“Stimulus hunger”: Individual differences in operant strategy in a button-pressing task

Bchav. Rcs. & Therapy. 1969, Vol. 7, pp. 265 to 274. Pergamon Press. Printed in England

“STIMULUS OPERANT

HUNGER” : INDIVIDUAL DIFFERENCES :U STRATEGY IN A BUTTON-PRESSING TASK Department

ANTHONY GALE of Psychology, University of Exeter (Received 4 March 1969)

Sunnnary-In a free operant situation, where four different sound reinforcements could be obtained 1~ reduce mild sensory deprivation, extraverts maintained a higher response rate than introverts and made more changes among stimulation sources but without obtaining a higher total duration of sound stimulation. There was no difference for stimulus preference between the personality groups; but both groups showed greatest preference for a 30 db white noise reinforcement as opposed to three variants of a 60 db 4,000 Hz tone. The results of earlier studies are interpreted in the light of these findings and the difficulties of providing direct experimental measures of “stimulus hunger” and sensory reinforcement are also considered. Epsenck’s (1967) model of the neurophysiological substrates of extraversion-introversion is extended to account for “stimulus hunger”. EXTRAWRTS are “stimulus hungry” (Eysenck, 1967) and when given the opportunity to seek for stimulation, they will do so (Howarth, 1964; Weisen, 1965). This stimulus-seeking characteristic is implied by several items on the ‘E’ scale of the Eysenck Personality Inventory (1964) and by many of the extravert traits as specified by Eysenck and Eysenck (1963). Extraverts are more inclined than introverts to describe themselves as seeking more frequent and greater amounts of stimulation (Cooper and Payne, 1967). Extraverts and introverts may also be distinguished on a number of sensory measures, the differences being in part accountable for in terms of “stimulus hunger”. Extraverts have higher sensory thresholds (Smith, 1968), higher pain thresholds (Haslam, 1966), greater tolerance for pain (Lynn and Eysenck, 1961) and greater intolerance for sensory deprivation (Petrie. Collins and Solomon, 1960). Stimulus hunger is attributable to a chronically lower level of cortical excitation in extraverts (Eysenck, 1967). Because of lower levels of cortical excitation, stimuli must be of greater physical intensity to reach perceived threshold. Thus to obtain equivalent subjective reports of stimulus intensity for the two personality groups, the physical intensity of the applied stimulus must be greater for extraverts. Eysenck (1963) presents amodel relating level of sensory input and hedonic tone as a function of personality; this model caters for all the above findings in relation to sensory thresholds and degree of tolerance for pain and sensory deprivation. The inferior performance of extraverts on vigilance tasks (Bakan, Belton and Toth. 1963) and the manner in which such performance may be improved, is also explicable in terms of low cortical excitation and stimulus hunger (Gale, in preparation, and see below). Indeed, Davies and Hockey (1966) find that high intensity white noise (which reduces stimulus hunger and raises cortical excitation) had a facilitatory effect on the visual vigilance performance of extraverts. An alternative explanation of the vigilance decrement may be made by reference to involuntary rest pauses (I.R.P.‘s) induced by a higher level of cortical inhibition and the generation of reactive inhibition (Eysenck, 1967). Since vigilance tasks typically involve a complex interaction over time of both sensory and response processes,

265

266

ANTHONYGALE

the most satisfactory explanation of individual differences in performance is likely to employ both the concepts of cortical excitation and cortical inhibition. Direct evidence of chronically lower cortical excitation in extraverts is provided by E.E.G. studies. The occipital LEG. is higher in voltage than that of introverts, both when the eyes are closed and external visual stimulation is absent (Savage, 1964) and when the eyes are open in the presence of continuous monotonous stimulation (Gale, Coles and Blaydon, in press). This higher voltage E.E.G. in extraverts may also be interpreted as an indication of a chronically lower level of reticula-cortical arousal, which is in itself one of the determinants of cortical excitation (Moruzzi and Magoun, 1949; Eysenck, 1967). On Howarth’s (1964) task, extraverts were more active in button pressing, both before and after satiation. Weisen’s (1965) task was an operant conditioning procedure where reinforcement for button-pressing was either a 3-set period of light and sound stimulation (“onset” condition) or a 3-set period of relief from light and sound stimulation (“offset” condition). Extraverts pressed more frequently in the onset condition and introverts more frequently in the offset condition. Thus the number of presses in both the Howarth and Weisen studies is a direct measure of the amount of stimulation obtained. (In Howarth’s study, any stimulation obtained is said to be by virtue of the act of button-pressing itself (Eysenck, 1967)). However, it is possible that button-pressing and obtained stimulation are to a certain degree dissociable. In a free operant situation where S may impose his own “schedule” on the task, different Ss may obtain identical total amounts of sensory reinforcement and yet employ different response strategies. Thus Ss may press frequently for short bursts of stimulation even when an identical period of stimulation might be obtained by one continuous press. Such a procedure allows for a distinction between the response characteristics of the situation (button pressing) and the sensory characteristics (reinforcement). Thus predictions concerning individual differences may be made both on the basis of reactive inhibition (generated by continuous button-pressing) and on the basis of stimulus hunger (generated by sensory deprivation). According to Eysenck (1957) extraverts generate reactive inhibiticn to response tasks more rapidly than introverts. In the case of forced continuous tapping, extraverts, because of the rapid generation,! of reactive ,inhibition, show a significantly higher number of I.R.P.‘s (Spielmann, 1963). Thus it may be predicted for example, that extraverts will alter their button-pressing stategy over time; for as stimulus hunger increases with continued exposure to sensory deprivation, so also does reactive inhibition increase (to the very operant response which leads to a reduction of stimulus hunger). Indeed, in certain circumstances, the effects of reactive inhibition to the operant response may become so much stronger than the need for stimulation that performance of the operant response is considerably reduced (Jensen, 1966). This experiment is designed to measure differences in button pressing strategy over time, between extraverts and introverts, in a free operant situation. SUBJECTS The Ss were 36 undergraduate students at the University of Exeter (average age 18 years 11 months). Two groups of Ss were selected on the basis of E.P.I. (1964) score: an extravert group (mean E score 16.6; standard deviation 1.7; range 14-21) and an introvert group (mean E score 7.1: standard deviation 2.4; range 2-10). The groups were matched for Neuroticism, no S having an N score greater than 11 (standard deviation for both

267

STIMULUS HUNGER

groups was 2.5; 9 females.

combined

range 6-l I).

APPARATUS

Each personality

AND

group

contained

9 males and

PROCEDURE

S sat in a dimly lit corner of a darkroom, separated from E by a suspended blanket. Facing S was a black console, from which protruded the knobs of four morse keys. The four keys were connected both to four pens on a four-channel pen recorder (run continuously at 1.5 cm per set) and to four signal lights. Thus, when S pressed a particular key, the corresponding pen on the recorder was displaced for the duration of the press and at the same time, the appropriate signal light warned the E to present one of four sound reinforcements to S. The reinforcements (provided by a Peters Audiometer) were as follows: (a) 30 db white noise (broad band); (b) 60 db 4,000 Hz (continuous); (c) 60 db 4,000 Hz (modulated at 2 cps) and (d) 60 db 4,000 Hz (modulated at 3 cps). Both the pre-test instructions and the sound reinforcements were delivered to S through earphones, binaurally. S (having removed his watch) was instructed to sit quietly for a “considerable period of time” and not to talk to E. Stimulation would be available at all times if S pressed the keys; the same sound being associated with the same key throughout the experiment. Not more than one key was to pressed by S at any one time and stimulation would only be available for the duration of the press. S was asked to use his preferred hand only. in the absence of automated apparatus, there would be a delay of approximately 1.5 set before stimulation occurred, therefore, rapid pressing would be to no avail. (As soon as S pressed and prior to the selection by E of the appropriate stimulation source, the output to S’s earphones was temporarily disconnected). S could press as frequently as he wished on any of the foul keys, or not press at all, there being no obligation to press. S was then asked to repeat these instructions. A testing period of 14 min then followed. Equal numbers of Ss in each experimental group were tested at one of two times (9 a.m. and 5 p.m.).

RESULTS The two personality groups are not differentiated in terms of Total Listening Time (Table l), although the group means are in the predicted direction (Fig. 1). However, the total number of presses is greater for extraverts (p
ANTHONY

268

GALE

24-

20-

INTROVERTS

a-

4-

Fro.

The major difficulty “stimulation”. In terms si~ifican~y more sound adopt a different strategy

1. Mean

listenq

time.

See Table 1.

DL%XJSSION in interpreting the results of this study lies in the definition of of the stimulation provided, the extravert group do not obtain reinforcement than the introvert group. However, the extraverts in obtaining stimulation; they press more frequently, change

2

4

8

6

IO

I2

14

minutes

FIG. 2. Mean number

of presses. See Table 2.

269

STIMULUS HUNGER

extraverts

minutes

FIG. 3. Mean number of changes between stimulation sources.

See Table 3.

between stimuli more frequently and their average listening time per press is shorter. This outcome is predictable in terms of Eysenck’s (1957) construct of reactive inhibition. Stimulation is contingent upon continuous pressing; but relief from continuous pressing allows for dissipation of reactive inhibition. Moreover, since there is in this experimental procedure a minimum delay of 1.5 set between presses, there is little opportunity for reactive inhibition to generate to repeated rapid pressing (which was predicted by Howarth (1964) but not demonstrated; but which is demonstrated in a paced pressing task by Spielman (1965)). On the other hand the present results are also predictable in terms of stimulus hunger. (“sound reinforcement It may be argued that alternation of “press “-“no-press”-“press” on”, “sound reinforcement off”, “sound reinforcement on”), provides a richer source of sensory stimulation than continuous press (continuous sound reinforcement). The sensory reinforcement provided in this study is certainly of lower hedonic value than the coloured lights and music employed by Weisen (1965). (The preference for white noise, which subjectively, provides a continuously changing input, is intuitively reasonable.) The view that interrupted stimulation is more satisfactory as a reducer of stimulus hunger is further supported by electrophysiological evidence, The maximum electrical response to continuous stimulation at the receptors, occurs at onset; “Phasic receptors respond to a prolonged stimulus by initiating a burst of rapid nerve discharges. The rate of firing decreases rapidly with time and may reach zero”. (Grossman, 1967). We may conclude therefore that extraverts, by adopting their strategy of frequent pressing and changing between sources, do in fact obtain more stimulation from our experimental procedure. Direct support for this assertion may be provided by an experimental procedure where S is given the opportunity to obtain identical sound stimulation from either of two sources; one requiring continuous press (as in the present study), the other requiring only a brief press (as in the Weisen study). It is predicted that extraverts would show a preference for the latter since such a procedure would not only provide more varied stimulation but would also be less conducive to the generation of reactive inhibition.

270

ANTHONY

TABLE

1. ANALYSIS

OF VARIANCE (P)

Source _~_____ Total Between subjects P S/P Within subjects r PT STIP

TAHLE 2

ANALYSISOF

GALE

FOR LISTENING AND TIME

d.f,

S.S.

503 =

1,832,250*554

35

79,715.054 -~ 5.513669 74,201.385 1,752,535.500

34 468 --

13 13 442

VARIANCE

9,013*192 I ,200~970

1,742,321,338

d.f.

Total

so3 =

28,582.427

35 -

I6,022.069

1 34 468 13 13 442

F

5,513,669 2,182.393

N.S.

693.322 92.382 3,941,903

N.S. N.S.

PERSONALITY(P)

AND

(T)

Source

P SIP Within subjects

PERSONALITY

MS.

FOR PRESSES, VARYING TIME

Between subjects

TIWE, VAKYING

(T)

S.S.

3,006*669 13,015~400 12,560.358 -539.288 320,858 !1,700~212

MS.

F

3,006.669 382.805

7,854”

41.48 24.681 26.47 I

N.S. N.S.

The Howarth (1964) study appears to contradict this assertion since in fact extraverts press rapidly and at a high rate. But Howarth’s task is of only 2 min duration and is insensitive, unlike the Spielmann (1965) study, to the measurement of pauses during pressing. In the present study, extraverts are not differentially affected by Time. There are two reasons for the absence of this interaction. Firstly, sensory deprivation is only mild and of relatively short duration (14 min) and therefore presses and listening time do not increase during exposure as a result of excessive stimulus hunger. Secondly, the unpaced nature of the task is unlikely to allow for the generation of reactive inhibition and therefore pressing does not reduce over time. as a result of reactive inhibition. Thus Ss may maintain a strategy which supports an equilibrium between the opposing influences of these two variables. The significant main effect for Time in the analysis of Changes (Table 3) is attributable to initial learning of the association between individual sound reinforcements and their manipulanda. She% tests show that the major difference lies between the 1st and 3rd min.

STIMULUS HUNGER

271

TABLE 3. ANALYSISOFVAR~ANCEPORCHANGES,VAR~INGPERS~NAL~TY(P) ANDTIME

SOUPX

d.f.

Total

503

Between subjects P SIP Within subjects

S.S.

MS.

F

10,134*968 6,022.825

895.999

895.999

S-942’

34 468

5,126.826 4,112.143

150.789

13 13 442

632.468 98.056 3,381*619

48-65 1 7.543 7.651

6.358t

*p
The question arises as to whether it would be more parsimonious to limit predictions to one construct, for it may be argued that given both the reactive inhibition and stimulus hunger constructs a logical see-saw develops where nny outcome may be accountable for. The stimulus hunger construct was devised largely to account for “stimulation seeking” behaviour by extraverts. It is difficult to set up conditions adequate to the task of quantifying stimulus hunger without employing an operant procedure. This of course involves a response measure, which in turn raises the necessity of predictions based on reactive inhibition. Studies on differential tolerance to sensory deprivation (where typically ‘no relief of stimulus hunger is available) provide an alternative source of information; but such studies have failed to present consistent data (Zubek, 1964). It would seem inevitable therefore that predictions concerning stimulus hunger must presuppose the necessity for predictions concerning reactive inhibition. As Eysenck points out, it is difIicult to predict the outcome of even very straightforward experimental procedures without calling upon a number of hypothetical constructs (Eysenck, 1965). We have omitted to mention that Eysenck (1963, 1967) not only asserts that extraverts are “stimulus hungry”, but that introverts are “stimulus aversive”. Apart from the data derived from Weisen’s (1965) “offset” condition, there is little direct evidence to support this view. In the present study, the introvert group were in fact active, although given the opportunity to refrain totally from obtaining sound stimulation. But the experimental design does not provide for a range of stimulation, from “moderate” (through “tolerable”) to “intense”. Moreover, it is also dificult to ascertain at what point on the arousal continuum the two groups were placed prior to obtaining stimulation. Thus the results cannot be fitted with great confidence onto Eysenck’s (1963) hedonic tone model. Moreoever, the four stimulation sources are difficult to rank in terms of richness; had this been the case, we would have predicted that when introverts did press, it would have been for milder or less complex stimulation. Thus the question of “stimulation aversion” in introverts remains open and is not answered by this study.

272

ANTHONY GALE

Eysenck (1967, p. 245) does not provide a sound theoretical basis for a relationship between low cortical excitation and stimulus seeking. In other words, why should extraverts work to raise cortical excitation; or alternatively, if extraverts are low-aroused, why do they not simply just fall asleep? We propose here a tentative model to explain this link between cortical excitation and stimulus hunger. This model is derived in part, from the arousal theory of Berlyne (1960) and extends Eysenck’s (1967) neurophysiological model. Berlyne asserts that arousal should be considered as a drive, subject like other drives to homeostatic principles. Thus individuals have an optimum arousal level for functional efficiency and states of arousal either above or below this optimum are unsatisfactory. Berlyne uses “unsatisfactory” in an hedonic sense where the origins of the discomfort caused by deviations from optimum arousal level are homeostatic and presumably not physiologically dissimiIar from other basic drives. We propose that the adjustment to obtain optimum levei might be (a) homeostatic, (b) anafogous to an acquired drive or (c) task or situation specific (see below). These alternatives are not of course mutually exdusive. Several studies support the view that extraverts are chronically low-aroused (below optimum) and introverts chronically high-aroused (above optimum) (Colquhoun and Corcoran, 1964; Corcoran, 1965; Eysenck, 1967; Gale Coles and Biaydon (in press)). Moreoever, this chronic level has a physiological basis; it is determined by the level of reticula-cortical bombardment (Eysenck, 1967). In order to relate this view to “stimulus hunger”, we must postulate secondly, a system designed to raise arousal level in extraverts or reduce arousal level in introverts in order to maintain the optimum level and sustain functional efficiency. Thus introverts reduce arousal by av~~dj~g stimulation and extraverts raise arousal by seeking stimulation. A physiological basis for this function resides in the corticoreticular relationship; both inhibitory and excitatory effects of the cortex on the reticular system have been demonstrated. The cortex can raise or lower reticular arousal directly (Bremer and Terzuolo, 1953; French, Hernandez-Peon and Livingston, 1955; SharpIes and Jasper, 1956; Hug&n and Bonvallet, 1957; Magoun, 1964) by either increasing sensory input or setting up “filters” against input at receptor level and thereby reducing sensory input via the collaterals to the A.R.A.S. (Hernandez-Peon, Sherrer and Jouvet, 1956; Sokolov, 1960). Moreover, there is an abundance of evidence for both positive and negative feedback loops between cortex and A.R.A.S. (Routtenberg, 1966). Thus, following Eysenck (1967) two types of arousal are postulated-reticular arousal (high or low) and cortical arousal (high or low). The former consists of an innate predominance or inhibitory function in extraverts and an innate predominance or excitatory function in introverts. The latter consists of acquired techniques, mediated by the cortex, to support functional efficiency and maintaining optimal arousal in the manner stated. An analogy may be drawn here with Thorpe’s (1960) notion of “hard” and “soft” clocks; the former innate, the latter modifiable by experience. Or again, with Kleitman’s (1939) notion of the ontogenetic development of “wakefulness of choice” as opposed to “wakefulness of necessity” (Morgan, 1965). Both personality types learn how to mitigate against the effects of an inherently maladaptive level of reticuiar arousal; extraverts by seeking stimulation and raising reticular arousal, introverts by avoiding stimulation and reducing reticular arousal. The extent of stimulus hunger (or aversion) at any particular time is determined by the sensory “richness” of the environment, and the level of functional efficiency required of the individual. How does such a theory cope with the findings on vigilance? Perception of the “wanted” signal presupposes an efficient level of arousal. But the repetitious and monotonous nature of the regular “unwanted” signal is conducive to habituation, inhibition, and Pavlovian

STIMULUS

HUNGER

273

sleep. The mechanisms for such inhibition reside at reticular level (Oswald, 1960; Moruzzi, 1964; Lynn, 1966). Thus not only does the extravert start the vigilance task at a low level of arousal, but the task itself is de-arousing. But the extravert subject must avoid sleep (since sleep in a vigilance task is punished); he therefore searches for stimulation within the experimental environment in order to raise arousal. In group tasks, such stimulation is readily available and the extravert is able to sustain functional efficiency by observing his fellow subjects (Colquhoun and Corcoran, 1964); the presence of the experimenter also provides a source of extraneous stimulation (Broadbent, 1959). But when continuous stimulus seeking is necessary, as in the more typical vigilance task (which approximates more closely to sensory deprivation) a vicious circle develops and signals are missed. However, once arousal has been raised as a result of the search for stimulation, performance might recover. Explanations of the vigilance decrement have focussed largely upon the initial decrement and often neglect to explain the final spurt in performance reported in several studies (Broadbent, 1959, 1964). This final spurt might be accountable for in terms of conditions conducive to this sort of cyclic variation in arousal. Although individual differences in vigilance performance are considered to be well established, there is in fact a paucity of evidence to support the earlier findings (McGrath, Harabedian and Buckner, 1968). The ideal testing ground for the theory presented above would be a vigilance task, where additional stimulation is available (Bakan, Belton and Toth, 1963) but where physiological monitoring provides a direct (or at least, operational) measure of basal arousal, within-task fluctuations of arousal (Eason, Beardshall and Jaffee, 1965; Daniel, 1967) and their relationship to both stimulus seeking and vigilance performance. REFERENCES BAKAN P., BELTONJ. A. and TOTH J. C. (1963) Extraversion-introversion and decrement in an auditory vigilance task. In Vigilance: A Symposium (Edited by D. N. BUCKNERand J. J. MCGRATH). McGrawHill, New York. BERLYNED. E. (1960) Conflicr, Arousal und Curio&y, McGraw-Hill, New York. BREMERF. and TER~UOLU C. (1954) Contribution a l’etude des mechanismes physiologiques du maintien de l’activite vigile du cerveau. Interaction de la formation rtticulee et de l’&zorce cerebrale dam le processus du r&veil. Archs in?. PhysioL 62, 157-178. BROADBENT D. E. (1959) Perception and Communication, Pergamon Press. Oxford. BROADBENT D. E. (1964) Vigil&e. Br. med. BuIl. 20, 17-21.COOPERR. and PAYNER. L. (1967) Extraversion and some asoects of work hehaviour. Person. fsvchol. . 20,45-57. C~LQUHOUNW. P. and CORCORAND. W. J. (1964) The effects of time of day and social isolation on the relationship between temperament and performance. Br. J. Sot. clin. Psychol. 3, 226-23 1. C~RC~RAND. W. J. (1965) Personality and the inverted-U-relation. Br. J. Psycho/. 56, 267-274. DAN~L R. S. (1967) Alpha and theta E.E.G. in vigilance. Percept. mot. Skills 25, 697-703. DAMESD. R. and HCICKEYG. R. (1966) The effects of noise and doubling the signal frequency on individual differences in visual vigilan& performance. Br. J. Psychol. 57, 381-389. _ _ EASONR. G., BEARDSHALL A. and JAFFEES. (1965) Performance and ohysiologioal indicants in a vigilance situation. Percept. mot. Skills 20, 3-13. EYSENCKH. J. (1957) The Dynamics of Anxiety and Hysteria, Praeger, New York. EYSENCKH. J. (1963) Experiments with Drugs, Pergamon Press, New York. EYSENCKH. J. (1965) A three-factor theory-of remhrisoenoe. Br. J. Psychof. 56, 163-181. EYSENCKH. J. (1967) The Biological Basis of Personalitv. Thomas. Sprinrzfield. EY~ENCKS. B. ‘G. and EYSENC~ H. J. (1963) The validity of questiormaires and rating assessments of extraversion and neuroticism and their factorial validity. Br. J. Psychof. 54, 51-62. FRENCH J. D., HJZRNANDEZ-PEON R. and LIVMGSX~NR. B. (1955) Projections from cortex to cephaiic brainstem (reticular formation) in monkey. J. Neurophysiol. 18, 74. GALE M. A. (in preparation) The relationship between vigilance performance, button pressing and physiological reactivity. GALE M. A., COLESM. G. H. and BI_AYD~NJ. (in press) Extraversion-introversion and the E.E.G.

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