The interactive effects of stimulus generalization decrement and contextual pre-exposure cues upon fear incubation

The interactive effects of stimulus generalization decrement and contextual pre-exposure cues upon fear incubation

Lkhw. RES. Thrr. Vol. 22. No. 1. pp. 31-39, Prmted in Great Britam All rights reserved 1984 Copyright 0005-7967’84 $3.00 + 0 00 f’ I984 Pergamon Pro...

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Lkhw. RES. Thrr. Vol. 22. No. 1. pp. 31-39, Prmted in Great Britam All rights reserved

1984 Copyright

0005-7967’84 $3.00 + 0 00 f’ I984 Pergamon Proas Ltd

THE INTERACTIVE EFFECTS OF STIMULUS GENERALIZATION DECREMENT AND CONTEXTUAL PRE-EXPOSURE CUES UPON FEAR INCUBATION

Division

of Social

and

Behavioral

THOMAS L. BOYD Sciences, University of South Carolina Parkway, Aiken. SC 29801. U.S.A. (Received

30 March

at Aiken.

171 University

1983)

Summary-Models of fear incubation may be described as explanations for the interference of Pavlovian extinction. From this perspective, the effects of several parameters upon the incubation phenomenon were examined. Fear incubation was found to be attenuated by manipulations associated with stimulus generalization decrement (Experiment I), as well as pre-exposure manipulations (Experiment 2). These findings were incorporated within existing models of incubation.

INTRODUCTION

An increment in the strength of a classically-conditioned fear response which occurs following a period of time when only unreinforced CS presentations are made has been referred to as ‘incubation’ (Eysenck, 1968). Empirical demonstrations of the incubation phenomenon have not been accepted uncritically (Bersh, 1980) nor have these demonstrations been entirely consistent. Inconsistencies in both outcome, as well as in procedural and parametric manipulations have prohibited sustained theoretical development. It is the intent of this paper to provide a brief theoretical sketch of existing incubation models, and to investigate empirically the role of several parameters which are expected to affect incubation. Eysenck’s (1968) explanation of the incubation effect combined the cumulative effects of Pavlovian extinction, occurring as a result of unreinforced CS presentations, with the offsetting effects of a theoretical ‘nocive’ or aversive, response-produced property of the fear CR associated with this CS. Presumably, under conditions during which the CR would be expected to be exceptionally strong (e.g. when the US was very strong), highly aversive response-produced properties of the fear CR would serve to strengthen (reinforce) the CS-CR association, thereby mimicking the previous effects of the US. According to Eysenck’s (1968) theory, this mimicking effect would serve to retard extinction or perhaps even enhance (incubate) the fear response, thereby interfering with the expected extinction effect. Surprisingly few theoretically-based experiments have been conducted in this area. Those existing experiments, on shock intensity for instance (e.g. Boyd, 1981; Nicholaichuk, Quesnel and Tait, 1982) differ in too many procedural details to allow comparison. Further, other investigators have discovered potentially relevant variables which, to this point, had remained unspecified from Eysenck’s (1968) early theorizing. For example, Gordon, Smith and Katz (1979) have reinterpreted earlier incubation findings in terms of a memory-reactivation model. According to their findings. enhanced vs decreased avoidance responding depended, in part, upon when during a retention interval following acquisition that forced CS exposure occurred. Their memory-reactivation model explains incubation as confronting organisms with cues which were present during original learning, thereby reactivating the memory of prior training. Whereas Eysenck (1968) spoke of the mimicking effect of the nocive response offsetting Pavlovian extinction, Gordon et al. ( 1979) have theorized that enhancement effects occur when a cueing of old learning precedes, in time, the organism’s learning of a new set of contingencies-Pavlovian extinction. Short CS exposures in extinction procedures (relative to no CS exposure) should provide an opportunity for cueing to occur first, thereby resulting in enhanced performance due to strengthened memory. At more sustained unreinforced CS exposure durations, the learning of a new contingency (e.g. extinction) 31

37

THOMAS

L. Bow

would be expected to begin to cancel the effects of incubation (e.g. Rohrbaugh and Riccio. 1970; Rohrbaugh Riccio and Arthur, 1972; Boyd, 1981). A further temporal relationship which was developed by Gordon et ~11,‘s(1979) research is that of the retention (temporal) interval between time of conditioning and extinction exposures. With short retention intervals. earlier conditioning memories theoretically are readily available. hence further CS exposure results in extinction. At relatively longer retention intervals. earlier conditioning memories are less readily available; therefore brief CS exposures serve to reactivate and perhaps strengthen these memories before extinction may occur. While obvious differences exist between these separate models of fear incubation. the ma.jor differences appear to lie within the selection of hypothetical constructs used to explain the phenomenon. The mechanisms or operation of these constructs appear rather alike. Eysenck ( 1968) spoke of incubation as an interference of extinction where strong, aversive nocive responses act to interfere with Pavlovian extinction. Gordon et ul.‘s (1979) memory-reactivation model asserts that the itierference of Pavlovian extinction occurs through a reactivation of conditioning memories, perhaps further strengthening these memories and resultant fear. A final theoretical mechanism of extinction which appears quite comparable to this formulation of incubation as an interference process may be seen in the application of Denny’s (1971) early elicitation;‘relaxation theory. Elicitation theory accounts for reduced CS fear over regular extinction trials by assuming that a combined relief-relaxation response ‘back chains’ or generalizes from a critical temporal period following CS offset (within approx. 150 set), to the actual period of CS presentation. In this manner, extinction represents a competing, relaxation response which begins to interfere directly with the conditioned fear response. The implication of this model is that by interfering with the relaxation response by either extending the presentation time of an unreinforced fear CS (e.g. Rohrbaugh and Riccio. 1970) or by increasing the relative strength of the fear response (e.g. Boyd, 1981) one may expect a retardation of fear extinction. An exacerbation of the fear CR may be expected should the fear response be directly conditioned to relaxation cues (see Denny, 1971). Upon more extended unreinforced CS presentations. the re-elicitation of the relaxation response eventually should occur, along with a subsequent reduction of fear to the CS. Accordingly. extinction represents conditioned relaxation to previous fear-eliciting cues. while incubation represents the interference of a relatively time-locked relaxation response. This brief theoretical sketch of models of fear incubation and extinction allows for the prediction of the effects of several experimental parameters upon the incubation effect. Experiment 1 was conducted in order to examine the effects of differential contextual (apparatus) cues upon incubation in rats. Due to a stimulus generalization decrement, it was expected that the conditioned fear response would be more easily reduced when exposure presentations were made in a chamber of dissimilar stimulus characteristics relative to the original conditioning chamber. Accordingly, incubation should be relatively easier to obtain following unreinforced CS exposures in the conditioning chamber as opposed to exposure in a dissimilar apparatus. As a hypothetical construct, it may be expected that memory reactivation will be stronger in the conditioning chamber. perhaps allowing for a greater incubation effect. Alternatively, the relaxation response should be more easily elicited in a neutral chamber as opposed to in the conditioning chamber during unreinforced CS exposure. Therefore, elicitation theory also allows the prediction of an interaction effect of temporal intervals of unreinforced CS exposure and differential contextual cues upon fear incubation. To the degree that the relaxation response is expected to interfere with the fear CR. incubation should be attenuated. Experiment I attempts to test these interaction effects within the context of a conditioned suppression design. EXPERIMENT

1

Subjects were 60 male, albino rats bred for experimental purposes in the USC-Aiken the start of the experiment they ranged in age from 85 to 129 days.

colony.

At

Fear incubation

33

Apparatus

Acquisition was conducted using a Lafayette Instrument One-Way Avoidance Box for rats (Model No. 85200) located in a walk-in, sound-attenuated room. The apparatus was comprised of a ‘shock’ chamber and an adjacent jump-up ‘safe’ chamber (see Boyd, 1981, for details). By activating a 28 V motor, the back wall of the safe chamber traversed horizontally, dumping the animal from the safe chamber on to the shock-chamber floor. A 4000 Hz tone was produced by a Camden Instruments audio generator (Model 258) and was delivered through a 10.5 cm speaker located at the center of the roof of the shock chamber. Ambient noise level measured by a Simpson (Model 886) sound-level meter was 60 f 2 dB (Scale C). The tone raised this level to 70 + 2dB. A BRS/LVE Shock Generator/Scrambler (SGS-004) delivered scrambled shock to the shock-chamber floor, measured at 55 V d.c. intensity. Timing of the CS-US interval was done by a Camden Instruments, g-Bin Universal Timer (Model 249). Response latencies were recorded by a Lafayette Instrument Event Timer (Model 5710) and Sodeco print-out counter (Type PN107). Lick-suppression testing was conducted in a separate, modified Gerbrands operant conditioning chamber housed in a sound-attenuated enclosure. The inner dimensions, as well as the size and spacing of the grid bars along the floor were distinctly different from the dimensions of the conditioning apparatus. A 4000 Hz tone produced by the Camden Instruments audio generator was measured at 70 f 2 dB and delivered through a 10.5 cm speaker located at the center of the roof of the drinking chamber. Procedure

A complete factorial design was used with three levels of CS exposure duration by two levels of contextual cues (3 x 2). All Ss received water deprivation (10 min of water per day) for 14 days. On Day 14, all Ss were given 10 min of lick training in the sound-attenuated drinking chamber. On Day 15, all Ss were placed in the automated one-way avoidance apparatus and trained to an acquisition criterion of 5 consecutive avoidance responses. The CS was a IO-set, 4000 Hz tone; the US was a scrambled 55 V d.c. shock stimulus. An avoidance response was defined as a jump-up response on to the safe chamber, which occurred within the IO-set CS-US interval (see Boyd, 1981). On Day 16, 30 Ss (Group S) were each placed on the shock-chamber floor of the original conditioning apparatus, with the back wall of the safe chamber in the ‘closed’ position preventing the jump-up response. Each S was placed in the chamber for a total of 6 min. Ten Ss in Group S were presented with 0 set of unreinforced tone exposure (Group S-O), 10 Ss were presented with 30 set of unreinforced tone exposure (Group S-30) and the final 10 Ss were presented with 300 set of unreinforced tone exposure (Group S-300). The unreinforced CS was presented such that an equal duration of tone would occur on either side of the half-way point during the 6 min of exposure to the conditioning apparatus (e.g. 2 min and 45 set into the interval for Group S-30; and 30 set into the interval for Group S-300). The remaining 30 Ss (Group D) were each placed on the dissimilar drinking-chamber floor, with the drinking tube retracted, for a total of 6 min. Ten Ss in Group D were exposed to 0 set of unreinforced tone (Group D-O), 10 Ss were exposed to 30 set (Group D-30) while 10 Ss were exposed to 300 set (Group D-300) of unreinforced tone in a manner identical to Group-S Ss. On Days 17-20, all Ss were tested for remaining fear levels in the drinking chamber using a suppression-of-licking measure. Similar to Levis and Boyd (1979) rats were allowed to lick the water tube for 300 licks plus 30 sec. Subsequent to this, a baseline of licking behavior was recorded for a period of 60 set (A). Immediately following this baseline period, licking was recorded while the experimenter presented the 30-see test tone (B). The remaining fear level was recorded by calculating a suppression ratio defined by (B/(iA + B) where 0.000 represents complete suppression of licking and high levels of fear during the tone presentation, while 0.500 represents no relative suppression of licking behavior. Results

The following acquisition indices were analyzed in the context of a 3 x 2 analysis with three levels of exposure duration and two levels of contextual cues: (1) mean total number of escape trials; (2) mean shock duration on escape trials; “RT 22, c

of variance

THOMAS L. BOYV

34 Table

I. Dependent

Mean total escape triala Mean shock duration Mean trial number of first avoidance response Mean total avoidance responses response Mean avoidance latency Mean response latency on last 5 consecutive

variables

of acquisition

dunng

Experiment

I

s-o

s-30

s-300

D-O

D-30

D-300

3.0 6.3 35

2.6 2.3 2.9

3.3 4.8 3.4

2.8 4.4 3.2

4.1 5.5 4.3

30 47 3.4

5.5

6.3

6.6

6.0

6.3

5.8

2.3

2.7

3.1

2.5

2.7

2.9

2.2

2.6

29

2.5

2.6

29

avoidancer

(3) mean trial number of the first avoidance response; (4) mean total number of avoidance trials; (5) mean avoidance response latency; and (6) mean response latency on the last 5 consecutive avoidance responses. Table 1 presents the separate group mean data for these indices. As expected, for indices 1-6, all main and interaction effects were nonsignificant. Table 2 presents the mean suppression ratios for each group during Days 17-20, while Fig. 1 presents the mean suppression ratios for each group during Day 20. A three-factor analysis of variance with repeated measures was performed, again with three levels of exposure duration and two levels of contextual cues, with repeated measures on 4 days of suppression testing. Significant main effects were obtained for both the days condition and the contextual cue condition, with F(3,177) = 27.6, P < 0.0001; and F(1,216) = 7.7, P < 0.006; respectively. A significant three-way interaction effect was obtained for the Days x Contextual Cue x Exposure Duration interaction, with F (6.177) = 2.6, P < 0.02. The Contextual Cue x Exposure Duration interaction approaches significance, with F(2,216) = 2.3, P < 0.10. As may be observed from Table 2 and Fig. 1, the obtained interaction effect appears to be a result of the differential rates of extinction of the fear response for Groups S-30 and D-30 relative to their comparison groups. In confirmation of this, specific group comparisons between Groups S-30 and S-O. and between Groups S-30 and S-300, on Day 20 were both greater than F( l/393) = 4.5, P < 0.05; indicating that Group S-30 was significantly more suppressed (i.e. fearful) relative to Groups S-O and S-300 on Day 20. In contrast, Group D-30 was less suppressed relative to Groups D-O and D-300 on Day 20, with the Group D-30 vs Group D-O comparison being significant at F (l/393) = 4.5, P < 0.05. Group S-30 was also significantly more suppressed relative to Group D-30 on Day 20, with F( l/393) = 14.09, P < 0.001. Correspondingly, the Group S-O vs D-O and S-300 vs D-300 comparisons on Day 20 were both nonsignificant. Specific comparisons performed across test days also reflect the differential rates of fear extinction as observed in Table 2. Test-day comparisons performed between Day 20 and all 3 remaining test days for Group S-30 were all nonsignificant at the 0.05 level of confidence. In contrast, for Group S-O, specific comparisons performed on Day 17 vs Day 20, and Day 18 vs Day 20 were both significant with F(1/393) = 13.18, P < 0.001; and F(1/393) = 11.1, P < 0.01: respectively. Similarly for Group S-300, test-day comparisons between Day 20 vs Day 17, and Day 20 vs Day 18 were both significant, with F(1/393) = 11.0, P < 0.001; and F(1/393) = 5.96, P < 0.025; respectively. For Groups D-O, D-30 and D-300, significant fear reduction was observed across days for all three groups. with the Day 20 vs Day 17 comparison being significant, with all

Table 2. Mean suppression

ratios

Test-davs

Group

I7

IX

for

Experiment

I groups

during

17-20

I9

20

S-O

0.006

0.026

0. IS7

0.247

s-30

0.067

0.041

0.076

0.079

s-300

0 000

0.059

0.145

0.220

D-O

0.000

0.037

0.201

0.187

D-30

0.000

0.075

0.268

0.328

D-TOO

0 Oh0

0. I78

0.258

0.220

Fear incubation

35

05r

S-O E-

s-30

S-300

cl*

D-30

o-300

GROUP

Fig. I. Mean

suppression

ratios

for Experiment

1 groups

during

Fs(1/393) > 5.7, P < 0.025. Further, the Day 20 vs Day 18 comparison groups D-O and D-30, with both Fs (l/393) > 5.1, P < 0.025.

Test-day

21).

was significant

for both

Discussion

Experiment 1 was conducted to test the interaction effects of differential temporal intervals of unreinforced CS exposure and differential contextual cues, upon fear incubation. It was predicted that extinction would be facilitated by unreinforced CS presentations in an apparatus dissimilar to that in which conditioning occurred. Accordingly, fear incubation should be attenuated. Suppression ratios calculated for Day 20 testing clearly reflect this expected relationship. For those groups receiving unreinforced CS exposure in the conditioning apparatus, an incubation effect was observed. That is, the group exposed to intermediate levels of unreinforced CS duration (Group S-30) displayed greater resistance to extinction relative to groups S-O and S-300. As predicted, this effect was attenuated for those groups receiving unreinforced CS exposure in the lick chamber prior to testing. A number of points need to be clarified with respect to these findings. Of critical importance is the observation that despite an obvious resistance to extinction displayed by Group S-30 relative to Groups S-O and S-300, intermediate levels of unreinforced CS exposure did not generate increasing fear levels across test days. An examination of Eysenck’s (1968) theoretical explanation of fear incubation need not lead one to conclude that systematic fear increases are to be expected, as Pavlovian extinction could equalize any CR strengthening by the nocive response. This effect could be theoretically possible, however, as a very strong nocive response could serve to strengthen the conditioned fear response, again offsetting the effects of extinction. Within a memory-reactivation model (Gorden et al., 1979) it is also not immediately apparent that an increase in fear following extinction should necessarily be observed. While it is certainly possible to develop a theoretical addendum consistent with this model to explain potential fear increases, it would not seem necessary from an empirical standpoint. Further, from Denny’s (1971) model one would not expect an exacerbation of the fear response relative to that observed during conditioning unless, perhaps, under relatively specialized conditioning experiences within which the response is directly conditioned to relaxation cues. Even then a fear-response exacerbation should be observed at conditioning rather than across extinction trials. A final observation of interest is the Test-day 20 difference between Groups S-30 and D-30 relative to their comparison groups. While Group S-30 was more resistant to extinction relative to Groups S-O and S-300, Fig. 1 reflects the greater extinction effect for Group D-30 relative to Group D-O, and a strong tendency for this effect relative to Group D-300 (though nonsignificant). A possible explanation for this effect may be seen in a recent experiment by Grelle and James (198 1) on the conditioned inhibition of fear. Following Denny’s (1971) model and consistent with Grelle and James’ (1981) finding, intermediate exposure to the CS in a neutral test environment (lick chamber) appeared to have the effect of conditioning a relief/relaxation response to the CS, thus establishing that CS as a conditioned inhibitor of fear and accounting for the apparent rapid reduction in the measured fear response. More sustained unreinforced CS exposure (i.e. Group

36

THOMAS L. BOYI)

D-300) likely regenerated a fear CR which interfered with this relief/relaxation response, thereby breaking-up the inhibition effect. While these findings appear to be incorporated easily within Denny’s (1971) model, they are not readily apparent from a memory-reactivation perspective. Experiment 1 demonstrated the role of contextual cues upon the incubation effect. Through a stimulus generalization decrement, the extinction interference effect observed during intermediate CS exposures was reduced. According to Denny’s (1971) elicitation theory, if extinction involves an excitatory conditioning effect of relief/relaxation to the CS, extinction should be facilitated by any process which is likely to enhance the relief/relaxation response. Experiment 2 attempted to test this effect. It was expected that the relaxation response may be more readily elicited during testing (and, therefore, facilitate extinction) if the organism is given pre-exposure to the neutral lick chamber. EXPERIMENT

2

Subjects were 64 (32 male. 32 female) albino rats bred for experimental purposes in the USC-Aiken colony. At the start of the experiment they ranged in age from 85 to 130 days of age. The number of male and female Ss was counterbalanced within groups.

Identical to Experiment 1, Ss were conditioned in a Lafayette Instrument One-Way Avoidance Box for rats (Model No. 85200) and given lick-suppression testing in the separate. modified Gerbrands operant conditioning chamber. The programming of this equipment was identical to that of Experiment 1 in all respects.

A complete factorial design was used with two levels of exposure duration, by two levels of contextual cues, by two levels of pre-exposure (2 x 2 x 2). All Ss received water deprivation (10 min of water per day) for 14 days. On days 12-13, the pre-exposure condition was manipulated, with one-half of the Ss being presented with 10 min/day of pre-exposure to the test chamber (water tube retracted) prior to conditioning (Group I); while the remaining Ss received identical exposure to a neutral chamber (carrying cage) to control for handling effects (Group II). On Day 14. all Ss were given 10 min of lick training in the lick chamber. On Day 15, all Ss were placed in the automated one-way avoidance apparatus to receive acquisition training. Here training was identical in all respects to that described in Experiment 1. Similar to Experiment 1, on Day 16 unreinforced CS exposure was presented in either the original conditioning chamber. or in the lick chamber. The CS presentation was identical in all respects to Experiment 1 with the exception that only the 0-see and 30-set intervals were presented. A summary of the Experiment 2 design may be seen in Table 3. On Days 17-20, all Ss were tested for remaining fear levels in the lick chamber, using a suppression-of-licking measure identical to the Experiment 1 testing. Results The following acquisition indices were analyzed in the context of a 2 x 2 x 2 analysis of variance, with two levels of pre-exposure, two levels of exposure duration and two levels of contextual cues: (I) mean total number of escape trials; (2) mean shock duration on escape trials; (3) mean trial number of the first avoidance response; (4) mean total number of avoidance trials; (5) mean avoidance response latency; and (6) mean response latency on the last 5 consecutive avoidance responses. Table 4 presents the separate group mean data for these indices. As expected, for indices 1-6, all main and interaction effects were nonsignificant.

37

Fear incubation Table 3. Experiment

2 design

Preexposure

condition

I. Lick chamber Exposure

duration

0-set 30-set

II. Neutral

Contextual cue-extinction Conditioning chamber (A) Lick chamber Group I-A0 (N = 8) Group I-A30 (N-z 8)

~.

Mean total escape trials Mean shock duration Mean trial number of first avoidance response Mean total avoidance responses Mean avoidance response latency Mean response latency on last 5 consecutive avoidances

(B)

Group l-B0 (N = 8) Group I-B30 (N-= 8)

Table 4. Dependent ~~~...

variables

chamber

Contextual cue-extinction Conditioning chamber (A) Lick chamber Group II-A0 (N = 8) Group WA30 ((v = 8)

of acquisition

during

Experiment

~_

(B)

Group II-B0 (N = 8) Group II-B30 (iv = 8)

2

Group

_.-

I-A0

I-A30

I-B0

I-830

II-A0

II-A30

II-B0

II-B30

3.75 9.3 4.0

3.25 4.13 3.63

3.5 3.96 3.5

3.5 4.9 I 4.13

3.5 5.6 3.75

4.25 5 33 5.0

3.13 6.06 3.38

3.75 3.54 3.38

6.0

6.13

6.0

5.7s

5.62

5.25

6.38

6.25

3.1

3.18

2.47

2.33

3.14

2.61

2.14

2.52

3.02

2.95

2.89

2.34

3.08

2.63

2.41

2.31

Table 5 presents the mean suppression ratios for each group during Days 17-20, while Fig. 2 presents the mean suppression ratios for each group during Day 20. A four-factor analysis of variance with repeated measures was performed on suppression ratios, again with two levels of pre-exposure, two levels of exposure duration, two levels of contextual cues and with repeated measures on 4 days of suppression testing. A significant main effect was obtained for the Days condition, with F(3/161) = 37.97, P < 0.0001. Significant interaction effects were obtained for the following: Exposure Duration x Contextual Cue, with F(1/64) = 4.04, P ==I 0.05; Contextual Cue x Day, with F(3/161) = 3.23, P < 0.02; Exposure Duration x Day, with F(3/161) = 2.53, P < 0.05; and Contextual Cue x Pre-exposure Condition x Day, with F(3/161) = 3.98, P < 0.009. Of particular interest are those findings which are revealed in the Contextual Cue x Pre-exposure Condition x Day interaction effect. As in Experiment I, this effect appears to be a result of differential rates of extinction of the fear response across days. Specifically, while the incubation effect observed in Experiment 1 was replicated in Experiment 2 [the Group II-A0 vs Group II-A30 specific comparison on Test-day 20, with F(l/225) = 4.09. P -=z 0.051 this effect is eliminated when pre-exposure training is given (the Group I-A0 vs Group I-A30 specific comparison on Test-day 20 being nonsignificant). As indicated by Fig. 2, Group II-A30 remained significantly more fearful on Day 20, relative to Group I-A30, with F(1/225) = 6.83, P < 0.01; demonstrating a clear indication of the effectiveness of the pre-exposure manipulation. In contrast to the incubation effect observed in Group II-A30 which was exposed to extinction presentations in the original conditioning chamber, Group II-B30 demonstrated a decrease in the suppression measure relative to Group II-BO, with this specific comparison approaching significance with F( l/225) = 2.94, P < 0.10, on Day 20. In effect, this result appears to replicate the Experiment 1 finding that extinction presentations in the lick chamber results in an extinction effect. This finding Table 5. Mean suppression ratio for Experiment Test-days 17 20

2 groups

during

Day Group

17

IX

19

20

I-A0 I-A30 I-B0 I-B30 II-A0 II-A30 II-B0 II-B30

0.003 0.000 0.052 0.072 0.000 0.000 0.000 0.027

0.129 0.061 0.000 0.055 0.230 0.150 0.109 0.073

0.153 0.297 0.163 0.337 0.236 0.171 0.125 0.261

0.247 0.324 0.141 0.371 0.272 0.094 0.279 0.430

3X

THOMAS

L.

Bow PRE - EXPOSURE

II

GROUP

Fig. 2. Mean

suppression

ratios

for Experiment

2 groups

during

Test-day

20

was bolstered further by the Day 20, Group II-A30 vs Group II-B30 specific comparison, with F( I /225) = 14.56, P < 0.00 I;once again demonstrating the effectiveness of the contextual cue manipulation observed in Experiment 1. This extinction effect following CS presentations in the lick chamber, was also observed in the pre-exposure group, with the Day 20, Group I-B0 vs Group I-B30 comparison being significant with F(1/225) = 6.83, P < 0.01. No further relevant group comparisons on Day 20 were significant. A further demonstration of differential extinction rates across groups is observed in specific comparisons performed between test days for individual groups. In a further replication of Experiment 1. and as demonstration of the incubation effect in retarding the extinction of the fear response, specific comparisons performed between Test-day 20 and all other test days with Group II-A30 were all nonsignificant. In contrast, specific comparisons performed on Group II-A0 between Test-day 17 vs Test-day 18, Test-day 19 and Test-day 20 were all significant at the 0.01 level of confidence, with all Fs (l/225) > 6.80. This, of course, demonstrates an extinction of the fear response. For Group I-A30, the pre-exposure manipulation clearly facilitated the extinction effect with Test-day 20 vs Test-day 17, Test-day 20 vs 18, and Test-day 19 vs both Test-days 17 and 18 being significant, with all Fs( l/225) > 7.1, P < 0.01. For those groups receiving unreinforced CS presentations in the lick chamber, only Group I-B0 demonstrated a retarded extinction effect, with no Test-day 20 comparisons being significant at the 0.05 level of confidence. DISCUSSION Experiment 2 provided a replication of the effects of a generalization decrement (i.e. contextual cues) upon the incubation effect as observed in Experiment 1. That is, extinction procedures were effective in reducing the conditioned fear response when unreinforced CS exposures were presented in a chamber of dissimilar stimulus characteristics relative to the original conditioning chamber. Further, Experiment 2 demonstrated the role of the pre-exposure manipulation in disrupting the incubation effect. To the extent that the pre-exposure manipulation allowed the organism to develop a strong ‘relaxation’ response, it would appear that extinction was facilitated by intermediate durations of unreinforced CS exposures. For those Ss not exposed to the pre-exposure manipulation, intermediate durations of unreinforced CS exposures appeared to retard the extinction effect, relative to no CS exposure. This, of course, occurred only in this group which received CS presentations within the original conditioning chamber. It should be noted that neither of these experiments was conducted to provide a critical test of the memory-reactivation model vs the relaxation model of fear extinction and incubation. Similar to the Experiment I findings, these results are consistent with Denny’s (1971) explanation of the extinction effect. While perhaps not readily apparent from a memory-reactivation interpretation of incubation, it may also be argued that the Experiment 2 pre-exposure manipulation had the effect of strengthening a memory either antagonistic to conditioning, or at least of the relative absence of fear. Accordingly. memory of the conditioned fear response may not readily transfer to the testing chamber. thereby attenuating the fear response and resultant incubation effect.

Fear incubation

39

Further experimental efforts must be made to determine the relative strength of these hypothetical constructs. For now, the present investigations point to parameters which appear to be relevant to the incubation effect. As observed in Experiment 1, the incubation effect which was demonstrated in Experiment 2 is best described as a retarded extinction effect rather than a relative increase in the conditioned fear response. These findings are closely akin to the limitations of the incubation findings as discussed by Nicholaichuk et al. (1982). While it may be that such a facilitation effect is not to be found within the present design, more parametric work is necessary to determine the viability of this critical issue. It may be that the present experiment generated a ‘floor effect’, as all groups were relatively completely suppressed during initial test days, leaving no room for observable fear increases. A final point to be noted is that within the relaxation model of extinction, Denny (1971) generated a potential therapeutic technique which would appear to be consistent with the present findings. Accordingly, one might envision a two-stage process of fear reduction within exposurebased therapy approaches, quite similar to the Experiment 2 manipulation. Patients may first be exposed to a fear-evoking stimulus, thereby generating a strong conditioned fear response. Through prolonged exposure, it is expected that this fear response will gradually diminish. At this point, the patient may be instructed, via previous training, to initiate a relaxation response during exposure to facilitate the process of Pavlovian extinction. While consistent with a relaxation interpretation of extinction, this approach to fear reduction is also viable from a standpoint of an opponent-process model of arousal (Solomon and Corbit, 1974). Clearly more experimental investigations concerning the temporal parameters of the fear and post-fear response are called for. Acknowledgements-The author would like to thank William J. House for his assistance Appreciation is also due to Donnie Fincher and Paula Skedsvold for running the Ss.

on the statistics

of this research.

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