Development of Stimulus Control under each Component of a ... · Luis Otero-Valles University of Florida . DEVELOPMENT OF STIMULUS CONTROL 2 Development of Stimulus Control under

DEVELOPMENT OF STIMULUS CONTROL

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Development of Stimulus Control under each Component of a Multiple Fixed-Ratio

Fixed-Interval Schedule of Reinforcement

Luis Otero-Valles

University of Florida


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Development of Stimulus Control under each Component of a Multiple Fixed-Ratio

Fixed-Interval Schedule of Reinforcement

In behavioral research, many experiments use a multiple schedule of

reinforcement, but little research has been conducted on the development of

stimulus control under a multiple schedule. Stimulus control refers to the

relationship between an antecedent stimuli and a subject’s response. When some

aspect of the antecedent stimuli is altered and results in altered responding, then

stimulus control is present with respect to that stimuli’s variance (Eckerman, 1969).

Once a relationship is established between a stimulus and reinforcement, the

established stimulus becomes a signal of reinforcement contingencies and increases

the probability of responding in the presence of that stimulus (Williams, 1976). An

established stimulus alters the likelihood of responding when it makes it more likely

a particular event will result in reinforcement (McPherson & Osborne, 1986). In

previous literature, stimulus control has been observed when a subject emits a

particular response under a certain stimulus and a different response in the absence

of that stimulus. For example, if, in the presence of the houselight, a response on a

lever will produce a pellet, then stimulus control would be obtained when the rat

presses the lever only in the presence of the houselight and never when the

houselight is off. In this example the houselight is the discriminative stimulus, the

lever press is the response, and the pellet is the positively reinforcing consequence.

These events comprise a three-term contingency, which typically must be present

for the development of stimulus control.


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Morse and Skinner (1958), however, showed evidence of stimulus control in

pigeons by delivering food in the presence of one stimulus and not in the presence

of another regardless of response. Then, once the pigeons were required to respond

to receive the food as reinforcement, rates of responding were much higher under

the stimulus with which reinforcement was initially paired. The contingency

between the initial stimulus and reinforcement, independent of a response, was

sufficient to exert control over responding even when reinforcement depended on

responding. That is, responding was greater under a particular stimulus due to its

prior association with reinforcement. Thus, that particular stimulus exhibited

stimulus control by affecting the subject’s behavior under its presence and in its

absence (Morse & Skinner).

Additionally, McPherson and Osborne (1986) showed control of behavior by

a stimulus using a three-key discrete-trial procedure with pigeons. Under one

condition, illumination of the right key initiated the trial. A response on a right key

produced the lighting of a center key, leading to reinforcement when pecked. In a

second condition, illumination of the left key initiated the trial. Following a left key

response, a response had to occur on the right key followed by a response to the

center key to produce reinforcement. Thus, the illumination of the left key became a

conditional stimulus, making right key responding more likely to follow a left key

response. In the absence of illumination of the left key, responding on the right key

was promptly followed by a peck on the center key. That is, the control of the left-

key stimulus is seen through the left key’s influence on a pigeon’s right key response


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rate through signaling an increase probability of reinforcement (McPherson &

Osborne).

The clear presence of stimulus control has caused many researchers to be

interested in and observe its development. Eckerman (1969) believed that the

development of stimulus control could be traced to correlation of stimuli and

reinforcement probabilities. In other words, stimulus control developed if there was

a higher chance of reinforcement under a particular stimulus. Thus, the given

stimulus becomes a cue of reinforcement when present and a lack of reinforcement

during its absence (Williams, 1976). In fact, under contrasting stimuli in which

responses under one stimulus are reinforced and not under another have been

found to sharpen effect of stimulus control (Morse & Skinner, 1958).

Strong stimulus control tends to result in the occurrence of contrast or

discrimination, whereas weak stimulus control tends to result in induction or

generalization (Pear & Wilkie, 1971; Wertheim, 1965). Yarczower, Gollub, and

Dickson (1969) studied stimulus control in the presence of other cues also

competing over the response’s control. One group of pigeons was exposed to

discrimination training, in which a multiple variable-interval (VI) 30-s extinction

(EXT) schedule was in effect. In the presence of a 550-nm wavelength keylight,

responses were reinforced (S+) according to a VI 30-s schedule, and in the presence

of a 570-nm wavelength keylight, responding was not reinforced (S-). A second

group of pigeons only was exposed to the VI 30-s schedule in the presence of the

550 nm stimulus. Generalization of responding to a range of other wavelengths

then was tested. Pigeons that had been trained on the multiple VI EXT schedule,


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responded substantially less relative to the other group when wavelengths of 560

nm or greater were presented. The authors proposed that the control from

alternative cues may have weakened stimulus control when associated with the

reinforcement schedule. That is, for the pigeons trained on the single schedule,

responding tended not to come under the control of the wavelength (i.e., responding

generalized to greater wavelengths as well). These findings suggest that the use of a

multiple schedule tends to enhance the development of stimulus control.

The power of stimulus control further can be demonstrated by three-phase

experiment conducted by Wenrich (1963). He discovered that if an operant (lever

press) was brought under the control of a discriminative stimulus (light), the rats

emitted responses even when only a conditioned reinforcer (buzzer) was presented

and even when satiated via pre-session feeding. If the operant was not trained in

the presence of a discriminative stimulus, then these rats responded well below

baseline levels for the conditioned reinforcer and when satiated.

Powell (1973) found that deprivation increased response rate under an

extinction stimulus. Interestingly, the lower the existing level of stimulus control,

the greater the absolute rate of responding, contradicting previous literature.

Deprivation’s effect on performance has been known to diminish in correlation with

higher accuracy developed during training. Powell found accuracy of discrimination

to decline as deprivation increased. A possible explanation, suggested by Powell, for

the mixed data with respect to the strength of stimulus control producing contrast

or induction may be due to the broad definition of a “strong” and “weak” stimulus

control during baseline. The two-component multiple schedules often employed in


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these types of arrangements, designate one component in which reinforcement can

be earned (S+) and one component in which reinforcement is not available (S-).

Then discrimination indices are obtained by comparing responding under

experimental conditions (e.g., pre-session feeding) to baseline responding. Rather

than defining a “strong” and “weak” stimulus, Richards (1974) was interested in

differential stimulus control under each component of a multiple VI 1-min VI 1-min

schedule in which the delay to reinforcement varied across components (i.e.,

delayed versus immediate). Generalization probes were administered in which the

orientation of a line displayed on the key was rotated at several degrees relative to

baseline orientation of the line. The results demonstrated that stimulus control was

weakened when the reinforcer was delayed. Furthermore, when the magnitude of

the delayed reinforcer was increased from 1.5 s of food access to 4 s, stimulus

control was weakened even more. Richards noted it was plausible, however, that

the observed weakening of stimulus control was rather the failure of stimulus

control to develop. He suggested that the large magnitude of delayed reinforcement

slowed the development of stimulus control and that if baseline had been extended,

then weakening effects may not have been permanent, which could have resulted in

little to no difference across the magnitude conditions. Although Richards never

experimentally addressed that explanation, his results do indicate that, under

certain conditions, stimulus control may develop at different rates for each multiple-

schedule component. The explanation provided by Richards was consistent with

results reported by Van Houten and Rudolph (1972). They found the presence of a

salient, but irrelevant, antecedent stimulus (i.e., houselight illumination) inhibited


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the development of stimulus control. Additionally, they, too, suggested that

extended exposure to the contingencies may have allowed responding to come

under the control of the relevant stimulus (i.e., airflow in mph).

Whereas Richards (1974) was interested in the manipulation of

consequences, Perikel, Richelle, and Maurissen (1974), like Van Houten and

Rudolph (1972), examined the effects of antecedent manipulations of visual stimuli

as factors contributing to the development of stimulus control. Pigeons were studied

under both a one-key and a two-key procedure. In the one-key procedure, pecks on

the center key—illuminated green—resulted in reinforcement only after

presentation of a long duration stimulus (i.e., houselight illuminated red for 10 s)

but not after shorter-duration stimuli (range: 1 – 8 s). The two-key component

signaled reinforcement for both long- and short- duration stimuli, depending on the

side of responding: Left key pecks were reinforced after long- duration presentation

and right key pecks were reinforced after short-duration presentation.

Discriminative control was seen under both procedures. In the one-key procedure,

the probability of responding on the green key following a long-duration stimulus

was always above .75. The probability of responding following a short-duration

stimulus initially remained low but later increased to above .25 when the duration

of the stimulus presentation was increased beyond 6 s. When the short-duration

stimulus was 8 s, discriminative control was eliminated (i.e., equal probability of

responding following both short and long durations). The two-key procedure

yielded higher accuracy, measured in percent correct responses, as the duration of

the shorter stimulus was steadily increment by 1 s across conditions. That stimulus


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control developed at all under the one-key procedure was quite notable because

pecking green following either a long- or short-duration stimulus would have

allowed the pigeon to earn the maximum number of available reinforcers in the

session. The contingencies arranged for the two-key procedure, however, did

require that the pigeon learn a conditional discrimination (left versus right) in order

to earn 100% of available reinforcers.

One of the key factors that has been found to influence stimulus control has

been the schedule of reinforcement. The way in which reinforcers are arranged

engenders particular rates and patterns of responding, and Lattal (1986)

demonstrated that organisms are quite sensitive to even subtle differences. He

compared responding under a multiple schedule with responding under a mixed

schedule. In the multiple schedule VI and variable-time (VT) components were

signaled by distinct visual discriminative stimuli, whereas in the mixed schedule,

component changes were not present. Of course, one source of discriminative

control in the mixed schedule would be response-reinforcer dependence (i.e.,

differential consequences in the VI and VT components). During the multiple and

the mixed schedule, response rates under the VI component were higher than those

under the VT component. In order to obtain control by response-reinforcer

consequences, it was necessary for the component-durations to be relatively long.

Response rates were steadily higher in VI component relative to the VT component

in the multiple schedule compared to the difference in rates in the mixed schedule,

indicating that the discriminative stimuli played an important role in determining

behavior.


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Responding under a fixed-interval (FI) schedule necessarily is controlled by

both the discriminative stimulus and consequence. The first response to occur after

the interval elapses results in reinforcement. Any responses that occur earlier do

not affect the probability of reinforcement. Therefore, a “scalloped” pattern of

responding is typical of FI performance. Little responding occurs early in the

interval, with response rates accelerating towards the end of the interval as the

organism temporally approaches reinforcer availability (Wilkie, 1974; Zeiler, 1970).

Fixed-ratio (FR) schedules specify more about the contingencies of reinforcement

than do FI schedules. In an FR schedule, a specific number of responses must be

completed to produce a reinforcer (Zeiler, 1968). FR performance often is

characterized by a “break-and-run” pattern of responding. Generally, a period of

nonresponding is evident at the start of a ratio, followed by steady, rapid

responding until a reinforcer is achieved. The probability of reinforcement

proportionally depends on and increases with the number of responses emitted. A

comparison of stimulus control in FI and FR schedules only has been studied in the

context of a matching-to-sample task (Ferster, 1960). Ferster reported higher

accuracy when the FR schedule was in effect. There are no direct comparisons of

acquisition and maintenance of stimulus control under FI and FR schedules in a

free-operant procedure (e.g., a multiple schedule) reported in the literature.

Williams (1984) speculated that the decline of research on the development of

stimulus control in operant paradigms may have been due to a shift of interest in

studying stimulus control in respondent arrangements. Another possibility is that

in free-operant arrangements, the presence or absence of stimulus control is


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revealed relatively easily by examination of cumulative-response records, so a lack

of interest in answering simple experimental questions could be to blame.

Answering “simple” questions with respect to stimulus control, could have

major implications in several important areas of behavioral research (e.g.,

behavioral momentum, behavioral economics, behavioral pharmacology). For

example, stimulus control interestingly has been shown to influence the effects of d-

amphetamine. Performance impairments that accompanied pre-session d-

amphetamine administration were minimized when stimulus control was strong

(Rees, Wood, & Laties, 1985). Similar effects were found when chlordiazepoxide

and phenobarbital were administered pre-session: Behavior under weak stimulus

control was more disrupted by drug effects (Thompson, 1975). That stimulus

control is able to modulate the effects of drugs underscores the importance of

identifying potential differential stimulus control, especially in different

components of a multiple schedule given that tolerance to drug effects also has been

shown to develop differentially depending on certain properties of each component

(e.g., Hoffman, Branch, & Sizemore, 1987).

The purpose of the present experiment was to assess the development of

stimulus control under each component of a multiple FI 5-min FR 30 schedule of

reinforcement. Behavior may be more sensitive to one set of contingencies over the

other due to the way the reinforcers are arranged. That is, behavior may come

under the control of the discriminative stimulus more quickly in a given component.

Whether responding comes under the control of discriminative stimuli differentially

is important with respect to understanding multiple schedule stimulus control.


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Furthermore, shedding light on the development of stimulus control also may help

shape future behavioral pharmacology experiments, especially those with aims to

identify behavioral determinants of acute and chronic drug effects.

Method

Subjects

Six experimentally naive adult male White Carneau pigeons (numbered 106,

113, 114, 400, 525, and 674) were obtained from Double-T Farms, Glenwood, Iowa.

The pigeons were maintained at 85% of their free-feeding body weight via post-

session feedings consisting of mixed grain and pellets. Outside of experimental

sessions, the pigeons were housed in individual home cages in a temperature- and

humidity-controlled colony room. The pigeons had free access to vitamin-enriched

water and health grit in their home cages.

Apparatus

The experiment was conducted using six pigeon operant-conditioning

chambers with interior dimensions of 35 x 30 x 35 cm. Three circular keys were

horizontally aligned on the front panel of the chamber. The keys measured 2cm in

diameter, were posited 5.5 cm apart, and were 23 cm from the chamber floor. Only

the center key was used in the present experiment. A minimum force of 0.098N was

required to activate the key. The activation of the center key produced a 30-ms

tone. A houselight was located 7 cm above the center key and 2 cm from the

chamber ceiling. An aperture measuring 5 cm by 5 cm was located 10 cm directly

below the center key and 11 cm from the chamber floor. When the hopper was

raised, the pigeon could access buckwheat, milo and hempseed through the


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aperture, which was illuminated during reinforcer presentations. All other lights in

the chamber darkened during reinforced presentations. A white noise at

approximately 95 dB was used in order to mask extraneous sounds in the rooms

containing the operant chambers. In an adjacent room, computers running EC-

BASIC software (Palya & Walter, 1993) controlled experimental events and

recorded data, and cumulative-response recorders provided live-time data

collection.

Procedure

Shaping. After the pigeons consistently approached and ate from the raised,

illuminated hopper, successive approximations to the target response were

reinforced in order to establish responding on the center key (illuminated white).

Once the pigeon reliably pecked the key, the following session consisted of an FR 1

schedule. The center key was illuminated white, responses to the center key

produced 3-s access to food, and the session lasted until the pigeon earned 60

reinforcers.

Multiple-schedule Procedure. The start of each session was signaled by a

5-min blackout. The FR component, signaled by a white key, always preceded the FI

component, signaled by a red key. A sequence of both components comprised a

block, and the session ended after 20 blocks. Completion of the FR requirement or

the first response after the interval for the FI elapsed produced 3-s access to food. If

the pigeon did not complete the FR requirement in 60 s or did not respond within

60 s after the FI elapsed, the component ended and no reinforcer was provided. A


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30-s blackout occurred between the FR and FI component, whether or not the

pigeon received a reinforcer.

The FR was gradually increased across session until the target FR of 30

responses was reached. Simultaneously, the FI was incremented by 1 min across

sessions until responding under the target FI of 5 minutes was achieved. Each ratio

and interval increase occurred only if the cumulative-response records and overall

response-rate data showed consistent responding within each session and

responding in all components appeared stable. The ratio schedule (FR 2, FR 5, FR 8,

FR 12, FR 20, FR 25, and FR 30) was increased each session for all pigeons, except

for Pigeon 400 for which FR 25 was excluded from the series. The interval schedule

(FI 1 min, FI 2 min, FI 3 min, FI 4 min, and FI 5 min) increased each session for all

pigeons. Thus, 6 sessions of training were conducted (5 sessions for Pigeon 400)

before the baseline schedule (a multiple FR 30 FI 5-min schedule of reinforcement)

was in effect. In this experiment, a total of 40 baseline sessions were conducted.

Results

Figures 1 through 6 show rate and latency data for individual pigeons. The

circles represent FR responding, and the triangles represent FI responding. The top

panels show two rate analyses. Overall rate was calculated by determining the

number of pecks emitted in the presence of the white (FR) or red (FI) key for the

whole session divided by the time the key was illuminated either white or red.

Average rate was calculated by determining the response rate in each of the 20 FR

component presentations and averaging them. Comparing overall rate and average

rate allowed us to analyze whether the session rate was representative of rates in


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each component. Similarly, the bottom two panels display two latency analyses.

Total latency was calculated as the time before the first response was upon each

component presentation. Average latency refers to the average of 20 component

presentations. Phase-change lines separate training and baseline data.

Figure 1 shows Pigeon 106’s data. Stimulus control began to emerge as early

as the second and third sessions, as FR and FI responding diverged dramatically

even during training. That is, when the FR and FI values were increased, FR rates

increased, and FI latency increased. During baseline, overall and average rates

under FR remained much higher than those under FI. Towards the conclusion of

baseline, FR rates still appeared to be increasing. FR latency remained much lower

than FI latencies. Rates and latencies on session 25 were atypical relative to other

sessions. With the exception of session 25, FR rates were always greater than FI

rates and FR latencies were always shorter, with FR performance appearing

somewhat more variable than FI performance. Whole-session performance

represented average rates and latencies well.

Figure 2 shows rate and latency data for Pigeon 113. Stimulus control was

observed within the second and third sessions, with FR and FI responding diverging

in training. FR rates increased, and FI latencies increased. During baseline, overall

and average rates under FR were much higher than those under FI. Rates under FR

continued to increase even after baseline was established. FI latencies were much

higher than FR latency and continued to increase across sessions. FR rates were

always greater than FI rates and FI latencies were always greater than FR latencies,


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with FR performance being slightly more variable than FI performance. Whole-

session performance was representative of average rates and latencies.

Figure 3 shows data for Pigeon 114. Stimulus control was observed in

training. After training, in the first few sessions of baseline, FI rates and latencies

decreased to FR levels. The first few sessions of baseline were atypical in

comparison to other sessions, with FI rates and latencies dramatically increasing

shortly after and continued to increase across sessions. FR rates increased as FI

latencies increased. During baseline, overall and average rates under FR were much

higher than rates under FI. After baseline was established, FR rates continued to

increase across sessions. FR latencies were much lower than FI latencies. FR rates

were always greater than FI rates and, with the exception of the first few baseline

sessions, latencies under FI were always greater than latencies under FR. Whole-

session performance was representative of average rates and latencies.

Figure 4 shows data for Pigeon 400. Stimulus control was apparent from the

very first session, with notable difference observed between FR and FI responding

in training. However, responding began to decrease in the first few sessions of

baseline. The food-hopper time then was increased from 3 seconds to 5 (denoted by

the second phase-change line), given that 3 second reinforcement was not sufficient

to maintain responding. A dramatic recovery of performance was evident in the

very first session in which the hopper time was 5 s. The hopper time was kept at 5

seconds for the duration of the experiment. FR rates increased, and FI latencies

increased. During baseline, overall and average rates were higher than rates under

FI. FR latencies remained much lower than FI latencies. FR rates were always


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greater than FI rates and FI latencies always greater than FR latencies, with FR

responding being somewhat more variable than FI responding. Whole-session

performance was representative of average rates and latencies.

Figure 5 shows data for Pigeon 525. Stimulus controlled began to appear

within the second and third session, with FR and FI responding drastically

diverging. FR rates increased, and FI latency increased. During baseline, overall and

average rates under FR remained much higher than those under FI. Rates under FR

drastically increased after training well into the conclusion of baseline, with

successively higher rates within each additional session. FR latency remained much

lower than FI latencies, with latencies steadily decreasing across sessions. FR rates

were always greater than FI rates and FR latencies were always shorter, with FR

performance appearing somewhat more variable than FI performance. Whole-

session performance represented average rates and latencies well.

Figure 6 shows data for Pigeon 674. Stimulus control was observed as early

as the second and third sessions, as FR and FI responding deviated greatly even

during training. FR rates increased, and FI latency increased. During baseline,

overall and average rates under FR were considerably higher than those under FI.

Towards the end of baseline, FR rates still appeared to be increasing and continued

to increase across sessions. FI rates remained unchanged throughout all sessions.

FR rates and latencies on the second to last session were atypical relative to other

sessions. With the exception of the second to last session, FR rates were always

greater than FI rates and FR latencies were always shorter, with FR performance


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appearing somewhat more variable than FI performance. Whole-session

performance represented average rates and latencies well.

Figures 7 through 12 show rates and latencies for sequential component

presentations across the first five and final five sessions for all pigeons. That is, the

data points represent reinforcer-by-reinforcer responding. Depicting the data in

such a way allows for not only a detailed comparison from which the development

of stimulus control (from the beginning of the experiment to its completion) can be

examined, but also reveals whether performance in each component was stable and

representative of whole-session rates and latencies.

Figure 7 shows Pigeon 106’s data. Stimulus control was evident in that

differential responding in FR and FI components occurred in the first session. The

degree of stimulus control seemed to strengthen across sessions, however. FR rates

initially were high, and they continued to increase such that response rates in the

last five sessions were higher than those in the first five sessions. FI rates initially

were low and consistent in the first five sessions. By the last five sessions,

responding was much more variable, with lower responding in the final component

than responding in the very first component. FR latencies were continuously low

across all sessions. Latencies under FI were widely variable in the first five sessions.

By the last five sessions, however, latencies were high and consistent.

Figure 8 shows Pigeon 113’s data. Stimulus control was observed

through differential responding in FR and FI in the first session. However, stimulus

control appeared to strengthen across sessions. FR rates initially were high in the

first five sessions. High rates of responding were maintained well into the very last


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session of the experiment.. FI rates initially were widely variable in the first five

sessions. By the last five sessions, responding became much more variable, with

responding drastically fluctuating lower and higher than was observed in the first

five sessions. FR latencies were considerably low across all sessions, yet, became

slightly more variable in the last five sessions. Latencies under FI were widely

variable in the first five sessions. By the last five sessions, however, latencies were

much higher and consistent.

Figure 9 shows data for pigeon 114. Stimulus control emerged as differential

responding was observed between FR and FI components during the first session.

Yet, stimulus control was shown to strengthen across sessions. FI rates initially

were widely variable in the first five sessions. By the last five sessions, responding

was much more consistent, with lower responding in the final component than

responding in the very first component. FR rates initially were high and such

responding was maintained well into the final 5 sessions, which contained modestly

higher rates in than was observed in the first five sessions. FR latencies were

continuously low across all sessions. Latencies under FI were widely variable in the

first five sessions with disconnected high and low responding. By the last five

sessions, however, latencies were consistently high and with much less variance.

Figure 10 shows Pigeon 400’s data. Stimulus control was observed within

the first session through differential responding between FR and FI components. In

addition, strengthening of stimulus control was also observed across sessions. FR

rates initially were high, and they continued to increase such that response rates in

the last five sessions were higher than those in the first five sessions. FI rates


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initially were low and consistent in the first five sessions. By the last five sessions,

responding was much more variable, with higher responding in the final component

than responding in the very first component. FR latencies were continuously low

across all sessions, with a slight decreasing pattern observed by the last five

sessions. Latencies under FI were widely variable in the first five sessions. By the

last five sessions, however, latencies were high and consistent.

Figure 11 shows Pigeon 525’s data. Stimulus control was evident in that

differential responding in FR and FI components occurred in the first session. The

degree of stimulus control seemed to strengthen across sessions, however. FR rates

initially were low, yet, they continued to increase such that response rates in the last

five sessions drastically higher than those in the first five sessions. FI rates initially

were low and consistent in the first five sessions. By the last five sessions,

responding was much more variable, with lower responding in the final component

than responding in the very first component. FR latencies initially were low, and

they continued to decrease such as latencies in the last five sessions were lower

than those in the first five sessions. Latencies under FI were widely variable in the

first five sessions. By the last five sessions, however, latencies were high and

consistent.

Figure 12 shows Pigeon 674’s data. Stimulus control became notable within

the first session though observed differential responding under FR and FI

components. However, stimulus control appeared to strengthen across sessions. FR

rates initially were high, and they continued to increase such that response rates in

the last five sessions were higher than those in the first five sessions. FI rates


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initially were low and slightly variable in the first five sessions. By the last five

sessions, responding was much more variable, with higher responding in the final

component than responding in the very first component. FR latencies were

continuously low across all sessions, with a slight decreasing trend observed by the

final five sessions. Latencies under FI were widely variable in the first five sessions.

By the last five sessions, however, latencies were high and consistent.

Figure 13 shows representative cumulative-response records from an

individual session for Pigeon 114 (top panel) and Pigeon 106 (bottom panel).

Vertical ticks represent individual responses, horizontal lines represent periods of

nonresponding, and diagonal ticks represent reinforcer delivers. Pigeon 114 had the

fastest rates and shortest latencies under FI, whereas Pigeon 106 had the slowest

rates and longest latencies under FI, with the pattern of responding resembling

typical FI performance, or a “scallop” pattern. For both pigeons, brief pausing

followed by rapid responding was evident in FR components. This figure shows how

FI performance can resemble behavioral patterns typical of an FR component for

individual subjects, although FI rates were always lower than FR rates.

Discussion

The purpose of the present experiment was to assess the development of

stimulus control under each component of a multiple FR 30 FI 5-min schedule of

reinforcement. Behavior may be more sensitive to one set of contingencies over the

other simply due to the manner in which reinforcers are arranged. That means that

behavior may come under the control of a discriminative stimulus more rapidly in a

one component than another. Whether responding comes under the control of


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discriminative stimuli differentially is important with respect to understanding

multiple-schedule stimulus control.

The results of this experiment showed stimulus control to take effect as early

the second to third sessions of training, through differential responding under FR

and FI components. However, differential responding increased across sessions

with FR rates and FI latencies surpassing initial responding by the end of the

experiment. Thus, stimulus control appeared to strengthen across sessions under

both FR and FI components. Furthermore, cumulative records showed that FI rates

might resemble behavioral patterns typically seen under FR components, for certain

subjects. As Fester (1960) described, FR performance often is characterized by a

“break-and-run” pattern of responding. Generally, a period of nonresponding is

evident at the start of a ratio, followed by steady, rapid responding until a reinforcer

is achieved. It appears, FI rates are able to mimic such steady responding until a

reinforcer is achieved in certain subjects. However, it is important to note that even

in the pigeons whose FI rates resembled FR, FR rates always surpassed FI rates.

These results were equally represented through whole-session performance as well

as average calculations of rates and latencies. That is, average session performance

reflected performance in each individual component.

The results of this experiment indicated that behavior came under control

rapidly under each component, with differential responding as early as the second

session of training. That is, under two varying stimuli, the subjects responded to the

signal of reinforcement contingencies and the likelihood of responding was altered

given the present contingencies almost immediately. FR rates increased at the same


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pace as FI latencies increased. At the same time, FI rates and FR latencies remained

relatively stable, thus indicating that stimulus control not only emerged but also

strengthened at comparable rates under FR and FI components in a multiple

schedule. This was particularly notable in the high FR rates and FI latencies during

the final five sessions of the experiments, in comparison to the initial five sessions.

While latencies are in fact, an absence of responding, they are still indicative

of stimulus control. Latencies continued to increase across sessions under the FI-5-

min component because reinforcers were never available towards the beginning of

the interval. Morse and Skinner (1958) described that behavior comes under the

control of a stimulus when reinforcement is associated with its presence.

Interestingly, even though FR provided more frequent reinforcement than FI, FI

reinforcement rate not only was sufficient to allow behavior to come under stimulus

control but it was strong enough to allow stimulus control develop comparably to

FR stimulus control.

The results from this experiment suggest that performance averaged across

sessions is representative of performance within each individual component.

Knowing the average performance compares to performance within each

component provides greater accuracy of a subject’s behavior. For instance, average

performance may become misleading due to outlier performance under individual

components. Thus, knowing responding within individual components is well

represented by average calculation across sessions further solidifies subject data.

Overall, results from this experiment include that stimulus control not only

emerges but strengthens equally once the relationship between stimulus and


23

reinforce is established, regardless of reinforce arrangement. These findings may be

applicable to researchers studying stimulus control under multiple schedules. For

instance, Powell (1973) claimed that the mixed data observed in his experiment

were caused by the broad definition of a “strong” and “weak” stimulus during

baseline. This experiment shows adequate acquisition and strengthening of stimulus

control under both FR and FI components, perhaps allowing further research to

study the strength and weakness of a stimulus based on the relationship established

between stimulus and reinforcer rather than the frequency of reinforcement.

Furthermore, bringing insight on the development of stimulus control also may help

shape future behavioral pharmacology experiments, especially those with aims to

identify behavioral determinants of acute and chronic drug effects. Additionally,

previous behavioral pharmacological studies have shown that average responding

does not appropriately represent performance in each individual component. The

fact that average and overall performances were represented in this experiment

brings to light the effect of pharmacological agents in average and overall

performance.

Basic schedule research, such as the present study, contributes by bringing

knowledge towards the control the environment exhibits on behavior.

Understanding how this power, deemed stimulus control, functions may bring

further knowledge towards environmental influences on behavior and its

development. While the mystery that is stimulus control is far from being solved, a

clearer picture of its emergence and development is observed with each passing

experiment. Behavioral schedule experiments still hold the capacity to bring insight


24

towards behavioral mechanism and the intricate relationship it hold with

environmental influences through the observed effects of stimulus control under the

varying schedules of reinforcement, one can argue, we are all under.


25

References

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Ferster, C. B. (1960). Intermittent reinforcement of matching to sample in the pigeon.

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effects as dependent upon fixed-ratio size. Journal of the Experimental Analysis of

Behavior, 47, 363–376.

Lattal, K. A. (1986) Response-reinforcer dependence and independence in multiple and

mixed schedules. Journal of Experimental Analysis of Behavior, 265-71.

McPherson, A. & Obsborne, J. G. (1986). The emergence of establishing stimulus control.

Psychological Record, 36, 375-386.

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26

Richards, R W. (1974). Inhibitory stimulus control and the magnitude of delayed

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Wenrich, W. W. (1963), Response strength of an operant under stimulus control with

satiated subjects. Journal of Experimental Analysis of Behavior, 6, 247–248

Wertheim, G. A. (1965), Behavioral contrast during multiple avoidance schedules. Journal of

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Wilkie, D. M. (1974). Stimulus control of responding during a fixed-interval reinforcement

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Williams, B.A. (1976) Behavioral contrast as a function of the temporal location of

reinforcement. . Journal of Experimental Analysis of Behavior, 26, 57-64.

Williams, B. A. (1984) Stimulus control and associative learning. Journal of Experimental

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27

Zeiler, M. D. (1970). Fixed-interval stimulus control. Journal of Experimental Analysis of

Behavior, 14, 291-299.


28

Figure Captions

Fig. 1. Overall, average, and total rates and latencies for Pigeon 106 across sessions. Circles

represented an FR component, triangles FI.











Fig. 7. Rates and latencies for sequential component presentations across the first five and

final five sessions for Pigeon 106. Data points represent reinforcer-by-reinforcer

responding.



responding.



responding.


29



responding.



responding.



responding.

Fig. 13. Representative cumulative-response records for Pigeon 114 and Pigeon 106.

Vertical ticks represent pecks, horizontal lines represent periods of nonresponding,

and diagonal ticks represent delivery of reinforcement.


30

Figure 1

Overall Rate

0 10 20 30 40

0

1

2

3

FI

FR

Average Latency

0 10 20 30 40

1

10

100

1000

106

Average Rate

0 10 20 30 40

0

1

2

3

Total Latency

0 10 20 30 40

10

100

1000

10000

Resp

on

ses p

er

seco

nd

Seco

nd

s

Sessions


31

Figure 2

Overall Rate

0 10 20 30 40

0

1

2

3

FI

FR

Average Latency

0 10 20 30 40

1

10

100

1000

113

Total Latency

0 10 20 30 40

10

100

1000

10000

FR

FI

Average Rate

0 10 20 30 40

0

1

2

3

4

Seco

nd

sR

esp

on

ses p

er

seco

nd


32

Figure 3

Overall Rate

0 10 20 30 40

0

1

2

3

Average Latency

0 10 20 30 40

1

10

100

1000

114

Total Latency

0 10 20 30 40

10

100

1000

10000

FR

FI

Average Rate

0 10 20 30 40

0

1

2

3

Resp

on

ses p

er

seco

nd

Seco

nd

s

Sessions


33

Figure 4

Overall Rate

0 10 20 30 40

0

1

2

3

4

Average Latency

0 10 20 30 40

1

10

100

1000

400

Total Latency

0 10 20 30 40

10

100

1000

10000

Average Rate

0 10 20 30 40

0

1

2

3

4

FR

FI

Seco

nd

sR

esp

on

ses p

er

seco

nd

Sessions


34

Figure 5

Overall Rate

0 10 20 30 40

0

1

2

3

Average Latency

0 10 20 30 40

1

10

100

1000

525

Total Latency

0 10 20 30 40

10

100

1000

10000

FR

FI

Average Rate

0 10 20 30 40

0

1

2

3

Seco

nd

sR

esp

on

ses p

er

seco

nd

Sessions


35

Figure 6

Overall Rate

0 10 20 30 40

0

1

2

3

Average Latency

0 10 20 30 40

1

10

100

1000

674

Total Latency

0 10 20 30 40

10

100

1000

10000

FR

FI

Average Rate

0 10 20 30 40

0

1

2

3

Seco

nd

sR

esp

on

ses p

er

seco

nd


36

Figure 7

0 50 100 150 2000

1

2

3

4

0 50 100 150 2000.0

0.5

1.0

0 50 100 150 2000.1

1

10

100

0 50 100 150 2001

10

100

1000

Fixed Ratio Fixed Interval

Pecks p

er

sL

ate

ncy (

s)

Successive Componets

First 5 Last 5 First 5 Last 5

Pigeon 106


37

Figure 8


38

Figure 9


39

Figure 10


40

Figure 11


41

Figure 12


42

Figure 13

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Development of Stimulus Control under each Component of a ... · Luis Otero-Valles University of Florida . DEVELOPMENT OF STIMULUS CONTROL 2 Development of Stimulus Control under