mice was fed immediately following their initial pace-down–shock feel. On the test trial these mice remained on the platform longer than mice that had not been fed afterward the preparation trial (see Figure 3.iv). Since the mice were hungry, the food had rewarding properties. If action-outcome learning about this advantage had occurred, the fed mice would have stepped down more quickly than the unfed mice in order to obtain the food. Since the opposite was observed, the change in behavior (longer step-down times) produced past the food cannot exist attributed to learning about its rewarding properties. Rather, the outcome of the food suggests that it modulated, or strengthened, the retentivity for the relationship between stepping-downwardly and shock. Consequent with this estimation and with consolidation theory, mice that were fed later on a filibuster did non show increased pace-downward times during the test.

Another demonstration (Huston, Mueller, and Mondadori 1977) showed that rewarding electrical stimulation of the lateral hypothalamus also produces memory modulation. Rats were trained to turn left for food in a T-maze. Every time they made an fault (by turning right) they were removed from the goal box and placed in a muzzle where they received rewarding lateral hypothalamic stimulation for several minutes. The rats that received this treatment learned to make the right response (the 1 that led to food, just away from rewarding stimulation) in fewer trials than rats in a control group that were not stimulated after either response. Since the rewarding stimulation improved memory for the location of nutrient when it was given only after the rats made errors, its effect cannot exist attributed to activity-result learning nearly responses that led to its rewarding properties. The effect can be explained equally a modulation of memory for the nutrient location, for the no-food location, for the correct response, or for all three of these (Packard and Cahill 2001).

The electrical stimulation in the T-maze experiment was delivered by the experimenters, but self-stimulation also produces memory modulation (Major and White 1978; Coulombe and White, 1980, 1982). Although electrodes in several brain areas support self-stimulation, suggesting that the stimulation in all of them is rewarding, postal service-training stimulation in only some of these areas produces retention modulation. This suggests that reward is not a sufficient condition to produce modulation.

Another series of experiments leading to the same conclusion compared the modulatory effects of mail-grooming consumption of sucrose and saccharin solutions (Messier and White 1984; Messier and Destrade 1988). The solutions were both preferred over h2o only were equally preferred to each other, suggesting that they had equivalent advantage properties. The memory modulation furnishings of these two solutions were tested by allowing rats to drink them afterwards paired presentations of a tone and a shock. The strength of the retentiveness for the tone-shock association was estimated by measuring the pause in drinking by thirsty rats produced by presentation of the tone lonely. The tone suppressed drinking more effectively in the rats that had drunkard sucrose than in the rats that had drunk saccharin after the tone-shock pairings. Since the solutions had equivalent rewarding properties, the modulatory effect of sucrose cannot be attributed to its rewarding properties.

Post-training injections of glucose only not of saccharin, in amounts comparable to those ingested in the consumption experiments, also improved retentiveness (Messier and White 1984), suggesting that the effect of sucrose was due to some mail service-ingestional effect, only not to its rewarding sense of taste. The memory-modulating action of glucose has been studied in detail in rats and humans (Messier 2004; Korol 2002; Gold 1991, 1992, 1995). For farther details encounter Chapter 12.

In human studies glucose is oftentimes consumed earlier acquisition of the memories it strengthens, with no diminution in its effect. This emphasizes that the post-training epitome is simply a method for demonstrating the modulatory deportment of reinforcers, not a requirement for them to accept this outcome. In fact, reminiscent of Thorndike's (1933a, 1933b) original studies on spread of effect (cf. Chapter ii), mere temporal contiguity of a reinforcing issue with the acquisition of a memory is sufficient for modulation to occur. The fact that reinforcers meliorate performance of learned behavior when they occur before the behavior has been learned is too farther evidence that modulation is not due to activeness-outcome learning about reward.

A related finding is that aversive postal service-preparation events also produce memory modulation (Mondadori, Waser, and Huston 1977; Huston, Mueller, and Mondadori 1977; Holahan and White 2002). In i study (White and Legree 1984) rats were given tone-stupor pairings and immediately placed into a different cage where they were given a brusque, strong daze (instead of drinking a sweet solution). When tested for suppression of drinking 2 days later, the shocked rats exhibited stronger memory for the tone-shock clan than rats that were not shocked and besides stronger memory than rats that were shocked two hours after training. These findings are all consistent with the assertion that retentiveness modulation is independent of the melancholia backdrop of reinforcers.

3.iii.3.1. Conditioned Modulation

Memory modulation by a conditioned aversive stimulus has too been demonstrated (Holahan and White 2002, 2004) (see Figure iii.5). Rats were placed into a small cage where they received several shocks and into a 2d distinguishable muzzle where they did not receive shocks. They were then trained to find nutrient in a Y-maze past forced entries into both the food and no-food artillery in a predetermined order. On the last training trial all rats were forced to enter the food arm subsequently which they were placed into either the shock or no-shock cage (no shocks were given at this time). Two days later the rats were tested on the Y-maze with no food in either arm. The rats in the group that had been placed into the shock muzzle afterwards maze training made significantly more correct responses (to the arm that previously contained food) than the rats that had been placed into the no-stupor muzzle (see Figure 3.5).

Figure 3.5

(See Color Insert) Conditioned modulation of arroyo behaviour by aversive stimulation. Rats were placed in a cage with a grid flooring and shocked, and alternately into a discriminable cage and not shocked. On the next 2 days the rats were given a total (more...)

This increased resistance to extinction cannot be attributed to action-outcome learning most the stupor because the rats were forced to run to the food-paired arm immediately before exposure to the shock cage. Activeness-event learning nigh the daze would have decreased their tendency to run to the food arm. Since the rats had an increased tendency to run to the food arm, the effect of exposure to the shock-paired cage is attributable to a memory modulation effect produced past exposure to the conditioned aversive cues in the daze cage.

In another control group, rapid extinction was observed in a grouping that was exposed to the shock cage ii hrs after the last Y-maze grooming trial. This result is consistent with the conclusion that the conditioned contextual cues in the shock muzzle evoked a conditioned retentivity modulation response.

3.3.iv. Westin-stay 50earning

Post-training reinforcers have been shown to modulate several different kinds of retentiveness, including cognitive instrumental responses (Williams, Packard, and McGaugh 1994; Gonder-Frederick et al. 1987; Manning, Hall, and Gilt 1990; Messier 2004), CCP learning (White and Carr 1985), and simple S-R associations (Packard and White 1991; Packard and Cahill 2001; Packard, Cahill, and McGaugh 1994).

In an case of South-R learning, the win-stay chore (Packard, Hirsh, and White 1989), rats were placed on the center platform of an 8-arm radial maze. Iv maze arms had lights at their entrances and only those arms independent food pellets. The other four arms were dark and did not incorporate nutrient. Entries into dark artillery with no food were scored as errors. On each daily trial a different set of four artillery was lit and baited with food. Since the food was in a different spatial location on each trial the lights were the merely data about the location of the food available to a rat on the middle platform (run into Figure 3.6). Rats acquired this S-R behavior slowly, achieving a charge per unit of 80%–85% correct responses later approximately xxx trials.

FIGURE 3.half dozen

Schematic diagram of win-stay task. White dots are lights at the entrances to artillery from the centre platform. Black dots are food. On each daily trial iv unlike arms are lit and baited with food. The other 4 artillery are nighttime and contain no food. The (more...)

Which reinforcement procedure produced this learned beliefs? There are two possibilities. Get-go, since the rats repeatedly meet the lit maze arms from the center platform, and since this beliefs is followed by nutrient reward, the increment in frequency of lit arm entries could be due to action-outcome learning about how the response leads to the nutrient reward. 2d, if a rat randomly enters an arm, passing the light at the entrance, and and so eats food at the cease of the arm, the retention modulation property of the food reinforcer would strengthen the clan between the light stimulus and the arm-inbound response. This type of learning has been described equally the conquering of a habit (Mishkin and Petri 1984; Mishkin, Malamut, and Bachevalier 1984), because nil is learned well-nigh the human relationship of either the stimulus or the response to the reinforcer.

Evidence against the action-upshot learning hypothesis was obtained using a devaluation procedure (Dickinson, Nicholas, and Adams 1983; Balleine and Dickinson 1992) in which consumption of a reinforcer is paired with injections of lithium chloride, which produces gastric angst. The conditioned aversive response produced by the food CS, known as conditioned taste aversion (Garcia, Kimeldorf, and Koelling 1955; Garcia, Hankins, and Rusiniak 1976) reduces or eliminates consumption of the reinforcer. In the instrumental learning context this is known as devaluation of the reinforcer. Sage and Knowlton (2000) trained rats on the win-stay task and then devalued the food reinforcer by giving lithium injections following consumption in the rats' home cages. On subsequent win-stay trials the rats continued to enter lit arms on the maze, only stopped eating the food pellets.

If the pellets rewarded the response to the lit arms, the change in their affective value should have attenuated the rats' trend to enter those arms. The fact that this did not happen suggests that advantage was not the ground of the response, but that information technology was due to a modulated or strengthened retentivity for the S-R association. This occurred when the reinforcer was consumed shortly after the rats entered each lit arm. Since neither Due south-R learning nor its modulation involves information most the affective properties of the reinforcer, devaluation of the reinforcer did not bear on the rats' beliefs.

3.4. SUMMARY

Reinforcement can be operationally divers every bit the procedure that occurs when the presence of some object or consequence promotes observable behavioral changes. The present analysis argues that these new behaviors are due to at least 3 different, independently interim reinforcement processes: action-consequence learning about rewarding or aversive consequences of behavior, conditioned arroyo or withdrawal, and memory modulation.

Although advantage is often assumed to be the only reinforcement process, evidence shown here suggests that this is not the example. Furthermore, when reward does influence behavior it tin can do so just as the result of either action-outcome learning or the sequential occurrence of Pavlovian workout and action-outcome learning.

Conditioned approach is another reinforcement procedure that tin can influence beliefs if the learning atmospheric condition allow a view of the CS from a distance. Although approach and reward are ordinarily produced simultaneously past naturally occurring reinforcers, there is evidence in the drug literature that approach and aversion co-occur, suggesting that melancholia states and approach-withdrawal behaviors consequence from independent processes (Wise, Yokel, and deWit 1976; White, Sklar, and Amit 1977; Reicher and Holman 1977; Sherman et al. 1980; Bechara and van der Kooy 1985; Carr and White 1986; Corrigall et al. 1986; Lett 1988; Brockwell, Eikelboom, and Beninger 1991).

Memory modulation is the third reinforcement process. It is continuously produced past contact with reinforcers and conditioned reinforcers, and affects all forms of learning. Situations in which no other form of reinforcement tin operate provide evidence that modulation is an independently occurring process.

The major difficulty involved in distinguishing among these reinforcement processes is that they can all human action simultaneously on different kinds of retentivity (White and McDonald 2002; McDonald, Devan, and Hong 2004). Analyses of a number of common situations used to written report reward, such every bit bar pressing or running in a runway, suggest that it is hard or impossible to show that reward is the only procedure that affects the learned behavior, suggesting that these may not be ideal for many purposes. When studying the effects of reinforcers, careful selection of the retentiveness chore—which, in turn, determines the blazon of learning from which the reinforcer activeness will be inferred—is disquisitional.

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