Choice in a self-control paradigm: effects of reinforcer quality

Behavioud

Processes,

22 (1990)

89

89-99

Elsevier BEPROC

00313

Choice in a self-control effects of reinforcer

paradigm: quality

George R. King and A.W. Logue State University

of New York at Stony Brook, Stony Brook, New York, USA

(Accepted 13 March 1990)

Abstract Pigeons

were exposed

to a self-control

larger, more delayed and smaller, type of grain associated with behavior was influenced delayed alternative alternatives. proportions

paradigm

each alternative)

by grain quality;

generally

the

they chose between quality

(i.e., the

was varied across conditions.

Choice

proportions

changed as a function

Furthermore,

in which

less delayed reinforcers.

Reinforcer

of responses

for the larger, more

of the grains associated with

percentage

deviation

decreased as a function

from

the response

mean baseline

of the relative

response

grain types associated

with each response alternative. Manipulation of reinforcer quality influence the degree of self-control typically exhibited by pigeons.

can significantly

Introduction Self-control can be defined as the choice of a larger, more delayed reinforcer over a smaller, less delayed reinforcer; impulsiveness is the opposite of self-control (Ainslie, 1974;

Grosch & Neuringer,

typically

impulsive

ber of factors

1981;

Rachlin,

1974;

Rachlin & Green,

1972).

Pigeons

(e.g., Logue, Chavarro, Rachlin, & Reeder, 1988). However,

such

as manipulation

of amount,

are

a num-

delay, and rate of reinforcement

(Logue and Chavarro, 1987), manipulation of past experience (Logue & Mazur, 1981; Logue, Rodriguez, Pena-Correal, & Mauro, 1984; Mazur & Logue, 197B), and the use of precommitment trol

procedures (Rachlin

demonstrated

(Logue, Smith,

by pigeons.

& Green, 1972) can affect the degree of self-con-

Other

factors,

such

& Rachlin, 1985) and level of deprivation

as intertrial

interval

duration

(Logue & Pena-Correal,

1985)

tend not to affect the degree of self-control demonstrated by pigeons. All of these studies have used the same type reinforcer (i.e., the same type of grain) for both response alternatives. This is despite the fact that reinforcer quality has been shown to significantly influence the behavior of nonhuman organisms under a variety 0376-6357/90/$03.50

0 1990

Elsevier Science Publishers B.V. (Biomedical Division)

90 of schedules of reinforcement. For example, influence responding on multiple (Beninger, tinger,

McSweeney,

Melville,

& Norman,

1981;

& Higa, 1988) and concurrent

ules of reinforcement stitutable;

(the present

for a discussion

Battalio,

Higa

& McSweeney,

(Hollard

discussion

of reinforcer

talio, Green, Basman, & Klemm,

reinforcer quality has been shown 1972; Beninger and Kendall, 1975; & Davison, assumes

McSweeney,

1971; Miller,

1976) sched-

that the reinforcers

substitutablity

see, Hursh,

1975; Kagel, Battalio,

Kagel, & Green, 1981; Rachlin,

1987;

1978;

Green, & Rachlin,

Kagel, & Battalio,

to Et-

are subKagel, Bat-

1980; Rachlin,

1980).

The lack of research regarding the effects of reinforcer quality on self-control is unfortunate, given that the above previous research indicates that reinforcer quality can significantly

influence

seem to indicate variations

behavior.

that organisms

Furthermore,

in resource and prey quality (Zeiler,

the opportunity

to pursue a low quality,

ity

a higher

to

pursue

Pulliam,

& Charnov,

model).

Furthermore,

conditions,

when

quality,

1977, more

(1982,

than

temporally

The present

experiment

was designed

in reinforcer displayed

of

reinforcer

quality

left responses reinforced

could attenuate

were followed

right

grain. In addition

responses

the strong

would

be sensitive will

to

forgo

(see,

under

relatively

is available,

diet

should

in which

of reinforcer

paradigm, and whether preference

Pyke, natural

pigeons

paradigm

the effects

e.g.,

the optimal

the

quality

variations

for immediacy

typically

paradigm (e.g., Logue et al., 1988). All reinforced

by a 6-s delay and then by 6-s access to grain, and all

were followed

to the reinforcers

differed in quality (high, past preference (amount

to examine

item

involving

laboratory

in a self-control

by pigeons in a self-control

prey

has argued that

demonstrate greater self-control than in a typical reinforcers are always of the same type. on the choice behavior of pigeons

considerations should

close prey item for the opportun-

distant

of the research

1983)

one type

paradigm

1988). For example, organisms

temporally

for a review

Collier

evolutionary

in a self-control

by a 2-s delay and then

differing

by 2-s access to

in amount and delay, the reinforcers

also

medium, and low). Quality was defined by differences in consumed in preference tests) for three different types of

grains. Grain type was used to vary reinforcer

quality

because Miller’s

(1976) work had

suggested that different grains are substitutable. Furthermore, Miller’s work indicated that although there were clear differences in grain preferences, these differences were small enough that the grains could be readily hedonically the case between a sucrose solution

compared, as might

not be

and tap water, for example.

Method Eight White

Subjects. ing weights, necessary

to

Carneau pigeons,

served as subjects maintain

the

maintained

in the present

pigeons’

weights,

conditions and consisted of mixed grain. This grains used in the present experiment.

at 90-95%

experiment. were mixture

given

of their

free-feed-

Supplemental

feedings,

following

experimental

did not contain

if

any of the

Apparatus. Home cage. The home cage was made of aluminum, 35 cm deep, 30 cm high, and 24 cm wide. The front of the cage was a grid with two apertures, each 8 cm wide and 6 cm high, and each located 4 cm from the bottom and 1 cm from a side of the home cage. Hooked to the outside of the apertures were two trays which normally contained the pigeons’ food and water. During the preference trays were replaced with two identical trays containing the grains.

tests

these

91

Experimental

The

chamber.

experimental

apparatus was an aluminum

box, 33.5

cm deep, 35 cm high, and 29.5 cm wide, enclosed in a sound-attenuated chamber. The front of the apparatus contained two round, Plexiglas response keys 2 cm in diameter, each located 5 cm from a side and 7 cm from the top of the apparatus. The response

keys required a force of 0.1 N to operate and could each be transilluminated

by a I-W

light.

Operation

below each response

of a key produced a brief

key, 11 cm from the bottom

feedback click.

and 4 cm from

Located 9 cm

each side of the

apparatus, was a 5 cm aperture which was illuminated by a 1.3-W light during reinforcement access periods. Illumination of the experimental chamber was produced by two 1.3-W houselights, located 7 cm from the back and 11 cm from each side of the apparatus. Located on top of the apparatus were two 7.5-W lights (red and green) that could illuminate via an 8-cm aperture. This

the chamber during

reinforcer

aperture was covered with

delay and access periods

translucent

Plexiglas,

and was

located 10 cm from each side and 13 cm from the front of the apparatus. Masking noise was provided by a fan operating continuously during the session. An IBM-XT

computer,

and recorded responses SKED). Procedure. and preference subjects

located in another room, controlled using a CONMAN

Familiarization tests

and preference

occurred

the experimental

program (CONMAN tests.

in the pigeons’

is similar

Familiarization

home

with

stimuli

to SUPERthe grains

cages. For familiarization,

all

were exposed to each grain type for 9 days, 25 g of grain per day. This

was

done in order to attenuate any neophobic responses the pigeons might have otherwise exhibited toward the grains. Hulled oats, hemp, and durham wheat were used because previous studies had indicated that there are clear differences between these grains (Ettinger, et. al., 1980; Miller, 1976).

in quality

Next, preference tests were conducted to determine the most, moderately, and least preferred grains for each individual pigeon. Each possible pair of the grain types was presented to each subject four times while

controlling

for grain position

(left vs.

right food tray). Each pigeon received one preference test per day, and each test consisted of IO-min access to 50 g of each type of grain. After the IO-min period, the grains were removed and reweighed, including any spillage, to determine the amount consumed. The IO-min period was selected because it allowed a subject sufficient time to sample both grains, but not so much time that a subject could consume both grains (Ettinger

all of

et al., 1981).

A Friedman’s one-way analysis of variance (ANOVA) the amounts of grain consumed and indicated significant

by ranks was performed on differences in consumption

(X2 = 13.0, p < 0.01). For each subject, the high quality grain type was then defined as that of which the subject consumed the most, the medium quality grain as that of which the subject consumed the median amount, and the low quality grain as that of which

the subject

conducted

ate the least (see Table

in the same manner as the initial

2). Post-experimental preference

tests,

preference

did not indicate

tests, any

changes in grain preference.

Predictions Given knowledge of the subjects’ preference structure for the different grain types, it is possible to predict the order of preference for the left response alternative, from

92 Table

1

Predicted

order of preferences

for each condition Ranking

for the left response

in the present

of predicted

preferences

alternative,

Grain type associated with

the left response

the right response

alternative

to smallest,

alternative.

(5),

alternative

Least preferred

preferred

Most preferred

Moderately

Moderately

Least preferred

preferred

preferred

Most preferred

Most preferred

Moderately

Moderately

preferred

preferred

Least preferred

Least preferred

Least preferred

Moderately

Moderately

Most

preferred

preferred

preferred

Most preferred

Least preferred

response

largest (1) to smallest

Grain type associated with

Most

largest

from

experiment.

as a function of the relative grain qualities associated with each Table 1 presents the predicted order of preferences for the left

response alternative, for the conditions in the present experiment. Note that, because constant values for the amounts and delays of reinforcement were used in the present experiment, response from

for

those

alternative

each other,

conditions

in which

or from

indifference.

procedure.

chamber. At the beginning

Tests

for self-control

of a session,

houselight

initiated

types

the High-Medium

reinforcement

with

were conducted

in the experimental

by a white

light.

green, the

Left key pecks that

a 6-s delay period, during which both keylights

the food hopper

period, the green houselight

each

different

and Medium-

the left key was transilluminated

were darkened, and the chamber was illuminated

end of the delay period,

associated

not be significantly

different from each other, nor should the be significantly different from each other.

right key red, and the chamber was illuminated produced a reinforcer

grain

should

In addition,

Low-conditions should not be significantly Low-Medium and Medium-High conditions Self control

the

are the same, preferences

and the

by a green light.

At the

was available for 6s. At the end of this was turned off, and both keylights

and the

white houselight were illuminated. Pecks on the red key that resulted in a reinforcer initiated the same sequence of events, except that the delay and reinforcement periods were both 2s, and the chamber was illuminated by a red, and not a green, light. These contingencies were in effect for the entire experiment. Reinforcers

were scheduled

dent, concurrent

according to a Stubbs and Pliskoff

variable-interval

(VI)

30-s

VI 30-s

schedule.

(1969),

nonindepen-

As each interval

of a

single VI 15-s schedule timed out, a reinforcer was randomly assigned, with a probability of 0.5, to either the left or right response key. The intervals of the VI 15-s schedule were constructed according to the procedure outlined by Fleschler and Hoffman (1968). The Stubbs and Pliskoff schedule required subjects to respond occasionally on both alternatives in order to receive reinforcement from either alternative.

This

procedure

insured

that the

relative

approximately equal for both alternatives, and therefore not vary as a function of reinforcer (grain) preference.

reinforcement that reinforcer

rates

remained

frequency

did

93 Table

2

Order

of conditions,

Condition

grain quality

used, and number

per condition. Number

Grouo 1 Grain Quality

Condition

of sessions

Grain

Left

Right

Left

Low Low Low

Low

Oats

Oats

38

Medium

Oats

Wheat

27

High

Oats

Hemp

21

Medium

High

Wheat

Hemp

24

Medium

Medium

Wheat

Wheat

35

Medium

Low

Wheat

Oats

17

High

Low

Hemp

Oats

49

High

Medium

Hemp

Wheat

18

High

High

Hemp

Hemp

24

‘Group

of

Sessions Grain

-

Number

2

Grain Quality

Grain Right

Left

of

Sessions

Subjects 8 and 12

Subjects 37 and 38

Left

Right

Left

Right

High

High

Wheat

Wheat

Hemp

Hemp

30

High

Medium

Wheat

Hemp

Hemp

Wheat

36

High

Low

Wheat

Oats

Hemp

Oats

15

Medium

Low

Hemp

Oats

Wheat

Oats

38

Medium

Medium

Hemp

Hemp

Wheat

Wheat

36

Medium

High

Hemp

Wheat

Wheat

Hemp

31

Low

High

Oats

Wheat

Oats

Hemp

22

Low

Medium

Oats

Hemp

Oats

Wheat

39

Low

Low

Oats

Oats

Oats

Oats

20

A 3-s changeover thus reinforcement

delay (COD) was in effect to decrease changeover responses of sequences of responses on both alternatives. The COD

vented the delivery

of a reinforcer

key to the other, or for 3 s following

for 3 s following

a changeover from

and pre-

pecking one

a reinforcer.

Sessions were terminated after 30 reinforcers. Conditions were changed after 5 days of stable responding. A pigeon’s responding was considered stable when its response ratio (the number

of left divided by the number

of right responses)

during

the last 5

sessions fell within the range of its response ratios for all previous sessions for that condition. In other words, a pigeon’s response ratios for the last five days of a condition

could not exhibit

more, all pigeons within

any new highs

or lows

a group were required

during

to exhibit

those

sessions.

stable responding

Furtherbefore

conditions were changed. Sessions were conducted 6-7 days per week. The subjects were randomly assigned to one of two groups. The order of conditions was counterbalanced across the groups, thus controlling for order effects. Table 2 lists the order of conditions, the grain quality used in each condition, and the number of sessions conducted per condition for each subject and group.

94 GROUP 2

GROUP 1

nu

t&L

Y-L

L-Y

YH

L-H

H-L

nu

mmmoN

Fig. 1. Response separately

proportions

for each subject.

the medium grain quality,

(left/left The letter

fright

responses)

H refers

un

L.Y Y-L ooNanoN

as a function

to the high grain quality,

and the letter L refers to the low grain quality

of grain quality

the left response the

conditions

to the

grain

type

associated

are arranged according to the predicted

largest to smallest

(see Table 1). The horizontal standard errors

with

right

alternative,

response

order order of response

line indicates of the mean.

indifference,

to

(see Table 2). The first

letter on the x-axis refers to the grain type associated with refers

pairs,

the letter M refers

second

letter

L-H

and the

alternative. proportions,

The from

and the bars are the

95

Results Figure 1 plots the mean proportion of responses for the larger, more delayed alternative (i.e., left/left + right responses) for each subject and condition. In referring ORouP 1

t.O-

al-

a,az-

1

H-L

KY

U-L

Fig. 2. Percentage deviation subject.

The x-axis

1

8mJECTIl. r

“.“-~-T

.

H*l

,

u-u

,

L.L

.

L-Y

,

WI

-1sI

.

L-H

from the mean baseline

response

proportions,

separately

is arranged in the same manner as in Figure 1. The horizontal

no difference

from baseline, and the bars are the standard errors

for each

line indicates

of the mean.

96

to the conditions, the first letter (H = High, M = Medium, and L = Low quality grain types) indicates the grain associated with the left response alternative, and the second letter indicates the grain associated with the right response alternative. The conditions on the x-axis are arranged according to the predicted order of response from largest to smallest analyses. Wilcoxon

(see Table 1). The significance

matched-pairs

in Figure 1 against indifference [T(7) = 0.01, High-Medium Medium-High

tests comparing the response

(i.e., a proportion

than indifference. A Friedman’s

two-way

analysis

presented

that the High-Low

[T(7) = 0.01, Low-Low

[T(7) = 3.01 conditions

No other comparisons

proportions

of 0.5) indicates

[T(7) = 0.01, High-High

[T(7) = 1 .O], and Low-High

proportions,

level was set at p I 0.05 for all

[T(7) = 0.01,

are significantly

larger

are significant.

of variance (ANOVA)

by ranks was performed

on

the response proportions presented in Figure 1. The results of the ANOVA were significant [N= 8, df= 8, X2 = 21.11 indicating changes in the response proportions as a function of reinforcer quality. The L statistic (Page, 1963) was calculated to compare the obtained and predicted order of response proportions (see Table 1). The L statistic was designed to specifically test hypothesis about the order of treatment effects when multiple treatments are present. The statistic was significant, indicating that the obtained

response

proportions

proportions [ L(8, 9) = 2,003]. The above Wilcoxon tests tions

are significantly

generally

follow

the

indicate that both the High-High

larger than indifference,

indicating

bias toward the larger, more delayed alternative. quality

were

deviations

analyzed

by expressing

from baseline.

predicted

Baseline

the

to response

and Low-Low

condi-

the presence of a response

Therefore,

proportions

order

the effects

of responses

of reinforcer as percentage

was taken as the mean of the response

proportions

for the conditions in which the grain types associated with both response alternatives were the same (i.e., the High-High, Medium-Medium, and Low-Low conditions). The response baseline

proportions response

for the remaining

proportion,

conditions

multiplied

this product, thus generating a percentage deviation condition.

Figure

proportions

2 presents

were then divided

the percentage deviations

separately for each subject, and condition

from

(other

corrected for. A Friedman’s performed on the response

from

the baseline

of changes in grain quality

response

than the conditions

The conditions

arranged in the same manner as in Figure 1. Figure 2 suggests changed as a function

mean

from baseline for each remaining

were used to generate the mean baseline condition). subjects

by this

by 100, and then 100 was subtracted

that

on the x-axis are

that the behavior of the

when the response

twoway analysis of variance (ANOVA) proportions presented in Figure 2. The

bias is

by ranks was results of the

ANOVA were significant [N= 8, df= 5, X2 = 12.91. The L statistic (Page, 1963) was calculated to compare the obtained and predicted order of percentage deviation from baseline. tions

The statistic

generally

follow

was significant,

indicating

that the obtained

the predicted order of response

proportions

response

propor-

[ L(8,6) = 6541.

Discussion The

present

experiment

demonstrated

changes

in responding

as a function

of

variations in reinforcer quality. These results are consistent with previous research indicating that reinforcer quality has a significant effect on responding when concurrent and multiple schedules of reinforcement are used (Beninger, 1972;

97

Beninger & Kendall, 1975; Ettinger Hollard & Davison, 1971; Miller, 1976). deviations

from

monotonically

mean baseline

et al., 1981; The response

response

proportions

decreasing trend as a function

with the left response

alternative,

ions of the present experiment

Higa & McSweeny, 1987; proportions and percentage exhibited

of the relative

an approximately,

grain quality

and these changes are consistent

with

of the L test). Therefore,

(see the results

associated the predict-

the effects of

reinforcer quality can attentuate the preference for immediacy typically exhibited by pigeons in a self-control paradigm (e.g., Logue, Chavarro, Rachlin, & Reeder, 1988), and therefore The

can affect the degree of self- control

generally

small

effect

of

probably due to the concurrent required

the subjects

reinforcer

exhibited

quality

in

dependent schedules

to respond

by pigeons.

the

present

experiment

of reinforcement.

on both response

alternatives

This

is

schedule

in order to recieve

reinforcement from either alternative. The use of concurrent independent schedules of reinforcement would probably have resulted in a larger effect of reinforcer quality. However,

under such schedules

the obtained reinforcement

rate for a given response

alternative varies as a function of the preference for that alternative. Therefore, the use of concurrent independent schedules in the present experiment would have resulted

in the obtained reinforcement

confounding self-control

the analysis alternative

the response significant

rate covarying with

of reinforcer

complicates

the analysis

The

reinforcer

presence

of reinforcer

quality,

the predictions

quality

of the present

is still

experiment.

during the Medium-High

and Low-High

a lesser

38. The

extent,

Subject

quality.

However,

large mean increase,

a

with

in Group

2,

is largely due to Subject 37, and to

in Group

2 experienced

conditions,

the

and this

High-Low could

have

bias for the larger, more delayed response

research on self-control

has been questioned

when

from baseline,

and the effect is consistent

and Low-High

exacerbated, or created, a strong response alternative. The adequacy of laboratory

The

conditions

subjects

before the Medium-High

$or self-control

present,

thereby

of a bias for the left,

bias is corrected for by using the percentage deviation

effect of reinforcer

condition

quality.

in pigeons as a general model

because of the failure

to easily

influence

the

magnitude self-control (Logue, 1988). However, the present results indicate that reinforcer quality can increase the magnitude of self-control typically exhibited by pigeons. Therefore, the present results are consistent with evolutionary considerations suggesting that organisms should be able to wait for higher quality, temporally distant resources (see, also, Logue, 1988; Zeiler, 1988). The results are also consistent with Collier’s

(1982,1983)

ment would

result

In summary,

assertion

that a more natural simulation

of the pigeon’s environ-

in increased self-control.

changes in reinforcer

quality

influenced

the degree of self-control

exhibited by pigeons. These results support previous procedures, all of which indicate that reinforcer quality

research using very different is a significant determinant of

operant behavior.

experiment

list

of variables

Finally,

that will

the procedure of the present result

in increased

self-control

advantage of being a more natural simultation

adds to the short

in the pigeon,

and has the

of the pigeon’s environment.

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Note

The present research was supported awarded to the first author and by NSF

by a Sigma Xi Grant-in-Aid-of-Research Grant BNS-8416302, A.W. Logue, principal

investigator. Comments by Jennifer Higa on previous versions of the manuscript are greatly appreciated. The authors would also like to thank F. Basile, L.J. Bonvino, and K. Kline, for their assistance in conducting Reprint requests should be sent to A.W. University

the experiment and analyzing the data. Logue, Department of Psychology, State

of New York at Stony Brook, Stony

Brook,

NY 11794, USA.