the role of gray's impulsivity in anxiety-mediated differences in resistance to extinction

The Role of Gray's Impulsivity inAnxiety-Mediated Di�erences in

Resistance to Extinction

CEÂ SAR AVILA* and MARIA ANTOÁ NIA PARCET

Universitat Jaume I, CastelloÂn, Spain

Abstract

Choice behaviour and extinction learning were studied in a group of 108 undergraduatesclassi®ed according to the Sensitivity to Punishment and Sensitivity to Reward scales(that measure Gray's anxiety and impulsivity dimensions, respectively). The learningtask consisted of continuous choosing between two response alternatives: one wascontinuously reinforced with a small reward and the other was partially reinforced witha greater reward. After 200 trials, one of the responses remained as in the previousphase, and the other was never rewarded in order to attain extinction. The main aims ofthe study were: (i) to replicate Avila's ®nding of lesser resistance to extinction ofsubjects having high scores on the Sensitivity to Punishment scale; (ii) to investigatewhether impulsives (subjects having high scores on the Sensitivity to Reward scale)chose more than non-impulsives the response associated with a continuous, smallreward; and (iii) to test, following the model of Patterson and Newman, whetherimpulsive subjects had a great resistance to extinction of responses highly associatedwith reward. Results supported all three predictions. Discussion is based on thecompatibility of the models of disinhibition of Gray and of Patterson and Newman.Copyright # 2000 John Wiley & Sons, Ltd.

INTRODUCTION

The behavioural inhibition system (BIS) is the conceptual substrate for anxiety in theneuropsychological theory of emotions developed by Gray (1982, 1987a). The BIS issensitive to secondary aversive stimuli including stimuli associated with punishmentand frustrative non-reward, novel, and intense stimuli. When activated, the BIS willproduce behavioural inhibition, and an increase in arousal and attention. Theseoutputs aim at the suppression of responses susceptible to being punished or non-rewarded, and cause a decrease in goal-directed responses manifested by passive

Copyright # 2000 John Wiley & Sons, Ltd. Received 15 March 1999Accepted 22 September 1999

European Journal of PersonalityEur. J. Pers. 14: 185±198 (2000)

*Correspondence to: CeÂ sar Avila, Apartado de Correos 224, Department de Psicologia BaÁ sica, Clõnica iPsicobiologia, Campus de la Carretera de Borriol, Universitat Jaume I, 12080 CastelloÂ n, Spain.E-mail address: [email protected]

avoidance and extinction. At personality level, the anxiety dimension is related to thedi�erent sensitivity of the BIS to secondary aversive stimuli: anxious subjects are moresensitive and show more behavioural inhibition to these stimuli than non-anxiousones.

Some research investigating individual di�erences in sensitivity to punishment andbehavioural inhibition in humans has con®rmed Gray's description of the BIS (Avila,MoltoÂ , Segarra and Torrubia, 1995; Corr, Pickering and Gray, 1995; Gupta andShukla, 1989; Torrubia, Avila, MoltoÂ and Grande, 1995). However, little evidenceexists for BIS-mediated di�erences in individual di�erences in sensitivity to non-reward and resistance to extinction. Avila (1994) conducted a study to investigatepersonality di�erences in resistance to extinction in the laboratory. Two groups ofundergraduates, classi®ed as anxious and non-anxious according to the Sensitivity toPunishment scale (Torrubia et al., 1995), completed a computer choice task. This taskconsisted of a continuous trial-by-trial choosing between two response alternatives.The task had two phases. In the ®rst, each response alternative was partially rewardedfor all the subjects: responses to button 1 were rewarded on 70 per cent of the trialswith a random win of 2 to 10 points, whereas responses to button 2 were rewarded on30 per cent of the trials with a random win of 8 to 20 points. In the second phase, oneof the responses remained as in the ®rst phase, but the other was never rewarded inorder to attain extinction. The computer selected the extinction button randomly foreach subject. The dependent variable was resistance to extinction indexed by thenumber responses to each button. Results show no di�erences in performance in the®rst phase, but anxious subjects show less resistance to extinction than non-anxiousones in the second phase. The main di�erences between both groups were obtained atthe beginning of the second phase, indicating that non-anxious subjects were slowerto associate their responses with non-reward.

Although the relationship between BIS level of activation and sensitivity tosecondary punishment and non-reward has been well established in these studies,there is also some research showing the possible mediating role of Gray's impulsivitydimension (i.e. sensitivity to reward). This possibility arises from two di�erentsources. First, at methodological level, some researchers have pointed out the di�-culty of obtaining pure punishment or reward situations in real-life or laboratory sets(see Corr et al., 1995; Gray, 1987b). Second, at theoretical and experimental level,Patterson and Newman (1993) have related learning from aversive events with Gray'simpulsivity.

Following Gray's model, the level of impulsivity is dependent on another andindependent psychological system: the behavioural activation system (BAS). The BASis activated by signals of reward and active avoidance, promoting approach behaviourand increments of arousal. Individual di�erences in BAS activation are related to theimpulsivity dimension of personality running from the neurotic extravert to stableintrovert quadrants in the Eysenckian space.

Gorenstein and Newman (1980) proposed that the septal syndrome is a good modelfor human disinhibition. According to their model, disinhibited individuals such asimpulsives, extraverts, and psychopaths display psychological processes similar toseptal-lesioned rats. These processes are the tendency to response perseveration andthe de®cit in response modulation (McCleary, 1966). These two concepts are highlyrelated. De®cits in response modulation are related to an inability to stop and re¯ecton the negative consequences of previously rewarded responses. These de®cits lead to

186 C. Avila and M. A. Parcet

Copyright # 2000 John Wiley & Sons, Ltd. Eur. J. Pers. 14: 185±198 (2000)

response perseveration, that is, to an exaggerated tendency to emit a dominantresponse despite punishment, extinction, or contingency reversal.

Research with undergraduates has shown that (neurotic) extraverts and impulsivesshow a greater tendency to perseverate in previously rewarded responses despitepunishment (Avila et al., 1995; Newman, Widom and Nathan, 1985; Patterson,Kosson and Newman, 1987). Thus, a hyperactive BAS could lead to passive avoid-ance de®cits when subjects are responding for reward. Patterson et al. (1987) showedthat this de®cit was associated with a lower re¯ectivity after punishment. Recently,Patterson and Newman (1993) have developed a four-stage model to explain thisprocess: (i) establishment of an approach response set that is stronger in impulsives;(ii) punishment, omission of reward, or delayed reward occurs unexpectedly, provok-ing an increment in arousal; (iii) this increased arousal leads to response perseverationin previously rewarded responses and to failure in response modulation (retrospectivere¯ection) in impulsives; and (iv) this lack of retrospective re¯ection produces a de®citin learning from aversive events consisting of a lower prediction of aversive conse-quences of behaviour.

This model has received great experimental support in the laboratory using mixedincentives (punishment and reward). However, less research has tested the modelusing non-reward instead of punishment. The extinction procedure developed in ourprevious study could serve this purpose because it provokes extinction after theestablishment of an approach response set. The main purpose of the present studywas to investigate the role of the BAS in the BIS-mediated di�erences in resistance toextinction. We used the Sensitivity to Punishment (SP) and Sensitivity to Reward(SR) Questionnaire to measure individual di�erences in BIS and BAS activity,respectively (Torrubia et al., 1995). Several studies have given support for the ideathat these scales reliably and validly re¯ect individual di�erences in Gray's dimen-sions (Avila, Parcet, Ortet and IbanÄ ez, 1999; Brebner and Martin, 1995; Torrubiaet al., 1995; Zuckerman, Joireman, Kraft and Kuhlman, 1999).

We have carried out some modi®cations to the procedure used in our previousstudy (Avila, 1994). First, the number of trials in each phase has been reduced to 200because the last trials were not relevant in the previous study. Second, reinforcingschedules associated with each response button have been changed to replicate ourprevious results showing anxiety di�erences in resistance to extinction using di�erentreinforcement contingencies. In the present procedure, responses to one buttonwere associated with a continuous reinforcement schedule, and responses to theother button with a 50 per cent partial reinforcement schedule. Third, the to-be-extinguished response was not always randomly selected: when one response wasselected more than 75 per cent of the time in the ®rst phase, this response wasextinguished in the second phase. This manipulation was conducted in order toincrease the probability of extinguishing responses associated with a strong expecta-tion of reward.

Our main hypotheses for the extinction behaviour were made separately for anxietyand impulsivity dimensions. First, we expected to replicate our previous ®ndingshowing that subjects having high scores on the Sensitivity to Punishment scale wouldshow less resistance to extinction when compared with low scorers. Second, nodi�erences were expected between the two anxiety groups in the acquisition phase.

We had two di�erent hypotheses which related the mediating role of the Grayimpulsivity dimension in the choice task. In the acquisition phase, we expected that

Impulsivity and extinction 187


subjects having high scores on the Sensitivity to Reward scale would choose thecontinuous more than the partial reinforcement schedule. Literature about choicebehaviour and matching law has distinguished impulsive and self-control behaviour:impulsives prefer more immediate but smaller reinforcers, whereas self-controls prefergreater and more delayed reinforcers (Williams, 1988). We expected to obtain similarresults using the Sensitivity to Reward scale as a measure of impulsivity.

According to Patterson and Newman's model, our second hypothesis was thatimpulsivity di�erences in resistance to extinction would be found when subjects hadto extinguish responses strongly associated with reward. Concretely, we hypothesizedthat subjects with high scores on the Sensitivity to Reward scale would have problemsto extinguish dominant than non-dominant responses. To test this hypothesis, we willcalculate an additional variable, called response preference, that would serve to divideat the median subjects that choose the to-be-extinguished response more than theother in the acquisition phase (establishing dominant responses) from subjects thatchoose both responses more similarly.

METHOD

Subjects

One-hundred and eight undergraduates (23 males and 85 females), enroled inPsychology classes at the Universitat Jaume I, completed the procedure of this studyin partial ful®lment of a course requirement. Mean age was 19.97 (SD � 3.33) with arange between 18 and 33 years.

Measures

All the subjects completed the Sensitivity to Punishment (SP) and Sensitivity toReward (SR) Questionnaire (Torrubia et al., 1995; Torrubia, Avila, MoltoÂ andCaseras, unpublished data). Each scale in this questionnaire is comprised of 24 itemswith a yes/no format. SP scale include items related to: (i) behaviour inhibition insituations involving the possibility of aversive consequences or novelty; (ii) worry orcognitive processes produced by the possibility of punishment; and (iii) emotionalstates such as fearfulness about aversive stimuli. This scale was correlated ÿ0.49 and0.56 with the Extraversion and the Neuroticism scales of the Eysenck PersonalityQuestionnaire (EPQ), respectively.1 The SR scale is comprised of items related to: (i)proneness to approach cues of reward; (ii) proneness to orientate attention towardpositive signals; and (iii) heightened conditionability to rewarding events. This scale iscorrelated 0.39, 0.28, and 0.44 with Extraversion and Neuroticism scales of the EPQ,and with the Impulsiveness scale of Eysenck and Eysenck (1978), respectively.

Four groups were formed on the basis of their scores on the Sensitivity toPunishment and Sensitivity to Reward scales, by dividing the subjects at the medianon these two dimensions calculated in a large undergraduate sample (Torrubia et al.,unpublished data). Subjects scoring 12 or higher on the Sensitivity to Punishmentscale were designated as anxious (SP�), and subjects scoring below 12 were classi®edas non-anxious (SPÿ). Similarly, males scoring 11 or above and females scoring nine

1These data were obtained from oa large sample of 2140 undergraduates (see Torrubia et al., 1995;unpublished data).



or above on the Sensitivity to Reward scale were designated impulsives (SR�),whereas subjects scoring below these cut-o� scores were classi®ed as non-impulsives(SRÿ). This breakdown resulted in four groups of 21 SPÿ SRÿ (seven males), 20SPÿ SR � ( four males), 25 SP � SRÿ (®ve males), and 42 SP � SR � (sevenmales), respectively. These four groups were not signi®cantly di�erent in sexdistribution.

Task and procedure

The task was controlled by a PC and the `1' and `2' keys on the computer keyboardwere used for responding. The task consisted of two di�erent phases with fouridentical blocks of 50 trials, in each of which subjects had to choose between tworesponse alternatives (trials were reduced in the present study because the last trialswere not relevant in our previous study). There was no interruption between the twophases. The procedure is summarized in Table 1.

The task was similar in the two phases. At the beginning of the task, subjects werepresented with two centrally located squares measuring 3� 3 cm2. Written inside eachsquare there were the expressions Button 1 and Button 2, respectively. Two 5� 2 cm2

rectangles appeared centrally located 4 cm and 7 cm below the other two, respectively.The expressions Points � with the points earned after each response and TotalScore � with the total number of earned points during the task appeared inside theserectangles, respectively. Points earned after each response were displayed for 1500 mswhile total earnings were continuously displayed during the task. A zero number wasdisplayed if no reward was given.

Subjects had to choose in each trial between responding to button 1 or button 2. Inphase I (the acquisition phase), responses to the two buttons were rewarded di�er-ently. Responses to button 1 were always rewarded with a random number of pointsranging from 2 to 11. Responses to button 2 were partially rewarded on 50 per cent ofthe trials with a random amount of points ranging from 8 to 21. The two responseswere programmed to give a slightly di�erent amount of reward: button 1 wasassociated with an average of 6.5 points per response, whereas button 2 wasassociated with an average of 7.25 points per response. This discrepancy was made inorder to increase the probability of choosing the partial reinforcement programwithout establishing an evident di�erence between the two response alternatives. Ouraim was also to reduce the possibility that randomness would produce a realadvantage for the continuous reinforcement program.

Table 1. Percentage of rewarded responses to each button in each phase

Extinction phase

Acquisition phase Continuous Partial extinction(all the subjects) extinction group group

Button 1% reward 100% 0% 100%(reward � 2±11 points)

Button 2% reward 50% 50% 0%(reward � 8±21 points)



In phase II (the extinction phase), responses to one of the two buttons were neverrewarded and responses to the other button were rewarded as in the acquisition phase.The selection of the to-be-extinguished response was made attending to two possi-bilities: (i) if subjects responded to each button in less than 75 per cent of the trials inthe acquisition phase, the computer randomly selected which button was rewardedand which button was not rewarded in the extinction phase; (ii) if subjects respondedto one button in more than the 75 per cent of the trials in the acquisition phase,responses to this button were never rewarded in the extinction phase. This manipula-tion was carried out to force subjects to extinguish responses after perseverating inthem in order to test the model of disinhibition of Patterson and Newman. As shownin Table 1, the extinction phase yielded two di�erent extinction groups. The 100 percent reward response was extinguished for the continuous extinction group, whereasthe 50 per cent reward response was extinguished for the partial extinction group.

All instructions were displayed on the monitor. Subjects were encouraged to earnthe maximum number of points. Responses to each button were recorded in eachphase.

RESULTS

Analyses were conducted separately for the acquisition and extinction phases.Di�erent ANOVAs were conducted including personality variables and extinctiongroup as between-subjects factors. As preliminary analyses on these two phasesrevealed no signi®cant e�ect caused by the sex, this factor was removed from lateranalyses.

Acquisition phase

We calculated the number of responses to button 1 to evaluate performance in theacquisition phase since all the subjects performed the same number of trials. Thisvariable was calculated separately in four 50-trial blocks. Means and standarddeviations of this variable for each personality group appear in Table 2. A total of 27per cent of subjects made more than 75 per cent of responses to button 1, and only 3per cent to button 2. Personality groups did not signi®cantly di�er in this aspect (w2(3,N � 108) � 5.02, p4 0.1).

Table 2. Means and standard deviations for the number of responses to button 1 (associatedwith continuous reinforcement) in the acquisition phase

SPÿ SRÿ SPÿ SR � SP � SRÿ SP � SR �n � 21 n � 20 n � 25 n � 42

Trials 1±50 M 29.67 35.35 32.96 32.69SD 9.78 6.21 5.47 7.91

Trials 51±100 M 28.67 37.60 33.20 31.52SD 10.95 6.44 8.29 7.71

Trials 101±150 M 27.33 37.40 36.00 32.40SD 12.31 7.32 9.03 9.16

Trials 151±200 M 27.43 37.40 32.72 34.84SD 13.51 7.50 9.67 9.72



A 4� 2� 2 ANOVA was conducted using block as the within-subjects variable,and Sensitivity to Punishment (low or high) and Sensitivity to Reward (low orhigh) as between-subjects variables. Planned comparisons conducted in order tostudy our hypothesis yielded a signi®cant main e�ect for Sensitivity to Reward,F(1,104) � 7.07, p5 0.01, indicating a higher tendency to respond to button 1 forSR � than SRÿ subjects (134 and 126, respectively). As expected, the SR �subjects chose the continuous reinforcement schedule more frequently than the SRÿones and were less prone to prefer less frequent, greater reward. However, this maine�ect was modulated by the SR� SP interaction, F(1,104) � 12.32, p5 0.01. As canbe seen in Figure 1, the SPÿ SRÿ displayed the least aversion to partial reinforce-ment. As obtained in our previous study, the Sensitivity to Punishment main e�ectwas not signi®cant.

A similar ANOVA conducted with points revealed no di�erences betweenpersonality groups in earned points. Thus, the personality di�erences in this phasewere not due to earnings, but to a di�erent response preference.

Extinction phase

Extinction was evaluated from the number of responses to the non-rewarded buttonin each of the four 50-trial blocks. Means and standard deviations for the fourpersonality groups are shown in Table 3. There were no signi®cant di�erencesbetween personality groups in the percentage of subjects that belonged to the partialand the continuous extinction groups (w2(3, N � 108) � 3.12, p4 0.10).

A 4� 2� 2� 2 mixed-design analysis of variance was conducted using block as thewithin-subjects factor and extinction group (continuous or partial), Sensitivity toPunishment and Sensitivity to Reward as between-subjects factors. This analysisyielded a signi®cant main e�ect for extinction group, F(1,88) � 4.28, p5 0.05,indicating that the continuous extinction group made more responses to the non-rewarded button than the partial extinction group. The block main e�ect was alsosigni®cant, F(3,300) � 201.44, p5 0.001, showing a decreased number of responsesto the non-rewarded button across blocks. This e�ect was modulated by thesigni®cant block� extinction group interaction, F(3,300) � 3.84, p5 0.02. This

Figure 1. Number of responses to button 1 in the acquisition phase for the four personality groups



interaction re¯ected a steeper decrease in the number of responses to the non-rewarded button across blocks for the continuous than the partial extinction group.

With respect to personality groups, planned comparisons were also conducted totest the hypothesis that subjects with lower scores on the Sensitivity to Punishmentscale would respond to the non-rewarded button more than high scorers. The SP �group made 22.4 responses to the non-rewarded button, whereas the SPÿ groupmade 28.5 responses. This di�erence reached signi®cance, F(1,100) � 4.50, p5 0.05.However, the e�ect was not equal for both extinction groups as shown in Figure 2:di�erences were signi®cant for the continuous extinction group (p5 0.05), but didnot reach signi®cance for the partial extinction group (p4 0.1). As hypothesized, theSensitivity to Reward main e�ect was not signi®cant. Given that this analysis did notcapture the possible e�ect of Sensitivity to Reward in the Sensitivity to Punishmente�ect, we conducted additional comparisons in order to investigate di�erencesbetween the SPÿ SR � and the SP � SRÿ groups, and between SPÿ SRÿ andSP � SR � groups, respectively. These revealed that the SP � SRÿ group had lessresistance to extinction than the SPÿ SR � group (p5 0.05), whereas no di�erenceswere found between SPÿ SRÿ and SP � SR � groups.

Although the Sensitivity to Punishment� block interaction was not signi®cant, theSensitivity to Punishment main e�ect was analysed separately for each block todetermine when the di�erences between personality groups are produced. Theseanalyses re¯ected that the observed di�erences between SP � and SPÿ subjects weresigni®cant for the ®rst block, F(1,100) � 4.72, p5 0.03, but did not reach signi®cancefor the other blocks. This di�erence con®rms results obtained in our previous studyshowing that di�erences in resistance to extinction between anxiety groups areproduced in the ®rst trials of the extinction phase.

Furthermore, the analysis of variance yielded a signi®cant Sensitivity to Punish-ment� Sensitivity to Reward� block interaction, F(3,300) � 3.56, p5 0.02. To

Table 3. Means and standard deviations for the number of responses to the non-rewardedbutton in the extinction phase

SPÿ SRÿ SPÿ SR � SP � SRÿ SP � SR �Continuous extinction group N 10 14 14 20Trials 1±50 M 16.70 15.00 12.14 13.40

SD 9.11 5.22 5.53 4.97Trials 51±100 M 8.60 7.69 3.5 7.30

SD 6.45 6.95 2.98 4.74Trials 101±150 M 3.50 5.36 2.64 3.90

SD 3.89 7.39 1.95 4.80Trials 151±200 M 3.40 4.79 1.07 2.95

SD 4.03 7.99 1.14 2.84

Partial extinction group N 11 6 11 22Trials 1±50 M 14.27 9.83 9.09 11.45

SD 5.25 5.12 3.24 4.55Trials 51±100 M 4.45 5.67 3.73 5.23

SD 3.41 3.08 2.97 4.37Trials 101±150 M 3.00 4.33 2.82 3.59

SD 3.16 2.34 3.19 2.97Trials 151±200 M 2.18 2.83 1.00 2.41

SD 1.60 4.62 1.34 2.36



investigate this e�ect, the Sensitivity to Punishment� Sensitivity to Reward inter-action was analysed separately for each block. These further analyses revealed adi�erent pattern of extinction for SP � SRÿ and SP � SR � groups. In the ®rstblock, both groups made less responses to the non-rewarded button than theSPÿ SRÿ group (p5 0.05), but there was no signi®cative di�erence between them.However, the SP � SRÿ group made fewer non-rewarded responses than theSP � SR � , SPÿ SRÿ and SPÿ SR � groups in blocks two and four (p5 0.05;see Table 2). No di�erences were found between the SP � SR � group and bothSPÿ groups in these blocks. Thus, a low sensitivity to reward seems to decrease theprobability of making non-rewarded responses in subjects with high scores in the SPscale in the last blocks.

Extinction depending on acquisition: extinction of a response highly associatedwith reward

A new variable, called response preference, was created to test the hypothesis derivedfrom the model of Patterson and Newman. This variable divided subjects at themedian on the number of responses to the to-be-extinguished button in the 200 trialsof the acquisition phase: subjects that had responded in more than 130 trials to the to-be-extinguished button were ascribed to the focused group (N � 51), whereas thosewith fewer than 130 responses to the to-be-extinguished button were ascribed to thedivided group (N � 57). The focused group was considered to establish a strongerresponse set for reward before extinction. The percentage of subjects belonging toeach group did not di�er signi®catively in each personality group (w2(3, N � 108)� 3.65, p4 0.10). However, as the continuous reinforcement program was preferredby more subjects, the percentage of subjects belonging to the focused group wassigni®cantly greater in this program as compared to the partial reinforcementprogram (w2(1, N � 108) � 43.75, p5 0.01).

Analysis of extinction was conducted including block, response preference ( focusedor divided), Sensitivity to Punishment, Sensitivity to Reward and extinction group.The analysis yielded a signi®cant interaction between block and response preference,

Figure 2. Number of responses to the non-rewarded button in the extinction phase for SPÿ and SP �groups



F(3,276) � 4.67, p5 0.01. This interaction re¯ected a great resistance to extinctionfor the focused than the divided group in the ®rst block.

Planned comparisons were conducted to test the hypothesis derived from the modelof Patterson and Newman. Concretely, we predicted that impulsives in the focusedgroup would show a greater resistance than the other groups. As shown in Figure 3,the SR � subjects belonging to the focused group (N � 28) made 31.1 responses tothe non-rewarded button, whereas SR � subjects of the divided group (N � 34),SRÿ subjects of the focused group (N � 23), and SRÿ subjects of the dividedgroup made only 22.4, 24.0 and 21.2 responses to this button, respectively. Thisdi�erence reached signi®cance, F(1,92) � 5.36, p5 0.02.

Taking into account these di�erences, the Sensitivity to Reward� responsepreference interaction was analysed separately in each block. This interaction wassigni®cant for the second (F(1,92) � 7.64, p5 0.01) and fourth (F(1,92) � 5.12,p5 0.05) blocks, approached signi®cance for the third block (p5 0.10), but was notsigni®cant for the ®rst block (p � 0.61).

DISCUSSION

The present study o�ers both a replication and an extension for our previous study(Avila, 1994). Concerning the replication aspect, individual di�erences in BISfunctioning measured with the Sensitivity to Punishment scale have been related toresistance to extinction. Despite changes in experimental procedure, subjects havinglow scores in the Sensitivity to Punishment scale have shown great resistance toextinction compared with high scorers, the di�erences being more evident in the ®rsttrials of the extinction phase when extinction is being learned.2 Similarly to ourprevious study, anxiety groups have not di�ered in choice behaviour during the

Figure 3. Number of responses to the non-rewarded button in the extinction phase as a function ofSensitivity to Reward and response preference

2In our procedure it will be useful to distinguish extinction learning and maintenance of extinction.Extinction learning is produced at the beginning of the extinction phase and would be directed related tothe sensitivity to non-reward. However, this factor could be di�erent from extinction maintenance, that isobserved after extinction learning. Thus, extinction maintenance is observed in the last blocks, and is morerelated to risk-taking behaviour (see Table 3).



acquisition phase. In summary, our experimental procedure could be considered as apowerful and sensitive tool to measure BIS-mediated resistance to extinction.

These results are consistent with a recent study showing more di�culties of lowSensitivity to Punishment subjects to form negative expectations after aversive events(Avila et al., 1999). The extinction process in this procedure could be interpreted as anindicator of the ability to perceive negative outcomes and develop negativeexpectations. Thus, low anxious subjects' greater resistance to extinction could bepartially attributed to a failure to develop negative expectations after responding.

This research also aimed to investigate the role developed by Gray's impulsivitydimension measured by the Sensitivity to Reward scale. The role of impulsivity in thisprocedure has been related to three di�erent aspects. First, scores on the Sensitivity toReward scale have been related to performance in the acquisition phase. Second, thismeasure has modulated the e�ect of Sensitivity to Punishment in extinction. Third,the Sensitivity to Reward scale has been used to directly test the model of disinhibi-tion in impulsive subjects of Patterson and Newman.

The results in the acquisition phase have yielded a main e�ect indicating thatsubjects prefer the continuous to the partial reinforcement schedule. However, thisgeneral tendency is greater in impulsives (i.e. the high Sensitivity to Reward group)than non-impulsives (i.e. the low Sensitivity to Reward group). This e�ect was notcompletely independent of the sensitivity to punishment since a low score on the SPscale potentiated the preference for the partial reinforcement in low impulsivesubjects. This in¯uence of Gray's anxiety may re¯ect BIS-mediated di�erences intolerance to frustration. In general, this result should be interpreted as a greatertendency of impulsives to prefer more frequent, smaller rewards as opposed to lessfrequent, larger rewards. This pattern is consistent with theoretical considerationsstudying choice behaviour paradigms that compared impulsive and self-controlbehaviour (Williams, 1988), and also with results obtained in subjects with hyper-activity disorder (Freibergs and Douglas, 1969; Parry and Douglas, 1983).

A second e�ect of Sensitivity to Reward was to modulate the maintenance ofextinction behaviour over time. Comparisons across groups have shown that theSP � SRÿ group had a higher tendency to inhibit responses to the non-rewardedbutton in blocks two and four, whereas the number of responses to the non-rewardedbutton made by the SP � SR � group was similar to both SPÿ groups in theseblocks. This di�erence between SP � SRÿ and SP � SR � seemed to be morerelated to risk-taking behaviour during maintenance of extinction than to extinctionlearning. Both groups have learned extinction in a similar way, but in subjects with anoveractive BIS, an underactive BAS should decrease the probability of respondingmore to the non-rewarded button once extinction learning has almost been producedbecause their lower approach tendencies avoid risky behaviour (Fowles, 1987). It isimportant to stress that this di�erence is not associated with low anxiety or with highimpulsivity traits, but to the combination of both traits.

Finally, one of the most interesting points in this study is to test the four-stagemechanism of disinhibition of Patterson and Newman using the extinction procedure.In our analyses we have distinguished subjects that had made the to-be-extinguishedresponse more frequently than the other in the acquisition phase (i.e. the focusedgroup) from those that had chosen both responses more similarly (i.e. the dividedgroup). Following the model of Patterson and Newman, a strong response approachto reward is necessary to initiate BAS-mediated response modulation de®cits. Our



results showed that impulsive subjects in the focused group, who had established astronger response approach to reward in the acquisition phase, had a greater resist-ance to extinction than the other three groups (Figure 3). Thus, response modulationde®cits of impulsives after non-reward seemed to appear only when subjects had toextinguish a response strongly associated with reward.

Block analyses revealed important results related to this greater resistance toextinction of impulsives in the focused group: there are no di�erences between groupsin the extinction learning in the ®rst block, but this group seemed to maintain a strongexpectation of reward associated with the extinguished response. These analysessuggest that disinhibition in impulsives seems not to be a mere learning de®cit, but themanifestation of more di�culties for suppressing an association between cues forreward and reward over time, once extinction learning has been produced.

Overall results shed light on the compatibility of the models of Gray and ofPatterson and Newman. We could describe two di�erent pathways of BIS-mediateddisinhibition (Avila, submitted; Gray, Owen, Davis and Tsaltas, 1983). The ®rstwould consist of a direct mediation of the BIS when activated by punishment andextinction cues: an underactive BIS would cause a lower processing of aversive stimuli(punishment and non-reward) and aversive cues (those for punishment and non-reward) leading to a lower probability of developing a negative expectation and to alower feeling of anxiety (Avila, 1994; Avila and Torrubia, unpublished data;Newman, Wallace, Schmitt and Arnett, 1997). The second pathway would consist ofan indirect mediation of the BIS: a strong BAS activation (characteristic in impul-sives) would promote BIS-mediated disinhibition (Patterson and Newman, 1993).Following the results of the present study, this kind of disinhibition could beattributed to a failure to extinguish reward associations. This failure could result fromresponse modulation de®cits of impulsives described by Patterson and Newman(1993).

This study serves to clarify the concept of sensitivity to reward. One importantdistinction is that made between the magnitude and contingency dimensions ofreward (see Douglas and Parry, 1994). One possibility is that impulsive subjects have agreater threshold of reward, so they would decrease the experienced magnitude ofreward. The second possibility is to understand Gray's impulsivity as the facility tolearn responses that are contingently associated with immediate reward. Presentresults are consistent with the second idea, that is, a greater sensitivity to reward (i.e.the BAS) predisposes to the establishment of dominant responses for rewardindependently of its magnitude. Further, the analysis of the extinction phase showedthat a high sensitivity to reward is also related to a greater di�culty for altering thesedominant responses by unexpected feedback (see Patterson and Newman, 1993).Overall, data suggest that BAS activity is associated with the di�erent disposition tolearn and the reluctance to suppress a variety of instrumental responses that lead toimmediate reward. In other words, the performance of impulsive subjects isin¯uenced more by the prospect of immediate reward and less by the overall historyof rewards.

To sum up, the extinction procedure seems to be useful for studying the individualdi�erences in resistance to extinction in humans. The present study has served tocon®rm and make compatible both Gray's and Newman's models of personality. Ourtheoretical considerations are related to the existence of two di�erent pathways toBIS-mediated disinhibition: one directly dependent on the activation of BIS and the



other dependent on the previous activation of BAS (Avila and Torrubia, unpublisheddata; Grande, Avila, MoltoÂ and Torrubia, 1993; Patterson and Newman, 1993).

ACKNOWLEDGEMENTS

We would like to thank two anonymous reviewers for their comments on a previousversion of this manuscript. We thank Phil Graystone for his help with English `¯ow'.This research was supported by a research grant P1A98-09 from the FundacioÂ Caixa-CastelloÂ .

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the role of gray's impulsivity in anxiety-mediated differences in resistance to extinction

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