S E N S O R Y A N D PREPARATORY F A C T O R S I N R E S P O N S E L A T E N C Y

I I . Simple reaction or compensatory interaction?

VIDKUNN COUCHERON THRANE

Forsvarets psykologiske avdeling, Norwegian Armed Forces, Oslo, Norway

THRANE, V. C. Sensory and preparatory factors in response latency. 11. Simple reaction or compensatory interaction? Scand. J. Psychol., 1960, r , 16~176.-The so-called simple reaction is viewed as a dynamically integrated organismic response, modifiable by sensory and preparatory factors and their interactions. The procedure used in presenting several variants of the focal stimulus regulates the specificity of the respondent’s preknowledge of stimulus, and thereby the opportunity for interaction as suggested. Additional results confirm the previous finding that the differential effect of stimulus intensity is inversely related to the degree of preknowledge. The interaction is therefore considered to be of a compensatory nature.

A reference to ‘the simplest psychical processes’ was frequently included in the titles of early reports on reaction time, but the authors had some difficulty in agreeing on just how simple, and therefore just how psychological the reactions were to be considered, although, in first proposing and defining the term Reactionsza‘t, a physiologist had specified that a conscious reaction must be involved (Exner, 1873, p. 609). Wundt, in his first definition (1880, p. 222), substituted ‘voluntary movement’ but emphasized that the major part of even the shortest times measured must be ascribed to higher central processes occurring after the stimulus has been presented.

Yet Exner (1874) soon found that the latency of the eyelid wink reflex is of the same order of magnitude as the simple visual reaction time. Moreover, his introspective account of the latter response is ‘an excellent description of a reflex act’ in the opinion of James (1890, p. 92), who himself regarded the habituated reaction as ‘a reflex action pure and simple, and not a psychic act’ (p. 90). In the same breath, however, James takes issue with Wundt by calling it ‘mythological psychology . . . to conclude that because two mental processes lead to the same result they must be similar in their inward subjective constitu- tion.’

REACTION DICHOTOMY

This and related controversial issues (cf. Woodworth, 1938, pp. 302-310) hinged upon an arbitrary delimitation of ‘the reaction’ to coincide in time with the interval being measured. The latter could be operationally defined in terms of a predetermined change in physical stimulation (excluding the warning signal) and a subsequent physical change ensuing from a predetermined movement by the subject.

The reaction under dispute was correspondingly confined to the organismic processes occur- ring within this interval, even by those who most strongly emphasized the importance of what happens prior to the stimulus. The latter processes constituted separate antecedent events, prerequisite for, but not part of, ‘the reaction’. Attempts made at ‘describing’ what is taking place demonstrate, however, how untenable the distinction is.

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Thus James wrote: ‘A foregoing psychic condition is, it is true, a prerequisite for this reflex action. The preparation of the attention and volition; the expectation of the signal and the readiness of the hand to move, the instant it shall come; the nervous tension in which the sub- ject waits, are all conditions of the formation in him for the time being of a new path or arc of reflex discharge. The tract from the sense-organ which receives the stimulus, into the motor centre which discharges the reaction, is already tingling with premonitory innervation, is raised to such a pitch of heightened irritability by the expectant attention, that the signal is instantaneously sufficient to cause the overflow. No other tract of the nervous system is, at the moment, in this hair-trigger condition . . . ,

Expectant attention” is but the subjective name for what objectively is a partial stimulation of a certain pathway . . . The signal is but the spark from without which touches off a train already laid. The performance, under these conditions, exactly resembles any reflex action. The only difference is that whilst, in the ordinarily so-called reflex acts, the reflex arc is a per- manent result of organic growth, it is here a transient result of previous cerebral conditions’ (James, 1890, p. 90 f.).

Cattell (1886) had written in a similar vein, suggesting however, as on later occasions, that ‘The stimulus causes two sorts of cerebral changes, the discharge of the motor impulse, and changes in the cortex, which are accompanied by consciousness. But.. . we think the movement does not follow on changes in consciousness, but is simultaneous with or actually prior to them. What volition is concerned in the process precedes the reaction and consists in preparing the motor impulse, which is reflexly discharged’ (Cattell & Dolley, 1895, p. 393 f.).

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Of special interest in the present connection is the observation that the more automatic the reactions appeared to be (as inferred from shorter and more regular latencies), the less they were influenced by changing experimental conditions, including varying stimulus in- tensity and alternate direction of attention to stimulus and movement (Cattell & Dolley, 1895, pp. 405, 410). Yet, for optimal efficiency to be achieved, the respondent ‘did not ... use great efforts to be quick, as we have found that this makes the reactions more ir- regular without appreciably shortening the time’ (p. 401). See aIso Dolley & Cattell (1894).

PREPARED RESPONSE Thus, the seemingly simple psychological processes turned out to be complex enough.

Our knowledge of them still leaves much to be desired, including to what extent voluntary reactions and reflex actions may have common features or be subject to the same modifying conditions (cf. Wiersma, 1921). It may be that there is no clear-cut boundary between them, and that the ‘brain reflexes’ of the early writers are very much akin to the conditioned responses of a later day. However, it is well to keep in mind that in reaction time work we are always dealing with prepared organismic responses, ‘developed under instructions deli- berately followed by the subject’ (Hilgard, 1931, p. 32), but also that verbal instructions may not be alone in governing the preparation. As one experienced R T investigator puts it: ‘Even in the simple form of the reaction-time experiment alternative sets are undoubtedly operating in spite of the experimenter’s intention’ (Davis, 1946, p. 389).

This phenomenon may in some connections be looked upon as a nuisance, e.g. when the investigator is Concerned primarily with the analysis of sensory or peripheral processes per se by means of response latency; but of greater significance is the challenge it offers to experimen- tal ingenuity in the study of dynamically integrated behavior even at relatively low levels of complexity. Nor do we have any reason to think that differential preparatory sets are operating in psychomotor responses only, although the concept of set grew out of R T studies. For

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instance, Davis (1946) has applied the concept of set to the process underlying time error in stimulus judgment by the constant method, and finds that alternative sets can be traced in this situation, too.

Students of conditioned responses have made similar observations. Thus, Razran found three qualitatively different types of salivary responses to the conditioned stimuli among his adult human subjects, and postulated that corresponding attitudes toward the experimental situations were adopted after a few combined stimulus presentations. In the same experimental situation and with the same stimuli, a subject’s response type remained fairly stable, but it varied considerably with the nature of the stimuli, kinds of instructions, and presence of other subjects in the room. The conviction was expressed that ‘. . . psychology has two fundamental laws: one, that every reaction is caused by a stimulus; two, that every qualitative change of a reaction is due to a contiguous activation of another reaction. And, important as it is to look for the stimulus of a reaction, it is even more essential to find the reaction that caused the change of reaction’ (Razran, 1935, p. 7).

At this point we are reminded of an early ‘new look‘ on perception by Stem, derived from observed individual differences in an experiment on the judgment of tonal change at varying rates (Stern, 1900a). As it happened, his two subjects represented ‘basically different types’ in approaching the task, for brevity referred to as objective and subjective (Stem, ~goob, p. IS). The objectively reacting person assumes a highly receptive attitude (‘giebt sich moglichst passiv den Eindruck hin, verhalt sich contemplativ’), adjusts himself readily to variations in the stimulus, and waits with the response until certain of his judgment. The subjective type, on the other hand, does not wait, but expects something; he is easily led by preconceived ideas to react before he is assured by his observation, and is in general impatient to respond. Stem did not consider these dispositions specific to the situation studied, but as signs of general persona- lity traits, and his chief purpose was to advocate a differential-psychological approach in ex- perimental psychology (cf. Jarl, 1958).

SENSORY AND PREPARATORY FACTORS I N RESPONSE LATENCY. I1

Thus, intra- as well as inter-individual variations in preparatory set, with or without con- comitant variations in experimental conditions, are the possibilities to be reckoned with, no matter how simple the task being studied appears to be. Reaction times are indices of organismic response processes which start no later than the preparatory signal. Johnson referred to the initial phase of these processes as ‘the primary response’ (1924, p. 22). The muscular movement whose latency is being measured (usually called the reaction), is pri- marily brought about by the subject’s intention to react and is only in a very secondary manner a response to the final or focal stimulus (Woodrow, 1915).

PREKNOWLEDGE OF STIMULUS It has been customary to speak of simple reaction time if only one of a predetermined

class of focal stimuli is presented in each trial and no alternative response movements are involved. Wundt (1880) incorporated a third requirement in his definition. If several va- riants of a stimulus class are being used during an experiment, the respondent must know in advance of each reaction which particular variant to expect; otherwise he cannot be maxi- mally prepared to respond to that stimulus. Operationally, this led to the traditional proce- dure of presenting any given stimulus variant for several consecutive trials before changing to another (an arrangement which also meets with fewer instrumental difficulties !).

Empirically, the claim has been made that simple R T is lengthened ‘where several stimuli of different intensity are used, the S not knowing which to expect; in general, the time varies inversely with the S’s foreknowledge of the conditions’ (Warren & Baldwin in Baldwin’s Dictionary, 191 I , p. 418). This generalization was apparently based exclusively on the rather

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meager evidence submitted by Wundt (1874, p. 739). When two sound intensities were presen- ted in irregular order over 24 trials to one respondent, mean RTs were twice as long and variability many times as large as on another occasion, when the same stimuli were given in a regular order. Only in the latter case, therefore, did Wundt consider the reaction a simple one, characterized exclusively by uncertainty as to the time of stimulus appearance. Since our last review of this topic (Jarl, 1957), two additional studies have been found in which similar com- parisons were made, but with rather negative results.

Von Kries & Auerbach (1877)~ in Helmholtz’s laboratory, wanted to determine what they called discrimination time by subtracting the simple R T for a given stimulus S, from the some- what longer RT when one of two or more different stimuli could be expected, but S, alone called for the single key-pressing response. Experimentally, the stimuli to be differentiated in the latter case were necessarily presented in irregular order. The simple reactions, on the other hand, were obtained under regular order (groups of 10-15 trials for each stimulus variant). In view of Wundt’s earlier finding, it would seem necessary to randomize the stimuli in both cases in order to make ‘recognition of the stimulus’ the only independent variable-cf. a remark in another connection by Woodrow: ‘In the case of choice reactions, where the psycho- logical processes involved are more complex than in the case of simple reactions, and where the subject does not know beforehand what change in stimulus to expect, degree of attention is lower than in the case of simple reactions’ (Woodrow, 1916, p. 317).

That the investigators may have been aware of this question is gleaned from their first ex- periment, in which two locations of faradic stimulation were to be distinguished. On the third of the seven experimental sittings the simple RTs were obtained under both regular and irregular order, as explained in a footnote to their Table I: ‘Ia identifies trials in which the two stimuli alternated irregularly, the subject having to respond to either without knowledge of their order. Although no discrimination was to be made in this case, one did not know which stimulus to expect. It will be seen that all the values conform to the shortest simple reaction times’ (von Kries & Auerbach, 1877, p. 311). ‘All the values’ referred to are four means out of a total of fifty. In any case, the small net ‘discrimination times’ obtained (21-36 ms) do not leave much room for the operation of a preknowledge factor in line with Wundt’s results.

Among a variety of R T problems studied in the early days of the Yale laboratory, Bliss (1893) also undertook a direct replication of Wundt’s experiment with one subject but more observations (about 60 per stimulus condition). Results are inadequately presented, but it ap- pears that irregularity produced no difference for the strong sound and only an increase of 12 ms for the weak, as compared with regular order. ‘These figures are in marked contrast to those of Wundt . . . . It can scarcely be that there was a greater difference between the sounds he used; the difference in the present case was so great that the loud sound, when the order was unknown, was greatly dreaded and always produced a decided shock’ (Bliss, 1893, p. 31).

In view of this statement it is surprising that the differential effect of the two intensities was no more than 12 ms under irregular order, and none at all under regular order. Perhaps the explanation lies partly in the fact that ‘scarcely a series passed in which there was not one or more reactions to the warning’ (p. 38). But we are also reminded of the observation by Cattell & Dolley referred to above, that the more ‘automatic reactions’ are less influenced by experimen- tal variations, and of the finding by Martius (1892) that varying stimuli have very little effect if any, within a wide range of loudness, when trained respondents maximize their attention.

The latter condition seems in any event to have been fulfilled in the Yale study, too, for Bliss remarks (p. 39) that ‘as soon as the habit is formed all our reactions are in the main brain re- flexes. But . . . quick reactions are something more. The reflex action left to itself is slow, com- pared with the reflex action with the concentrated effort of the mind to hurry it along.’ I t may well be that such maximal effort tends to counteract generally the influence of other variables, but the issue is still far from settled (cf. Thrane, 1960, pp. 92 ff.).

The moderate effect reported by Bliss is more in harmony with our own finding (Jarl, I957), when six subjects reacted to three visual stimuli of moderate intensities and maxi-

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mally about one log unit apart, presented in both ways on each of four sittings. For all in- tensities and subjects combined the difference in R T between procedures was only 2 ms, and in favor of irregular order at that. When the comparison was made separately for each intensity, the differences were negligible in the case of the two lower brightnesses, whereas four of the six subjects had appreciably longer latencies for the brightest stimulus with specific preknowledge than without. The net result for the group as a whole was greater differential effect of intensity under irregular order of stimulus presentation (5 % of the RT to the weakest stimulus, as compared with 13 % under regular order).

In the latter respect only is there full agreement between the results of Wundt, Bliss, and the writer. However, the former investigators overlooked this aspect of their data.

COMPENSATORY SETS

Basic to Wundt’s interpretation of results, and consequently to his definition of simple reaction time, is the dual assumption that specific preknowledge ensures maximal and there- fore comparable degrees of attention to all variants of the focal stimulus (except for stimuli at the very extremes of intensity scales, where the anticipation of stimulus strength becomes inadequate). We have argued, on the other hand (Jarl, 1957), that instead of simplifying the processes involved, specific preknowledge may complicate matters by allowing preparatory adjustment, or the primary phase of the response, to vary systematically with the nature of the expected stimulus. If such interaction be of a compensatory nature, as suggested by Johnson (1923), we would expect any differential effect of stimulus intensity to be less under regular than under irregular order of stimulus presentation.

The available evidence is limited but compatible with the hypothesis. With the two subjects in the experiments of Wundt and Bliss, preknowledge resulted in a relatively greater shortening of latencies for the weaker of two sounds, whereas with our respondents it was associated with prolonged latencies for the brightest of three lights.

Johnson envisaged a set of stimulus variables determining the sensory adequacy of the final reaction signal (the sensory factor), and a set of organismic variables constituting the subject’s neuromuscular set or preparatory effort (the attentional or volitional factor). If the latter factor is left free to vary, and the sensory adequacy of stimulation is decreased below a critical value, the subject will begin to increase his effort (unless, we may add, already maximized). Above this critical value, on the other hand, his effort will tend to diminish. As a result, the more adequate stimuli from the point of view of sensory excitation may not be the optimal ones in regard to the latency of a prepared motor response.

Johnson thus postulated bi-polar interaction effects of opposite signs, so to speak. Theoreti- cally, however, compensatory behavior may occur at any one side of a critical value without necessarily involving the other. For convenience we may speak of positive compensation when decreasing (less adequate) values of a variable elicit relatively more efficient preparatory sets (as assumed to be the case in Wundt’s and Bliss’ experiments), and negative compensation when increasing values give less efficient performance than under conditions which preclude the formation of differential preparatory sets (as our results indicated).

The possibility of a negative compensatory interaction effect, not involving a stimulus vari- able, had been suggested earlier by Woodrow (1914). Experimenting with regular foreperiods of different duration, one of the two subjects (both highly practiced in the ‘motor’ type of response set), had his optimal foreperiod at I sec rather than at z sec which Woodrow consi- dered ‘no doubt’ normally to be the case. Judging the RT with the 2-sec foreperiod unusually

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long, rather than the R T with the I -sec foreperiod exceptionally short, ‘a plausible explanation may be that the subject felt that the reaction was so easy to perform quickly with this length of interval, naturally the easiest, that he did not try as hard as in the other cases’ (p. 83).

SUPPLEMENTARY EXPERIMENT

The results of our first experiment were regarded as ‘suggestive rather than conclusive. The small intensity differences employed are probably not the most favorable ones for testing Johnson’s hypothesis’ (Jarl, 1957, p. 238). Differences of such order of magnitude are, on the other hand, of particular relevance for the use of response latency as a tool in perceptual research. For this reason it was of interest to see if the results could be repeated under similar conditions.

An opportunity arose at the University of Virginia in 1941 in conjunction with another investigation. A senior graduate student (T) with whom the writer was co-operating, ex- pressed skepticism regarding Johnson’s hypothesis, and volunteered to demonstrate as a subject that, in any event, acquaintance with the hypothesis would nulIify any compensatory tendencies.

Procedure Two visual stimuli of 4 and 16 mL (40 and 160 Trolands), here referred to as D (dim) and

B (bright), were exposed foveally for 0.5 sec after randomly arranged foreperiods of 1.25, 1.50, and 1-75 sec, following a momentary auditory warning signal. Sixty reactions were made on each of four sittings, of which the last three were on the same day. On every sitting the stimulus variants were first given in grouped regular order (starting with 15 reactions to D on sittings I and 3), followed by random order of presentation. Six practice trials started each session. Another subject (M), a junior graduate student unacquainted with the problem, served only for one sitting.

Results Table I gives the results, with the means for the brightness presented first under regular

order on any one sitting in italics. As planned, this limited experiment does not permit a comparison of average speed under

the two procedures. We note, however, that the respondents are consistently quicker during the first haLf of each sitting, when regular order was used. During the preceding six weeks T had given 150 reactions to brightness D alone, distributed over three sittings with mean RTs of 214, 237, and 226 ms, and on every sitting the first half had the shorter mean RT. Subject M had three weeks earlier given 60 reactions to D alone, also with loss in average speed during the second half (245 vs. 292 ms). His speed is by now considerably improved, generally, and he is evidently not disturbed as markedly as Wundt’s subject, if at all, by the unusual irregularity of stimuli.

The diflwentiul eflect of the two lights is consistently greater under irregular than under regular order, it being practically nil in the latter case. (For subject T it is -0.3 ms when reacting first to D under regular order, and 3.3 ms when B comes first.) As in the experiments of Wundt and Bliss, the smaller differential effect of regularly presented stimuli is due to a relatively greater improvement in speed for the weaker of the two stimuli (positive compen- sation).

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TABLE I. Reaction times in milliseconds for retinal illuminances of 40 (0) and 160 ( B ) Trolands, presented foveally in regular and irregular order to two subjects.

Means in italics signify primary position of the stimulus variant under the grouped regular order.

Subject and

sitting

n per Regular order Irregular order stimulus Mean RT Diff. Mean R T Diff. variant D B D-B D B D-B

1.5 188 190 - 2 207 I 98 9 15 206 203 3 252 22.5 27 15 201 200 I 219 201 18 1.5 192 189 3 202 I95 7

60 197 196 I 220 205 15 15 222 2 2 0 2 235 216 19

At the end of the third sitting for T, he reacted (on his own initiative) six times to D and five times to B in irregular order but with preknowledge, the particular brightness being requested by the respondent in advance of each reaction. Under this condition mean R T for D is 233 ms and for B 228 ms, leaving a differential effect of 5 ms as compared with 18 ms under the preceding irregular order without preknowledge.

CONCLUDING REMARKS

We have seen that there is evidence for both positive and negative compensatory interac- tion between stimulus and organismic factors in the so-called simple reaction times. Or, sticking to the facts alone, regular presentation of stimulus variants produces less differential effect on response latency than when the same stimuli are given in random order. This dis- crepancy, regardless of further interpretation, must be ascribed to changes in preparatory set during the initial phase of the total organismic response, which starts no later than the warning signal.

Regular stimulus order provides the subject with specific knowledge regarding what stimu- lus variant to expect. Such preknowledge may perhaps improve response efficiency generally. I t will be recalled that Wundt’s subject responded considerably more quickly to both loud- nesses under regular than under irregular order, although more so in the case of the weaker sound. I t was the common difference which caught Wundt’s interest. It is conceivable, however, that both a general and a differential effect can be at work concurrently. General response efficiency may be higher when nearly the same preparatory set can be maintained for several successive trials, than when experimental conditions call for, or permit, frequent changes in set. Yet, if these changes also vary systematically with the nature of the expected stimulus, as has been demonstrated in some cases, differential interaction is also involved.

Today, many will regard a hypothesis of compensatory interaction as reasonable enough, but it was a big step at the time to apply it to ‘the simplest psychological processes’. In fact, it has been rather neglected by later R T investigators (cf. Jarl, 1957), perhaps because Johnson did not put it to a direct test. In other connections, as when dealing with appropriate designs for studying the effects of various impairing agents on behavior, he continued to

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stress the danger in accepting the performance of some selected function as an unequivocal index of efficiency. Such pre-experimental assumptions may even lead to absurd conclu- sions, e.g. that a light dose of alcohol produces greater impairment than double the dose. To quote: ‘In other words, all these studies presupposed that the subject would not compen- sate, as by releasing new supplies of available energy, by neglecting one set of tasks to per- form another, or by substituting one mechanism for another. The fact is that the human organism is most remarkable for its compensations; that when it ceases to compensate, we call it “dead”’ (Johnson, 1940, p. 342).

One result of the present experiment (subject T on the third sitting) suggests that it is lack of specific preknowledge, and not the irregularity of stimulus presentation as such, which is primarily responsible for the greater differential effect of stimulus intensity under irregular order. This question has been taken up in a further experiment, to be described in the following report.

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