snc as a function of deprivation condition_riley_79

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Successive Negative Contrast as a Function of Deprivation Condition Following Shifts inSucrose ConcentrationAuthor(s): Edward P. Riley and William P. DunlapReviewed work(s):Source: The American Journal of Psychology, Vol. 92, No. 1 (Mar., 1979), pp. 59-70Published by: University of Illinois PressStable URL: http://www.jstor.org/stable/1421479 .

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AMERICAN OURNALOF PSYCHOLOGYMarch1979,Vol. 92, No. 1,pp. 59-70?1979 Board of Trustees of the Universityof Illinois0002-9556/79/0300-0059$1.20/0

Successive negative contrast as a function of

deprivation condition following shifts insucrose concentration

Edward P. Riley William P. DunlapStateUniversityof Tulane UniversityNew Yorkat

Albany

Successivenegative contrast was measured in terms of lick rate followingreduction n sucroseconcentration n bothdeprivedand adlibrats.The adlib

group showedsubstantialdecrements in lick rate that did not diminishoverfour postshiftdays.The deprivedgroupshowedalargebut transientcontrasteffect. When downshifted a second time, the deprived subjectsshowed adecrement to control levels, whereas ad lib subjectsagain showed durablecontrast.In a second phase of the experiment, deprivationconditionswerereversed and the

groupsshowed

patternsof contrast

appropriateto the

currentdeprivationcondition regardlessof prior deprivationhistory. Thefindings are discussed in terms of the hypothesis that ad lib and deprivedsubjectsattend to different aspectsof reward.

When animals are shifted from a large reward magnitude to a smaller

one, they often evidence a reduced level of performance compared toanimals receiving only the smaller reward. This effect, successive

negative contrast, was reported by Crespi in 1942 and has since been

replicated under a variety of conditions and paradigms.Although successive negative contrast is a pervasive phenomenon,

its occurrence appears to be influenced by the organism's drive level.

For example, Ehrenfreund and Badia (1962), Ehrenfreund (1971),Cleland, Williams, and DiLollo (1969), and Flaherty and Kelly (1973)have all failed to obtain contrast in low-drive subjects. However,

Capaldi and Singh (1973) did report successive negative contrastunder conditions of low deprivation severity and suggested that con-trast would occur in low-drive animals if conditions for obtaining

contrast were made optimal. Panskepp and Trowill (1971), using awithin-subject procedure, also reported negative contrast in low-drive

subjects when sucrose concentration was reduced and lick rate wasused as the dependent measure. Flaherty and Largen (1975), also

utilizing a within-subject design and shifts in sucrose solutions, found

59



RILEY AND DUNLAP

negative contrast in ad lib rats. Further, this within-subject contrast in

ad lib subjects tended to get larger as a result of continued experiencewith downshifts in reward.

Since in these within-subject paradigms each animal was allowedseveral comparisons between the large and small rewards, the presentstudy was designed to investigate the influence of deprivation oncontrast using sucrose as the reward, as in the previous two studies, butin the more traditional successive contrast paradigm. In this proce-dure animals are allowed access to a sucrose solution for a fixed time

daily and subsequently shifted to a lower concentration. Contrast can

be measured by comparing either lick rate or amount consumed bythe downshifted animals to subjects experiencing only the lower con-centrations (e.g., Flaherty & Hamilton, 1971; Gordon, Flaherty, &

Riley, 1973). This paradigm may also optimize conditions for contrastas suggested by Capaldi and Singh (1973), since contrast is not usuallyfound with instrumental response measures using sucrose solutions asreward (Flaherty, Riley, & Spear, 1973; Rosen & Ison, 1965; Collier,

Knarr, &Marx, 1961), but is readily found when lick rate is measured.

Also, Flaherty and

Largen(1975)

reported

a

tendency

for

negativecontrast to increase in ad lib subjects as a direct function of the num-ber of experiences with reward shifts. The present study, therefore,

planned on using multiple shifts within the more standard contrast

paradigm to try and replicate this finding.

PHASE 1

METHOD

SubjectsForty naive male albino rats obtained from the D. R. Hilgendorf Co.,

Middleton,Wis., served as subjects.They were 107 days old at the startof

trainingand werehoused individuallyunderconstant ow-level llumination.Waterwascontinuouslyavailable or all subjects.

Apparatus

Testingwasconductedinasquarechamber30 cmon a side and23 cmhigh,enclosed in a sound attenuated box equippedwith a shielded71/2Wbulb forilluminationand a fan for ventilation. Three sides of the chamber were

painted grey and the fourth was transparent Plexiglas which allowed thesubjects o be observed withinthe chamberthrough a one-waymirror n theouter enclosure.Centered on the Plexiglaswall3.5 cm above the floor wasa

squarePlexiglasrecess5 cm on a side and 2.5 cm deep. A bottle witha metal

drinkingtubeelectricallynsulatedwithGC Electronics nsulVoltwas locatedbehinda 1.2cmhole in the farwallof therecesssuchthatitstipwasflushwiththe outside edge of the wall. The wall was 0.6 cm thick. A photocellbeam

60



SUCCESSIVENEGATIVECONTRAST

crossing the Plexiglas recess allowed time spent at the drinking tube to bemonitored. The floor of the chamber was white plastic covered with an

aluminum expanded-metal grid which was connected to one side of a drink-ometer circuit (Scientific Prototype Mfg. Corp., Model 101K). The other sideof the circuit was connected to a piece of wire immersed in the sucrosesolution. Recording of all dependent measures was done automatically byadjacent electromechanical counters and timers.

Procedure

Subjects were assigned to one of four groups defined by the factorialcombination of preshift sucrose concentration (32% or 4%) and deprivationcondition (ad libitumor 80% of predeprivation body-weight). Assignment of

deprivationcondition was

random,but

subjectswithin each

deprivation con-dition receiving different sucrose concentrations were matched for predepri-vation body-weight. Mean body-weights prior to deprivation were 370.3 gmsfor ad lib subjects and 370.8 gms for deprived subjects.

Pretraining began after the deprived subjects were reduced in body-weight.On each of four pretraining days, each subject was handled and given 2 ml ofthe sucrose solution appropriate to its group assignment in the home cageprior to its daily weighing. Following this pretraining, each subject was placedinto the test chamber daily and the number of licks and time at the tube wererecorded for 5 min. Duration at the tube was recorded when the subjectplaced his head within the recess, interrupting the photobeam. The bottle on

the apparatus contained a solution with sucrose concentration appropriate foreach subject's group assignment. After 12 preshift days, the 32%subjects wereshifted to 4% sucrose for four days. Following this initial downshift, the 32%subjects were shifted back to 32% for three days and then downshifted againto 4%for an additional four days. The 4%subjects were maintained on the 4%sucrose solution through this phase. Subjects were run in squads of eight;assignment to squads was random, with the restriction of equal group rep-resentation within each squad. The running order within a squad wasrandomized daily. Subjects were weighed, and deprived subjects were fed

approximately 15-30 min after the last animal in the squad was run. Su-crose solutions were mixed with

tap wateron

a weight-per-volume basisevery second or third day and served at room temperature.

RESULTS

As can be seen in Figures 1A and 1B, the deprived groups lickedmore and spent a greater amount of time at the drinking tube than didthe ad lib groups on those days preceding downshifts in reward

quality. Also, the 32% groups were superior to the 4%groups.

Statisti-cal reliability of these effects was tested by analysis of variance usingdeprivation condition and preshift concentration as between-subjectfactors and days as a within-subject factor. Analysis of drinking be-havior on the two days prior to the first shift (days 11 and 12) indicatedthat deprived groups licked more, F (1, 36) = 195.99, p < .01, and

61



RILEY AND DUNLAP

A* 32% - DEPRIVEDo 4% ---AD LIB.

< SHIFT < SHIFT

1600-

C-)

I 1200-

oE

800-

0t

400-

0

rz-)

.C3 -0-,L _1$=

1-2 3-4 5-6 7-8 9-1011-12 13 14 15 16 -17 18 19 20 21 22 23

DAYS

Figure 1. Effect of deprivationand concentrationon totalnumberof licks(A)and percent of time at the tube (B) as functions of days and reward shiftsin Phase 1.

spent a greater amount of time at the tube, F (1, 36) = 230.52, p < .01,than ad lib groups. The 32% groups showed similar effects as com-

pared to the 4% control groups with both dependent measures, F

(1, 36) = 7.78, p < .01, and F (1, 36) = 9.27, p < .01, respectively.Although differences due to sucrose concentration were slightlylarger for the deprived subjects, no significant interaction between

62



SUCCESSIVE NEGATIVE CONTRAST

deprivation condition and preshift concentration was found. When

the experimental groups were returned to the 32% concentration

prior to the second shift, the number of licks and time spent at the tubeincreased on the first upshift day, then stabilized over the next two

days. Again, an analysis of the two days preceding the second shift

(days 18 and 19) indicated that the deprived groups licked more,F (1, 36) = 128.71,p < .01, and spent a greater amount of time at the

tube, F (1, 36) = 156.50, p < .01, than the ad lib groups. The 32%

subjects licked more than 4% subjects, F (1, 36) = 7.95, p < .01, butdifferences in time at the tube failed to reach

significance,F

(1, 36)= 4.03,p = .052.

Following the first downshift in reward, both experimental groupsshowed abrupt decrements in number of licks and duration at thetube. These decrements were below the levels recorded for the ap-propriate 4% control groups; therefore, contrast effects were ob-tained under both deprivation conditions. Over the four postshiftdays, the deficits shown by the 32% deprived group diminished and

appeared to be gone by the second or third session. For the ad lib

group, on the other hand, the deficit was as great at the end of the fourdays as on the first switch day. Following the second downshift to 4%,the two experimental groups again showed an abrupt decrement inboth number of licks and time spent at the tube, but the deprivedgroup showed little evidence of contrast, while the ad lib groupshowed an effect somewhat larger than following the first shift. Again,contrast lasted over the entire four postshift days for the ad lib group.An analysis of variance was performed on data from both the first and

Second shifts, thus shift, as well as days, was a within-subject factor.

The temporary nature of the deficit below the 4% level shown by the32% deprived group was supported by a significant deprivation xconcentration x days interaction, F (3, 108) = 8.86,p <.01, for licks,and F (3, 108) = 5.57, p <.01, for time at the tube. The reduction incontrast for the deprived group, as opposed to a slight increase for thead lib group, from shift 1 to shift 2, was supported by a significantdeprivation x concentration x shift interaction, F (3, 108) = 13.14,p< .01, for licks, and F (3, 108) = 7.19, p < .01, for time spent at thetube. The lower order effects of deprivation, concentration,

depriva-tion x concentration, shift, days, and concentration x days were also

significant. Separate analyses on the first postshift day of the secondshift (day 20) indicated that the small decrement in the deprivedgroup depicted in Figure 1 was not significant, F (1, 18) = 2.03,p >

.05; however, the effect was significant in the ad lib group, F (1, 18)= 14.82,p <.01.

63



RILEY AND DUNLAP

PHASE 2

The striking difference in the permanence of contrast effects shownby the ad lib group in comparison to the deprived group raises impor-tant questions about the basic mechanism underlying successive nega-tive contrast. In particular, it might be hypothesized that subjectsunder food deprivation undergo some associative process in the con-

trast paradigm which causes contrast to dissipate. If differential learn-

ing dependent upon motivational level is important in determiningthe occurrence and permanence of contrast effects, differences due to

prior deprivation experience mightbe

apparentwhen both

groupsperform under the same motivational condition. In Phase 2 all groupswere placed on an ad libitumregimen, and another reward shift wasmade. Next, all groups were placed on the 80% deprivation scheduleand the contrast procedure again repeated.

METHOD

Subjects

and

apparatusThe subjectsand the apparatus rom Phase 1wereunchanged.

Procedure

Proceduraldetailsother thanthose associatedwith maintenanceconditionsremained unchanged from Phase 1. Following Phase 1, all subjectswereallowedaccess o food andwateradlibitumor the next 15days.After fivedayson thismaintenance ondition,the32%subjectsagainweregivenaccess o the32%sucrose solutionfor five daysand then downshifted to 4%for an addi-tionalfourdays.The dayafter thelastpostshiftday,allsubjectswereweighedand then put on the 80%body weight deprivation regimen identical to the

deprived conditionof Phase 1. After seven days under this condition, sub-jects wereagain put throughanother shift sequence;the 32%subjectswereallowed accessagainto 32% sucrosefor four daysand then downshiftedforanother four days. Throughout this phase, the 4% subjectscontinued onthe4%solution.

RESULTS

All subjects ad libitum

Although the formerly deprived groups had free access to food for

five days prior to the start of Phase 2, their mean body weights werestill less than those of the groups maintained continuously on adlibitum

food; 430 and 445 gms for the formerly deprived 32 %and 4 %groups,respectively, versus 482 and 485 gms for the continuously ad lib

64




groups. The mean number of licks and the duration spent at the tube

are depicted in Figures 2A and 2B. Prior to the shift, the formerlydeprived 32% group licked more and spent more time at the tube than

did the other three groups. Analysis of variance with prior deprivation

history and concentration as between-subject factors and days as a

within-subject factor for the last two preshift days indicated a signifi-cant deprivation history x concentration interaction, F (1, 36) = 4.66,

p < .05, for licks, and F (1, 36) = 5.40, p < .05, for time spent at the

tube. The main effect of prior deprivation history was also signifi-cant. An abrupt decrease in licks and duration at the tube from pre-

shift levels followed the downshift in sucrose concentration. Thedeficit below control level is long lasting regardless of deprivation

history, persisting over all four postshift days. This effect is supported

by a significant main effect of concentration, F (1, 36) = 25.38, p <

.01, for licks, and F (1, 36) = 20.83, p < .01, for time spent at the tube,

yet no interaction with prior deprivation history was significant(Fs < 1 for both measures).

All subjects deprived

The mean number of licks and the duration at the tube with allsubjects deprived are also presented in Figures 2A and 2B for the four

preshift and four postshift days. As can be seen, the 32 %groups licked

more and spent a greater amount of time at the tube than the 4%

groups prior to the shift. An analysis performed on the last two

preshift days showed a significant concentration effect, F (1, 36) =

32.05,p < .01, for time at the tube. Following the downshift in reward,both licks and duration dropped abruptly, falling below the levels of

controls. However, over the four postshift days the shifted groupsreturned to the control level. An analysis over four postshift daysindicated a significant concentration x days interaction, F (3, 108) =

3.67 p < .05, for licks, and F (3, 108) = 7.93, p < .01, for time at the

tube. Again, no interaction with previous deprivation history was

significant, although a significant prior deprivation main effect wasfound with the lick measure; formerly deprived subjects licked moreoverall than formerly ad lib subjects.

DISCUSSION

In addition to finding a successive negative contrast effect with

deprived subjects, an equally strong effect was found for ad lib sub-

jects. This demonstration of successive negative contrast in animalsunder zero food deprivation is in clear opposition to the usual findings

65



RILEY AND DUNLAP

A

ALL s DEPRIVED

V~~~~~~

/ -,

J#

$'

SHIFT< > r--

,, {'^ -~e

.,,o.~ dJ

I I I I I I I I

24 25 26 27 28 29 30 31 32

DAYS

* 32%

o 4%

FORMERLYEPRIVED

--- FORMERLYDLIB.I I I I I I 3

33 34 35 36 37 38 39 40

Figure 2. Effect of deprivation and concentration on total number of licks (A)and percent of time at the tube (B) as functions of days and reward shiftsin Phase 2.

in the runway, where the occurrence of negative contrast has been

found to be directly related to the severity of deprivation (Ehren-

freund & Badia, 1962; Cleland et al., 1969; Ehrenfreund, 1971;Flaherty & Kelly, 1973). For the deprived group in the present study,contrast effects diminished over the four postshift days, while for the

ad lib group, contrast persisted over the entire test period. In this

latter group the magnitude of the contrast effect wasjust as large on

the last postshift day as it was on the first. Capaldi and Singh (1973)

ALL s ADLIB.

1600-

C.)

1200-o

ct

0

? 800-z

_J

8 400-I-

110-c .

4r.--f

100- B

II

75-

50-

25-

L&J

co

fI-

C-)i

Wui

66

F---e

0-

10-"~_'

l




also reported a slight (although nonsignificant) tendency for theirlow-drive

subjectsto show more sustained contrast than high-

drive subjects.The durability of contrast with ad lib subjects is supported by the

fact that large contrast effects reappeared for this group, while a

significant effect was absent following the second shift in deprivedanimals. Capaldi and Lynch (1967) also failed to obtain a return of

contrast in deprived subjects following multiple downshifts. Followingthe second shift in the present study, the ad lib group again showed adurable contrast effect which did not dissipate over days and ap-

peared to be as large or larger than contrast shown following the firstshift. Flaherty and Largen (1975), using 32% and 4% sucrose solu-

tions, also reported a tendency for ad libitumanimals to show increased

negative contrast following repeated shifts in a within-subject contrast

paradigm. Using a similar within-subject procedure, Panskepp andTrowill (1971) also found a negative contrast effect in low-drive ani-mals following a reduction in sucrose, but contrast shown by low-drive

subjects was, if anything, less durable than that of high-drive subjects.The discrepancy between these two studies may be that in the latter

study only a single within-day downshift occurred, while in theformer, multiple within-day shifts occurred over a series of days. The

present results thus support the findings of Flaherty and Largenand extend them to the more traditional successive contrast paradigm.

The finding in Phase 2 that contrast returned for the group whichhad previously been deprived, when tested under ad libitum mainte-nance conditions, argues against the possibility that some permanentchange resulted from repeated experience with reward shifts underdrive. The occurrence of contrast and the durability of contrast were

clearly functions of current deprivation conditions and not depriva-tion history. Subjects shifted from deprivation to ad libitum condi-tions acted like continuous ad libitum animals following a rewardshift. Likewise, when the ad lib group was placed on deprivation,their behavior was indistinguishable from subjects which had experi-enced prior deprivation.

Of primary importance is the isolation of the factors responsible forthe differences in the durability and repeatability of contrast for ad libas

opposedto

deprived subjects.One

possible interpretationis that

different aspects of the reward are important to the organism underdifferent deprivation conditions. When sucrose concentration is var-

ied, two aspects of the reward may be assumed to change. The newsubstance will taste different and also provide different postinges-tional consequences, such as calories. Thus, when sucrose concentra-

67



RILEY AND DUNLAP

tion is reduced, the subject receives a different tasting reward, as well

as a reward containing fewer calories. The deprived group, like the ad

lib group, may upon experiencing a downshift in reward, experiencesome frustration, show generalization decrement, or react to the in-

centive value of the reward in relation to past reinforcement experi-ence (e.g., adaptation level). However, none of these processes lower

the motivation of the animal. Presumably, deprived subjects learn that

the new substance, although less palatable, does reduce drive. Con-

trast effects would be expected to dissipate as the organism learns thatthe new reward does satisfy a need state; also, contrast would not be

expectedto recur

following subsequentshifts. The ad lib

subject maylearn that the new substance contains calories, but this aspect of the

reward is not of primary importance in determining behavior for less

strongly motivated subjects. The nondeprived animal probably reacts

on the basis of taste factors alone. Such an account of the behavior of

ad libitum subjects is compatible with an interpretation of contrast

based on adaptation level theory (Bevan, 1963, 1966, 1968). Thus, as

long as the animal can remember the original solution, it may show

contrast, since the mechanism presumed to cause dissipation of con-

trast for deprived subjects is of little consequence to the nondeprivedorganism. Mook (1974) has reported that while animals almost uni-

versally prefer sweetened fluids to unsweetened ones, they rarely pre-fer sweetened liquid diets to unsweetened ones. He postulates that

sweetness identifies a substance as food and, as such, releases feedingin the hungry animal. When sweetness is a redundant cue for a food

source, it has little effect upon the animal. It has been stated that a

sugar solution "is at once fluid, food, and fun" (Mook, Walshe, &

Farris, 1975), and such an account is in accord with the present

interpretation. Ad lib animals may respond to the sweetened solutionsas a food source, but it is the hedonic property that is relevant, while

"eating"behavior is released by the sweet taste in deprived animals.

Such an account may also explain why septally damaged rats con-

tinue to react to decreasing concentrations of sucrose followingnumerous downshifts while normals do not (Flaherty & Hamilton,

1971). Flaherty and Hamilton have postulated that septal rats are less

responsive to postingestional cues (e.g., calories) than normals and

overresponsiveto taste cues, thus,

theywould be

expectedto behave

more like the ad lib rats in the present study.One difficulty with this notion, however, is that it would require

successive positive contrast to be a relatively enduring phenomenon inlow-drive subjects. At present, data supporting this idea are somewhat

equivocal. Flaherty and Largen (1975) found large positive contrast

68



SUCCESSIVENEGATIVECONTRAST

effects that did not diminish over the course of the study in ad libitum

rats. Panskepp and Trowill (1971), however, found large but transi-

tive positive contrast in low-drive subjects. This failure to obtain stablecontrast might be explained by the fact that the low-drive subjects,

although responding to taste, do satiate on calories and sheer bulk. As

the animals in the latter study had been consuming 12%sucrose for 2min and then a large amount of 32% sucrose following the upshift, it

is not surprising that a high lick rate was not maintained. Perhaps the

best evidence for sustained positive contrast is provided by Shanab,

France, and Young (1976), who used an instrumental response, su-

crose reward, and thirsty rats. Although the occurrence of positivecontrast was dependent upon a shift from a frustratingly small re-

ward to a large reward, when it occurred it was extremely durable.

Since Emits and Corbit (1973) have shown that thirst increases su-

crose intake only marginally above ad libitum intake, it might be

assumed that the animals in the Shanab et al. study were undera low-deprivation regimen.

The present paradigm seems ideally suited for further investigationof phenomena associated with reward shifts in ad libitumanimals. The

fact that previous studies have failed to find contrast in low-driveanimals while shifting reward quantity may be because low-drive

subjects are not sensitive to this reward manipulation. The presentprocedure of shifting sucrose concentration, a qualitative manipula-tion, may take advantage of the fact that deprived and ad libitum

animals respond to different aspects of the reward.

Note

Requests orreprintsshould be addressedto EdwardP.Riley,DepartmentofPsychology,StateUniversityof New Yorkat Albany,Albany,NY 12222.Theauthors would like to thankDr. NormanGreenfeld for his commentson anearlierversionof thispaper.Receivedfor publicationJune 10, 1977;revisionreceivedMay5, 1978.

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snc as a function of deprivation condition_riley_79

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