The orienting response and stimulus significance: Further comments

The orienting response and stimulus significance: Further comments

Biological Psychology 12 (1981) 171-185 North-Holland Publishing Company THE ORIENTING RESPONSE AND STIMULUS SIGNIFICANCE: COMMENTS FURTHER Alvin S...

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Biological Psychology 12 (1981) 171-185 North-Holland Publishing Company

THE ORIENTING RESPONSE AND STIMULUS SIGNIFICANCE: COMMENTS

FURTHER

Alvin S. BERNSTEIN Department Accepted

of Psychiatry, State University of New York, Brooklyn, NY 11203,

for publication

U.S.A.

9 July 1981

Siddle’s (1979) assertion that the significance hypothesis is based on tautological argument regarding the effects of intensity decrease refer only to two papers which first suggested the need for research into determinants other than mismatch. Studies testing specific predictions followed in various laboratories, and it is their results that support the hypothesis. The hypothesis never depended on intensity decrease, and the charge of nonreplicability is incorrect. Siddle’s argument concerning response stereotypy cannot account for the data showing response to significant ‘novelty’ coupled with nonresponse to nonsignificant ‘novelty’ in the same OR component, or for that showing consistent differences in various components between randomly selected groups. Arguments based on trait-lability are inadequate since tests of the lability hypothesis have confounded trait factors with the differences in stimulus assessment they hope to test. The significance hypothesis emphasizes stimulus information in the OR, sig-

nificance serving to limit access to central processing channels to those signals whose information is relevant for the organism. OR components are seen as long-latency responses elicited after automatic early detection of uncertainty and significance, and reflect higher processing of significant information. A distinction between involuntary and voluntary phases of attention is acknowledged, but it is questioned whether OR components can be assigned to the former because of the frequent failure of ‘automatic’ ORs to innocuous stimuli, the long latency of most components, and failure to demonstrate structural differences between the classes of response.

I wish to reply to Siddle’s (1979)

criticism

of the ‘significance

hypothesis’

of the

orienting response (OR), and to elaborate further the nature of the OR and the role played by stimulus significance. Noting that stimulus significance was not independently defined in two early papers (Bernstein, 1968, 1969), Siddle alleges the significance hypothesis is based on posr hoc and tautological argument (Siddle, 1979, p. 304). Siddle’s point depends on his contention that the hypothesis rests on the 1968-1969 studies, and this is quite incorrect. These studies predated the significance hypothesis and were intended merely to test specific aspects of Sokolov’s (1963) neuronal model theory. In 1968 I wanted to determine whether the OR reflected stimulus ‘novelty’ without bias for stimulus ‘quality’, and in 1969, to test whether detection of ‘mismatch’ would necessarily result in an OR. This widely held assumption had never actually been tested. Many studies demonstrated that mismatch couZd elicit ORs, but none 0301-051

l/81/0000-0000/$02.7.5

0 1981 North-Holland

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had asked whether it had to do so - quite a different proposition. In both cases the data did not support Sokolov. Stimulus intensity increase elicited ORs more effectively than an equivalent intensity decrease (Bernstein, 1968). In addition, subjects were frequently able to detect stimulus change without displaying an OR, whether one examined the electrodermal, heart rate, finger pulse volume, or pupillary component (Bernstein, 1969; O’Gorman, Mangan and Gowan, 1970; O’Gorman, 1972; van Olst, 1971; Brown, Morse, Leavitt and Graham, 1976; Koepke and Pribram, 1966,1967; Peavler, 1974). The 196881969 papers relate to the subsequent significance hypothesis primarily insofar as such findings made it necessary to consider what factors besides mismatch might be involved in triggering ORs. Certain aspects of the 196881969 data (Heightened response to stimuli which became louder or brighter; heightened responsiveness in subjects displaying slower habituation and persistently rising conductance levels during pretest trials despite evidence of nondifferentiated initial tonic and phasic reactivity) suggested to me that stimulus significance might be such a factor. The speculative nature of this suggestion was underscored repeatedly (Bernstein, 1968, 1969; Bernstein, Taylor, Austen, Nathanson and Scarpeli, 1971) and the need for further research was emphasized. I then began a series of studies to test this. In each, stimulus significance was explicitly defined, and specific predictions were made (Bernstein, 1973; Bernstein et al., 1971; Bernstein, Taylor and Weinstein, 1975; Bernstein and Taylor, 1979). Bernstein, Taylor, Weinstein and Rauscher (unpublished) examined the role of significance on more tonic aspects of the OR. Other studies explored the role of stimulus significance in psychopathological populations (Bernstein and Taylor, 1976; Bernstein, Schneider, Juni, Pope and Starkey, 1980). During this time other laboratories carried out independent tests of stimulus significance as well, with results similar to ours (Brown et al., 1976; Hulstijn, 1978; van Olst, 1971; van Olst, Heemstra and ten Kortenaar, 1979; Greene, Dengerink and Staples, 1974; Ray and Piroch, 1976; Verbaten, Woestenburg and Sjouw, 1980; among others). It is these subsequent studies, none labelled as tautological by Siddle, that sustain the significance hypothesis. While Siddle’s claim that our 1968-1969 data could not be replicated is thus somewhat tangential to the significance issue, it does warrant reply. Siddle bases his claim on the fact that others have reported that intensity decrease can elicit ORs. Siddle mistakes my position since I never concluded that intensity decrease cannot elicit increased OR. Rather, the point made was that intensity increase elicited substantially more frequent ORs than did intensity decrease, a conclusion correctly cited by other writers (e.g., O’Gorman, 1973; Graham, 1973), and replicated by Maltzman, Harris, Ingram and Wolff (1971) and van Olst (1971) among others. While small ns limit their usefulness, O’Gorman et al. (1970) also obtained results closer to ours than to Siddle’s. Indeed, O’Gorman (1973) concluded that intensity decrease was ineffective in renewing habituated OR. Siddle and Heron (1977) may have seen less nonresponsiveness because half their test-trials occurred after 20 habituation trials rather than the 10 (or in one case 15) used in our studies.

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Edwards (1975a, b) reported that an intensity decrease following four, six, eight or ten habituation trials produced only a further decrease in skin conductance response (SCR) amplitude. A slight increase was noted after 15 habituation trials, but only with 20 or more did a reduction in tone intensity effectively result in increased SCR. Magliero, Gatchel and Lojewski (1981) confirmed this. These data demonstrated that subjects often perceive ‘novelty’ without displaying an OR, disputing Sokolov’s mismatch-reflexive position. As O’Gorman noted: ‘Sokolov’s account of the OR makes no provision for the fact that some subjects although aware of a change in stimulus conditions do not orient to it.’ (1973, p. 468). The same point is made even if one accepts Siddle’s (1979) estimate of 27% or, in fact, if one notes the still sizeable frequency with which subjects detecting an intensity increase also fail to response (Bernstein, 1968, 1969). It is important to move beyond the issue of intensity. Had nonresponsiveness been demonstrated solely with regard to detected change in stimulus intensity, it might not have required major revision of orienting reflex theory to accomodate this circumscribed exception to the automatic-response rule. It is the demonstration that subjects may perceive change in a wide array of stimulus attributes (e.g., intensity, pitch, duration, interstimulus interval, in speech syllabes, in some aspect of a compound stimulus, or omission of the stimulus itself, see O’Gorman, 1973) without necessarily displaying an OR that undermines the reflexive view. The incidence of OR nonresponsiveness in subjects detecting various kinds of change commonly ranges between 40-60% (O’Gorman, 1972; O’Gorman et al., 1970; van Olst, 1971; Koepke and Pribram, 1966,1967; Magliero et al., 1981). Siddle (1979) contends it would be difficult for me to account for the differences in nonresponsiveness produced by some changes as compared with others since there are no a priori reasons for assuming any to be more significant than others. While, for the most part I agree, one exception may be in stimulus intensity increase. Soviet writers emphasize the existence of certain prepotent OR cues (Razran, 1961). Bernstein (1968) suggested that greater responsiveness to increased loudness or brightness might be part of a heightened OR sensitivity to stimuli indicating ‘something approaching the organism’ (p. 128). This proposal was then tested by Bernstein et al. (1971). The data showed that apparent movement toward the observer elicited substantially larger and more prolonged ORs in both electrodermal and finger pulse volume response despite the independence demonstrated between them, and despite previous familiarization with these stimuli. An association between biased OR to intensity increase and that to stimuli approaching the observer seems a viable possibility, and accounts for the results without difficulty for the significance hypothesis. Indeed, it is Siddle who would have difficulty with these results since his suggestion of a difference in ‘stimulus energy’ (Siddle, 1979) cannot apply. Both size and brightness of the stimulus field remained constant between the approach and recede conditions. It seems more likely that an otherwise innocuous stimulus begins to elicit ORs when seen to approach because such approach increases the probability that the stimulus may somehow engage the ob-

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server, and that OR sensitivity for intensity increase may relate to the fact that increased brightness and loudness are cues normally associated with such approach. Siddle (1979) suggests that, since much of the work testing the significance hypothesis examined response in only one system, subjects failing to respond to nonsignificant stimuli may have been responding in another, unrecorded system. Differences in response stereotypy might thus account for the data without the need for a stimulus evaluative process. It is certainly important that simultaneous cross-component recordings be made. One such study in my laboratory (Bernstein et al., 1971) found highly concordant results in SCR and finger pulse volume responses supporting the significance hypothesis; additional study is underway. However, despite agreement on the need for multi-response research, I do not believe Siddle’s argument can account for the existing single-response literature supporting the hypothesis. For one, several authors (e.g., Bernstein and Taylor, 1979; Peavler, 1974;van Olst and ten Kortenaar, 1977) tested single-component response by providing both significant and nonsignificant stimuli to the same subjects, reporting substantial response to the significant signals only. Such differential response within a given response system cannot be explained by Siddle’s argument. Further, others have shown that samples unresponsive to nonsignificant stimuli displayed similar reactive capacity in the system under study to the subjects responding to significant stimuli (e.g., Brown et al., 1976; Ray and Piroch, 1976). Finally, in the single-response literature different laboratories have focused on different OR components. To extend Siddle’s argument across these studies would require that SCR investigators (e.g., Bernstein et al., 1975; Ray and Piroch, 1976) somehow recruited an uncommon number of electrodermally unresponsive subjects and that these were selectively assigned to the nonsignificant condition. Where the focus shifts to another system, it would require the sampling bias to shift as well, so that cardiac studies (Brown et al., 1976; Greene et al., 1974) were selectively sampling and mis-assigning cardiac rather than electrodermal nonresponders, while those studying pupillary response (Peavler, 1974; van Olst and ten Kortenaar, 1977) were somehow selecting biased samples of pupillary nonresponders. Bernstein (1979) noted that an OR which responded automatically to stimulus novelty would be maladaptive since it would frequently disrupt ongoing behavior and occupy precious channel capacity merely to facilitate input of useless information. Siddle (1979) maintains that long-term habituation would protect against excessive orienting. He might equally have cited generalization of habituation as a similar factor. Siddle overlooks the limited nature of such factors. The effect of habituation does decline over time. While Siddle notes savings in habituation on retest for ‘intervals of up to one week’ (p. 307), human experience extends beyond that. The effect of generalization depends on the ability to accomodate current stimuli on some existing gradient, and falls off as perceived similarity lessens. In addition, neither effect will block response; they simply diminish it. At best, where some previous habituatory experience is still effective, it will merely somewhat

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lessen the intensity and somewhat shorten the duration of some maladaptive intrusions . Siddle (1979) maintains that system lability is a more effective OR determinant than is stimulus significance. This was first suggested by O’Gorman (1972) who found that subjects responding to stimulus change showed more frequent nonspecific responses (NSRs) preceding the initial experimental stimulus than did nonresponders. Considering NSR as an index of trait lability, O’Gorman assumed that low-NSR ‘stabile’ systems were nonresponsive, under strong tonic inhibitory control. He proposed that response was determined by the degree of system lability rather than by considerations of stimulus significance. The ‘lability hypothesis’ thus retains Sokolov’s conception of an orienting rejZex contingent solely on stimulus mismatch, adding only the limiting factor of system lability. This extends an earlier argument by Morgenson and Martin (1968) who attempted to explain the relationship between the OR and conditionability by stating that ORs merely reflected increased general reactivity in a given peripheral system. Subsequent studies did not support this view (Fuhrer, Baer and Cowen, 1973; Ohman and Bohlin, 1973) indicating instead that the OR reflects ‘problem solving’ processes in conditioning involving the discovery of significant stimulus relationships (Baer and Fuhrer, 1970; Maltzman, 1979). Attempts to relate all OR simply to peripheral reactivity also fail, for several reasons. For one, animal studies indicate that electrodermal lability as indexed by NSRs does not itself determine whether an OR is elicited by a novel stimulus. Kimble, Bagshaw and Pribram (1965) separated monkeys into NSR labile and stabile groups and found no differences in OR to stimulus change. Groups differed only in habituation, labiles habituating more slowly. Pribram, Reitz, McNeil and Spevack (1974) found that amygdalectomy severely altered electrodermal lability,producing ‘hyperstabile’ or ‘hyperlabile’ animals displaying 2-l 1 or 28-30 NSRs respectively per 2 min interval, compared with the normal 18-22. Despite such differences, all amygdalectomized animals showed the same diminished OR. Pribram suggests the amygdala determines stimulus significance. Autonomic ORs are not elicited if significance is not detected; differences in peripheral lability themselves do not account for this. The same seems to be true for humans. Siddle (1979) implies that the relationship between NSR frequency and OR engagement is as ‘well documented as that between NSR and habituation. This is not the case. While correlations between NSR and speed of habituation have been consistently reported, that between NSR and OR onset is poor as ohman and Bohlin (1973) noted. In a paper cited by Siddle, Crider and Lunn (197 1) concluded that, while NSR and habituation appear to be ‘alternative indices’ of lability, ‘electrodermal lability appears to be independent of allied concepts such as orienting reflexiveness’ (p. 146). Koepke and Pribram (1966) also found NSR and habituation to be related, but found no difference between labile and stabile subjects in OR magnitude anywhere over the first six trials.

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Thus, while not determining the engagement of an OR, NSR-lability does appear to reflect the time needed to disengage the system once other (central-evaluative?) factors elicit the response. ’ Attempts by O’Gorman (1972) and Siddle et al. (1979) to demonstrate a primary role for NSR trait-lability in determining electrodermal OR are compromised by two problems. They define trait-lability on the basis of a single measure on one test occasion, and they select as that occasion the ‘resting period’ preceding the first stimulus of the very experiment in which it is to serve as an independent variable. To support their definition, O’Gorman and Horneman (1979) examined NSR frequencies on 2-week retest under conditions of relaxation, vigilance, and mental artihmetic. While demanding tasks increased NSR, indicating important state-variance, significant correlations were obtained across conditions, indicating trait-variance. However, Baugher’s (1975) results contradict these. On 24 h retest under both rest and vigilance, he did not find substantial correlations across conditions, ‘suggesting that (NSR) does not possess any strong “trait-like” characteristics’ (p. 255). Lacey and Lacey (1958) first obtained results supporting O’Gorman and Horneman, but were unable to replicate in a second study whose results support Baugher. With such an uncertain literature it is difficult to accept with confidence the O’Gorman-Siddle procedure for identifying labile and stabile subjects. Crider and Lunn (197 1) also stressed ‘the dubious validity of single-session determinations of lability’ and ‘the importance of repeated testings for achieving stable individual difference estimates’ (p. 148). When the single measurement occurs in the opening minutes of the experiment intended to test lability vs. significance, the problem is compounded. Bernstein (1973) demonstrated that NSR-lability was a flexible characteristic reflecting assessment of situational demands. When listening to tones which might deliver significant information, NSR frequency rose to ‘labile’ levels, returning to ‘stabile’ levels immediately afterward. Listening to the same tones when the information had no significance, NSR remained ‘stabile’ throughout. Similar results are reported by Baugher (1975) and are supported by Maltzman and Raskin (1979). Because of this, the O’Gorman-Siddle procedure may confound true differences in trait-lability with differences in subject judgements regarding the procedures to be experienced. Those anticipating a potentially significant encounter are likely to raise NSR levels to the labile range, while others, accepting the ‘innocuous’ explanation, remain in the stabile range. Trait-lability may be confounded with the very judgements of stimulus significance it is intended to test.

1 It would be interesting to determine whether this relationship itself reflects differences only in peripheral activity per se, or rather, some more central factor relating either to rate of information processing or to criterion values determining the point at which ‘sufficient’ information has been assimilated.

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Siddle et al. (1979) report that subjects responding to a stimulus-change trial also showed larger responses to the initial habituation trial, and consider this further evidence of greater lability in responder-subjects. Magliero et al. (1981) report a similar finding. However others have shown that test-trial responders and nonresponders may show similar initial responses in both phasic and tonic reactions (Bernstein, 1969; Ray and Piroch, 1976; Brown et al., 1976). Differential test-trial response is by no means limited to subjects showing generally heightened responsiveness. Further, as Magliero et al. noted, a relationship between test-trial and initial-trial OR in the same experimental test ‘is not inconsistent with Bernstein’s significance hypothesis. Subjects who perceive the experiments as being a significant event may be more responsive both initially and on the test-trial.’ As with NSR, ascribing heightened lability to subjects displaying larger SCRs to the initial habituation stimulus confounds variance due to system reactivity with that due to differences in evaluation. Magliero et al. (1981) report also that SCR to a change trial occurring after an average of eight or nine habituation trials was determined in large measure by initial state (i.e., by skin conductance level (SCL) preceding the first habituation trial, and by SCR amplitude to that trial). This appears to support the lability hypothesis. However, Magliero et al. noted something interesting when the number of habituation trials was extended to 21. The predictive usefulness of initial state variables now declined significantly, while that of ‘variables representing change in electrodermal state over the session’ (relative increase in SCL over trials and number of responses across trials) increased significantly, becoming a major predictor of testtrial response. * The same change-of-state variables were associated with differential test-trial response in Bernstein (1969). The Magliero et al. shift in predictor variables is consistent with the significance hypothesis, emphasizing a dynamic, continuing evaluation of stimulus and task rather than a static lability trait. Siddle (1979) contends the fact that test-trial responders in Bernstein (1969) showed slower initial habituation supports an interpretation in terms of lability. In fact, responders initially habituated more slowly and also showed a differential

’ Magliero et al. (1981) determined the predictive variance associated with initial-state and change-of-state variables by means of a hierarchical multiple regression which underestimates the values for the change-of-state indices relative to those for initial-state. The hierarchical regression used always entered initial-state variables first, and change-of-state variables last. Thus, any variance shared between the two sets of variables was attributed to the initial-state predictor and partialled from the subsequently entered change-of-state predictor. The authors’ correlation matrices display such shared vairance, especially between habituation trials and each initial-state index. The logic dictating this particular order of entry, namely temporal sequence, is understandable but not necessarily compelling. Other orders of entry could be defended as having equal face validity, For example, suggesting that indices of state closest in time to the stimulus change would be most relevant in determining OR to such change would enter the change-of-state variables first. It would be interesting to determine the variance associated with each type of predictor in such an analysis.

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increase in conductance levels. However, there were no reliable differences between test-trial responders and nonresponders in SCR to the initial habituation trial, in SCL preceding that trial, or in tonic change in SCL produced by the start of habituation trials. Since these initial trials preceded the test-trial by only a few minutes, Siddle’s argument based on static lability differences between test-trial responders and nonresponders cannot hold up. Rather, it was evident that, after showing equivalence across subject groups at the outset, electrodermal lability altered over the next few minutes so that it was higher in responders at the time of the test-trial. Again, it is not static lability but continuing evaluation of task and situation that determines system reactivity, response to test-trial, and thus the reactivity-test-trial OR relationship. Siddle (1979) cites the Siddle et al. (1979) data as supporting the role of lability rather than stimulus significance in determining SCOR. However, there are flaws here which make Siddle’s conclusion premature. In the first study, Siddle et al. (1979) assigned stimulus significance by requiring some subgroups to press a switch at the offset of each 5 set tone, while others merely listened without responding. After establishing of&? as the significant stimulus, Siddle et al. (1979) chose to compare groups in response to tone onset, 5 set distant. By focusing on a relatively peripheral event rather than on the targeted significant one, Siddle et al. blur the effectiveness of the distinction Illustrative data were presented by between significance and nonsignificance. Greene et al. (1974). Also using long tones, they demonstrated that subjects would respond differentially to tone onset or offset, depending simply on which aspect was made significant by instructions. Greene et al. concluded that ORs ‘will be observed during that portion of the stimulus in which information relevant to the requested judgement is presented’ (1974, p. 645 my emphasis). Other problems exist as well. Their instructions merely required reaction time (RT) subjects to press a switch to the offset of any tone. The change in pitch on the test-trial thus altered an irrelevant aspect of the stimulus, thereby creating an ambiguous stimulus event of no more specific signifiance for RT subjects than for nonRT. Stimuli received in such ambiguous circumstances impose the burden of determining significance on the assessment of each subject (Iacono and Lykken, 1979). Depending on their individual judgement, Iacono and Lykken predict some subjects will and others will not decide the change involves something significant. The increased frequency with which ‘significance’ is judged by nonRT subjects on the ambiguous change-trial would further narrow the differences between RT and nonRT subjects on that trial. In contrast, Ray and Piroch (1976) obtained a clear significance effect by altering the significant stimulus component. Their subjects received simultaneous tone-light stimuli with RT subjects required to press a button to each light while nonRT subjects did nothing. On the change-trial the light component was omitted. Here, Ray and Piroch found increased SCR only among RT subjects, concluding that ‘omitting a task-relevant stimulus is more dishabituating than simply omitting a stimulus’ (p. 83).

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The attempt by Siddle et al. (1979) to discount Ray and Piroch’s evidence on the grounds it only ‘involved a decrease in stimulus energy’ is inadequate. Even if one accepts their premise regarding ‘energy decrease’ it could not account for the differential results obtained, with stimulus-significant subjects responding on the test-trial to the same ‘decrease in stimulus energy’ to which the nonRT subjects largely failed to respond. The second Siddle et al. (1979) experiment, involving a test-trial change to the subject’s own name vs. a neutral name, used a questionable analysis. The data displayed in their fig. 2 (p. 524) indicate that both NSR groups given ‘own name’ show increased SCR magnitude, approaching or surpassing that of the initial trial and clearly greater than that shown in any habituation block. In contrast, the low NSR-neutral name sample shows a continuing decline on the test-trial, while the high NSR-neutral name sample reveals an increase in SCR relative to the preceding block, but only reaching levels seen in habituation blocks 2 and 4, well below that of the initial trial. The high NSR-neutral name sample appears to have been more variable during habituation. By comparing test-trial SCR only with the preceding two or three trials Siddle et al. may capitalize on one swing of this less stable curve. Testing change-trial response against only the last few isolated prechange trials is inappropriate in a sample displaying considerable variability over the prechange trials. I do not dispute the potential importance of trait-differences in system responsiveness. Rather, I think that proper study of trait-lability as an independent factor here has not yet been made. To do so one must record reactivity over differing occasions and conditions. Until then we cannot safely define its role, much less conclude it eclipses that of stimulus significance. Siddle (1979) suggests that significance may relate to information processing rather as if this were foreign to the stated purpose of the significance hypothesis. The debate about significance should not obscure the fact that the hypothesis emphasizes stimulus information as the crucial factor in the OR at least as strongly as does Siddle. Stimulus significance serves essentially to limit access to the central information processing-OR associated system to those signals whose information carries some relevance for the organism from among the much larger set of uncertain stimuli available at the receptors whose unlimited access would uselessly overburden this system (e.g., Bernstein, 1979, p. 576). This is related in part to statements by Ohman (1979) that ‘autonomic components of an OR denote a call initiating processing in a central channel with limited capacity’ (p. 444), with ORs and central processing engaged ‘only when the preattentive processes fail to handle a stimulus’ (p. 449). Viewing the OR in terms of stimulus information makes sense of recent findings which challenge the traditional view of rapid habituation as a ‘major definitional requirement of an OR’ (Siddle, 1979, p. 307). Bernstein and Taylor (1979) reported that no habituation occurred over eight trials provided the significant stimulus involved retained its information value over trials. A common mistake is to

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confuse the physical characteristics of a stimulus with its informational value. Since most OR studies involve merely the repetition of a given stimulus, stimulus informational value in these instances is represented by its physical-temporal characteristics. Repetitive exposure quickly reduces uncertainty here, and ORs do habituate rapidly in the customary OR study. The explanation, however, is not to be sought in terms of stimulus familiarization per se, but in the loss of stimulus informativeness. Thus, when Bernstein and Taylor (1979) sustained information value by manipulating tone-sequence unpredictably over trials, OR habituation was not seen despite the fact that stimulus familiarization occurred since the same tones were used in every trial. Similar results are reported by Graham, Putnam and Leavitt (1975) studying prestimulation effects on startle eyeblink. Siddle (1979) suggests that ORs to signal stimuli may be associated with voluntary attention, and mismatch or nonsignal ORs with involuntary attention. Such a division is suggested by Maltzman (1979) and Ghman (1979). Some such distinction occupies an important place among contemporary attention theorists (e.g., Neisser, 1967; Shiffrin and Schneider, 1977) who differentiate ‘preattentive’ from ‘attentive’, ‘automatic’ from ‘controlled’ processing, and the like. I do not dispute the importance of a distinction between early, automatic processing of input independent of motivational or significance factors, and a subsequent, more selective processing of relevant input, but question whether available evidence permits one to consider components of the OR as associates of early automatic processing. Instead, I suggest that such components are more readily associated with the later, more selectively focussed stage. My reservations concerning an ‘involuntary OR’ rest on the frequent demonstrations of nonresponsiveness to innocuous stimuli, the latency of OR components, and the absence, so far, of convincing structural differences between ‘voluntary’ and involuntary’ ORs. Those proposing an involuntary OR indicate that its appearance is determined solely by stimulus novelty. As such it is an automatic novelty response identical to Sokolov’s mismatch-reflex. Yet, it has been consistently demonstrated that innocuous novelty can be detected without an OR, often in 40-60%f those detecting it. How can one reconcile this absence with an OR tied automatically to stimulus novelty? From its association with simple mismatch as well as its automatic nature, the involuntary OR would be expected early in the processing sequence. Naatanen (1975) emphasized that the latency of the evoked potential P300 is too great for it to be involved in early novelty detection. Rather, he called P300 ‘sequelae’ (p. 272) to the identification of significant input, associated with the specific processing of significant information. The point appears equally valid for all autonomic components as well, since their latencies are even longer. Accordingly, I would suggest that virtually all such components are elicited after stimulus uncertainty and significance are established, and are associated with the increased processing and storage needs imposed by significant but uncertain input. I do not dispute the likely existence of some mechanism responsive to stimulus

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novelty per se early in the processing sequence. I do question whether such a mechanism, triggered by any mismatch and therefore frequently responsive to noise, would have the same direct access to high level central channels as does the response triggered by uncertainty in a significant signal. Since such maximum-processing channels almost certainly have limited capacities, it would seem necessary that they be elicited selectively. Naatanen (1981) suggests an N2 component with a 100-200 msec latency may index just such automatic mismatch-processing, terminating quickly if the deviant stimulus is judged nonsignificant. (I would therefore suggest that, unlike the P300, such N2 would not correlate with autonomic ORs.) One possible exception to this rule for autonomic responses is the intra-cycle cardiac slowing described by the Laceys. In addition, saccadic eye movements may also be associated with early ‘automatic’ processing rather than with ORs reflecting central attention. Lacey and Lacey (e.g., 1980) have shown that significant informative stimuli produce a dramatic lengthening of the cardiac (R-R) cycle within which they occur. The nature of the effect is largely determined by the point within the cycle at which the stimulus occurs - signals within the early portion slow that very same cycle, while those occurring late in the cycle slow the next following one. However, the issue is more complex. The Laceys have shown intra-cycle cardiac slowing to reflect two different effects, one associated with the P300, elicited by targeted tones and reflecting postsignificance processing in the Lacey’s view, the other a response to nontargeted standard tones, reflecting earlier processing called ‘stimulus registration’. Regarding saccadic eye movement, Verbaten et al. (1979, 1980) found that these reflected differences in stimulus uncertainty for nonsignificant stimuli, while skin conductance OR did so only when stimuli were significant (as in Bernstein and Taylor, 1979). Verbaten et al. concluded that eye movement represented a ‘more primary’ information processing phase, while SCOR reflected a later phase associated with ‘active mental processing’ (1980, p. 18). Supportive evidence comes from vigilance studies where it was noted that observers often failed to detect signals even though they had fixated them (Schroeder and Holland, 1968; Mackworth, Kaplan and Metlay, 1964). These subjects are described as ‘looking without seeing’ (Schroeder and Holland, 1968). From such findings, Jerison concluded that ‘paying attention cannot be equated in a simple way with eye fixation’ (1968, p. 445). Posner (1980) also showed that central processing could be dissociated from eye movement. Saccadic eye movements may thus be associated with input into the peripheral channel, but not necessarily with the increased central processing with which the OR is associated. If separate ORs exist, one should be able to define different response characteristics for each. Maltzman (1979) does hypothesize that voluntary ORs are mediated by the left cortical hemisphere, involuntary by the right. Assuming hemisphere specifity would yield laterally asymmetric SCORs, Maltzman tested this during conditioning. Initial response should be right hemisphere-involuntary. As subjects

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establish the significance of the CS, left hemisphere-voluntary ORs should emerge causing a reversal of asymmetry. The data did not support the hypothesis (Maltzman, 1979). Maltzman (1979) also suggests that voluntary ORs are mediated by the prefrontal cortex. This is based on work by Luria and Homskaya (1970) reporting abnormal ORs to innocuous stimuli among patients with both frontal and posterior lesions. When stimuli were made significant (by asking subjects to count them, etc.), ORs were normalized for patients with posterior lesions but not for frontal patients. Maltzman interprets this as supporting the separation of voluntary and involuntary ORs, with the former differentially mediated by the frontal cortex. These data however, do not fully support Maltzman’s thesis since frontal patients displayed the same disturbance of ‘involuntary’ OR to innocuous stimuli as posterior-lesioned patients, as well as an equal degree of abnormality in ‘voluntary’ and ‘involuntary’ ORs. Fully supportive evidence would require that frontal patients display abnormal ORs to significant signals but normal response to innocuous ‘voluntary OR’ stimuli. It is equally reasonable to suggest frontal involvement in all ORs from Luria’s data, possibly via fronto-limbic circuits affecting significance assessment (Bernstein, 1979). Luria and Homskaya do suggest such circuits are part of the OR, while evoked potential studies by NLatanen (198 1) note frontal involvement as the hallmark of any OR activity. The voluntary-involuntary OR distinction seems based so far more on assumed differences in antecedent conditions than on demonstrable differences between the responses themselves. Siddle questions the usefulness of the significance hypothesis. Like any theoretical proposal, it is useful insofar as it serves to integrate otherwise disparate findings and enables one to make testable predictions specifying the behavior of the variable in question under various conditions. In both senses, the hypothesis has demonstrated considerable heuristic value. In addition, it suggests a means of coordinating processes whose seeming separation is a puzzle in the literature. Noting poor communication between physiological/OR and psychological/attention studies, Venables considers the main difference ‘to be that the stimuli to which the organism orients are primarily those which are novel, whereas those to which the organism attends are those which are important’ (1973, p. 263). In rat studies, Roberts and Young (197 1, p. 508) concluded that two ‘alternative interpretations’ were possible for the mechanism mediating electrodermal response, ‘a motivational system’ and an ‘attentional or perceptual mechanism [such as] Sokolov’s’. Our work indicates that these are not competing alternatives but complementary parts of a single process.

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