The orienting response and stimulus significance: further comments

Infant visual habituation

The use of visual habituation in the study of infant cognition and learning is reviewed. This article traces the history of the technique, underlying theory, and procedural variation in its measurement. In addition, we review empirical findings with respect to the cognitive processes that presumably contribute to habituation, studies of developmental course and long-term prediction, as well as recent attempts to address or explain the phenomenon of visual habituation through the use of mathematical or quantitative models. The review ends with an appeal for a return to the study of habituation per se as a valid measure of infant learning, rather than relegating the phenomenon to its use as a technique for familiarizing infants in procedures testing for discrimination or recognition.

The skin conductance orienting response to semantic stimuli: Significance can be independent of arousal

The characteristics of stimuli that elicit skin conductance responses (SCRs) have been conceptualized in varied ways, with strong emphasis on the significance or arousing quality of stimuli. Our goal was to determine whether "significance" can be shown to have an effect on SCRs independent of "arousal," using words as stimuli. Ratings of words indicated that significance is partially independent of arousal. In Study 1, SCRs from 43 participants during presentation of 20 significant, nonarousing words with a negative valence that were either depression related or potentially self-referent and 20 nonsignificant words matched on valence and arousal showed a main effect of significance. In Study 2 (N=44), significant, nonarousing words were sampled more broadly to examine the effects of self-reference and valence. Significance, rather than just negativity or self-reference, elicited SCRs independently of arousal. SCRs to significant words may reflect cognitive and attentional processes that, in turn, might prove useful for the assessment of the cognitive aspects of anxiety.

The relationship between skin conductance hyporesponsivity and perseverations in schizophrenia patients

BACKGROUND

It has been reported that approximately 45% of schizophrenia patients versus 10% of normal comparison subjects are classified as skin conductance hyporesponders (SCOR-HR: the lack of a robust orienting response) when exposed to innocuous tones. We studied the skin conductance orienting response (SCOR) of schizophrenia patients during the exposure to complex and abstract stimuli. We investigated two questions: 1) would the same percentage of schizophrenia patients be classified as SCOR-HR when the orienting stimuli are complex and abstract as when they are innocuous tones; and 2) whether SCOR-HR schizophrenia patients have associated frontally mediated neurocognitive deficits.

METHODS

Thirty-one schizophrenia patients and 29 normal comparison subjects were presented with the Rorschach inkblot test while their SCORs were recorded. Schizophrenics were divided in two groups: SCOR-HR and SCOR responders. Demographic and clinical comparisons were made between the two groups. Rorschach responses were scored for the presence of perseverations.

RESULTS

Forty-five percent of the schizophrenia patients were classified as SCOR-HR versus 10% of the normal comparison subjects. Among the schizophrenia patients, SCOR-HR was associated with increased perseverations, which were in turn correlated with the Scale for the Assessment of Negative Symptoms scores.

CONCLUSIONS

It appears that SCOR-HR in schizophrenia is not a function of the "meaningfulness" of the stimuli. When SCOR status was combined with the measure of stuck-in-set perseverations, a pattern of results emerged lending indirect support to the hypothesis that relates SCOR-HR to frontal impairment and to the idea that SCOR-HR schizophrenia patients may represent a specific subgroup.

Electrodermal responsiveness, clinical variables, and brain imaging in male chronic schizophrenics

We investigated the variables related to electrodermal nonresponsiveness in male chronic schizophrenics. In a comparison of 31 male chronic schizophrenics and 20 male normal controls, the schizophrenics showed a much higher incidence of nonresponders in phasic electrodermal responsiveness, and fewer spontaneous fluctuations (SFs) in tonic electrodermal activity. Among the schizophrenics, nonresponders showed fewer SFs and lower tonic skin conductance level (SCL). They also had more neuropsychological abnormalities of cognitive function and more severe symptoms (both positive and negative). Furthermore, patients with structural abnormality of the brain revealed by computerized tomographic measurements (increased ventricular brain ratio and maximum diameter of third ventricle) were overrepresented among electrodermal nonresponding schizophrenics. These findings suggest that electrodermal nonresponsiveness in chronic schizophrenic illness might be considered as a functional index associated with greater neuropsychological abnormalities and more severe symptoms.

Event-related potentials and autonomic responses to a change in unattended auditory stimuli

Event-related brain potentials (ERPs) and autonomic nervous system (ANS) responses to occasional pitch and rise-time changes in a task-irrelevant auditory stimulus repeating at short intervals were measured while the subject performed a difficult intellectual task (Raven Matrices). It was found that deviant stimuli elicited the mismatch negativity (MMN) component of the ERP even when they elicited no ANS response. There was no significant difference in the mismatch negativity between trials in which the skin conductance response was or was not elicited. The pitch deviant tone also elicited heart rate deceleration, whereas the rise-time deviant tone tended to elicit a later heart rate acceleration. Neither heart rate change correlated with the mismatch negativity. The pattern of results obtained suggests that the mismatch negativity is generated by an automatic discrimination process associated with the cerebral events initiating the orienting response to stimulus change, but does not necessarily lead to the orienting response elicitation. Longer-latency ERP components tended to show slight covariation with ANS responses. The P3 was larger when a skin conductance response was elicited than when it was not elicited. Further, heart rate change trials tended to be accompanied by larger slow waves than trials with no heart rate response. Heart rate acceleration trials were accompanied by a larger slow parietal positivity and a smaller frontal negativity than were heart rate deceleration trials.

"Initial-" and "change-orienting reactions": an analysis based on visual single-trial event-related potentials

The present study was concerned with brain potentials elicited by, respectively, the first of a series of stimuli ("initial-orienting reaction", I-OR), and infrequent deviants ("change-orienting reaction", C-OR). Single-trial event-related potentials (ERPs) to visual stimuli were estimated from recordings at Oz, Pz, Cz and Fz. The design included both a habituation series as well as a series of occasional deviant trials against a background of standards. This was done with both task-relevant and neutral stimuli, and in two interstimulus interval (ISI) conditions: 2.45 s and 8.45 s. In the latter ISI condition, skin conductance responses (SCRs) were recorded as well. Decrease (Habituation) in the habituation series was found for a non-specific N1, a posteriorly distributed P3, and the SCR, but not for P2-N2. Deviant stimuli produced an enhancement of the central P2-N2, the P3, the N1 (on the first few deviant trials only, in both ISI conditions), and the SCR (with task-relevant stimuli only). Elongation of ISI delayed both short-term and long-term decrease of P3, but had no effect on enhancement of P2-N2 due to stimulus deviance. It was concluded that, with respect to ERP parameters, the I-OR is marked by the N1, whereas the C-OR coincides with the P2-N2.

Brain potentials reveal covert facial recognition in prosopagnosia

Brain potentials were recorded in a prosopagnosic patient, in response to familiar and unfamiliar faces he was asked to recognize. The amplitude of the P300 component was found to be an inverse function of probability for each category of faces despite the patient's inability to consciously recognize the familiarity of these faces. In addition, P300 latency varied from 700 to 800 msec according to the familiarity of the faces, and P300 scalp location was different as a function of faces probability and overt recognition. The results imply that covert facial recognition may be evidenced in using event-related potentials of the brain. They also demonstrate that automatic and covert processing of face familiarity are preserved, but prolonged in this patient.

Effects of task relevance on habituation of visual single-trial ERPs and the skin conductance orienting response

Single-trial event-related potentials were recorded at Oz, Pz, Cz, and Fz, concurrently with skin conductance reactions and fixation behavior in a habituation paradigm. A total of 48 subjects received 16 identical visual stimuli; 24 of them were instructed to pay attention, whereas the other half were given a neutral instruction. Two early negative components (N1 and N2), as well as a late positive component (P3) were identified. N1 and skin conductance reaction (SCR) showed fast decrement over trials, whereas N2 and P3 habituated slowly. Habituation of N1 and SCR was delayed by task instructions; N2 was hardly seen at all in the neutral condition. The task effects on N1 and N2 were observed only at Oz. It is concluded that the processing of relevant stimuli differs structurally from the processing of neutral stimuli; this difference may be observed even at a latency of 100 ms. The N1 appears to be related to the SCR, whereas this does not hold for P3; the N2 is related to selection negativities reported by other authors.

The effects of selective inattention upon the electrodermal orienting reflex: a test of information-processing theory

Information-processing theories of the orienting reflex (OR) predict that disruptions of attention which impede the registration of a stimulus in memory should retard habituation of the OR. Studies examining effects of selective inattention upon rate of habituation of skin conductance responses (SCRs) to concurrently presented stimuli have yielded inconsistent results. We employed a dichotic vigilance task calling for selective attention to either male-voice or female-voice words. Comparisons between previously attended versus nonattended stimuli were subsequently conducted for habituation of SCR, as well as for a direct measure of recognition memory. Although there were unequivocal differences in long-term memory between attended and non-attended material, there was no clear evidence for corresponding differences in either initial magnitude or rate of habituation of SCR. These data, which replicated results from an earlier study, failed to demonstrate an effect of memory on the OR as predicted by information-processing theories.

The effects of uncertainty and task-relevance on habituation and recovery of the electrodermal and visual orienting reaction

Habituation and recovery of the skin conductance reaction (SCR) and visual orienting reaction (VOR) were investigated. Half the subjects (total N = 48) were instructed to memorize a complex visual stimulus (TR), while the other half received a non task-relevant instruction (NTR). All subjects were exposed to two series of 16 identical stimuli. At trial 17 the location of the stimulus changed. Half the subjects in both groups received a priori information about the stimuli, the other half did not. Task-relevance led to slower SCR habituation and longer VORs. In the TR condition the VOR latency time rapidly decreased, indicating the development of a set. In terms of SCR frequency, but not in terms of SCR magnitude OR recovery was stronger in the task-relevant condition. However, all subjects oriented visually to the stimulus change. No habituation of the VOR was found using a drift-free technique for measuring eye-movements. It is concluded that the SCR and the VOR latency data supply evidence for a structural difference between task-relevant and task-irrelevant ORs.

Habituation of early and late visual ERP components and the orienting reaction: the effect of stimulus information

Single trial event-related potentials at Fz, Cz, Pz and Oz were measured concurrently with pupil reactions and skin conductance reactions in a habituation paradigm. One group of subjects (n = 16) was given 36 simple visual stimuli and a second group (n = 16) 36 complex visual stimuli of equal duration, brightness and dimensions. No task-relevance was given to the stimuli. Under these circumstances we found rapid habituation (within 6 trials) of the vertex N1. Because we used long, variable interstimulus intervals, the N1 decrease could not be explained by refractory effects. Habituation rates of N1 and the concurrently measured SCR did not differ. Although the P3 showed significant habituation over the 12 trials (except at Oz), it habituated slower than the N1 and the SCR. The complex stimulus condition elicited larger P3b waves. No effect of stimulus complexity was found on the N1 and the SCR. The relevance of these results for the OR is discussed.

Effect of the orienting response on sensory discriminability

The effects of orienting responses to different types of stimuli on acquisition of information were studied. Subjects underwent a standard habituation series of 15 trials. On Trial 16, they received one of following three stimuli: (a) no-change stimulus--same stimulus as habituation stimulus, (b) innocuous-change stimulus, (c) significant-change stimulus--the subject's own name. These orienting stimuli were followed 500 msec. later by an imperative stimulus (100 msec.) which contained a number of Chinese characters. The subjects were then unexpectedly asked to recall and recognize these characters. Recall and recognition were consistently superior in conditions with significant and innocuous change relative to no change, which indicated that the orienting response to unexpected stimuli is related to a generalized perceptual enhancement. The data pose problems for the position that the orienting response reflects only the passive 'registration' of the eliciting stimulus information. While digital pulse-amplitude data showed no difference among the conditions for the change trial, these conditions were differentiated by electrodermal and cardiac changes.

The effect of stimulus significance on relatively sustained (tonic-like) and relatively transient (phasic-like) aspects of electrodermal, heart rate, and eyeblink response

To examine the influence of stimulus significance on more sustained as well as transient aspects of electrodermal, cardiac (HR), and eyeblink response, a 21-sec tone was sounded in one ear or the other. A click occurred during many tones, and a light followed offset by 9 sec. Four groups were studied: one pressed a pedal immediately on hearing any click; another only on click during tone in a specified ear; a third also responded only to the specified ear, but withheld press until the light; a fourth listened without any response. Results confirmed the important role of stimulus significance in each system whether between- or within-subject comparisons were made. Sustained responses were seen only when a significant signal was sought, involving in each case sustained HR deceleration, slowed blink rate, and heightened electrodermal level. Transient response to click and light also appeared only when there were significant signals. Response to tone-onset gave more ambiguous results. ANOVAs of response magnitude suggested that onset of nonsignificant tones might have elicited ORs, while binomial tests indicated these were not elicited with better than random frequency anywhere but on those trials occurring more frequently at the experiment's onset. Interpretations consistent with both the significance hypothesis and with a distinction between automatic and voluntary ORs can be made only here. Motor response had no effect on electrodermal or eyeblink response, and on HR was associated only with increased acceleration 1-2 sec after pedal-press. Studies using small motor responses to establish stimulus significance are therefore not likely to be substantially biased by the response itself.

Stimulus information and habituation of the visual event related potential and the skin conductance reaction under task-relevance conditions

The influence of information value of visual stimuli on habituation of event related potentials (ERPs) at Fz, Cz, Pz and Oz and of the skin conductance reaction (SRC) was investigated under task-relevance condition. An improved Wiener filter was used to reduce the number of stimulus presentations to estimate an ERP. Twenty-six subjects received two times a block of 36 stimulus presentations. Half of the subjects received a stimulus with a high information value in terms of complexity and then a stimulus with a low information value. The other half of the subjects received the reversed order. Wiener filtered ERPs and SCRs were determined over ensembles of six stimulus presentations. The habituation of the P300 component was restricted to the fronto-central leads, and was delayed when compared to the results of a former study (Woestenburg, Verbaten and Slangen, 1981b) where non-signal stimuli were used. Also information effects were noticed on these fronto-central leads, but not on the SCR. This reaction habituated as in the former non-signal study. The P300 at the parieto-occipital leads showed larger amplitudes than the fronto-central P300 and these components did not habituate. At the Oz lead early waves habituated and late waves increased during ensemble 1 to 6.