Animal Learning & Behavior1978, 6 (2), 235-243

Experiential aspects of exploratorybehavior in rats

EDWARD P. SARAFINOUniversity ofColorado, Boulder, Colorado 80302

Twenty-four male rats were reared under three feeding conditions. These conditions manip­ulated the number and variety of exploratory behaviors required to obtain diets of powderedfood and water in feeding boxes. One group performed minimal exploratory responses toobtain their diets. Another group shuttled between two feeding stations, thereby executingseveral exploratory components, primarily locomotor. The third group performed a considerablenumber and variety of exploratory components in search of their diets, located unsystematic­ally throughout the feeding box. Adult testing occurred without food and water in an apparatusresembling the feeding boxes. The results showed that exploratory behavior was affected byfeeding conditions, enhanced with increased dietary deprivation, and reduced across bothtrials and within-trial intervals. These results indicate that the particular exploratory behaviormeasured must be selected by reference to the subjects' prior experience.

Many studies have assessed the effects of earlyexperience on exploration. Typically, the experimentalmanipulation involves rearing the subjects under dif­ferential amounts and varieties of environmentalstimulation. Environments of relatively low stimula­tion are generally referred to as "deprived" or"restricted"; those of relatively high stimulation aretermed "enriched" or "free." Although some inves­tigators have found that rearing enrichment enhancesexploration (e.g., Forgus, 1954), others have foundreduced exploratory activity (e.g., Zimbardo &Montgomery, 1957a) and others have reported noeffect of rearing environment on exploration(D'Amato & Jagoda, 1962; Ehrlich, 1959).

Because studies of the effects of environmentalstimulation have employed different stimulation con­ditions and behavioral measures to infer exploration,the resolution may lie in the relationship betweenrearing conditions and behavioral measures. Such aresolution is suggested by the outcome of a study(Lore & Levowitz, 1966) in which rats raised in a"free" environment showed faster emergence fromtheir home cages but less object exploration thanrats raised in a relatively restricted environment.Here, two measures of exploration were affecteddifferently by the rearing conditions employed. If

This paper is based upon a dissertation submitted to the Univer­sity of Colorado in partial fulfillment of the requirements for thePhD degree, and was supported in part by National Institute ofHealth Predoctoral Fellowship I FOI MH46142-01. The authorexpresses appreciation to R. C. Miles, thesis advisor, and toJ. Armstrong and D. Cory who assisted in data collection. Theauthor's present address is Department of Psychology, TrentonState College, Trenton, New Jersey 08625.

different behavioral measures reflect different com­ponents of exploratory activity, it may be that spe­cific components of exploratory behavior may bemodified differently by specific aspects or contingen­cies of the rearing environment. One way to test thisproposition is to institute systematic rearing condi­tions designed to modify specific components ofexploration by associating them differentially withfood and water.

An approximation to such rearing conditions wasstudied by Woods and Bolles (1965). They assigned19-day-old rats, 11 to a cage, to three ad-lib feedingconditions: (I) food pellets scattered on the floor,(2) food pellets in two hoppers mounted in fixedlocations, and (3) liquid Metrecal in fixed locations.After approximately 60 days, the subjects were testedindividually, either sated or hungry, for one 3D-minsession in an open field which had miscellaneousobjects of hardware on the floor. Water bottles werein fixed locations for all conditions. While the over­all statistical analysis revealed a significant effectof the three feeding conditions, no significant differ­ence in exploration was found between the two solid­food conditions. [This individual comparison wasanalyzed by me with data supplied by ProfessorWoods. These calculations yield t(42) = 0.424,P > .20.] Failure to find differential exploration as aresult of the two solid-food conditions may be dueto several factors. For example, since the rats werehoused in groups, the opportunity to perform thespecific behavioral components measured in explor­atory testing may have been reduced. Also, it ispossible that small pellets from the fixed hoppersfound their way into the cage, thus making theconditions more similar.

235

236 SARAFINO

WELL

PHOTOCELL¥ (LIGHT SOURCE)'t-------.i

PLEXIGLAS STRIP(FOOD TRAY)

DesignThe 3 by 2 by 8 by 5 factorial design consisted of three feeding­

experience conditions, two levels of food and water deprivation,eight trials, and five 3-min intervals within trials. The subjectswere assigned to three independent groups (feeding conditions)and tested repeatedly across drive conditions. trials. and within­trial intervals.

The three feeding conditions were as follows. The subjects in the"low variety of exploratory components" (LEC) condition wererequired to perform only minimal exploratory responses in orderto obtain food and water. The second condition, "moderate var­iety of exploratory components" (MEC), required subjects toshuttle between two fixed feeding stations in order to obtainfood and water. Thus, some exploratory components, primarilylocomotion, were associated with drive reduction. In the thirdcondition, "high variety of exploratory components" (HEC).food and water were located unsystematically throughout the feed­ing box. The subjects were required to search for their diets,thereby performing a variety of components of exploratorybehavior.

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offspring. The experiment was run in two replications. Each repli­cation was run with four subjects under each of three feeding­experience conditions. The colony room was maintained underconstant illumination day and night.

ApparatusThe apparatus consisted of three identical feeding boxes and

one exploratory maze. The feeding boxes (61 ern long x 61 ernwide x 35.6 ern high) were constructed of wood, painted a darkgray, and had a small (20.3 ern x 12.7 ern) observation aperturein the ceiling. Illumination in the box was provided by threelow-wattage bulbs and was brighter than outside the box. Feed­ing cups, 48 located on the walls, 2 on the floor, and 4 atopcylindrically shaped pedestals. were attached to the box. The loca­tion of food cups was always identical in all of the three feed­ing boxes. Two of the feeding cups were in a fixed location onthe floor. The bottom of each of these two cups was actuallya food well in a continuous strip of Plexiglas. This Plexiglasstrip (food tray) could slide out from below the floor to permitrefilling the well with powdered food. A top-view illustration ofthe apparatus can be seen in Figure I (only two feeding cups areshown in each box). Each food station (in Figure 1) had a con­tainer of powdered food. A water trough encircled the interior ofthe feeding boxes. A picture of the interior of a feeding box isshown in Figure 2. One photocell, mounted 4.5 ern above thefloor, scanned across the box to obtain an estimate of activity

METHOD

Studies undertaken to determine the effects ofappetitive drives on exploratory behavior, comparingperformance under satiation with performance underat least 22 h of deprivation, have not systematicallyassociated dietary acquisition with the behavioralcomponent measured. Although several studies havefound that deprivation enhances exploration in rats(e.g., Adlerstein & Fehrer, 1955; Bindra & Palfai,1967; Bolles & de Lorge, 1962a), others have foundno effect (e.g., Bolles& de Lorge, 1962b; Hall, Low,& Hanford, 1960; Welker, 1959). Yet others havefound a decrease in exploration with increases indeprivation (Chapman & Levy, 1957; Zimbardo &Montgomery, 1957b). Although these findingsappear contradictory, the source of the inconsistencymay, once again, lie in their diverse experimentalconditions and their relationship to the behavioralmeasures observed. Two experiments have found dif­ferential effects of drive on two behavioral measures(de Lorge & Bolles, 1961; Kamback, 1966). In bothstudies, deprivation enhanced "object exploration"(e.g., manipulating or sniffing objects) but had noeffect on "nonobject exploration" (e.g., perambula­tion or sniffing floor, walls, and ceiling). In addi­tion, the experiment by Woods and Bolles (1965),described earlier, found that while deprived subjectsshowed more total exploration than sated subjects,a complex pattern of effects was revealed for meas­ures of object exploration and nonobject exploration.Such findings suggest that the complex relationshipof appetitive motivational effects might be clarifiedif the motivation was associated with the specificexploratory components that are measured.

Several experiments have reported that exploratoryactivity decreases both within and across trials(Brookshire & Rieser, 1967; Ehrlich, 1959; Foshee,Vierck, Meier, & Federspiel, 1965). These studies havegenerally used very simple exploratory apparatuses,e.g., a Y-maze, painted gray throughout and devoid ofobjects. Experiments using more complex apparatuseshave found less consistent results (Adlerstein& Fehrer,1955; Glanzer, 1961). Typically, the experimentaldesigns included (1) fewer than seven trials and(2) trials lasting only 10 min or less. No studies haveexamined the course of exploration in a highlycomplex apparatus over long periods of time.

The present experiment was designed to provide atest of the position that components of exploratorybehavior are modifiable differentially through exper­ience. Specific and intensive differential rearing pro­cedures were followed by observation of corres­ponding behaviors during adult exploratory testing.

SubjectsPregnant Long-Evans hooded rats were obtained from the

Maxfield Animal Supply Company. The subjects were 24 male Figure 1. Top view illustration of feeding boxes.

EXPERIENTIAL ASPECTS OF EXPLORATORY BEHAVIOR 237

Figure 2. Feeding box interior.

in the feeding box. It scanned twice across the box by using amirror to reflect the beam (see Figure I).

The exploratory maze was approximately twice the area of thefeeding box, measuring 81.3 em long x 83.8 em wide x 36.9 emdeep. The floor and outer walls, inside the maze, were made ofwood painted a dark gray. The interior structure included cubicles,runways, and objects. The floor plan was such that four cubicles(34.5 em long x 34.5 em wide x 36.9 em deep) were located inthe corners of the maze, separated by 15.2 em wide runways.The two partitions forming the cubicles were made of clearPlexiglas, and each partition had one (10.2 x 10.2 em) entrance­way. The objects, all made out of unpainted metal, were modifiedhardware and houseware items (e.g., spoons). These objects werechosen, modified, and mounted such that they resembled the foodcups, pedestals, and water troughs used in the feeding box. Theinterior remained constant throughout the experiment. The ceilingof the maze was made out of clear Plexiglas with two layers ofaluminum screening. The aluminum screening was used so thatthe subject's vision outside of the maze would be impaired andso that the subject could not see his own reflection in the Plexiglasceiling. Four l5-W soft-white incandescent bulbs illuminated theapparatus. One bulb was located in the ceiling at each cornerof the maze. The experimental room was very dimly lit, illum­inated only by two 15-W red bulbs mounted in a fixture whichadditionally filtered the light through Kodak No. 29 Wratten fil­ters. These filters were selected on the basis of visibility curvesreported by Graham and Riggs (1935) and Granit (1941). Whiterat vision is insensitive at the spectral wave lengths penetratingthe No. 29 filter. Photocells, mounted at the corners of the maze,scanned the diagonal 4.5 em above the floor. A start box (25.4 emlong x 17.7 em wide x 17.7 em deep), located at the end of arunway, had a photocell to scan 4.5 cm above the floor acrossthe guillotine-door entranceway to the maze. The opposite wallof the startbox was movable, as a piston, to gently force the ratinto the exploratory maze if it did not leave the box within a4-min time limit. (This device, however, was never required.)All photocell light sources were filtered with Kodak No. 29Wratten filters. Photocell beam interruptions were recorded onSodeco electromechanical counters located in another room.

On days when feeding did not occur in the feeding box, ad-libfood and water were available in the rats' home cages. The cages(22.9 em long x 17.7 em wide x 7.7 em high) were constructedof a hardware-cloth floor and front wall and three galvanizedmetal walls. The home cages were modified to simulate the feeding­box conditions. Feeding inserts, constructed of white Plexiglas andconsisting of a floor and two walls, were placed in home cages.Food and water troughs were mounted on these walls. This arrange­ment was necessary in order to insure that the subjects obtaina sufficient diet for normal growth and development. In a pilot

study conducted after weaning, it was determined that rats did notconsume a sufficient diet of powdered food and water whenallowed two I-h feeding periods per day; growth was stuntedcompared with that of normally reared littermates.

Rearing ProcedurePreweaning conditions. Purina food pellets and water were

available ad lib for the mothers in each brooding cage. This feed­ing regimen continued until the offspring were 12 days old. OnDay 12, food and water were removed from their cages. Thence­forth, the mothers were removed to feed on wet mash for 2 heach day. Male pups were handled equally each day while theirmothers were feeding. Sexing of offspring was determined beforeDay 12, and females were removed.

Postweaning conditions. The subjects were weaned on Day 25and assigned to the differential-feeding-experience groups. Assign­ment was accomplished by a split-litter technique and the subjectswere matched, as nearly as possible, by weight. Beyond theserestrictions, assignment was random. The subjects were housedin individual home cages where ad-lib food and water were avail­able for the first 5 days after weaning. To further insure thehealth of the rats, a vitamin supplement was added to their wateruntil approximately Day 70.

On Days 28 and 29, the subjects were placed as a group(four rats) in their feeding box for I h each day, without thepresence of food or water, to familiarize them with the environ­ment and reduce neophobic reactions. Then, on Days 30 and 31,the rats were placed individually in the boxes, and on Day 31inserts were removed from the home cages. On every other day,until Day 40, the rats obtained their diets in the feeding boxes;on alternate days, inserts were placed in their home cages allowingfree food and water.

Feeding box experience. Performance in the feeding boxes re­quired training of specific food-getting responses for the MECand HEC groups. Consequently, certain temporary procedureswere introduced. On days when feeding occurred in the feedingboxes, training was conducted twice (morning, afternoon) per day.Control was exercised to assure equal handling and equal time inthe feeding boxes across groups. Training continued until: (1) allpossible reinforcements were randomly located for the HEC group,(2) the MEC subjects were reinforced on a variable-ratio schedulefor alternately approaching the two feeding cups on the floor,and (3) the subjects in the MEC and HEC groups reached acriterion of five reinforcements obtained in the first 7 min of afeeding session. Once all rats reached the training criterion, theywere permitted one feeding session on each "feeding-box" day.Obtaining their diets was then contingent upon performing behav­iors which corresponded to their feeding condition. The feedingschedule was gradually modified throughout rearing experiencesuch that the subjects were forced to depend more on obtainingtheir diets in the feeding boxes than on home-cage feeding.

In the feeding box, a total of 18 equally sized powdered foodreinforcements per session was available to each subject in boththe MEC and HEC conditions. For the LEC subjects, all foodwas on the floor, none in any food cups; water was available inall sections of the water trough. Sand was placed in 18 of theLEC food cups. In the MEC condition, food was obtained onlyin the two food cups on the floor; water was available only inthe sections of the trough close to these two food cups. In orderto obtain all 18 reinforcements, MEC subjects were required tomake a total of 54 contacts alternately with the two food cups.Food appeared in the cups on a variable-ratio schedule of threecontacts to one reinforcement. The HEC group had their 18reinforcements placed randomly in the 54 food cups; water wasavailable in half of the water trough sections. The locationsof the rewards were changed every other feeding-box day. Thefood cups were repositioned four times during rearing. Thesechanges were unsystematic. Food-cup locations were identical forall conditions. Food and sand floors were changed every other day.

238 SARAFINO

RESULTS

Figure 3. Percent of total response occurrence and mean fre­quency of occurrence (per minute), across all trials, for the com­ponents: grooming (G), freezing (F), locomoting (L), immobilesniffing (IS), mobile sniffing (MS), climbing (e), rearing (R),and gnawing (N). Mobile sniffing refers to sniffing behavior whichoccurred in conjunction with behaviors which are relatively mobilein quality, e.g., locomoting and rearing.

limbs touch floor. (6) Rearing-Body raised on hind feet; fore­paws may be touching objects or walls; includes sitting up.(7) Gnawing-Chewing or masticating objects. (8) Manipulating­Grasping and handling; does not include merely leaning or touch­ing. (9) Inactive-relaxed-Lying down; abdomen touching floor;motionless; includes sleeping. (10) Other-Any other behavior notdescribed above; e.g., yawning, stretching.

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The subjects were scored for 10 behavioral com­ponents of exploratory behavior; however, becausethe components of gnawing, inactivity-relaxed,manipulating, and "other" were observed infre­quently, they were not analyzed completely.

Figure 3 presents the overall basic pattern ofexploratory activity performed by the rats in theexploratory maze. Clearly, sniffing, locomoting, andrearing predominate. Although behavioral patternsother than mobile sniffing are not mutually exclusive(e.g., climbing and rearing sometimes occurredtogether), this bar graph, nevertheless, illustrates therelative predominance of individual components per­formed by rats in the present apparatus.

Statistical analyses were applied to the frequencydata for the six pertinent behavioral components:rearing, locomoting, immobile sniffing, climbing,freezing, and grooming. Four-way analyses of var­iance were computed for the factors of feedingexperience, food and water deprivation, trials, and

Behavioral MeasuresThe following behaviors were selected for observation on the

basis of previous research in the field. Although these behavioralmeasures are neither mutually exclusive nor independent, it wasfound that they are reasonably exhaustive (without the "other"category): (1) Grooming-Animal cleans, scratches, or licks body.(2) Freezing-Animal stands or sits with all four limbs touchingfloor; motionless for more than very brief moment; eyes are open.(3) Locomoting-At least two limbs in motion on floor; walks,runs, or turns. (4) Sniffing-Nose twitches and rapid vibrissaemovement; includes poking nose at object and nose being veryclose to floor while locomoting. (5) Climbing-None of four

The feeding procedure was identical on each feeding-box day.Before each feeding session, the walls of the feeding box weresprayed with a vinegar-water solution. This was done to matchthe odor of the solution used to clean the exploratory maze (seebelow). The subjects within each group were always fed individ­ually in the same order and in the same feeding box. Three rats,one from each feeding condition, were fed simultaneously. Theexperimenter was stationed equidistant from each box and in thesame position relative to the orientation of the feeding boxes(see Figure I). Identical experimenter activity was performed foreach Teeding box on each MEC trial (except that no food wasactually placed in the LEC and HEC wells). This procedurecontinued within each session until 54 trials had been conductedwith an MEC subject or until 30 min had elapsed. All rats werethen removed from the apparatus.

In order to control for the amount of food consumed duringfeeding sessions, a weight record was taken each "feeding-box"morning prior to feeding. The LEC weights served as the base,since obtaining food was easiest for this group. If the overallweights of the MEC or HEC groups differed from LEC by greaterthan 10010, an adjustment in size of reinforcement was made forthe MEC and HEC groups. Changes in the size of reinforcementswere also contingent upon changes in feeding schedule and thesubjects' age. Throughout rearing, reinforcement size was grad­ually increased from 0.12 to 0.48 g.

Exploratory test. On Day 87, exploratory testing commenced.The testing procedure was identical for each subject in everysession. A subject was placed in the startbox and allowed I minfor orientation and exploration. The guillotine door was thenlifted, exposing the exploratory maze. Once the rat's forepawscrossed a starting line, the door was lowered, making sure notto hit the animal, and the exploratory test was begun. At theend of each 15-min test, the rat was returned to its home cage.Before each session, the floor of the maze was sponged with avinegar-water solution to eliminate odor trails.

The subjects were observed during exploration by the experi­menter. A record was taken of their behavior using a time-samplingtechnique. At the sound of an electric timer, every 6 sec, the rat'sbehavior was recorded.

Counterbalancing techniques were applied to the sequence oftrials and deprivation conditions. A coordinated counterbalancingwas used to determine the order in which subjects from each groupwere tested. For each subject, feeding occurred in his home cageon a 36-h food-and-water deprivation schedule followed by 12 hof free feeding every other day. This, of course, was staggeredacross subjects as a consequence of restrictions produced bycounterbalancing. Exploratory testing occurred within the 36-hprivation periods. On any test day, each rat was tested undereither low deprivation (a mean of approximately 4 h after insertswere removed from their home cages) or high deprivation (a meanof approximately 28 h after inserts were removed). All exploratorytesting was conducted during the day.

Throughout the 20-day testing phase of the experiment, a max­imum total gain in body weight, amounting to 7% of their pre­testing weight, was permitted for the animals. This allowable gainwas based upon normal weight gains of rats during comparableage periods.

EXPERIENTIAL ASPECTS OF EXPLORATORY BEHAVIOR 239

Table IStatistical Summary of F Values for the Six Four-Way Analyses of Variance

Main Effects

ExploratoryComponent

FeedingConditions(df= 2/21)

Across WithinDeprivation Trials Trials Interactions and(df= 1/2l)(df= 7/l47)(df= 4/84) Comments

Immobile Sniffing 3.35, .05> p < .10

l6.93tt

45.67tt Within Trials by Across Trials F(28/588) = 4.l8tt

l3.52tt

p> .05 2.42*

33.36tt 4.26tt

p> .05 3.75tt

l2.89t 17.92tt

20.4 Itt 2.59* 40.20tt Also see text for analysis of rearing-plus-sniffing

p > .20 23.23tt l22.84tt See text for analysis of locomoting-plus-sniffing

Feeding Conditions by Deprivation8.54tt F(2/2l) = 4.02* And see text for post hoc

comparisons within interaction

p > .05

P > .05

p> .20

9.59t

p> .20

Rearing

Locomoting

Climbing

Freezing

Grooming

"p < .05**p < .01

tp < .005tt» < .001

3-min intervals within trials, with repeated measureson the last three factors. Table I presents the statis­tical outcomes of these six analyses. Interactionsbetween the factors were infrequent and generallynot highly reliable. Newrnan-Keuls tests were usedfor post hoc comparisons.

Rearing BehaviorRearing is a component that was expected to be

performed most frequently by the HEC subjects.Analysis revealed highly significant differences forboth main effects (refer to Table I for statisticalreports). Increased food and water privation enhancedrearing behavior. Although the overall effect ofexperience is reliable and the means are in the pre­dicted direction, the difference between the HEC andMEC groups did not reach significance (p > .05).

Analysis of the temporal course of rearing behav­ior revealed a reliable decrease in rearing as a func­tion of trials. Over within-trial intervals, the signi­ficant overall effect is not linear; more rearing(p < .05) was performed during the second within­trial interval than during the first and fifth intervals.Frequency of rearing behavior increased from thefirst to the second within-trial interval and consist­ently declined thereafter.

Since the exploratory components observed werenot mutually exclusive, combinations were recordedwhen they occurred. The HEC feeding conditionswere designed to reward not only rearing behavior,but the more specific combination of rearing andsniffing. Consequently, a separate one-way analysisof variance was calculated to examine the effect offeeding experience on rearing-plus-sniffing. This re­vealed a reliable [F(2,21) = 4.360, p < .05] experien­tial effect. A Newman-Keuls analysis subsequentlyshowed that the HEC group performed significantly(p < .05) more rearing-plus-sniffing responses thandid the MEC and LEC groups, which did not differ(p > .05).

LocomotingBehaviorAnalyses of these data showed no effects of either

feeding experience or deprivation on locomotoractivity. Since one of the feeding experience treat­ments, MEC, was designed to specifically reinforcelocomotor behavior in a similar stimulus environ­ment, these findings are especially important. At thesame time, highly reliable decreases in locomotingwere found across both temporal variables, trialsand within-trial intervals.

Once again, it is instructive to examine combina­tions of exploratory components; in this case,locomoting-plus-sniffing. Here, locomotion is rela­tively slow and sniffing of the floor, and of the lowerwalls and objects, is present. This behavior wouldbe expected most frequently by the LEC subjects.A one-way analysis of variance of these data revealeda highly significant [F(2,21) = 7.217, p < .005]effect of feeding experience. Subsequent Newman­Keuls tests showed that the LEC subjects performedreliably (p < .01) more locomoting-plus-sniffingthan both the MEC and HEC groups, which did notdiffer (p > .05).

ImmobileSniffing BehaviorAnother component of exploratory behavior

which was expected to be more prominent in theLEC subjects' behavior is immobile sniffing. Al­though no significant effects of food and water dep­rivation were found, the experience factor approach­es significance (p < .10).

A clearer main effect of experience was revealedby a three-way analysis of variance which was per­formed earlier for another purpose. This analysisyielded a reliable [F(2,21) = 3.850, p < .05] differ­ence between feeding conditions while showing noeffect (F < 1.0) of food and water deprivation. Sub­sequent Newman-Keuls comparisons within thisthree-way analysis indicated that subjects in the LECcondition made reliably (p < .05) more immobile

240 SARAFINO

2.10sniffing responses than both the HEC and MECsubjects, which did not differ (p > .05). Thus, theLEC subjects performed the most immobile sniffingresponses. The interaction involving feeding condi­tions and deprivation, depicted in Figure 4, indicatesthat deprivation influenced immobile sniffing behav­ior differently for the LEC subjects compared withboth other conditions. Newman-Keuls comparisonsshowed no differences (p > .05) between the threefeeding conditions under low deprivation. However,under high deprivation there were reliable differences(p < .05) between the LEC group and both the MECand the HEC groups, which did not differ (p > .05).

1.90

1.10

Climbing BehaviorClimbing is a component of exploration that was

expected to be performed most frequently by theHEC subjects, for their food-getting experience veryoften required them to climb to the food. Althoughthe means are in the predicted direction, the effectof feeding experience was not statistically reliable.However, the main effect of privation was highlysignificant. Climbing occurred more frequentlyunder high deprivation than under low deprivation.

Climbing was reliably increased as a function oftrials. A significant overall main effect was alsofound across within-trial intervals, but this functionis not linear. Newman-Keuls analysis revealed thatmore (p < .05) climbing was performed during thesecond within-trial interval than during the first andfifth intervals. Thus, climbing frequency increasedfrom the first to the second within-trial interval anddecreased thereafter.

Freezing BehaviorFreezing behavior was not required of any feeding

condition in order to obtain food and water. Neither

2.75

.90

2

TRIALS

Figure 5. Mean freezing (per minute) for the five within-trialintervals (I) as a function of trials.

feeding conditions nor deprivation treatments wereshown to affect freezing.

At the same time, highly reliable increases in freez­ing were revealed as a function of both of the tem­poral variables, trials and within-trials intervals.Furthermore, a strong interaction was found betweenthe two temporal variables. It can be seen in Figure 5that the effect of within-trial intervals appears to beaugmented as trials advance. This graphical view wasconfirmed by Newman-Keuls comparisons of thefirst and fifth within-trial intervals for the first andeighth trials. This analysis revealed no effect (p > .05)of within-trial intervals for Trial I while yielding asignificant (p < .01) difference between the first andfifth within-trial intervals for Trial 8. Thus, thefunctions do, in fact, diverge; the incrementing effectof time within trials on freezing behavior increasedacross trials.

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Figure 4. Mean immobile sniffing (per minute) for the LEC,MEC, and HEC feeding conditions as a function of mean hoursof deprivation.

Secondary Data AnalysesIn addition to the time sampling of behavioral

components in the maze, secondary data, concernedwith maze exploration and validating design assump­tions, were analyzed with appropriate statistical tech­niques. Neither beam interruptions in the exploratorymaze nor startbox leave time (latency) were affected(p > .20) by feeding experience or food deprivation.

Grooming BehaviorAs with freezing behavior. feeding conditions did

not require the subjects to perform grooming behav­iors in order to obtain their diets. Hence, it is notsurprising that no effect of feeding experience wasfound. There was, at the same time, a reliable de­crease in grooming with increasing dietary privation.Moreover, grooming increased as a function of bothtrials and within-trial intervals.

28

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EXPERIENTIAL ASPECTS OF EXPLORATORY BEHAVIOR 241

But both measures showed a significant (p < .(01)decline across trials.

As the experimental design assumed, (1) the threefeeding experience groups did not differ (F < 1.0)in weight during the period from assignment of sub­jects to groups through testing, and (2) counter­balancing procedures produced no significant ordereffects (p > .05). Finally, as a reliability check againstobserver subjectivity, during 48 (12.5070) of the 384total test trials, a second observer was present. Inthese trials, the writer and the second observer scoredthe subjects' behavior simultaneously but indepen­dently. For each time sample, complete agreementwas scored 1.0 points and complete disagreementwas scored 0.0 points. Because more than one com­ponent could occur simultaneously, partial agree­ment was possible. In such instances, 0.5 points wasscored. The total points for agreement divided bythe total points possible across all 48 trials yielded88.63070 agreement.

DISCUSSION

An overview of the effects of feeding experienceclearly shows that, if specific behavioral componentsof exploration are systematically associated with dif­ferential feeding contingencies and examined individ­ually, the behavioral topographies employed in one'sexploration are experientially modifiable. The com­ponents of exploratory behavior examined wereselected on the basis of prior research and theirexpected relationship to present feeding experiencemanipulations. For the most part, the specific behav­iors were affected by prior feeding experience. Thesecomponents are rearing, rearing-plus-sniffing,immobile sniffing, and locomoting-plus-sniffing.Only two behaviors, locomotion and climbing, didnot demonstrate an experiential effect. Since no dif­ferential feeding conditions were related to groomingand freezing behaviors, finding no differences inthese behavioral measures as a function of feedingexperience is consistent with expectations.

Although these findings may have relevance to the"nature-nurture" controversy (see, e.g., Brown,1953; Dember & Earl, 1957; Harlow, 1953a, 1953b),they probably make a more significant contributionto the study of exploratory behavior by pointing outthat the dependent variables, typically measured toinfer exploration and curiosity, interact with anteced­ent environmental factors. In addition, although thecontingencies defining the rearing conditions in thisexperiment were appetitive, other consequences mayalso influence exploratory activity. For example,Taylor (1974) has shown that both stimulus changeand complexity may serve as incentives in explora­tory behavior. Therefore, the potential sources forinfluence on measures of exploratory activity arediverse.

Locomotion, probably the most commonly em­ployed measure of exploratory behavior in rats, wasunaffected by both feeding-experience and privation.This finding is consistent with the lack of effectof these variables on two related measures, beaminterruptions in the maze and latency to leave thestartbox. Such results regarding the locomotion com­ponent may be due, in part, to statistical "ceilingeffects." That is, since locomotory behavior occurredso frequently, there was little room for enhancementby experimental manipulations. Comparative datarevealed that, while in the present experiment 25.96070of the total responses were locomotor, the corres­ponding percentage in Prescott's (1970) study is 17.1(estimated from his Figure 1). Since the present ex­ploratory maze was much more visually complexthan Prescott's, a ceiling effect undermining theeffects of experimental manipulations on locomotionbecomes plausible given the observation by Bollesand de Lorge (1962b) that "the size of the depriva­tion effect seems to depend upon the level of explor­ation that occurs in the test situation. In the presentcase, where the rat is tested in a highly complexnovel situation which sustains exploration at a highlevel, the effect is small in absolute terms. Usingthe less complex apparatus, de Lorge and Bolles(1961) found that deprivation raised the incidenceof exploration" (p, 226).

Climbing behavior also showed no effect of feed­ing conditions. This was contrary to expectation,since only under the HEC condition were the ratsspecifically rewarded for climbing in the feeding box.Failure to find experiential effects with this com­ponent may be related to the fact that for everyapparatus, including living cages, the exit was viathe ceiling. Thus, climbing behavior in the maze mayhave, in part, been an effort to seek release from anenvironment that did not satisfy appetitive needs.Support for this explanation comes from the findingsthat (1) climbing was augmented by dietary depriva­tion for subjects in all feeding conditions and(2) across within-trial intervals, extinction of climb­ing responses occurred with nonreinforcement, i.e.,release was never contingent upon climbing.

An overview of the privation effects on the variousbehavioral measures supports the expectation thatfood and water deprivation would increase thosebehaviors which were affected by feeding conditions.Since the feeding and test apparatuses were visuallysimilar, this finding is consistent with the hypothesisof Hall, Low, and Hanford (1960), which suggeststhat exploration is more likely to be enhanced byappetitive privation if prior reinforcement has beenassociated with the stimuli in the test environment.

Grooming and freezing behaviors, generally con­sidered to compete with exploration (e.g., Bolles &de Lorge, I962b), were expected to decline withincreasing appetitive motivation, as suggested by

242 SARAFINO

prior investigations of exploration (Prescott, 1970)and of runway behavior (Cotton, 1953). Whiledietary privation reduced grooming frequency, noeffect was revealed for freezing. The lack of effectfor freezing behavior may be reasonable if thereare two kinds of freezing responses, one which is aresponse to fear arousal (Doyle & Yule, 1959; Riess,1945) prior to habituation and one which perhaps"bridges" successive exploratory components. Thefunction of this bridging would be to provide an'opportunity for the organism to inspect the stimulussurround and determine what to explore next. Inspec­tive freezing would increase with time of exposurebecause discriminations must be made as to howsufficiently certain stimuli have been explored pre­viously. Consistent with this interpretation, Denny(1975) has reported that, following considerable ha­bituation time, rats show a free-choice preference forhigh complexity. If freezing behaviors were measuredunder such conditions, it is likely that they wouldbe serving the inspective function. Note that thisinterpretation proposes three phases of stationaryreaction to novel stimulation: fear, inspection, andboredom. The final phase, boredom, was mostaccurately reflected in the "inactive-relaxed" measurein the present experiment.

The fact that freezing behavior was found toincrease both within and across trials is consisentwith results reported by Bindra and Spinner (1958).Their rats were tested for several behavioral measuresin a small (30.6 x 30.6 x 30.6 ern) chamber. Anal­ysis revealed an increase in freezing behavior withinthe single 15-min test trial. Of the few studies ofexploration which measured freezing behavior, onlyBindra and Spinner (1958) report these data overtime. Other investigators typically pool the data(e.g., Woods & Davidson, 1964). Since the presentsubjects were rarely scored as "inactive-relaxed" andsince it is unlikely that fear would increase with timein such situations, the increase in freezing could beaccounted for by the inspective function. Further­more, the interaction depicted in Figure 5 indicatesthat the increasing use of inspective freezing withintrials accelerates across trials.

It is likely that there are subtle behavior distinc­tions between the two types of freezing (Tobach,Note 1). One possible distinction may be the lengthof the freezing period. Bolles and de Lorge (1962b)observed that their rats "generally either froze onlymomentarily or for periods longer than 15 seconds"(p. 224). Other possible distinctive features mightinclude "absence of sniffing, body tenseness, shallowbreathing" (Bolles & Collier, 1976, p. 7), piloerection,and teeth chattering.

The consistent finding that exploration decreasesboth within and across trials in simple apparatusesis extended to exploration in a very complex explora-

tory maze. Generally, it can be said that grooming,freezing, and immobile sniffing increased bothwithin and across trials, while locomotion and rear­ing decreased. Climbing behavior increased acrosstrials, but decreased within trials. Actually, thewithin-trial functions for climbing and rearing showa reliable increase initially followed by a monotonicdecrease. Performance of these components duringthe first 3 min may have been depressed as a resultof the initial burst of locomotion which took placeupon entering the maze. During the first within-trialinterval, locomoting was the predominant behaviorcomponent. It contributed 33.91 CTfo of the behavioralcomponents observed, even more than total sniffing.Thus, initially the animals were highly active in theexploratory maze but changes in behavioral topo­graphies occurred with time. Considering the factthat the behavioral topographies were, in part, aresult of prior experience, the decreases in measuresof exploratory activity are viewed as reflecting both(I) habituation and extinction to novelty effects, and(2) extinction functions for prior appetitive reinforce­ment of these specific behaviors.

Exploratory behavior, as examined experimentallyand in real life, is clearly experientially modifiable.Each component of exploratory activity may be in­fluenced separately, or as part of a constellation ofresponses, depending upon the environmental contin­gencies. This is not to say, however, that each com­ponent is equally modifiable. Bolles (1970) andSeligman (1970) have advanced the intriguing pro­posal that not all stimulus and response events areequally conditionable; innate predispositions maydetermine the associability of particular events. Butbeyond the issue of degree of conditionability, thepresent results indicate that the specific behaviorsmeasured to infer exploration must be selected andconsidered with reference to the experiential back­ground of the subjects.

REFERENCE NOTE

I. Tobach, E. Personal communication. 1971.

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(Received for publication March 30, 1977;revision accepted October 6, 1977.)