Imperative Signal Research Articles

Intensity of imperative signal influences on redundancy deficit and latency in process schizophrenics.

The resilience of the redundancy deficit pattern of schizophrenic reaction time performance was explored by examining the resistance of redundancy deficit to an experimental manipulation of imperative signal intensity. Aversive levels of stimulation have been used to alter motivation and shown to normalize schizophrenic performance in other research. In this study, 20 schizophrenic patients were administered a reaction time task under conditions of usual motivation and, 1 day later, under conditions of aversive motivation induced by high decibel levels of stimulation. The redundancy deficit pattern was observed with usual motivation but not with so-called biological motivation. The results are discussed from the points of view of the utility of redundancy deficit as an index of vulnerability to schizophrenia, implications for attentional and motivational theories of schizophrenia, and finally, in terms of the more general role of aversive stimulation in schizophrenic deficit. The finding that redundancy deficit is ameliorated by aversive motivation is consistent with theories suggesting that schizophrenics respond primarily to negative motivation. Garmezy's suggestion that the common denominator of the multiplicity of schizophrenic deficits may lie in motivational factors, particularly the prepotent avoidance motive, is supported by these results.

Motor Preparation at a Cortical and at a Peripheral Level

Publisher Summary This chapter discusses motor preparation at a cortical and at a peripheral level. When interstimulus intervals (ISIs) of long duration are used, at least two slow negative potentials are observed between a warning signal (S 1 ) and an imperative signal (S 2 ). The first potential has the form of an inverted U-curve, which reaches its peak within 1 sec after S 1 , whereas the second potential gradually develops during the ISI, and reaches its maximum toward the end of this interval. The first potential seems to be dependent on the physical and the psychological properties of S 1 , whereas the second potential seems to be affected by the type of task required at S 2 . Because of its occurrence toward the end of the ISI and its contingency to S 2 , the second potential seems most closely to resemble the “classical CNV” obtained with short ISIs (e.g., 1 sec), and therefore it is called terminal CNV.

Spinal reflexes as indicator of motor preparation in man

During the fixed foreperiod (4 sec) of two reaction time experiments, using 80 subjects, Hoffman reflexes were simultaneously evoked in both legs in a pseudorandom order at 13 different measuring points. The purpose of the study was to investigate the time course of amplitude changes in both legs, in muscles both involved and not involved in the response. In Experiment 1, subjects responded after the imperative signal by a plantar flexion of either the right or left foot. Thus, reflexes were evoked via the motoneuron pool relevant for the response and via the contralateral irrelevant pool. In Experiment 2, subjects pressed a button with either the right or the left index finger. Thus, reflexes were evoked via motoneurons, irrelevant for the response. Reflex amplitudes during the foreperiod were larger than during the intertrial interval (ITI). An early increase was found at 100–200 msec after the warning signal. Thereafter, amplitudes decreased but remained larger than during the ITI. After 1,000 msec, a steady increase was found, with the largest amplitudes near the end of the foreperiod. Amplitude changes were not different for relevant and irrelevant muscles. It was concluded that the second increase might be part of a motor preparation process.

Occipital rhythmic activity within the alpha band during conditioned externally paced movement

The time-dependent behaviour of the power within the alpha band during conditioned movement was studied from the scalp EEG of 9 normal humans. Two tasks were used: (1) button pressing at imperative signal S 1 and release at signal S 2; (2) button pressing at imperative signal S 2, preceded by warning signal S 1. Together with a complex correlate of the CNV and EPs, the components of power decrease related to initiation of movement were not clearly identifiable in the central areas. They were sharply isolated in the occipital areas, using tone as the imperative signal. During initiation of movement a significant short-lasting decrease in power of the occipital alpha activities was observed in all 9 subjects. However, ‘mu activity’, tested in the classical manner and with help of power spectra, was not present in some of these subjects.

Orienting and defensive responding in the electrodermal system: palmar-dorsal differences and recovery rate during conditioning to potentially phobic stimuli.

ABSTRACTIt was suggested that the effects of fear‐relevant pictures as conditioned stimuli (CSs) for electrodermal responses may be explained if it is assumed that they produce conditioned defense responses (DRs), as opposed to the orienting responses (ORs) that are produced by fear‐irrelevant stimuli. Some propositions in Edelberg's theory of electrodermal activity were used to differentiate between DRs and ORs in a test of this hypothesis. Groups of subjects were conditioned to fear‐relevant (snakes and spiders) or fear‐irrelevant (flowers and mushrooms) CSs by means of an aversive (electric shock) or a non‐aversive (imperative signal for a reaction time (RT) task) unconditioned stimulus in long interval differential paradigms. The neutral‐shock, phobic‐RT, and neutral‐RT groups showed no palmar‐dorsal differences either in magnitude, probability or amplitude, and no conditioning in the recovery rate measure. However, the phobic‐shock group showed a peak of dorsal magnitude early in training that subsequently habituated whereas the palmar magnitude data indicated a gradual conditioning effect that lasted throughout the 20 extinction trials. In addition, it showed slower recovery to the reinforced than to the nonreinforced stimulus. These data are taken as support for the hypothesis.

An early cue sometimes impairs process schizophrenic performance

BACKGROUND The simple reaction time task THE SIMPLE reaction time task is well known for its sensitivity to schizophrenic pathology. The precision of the procedure, the replicability of results, and the salience for theorizing about the nature of attentional deficits in schizophrenic pathology have made it a virtual “north star” of schizophrenia research.1 In its basic form the task has three primary stimulus features comprised of two signals with a delay interval between. The first signal is an alerting or “ready” signal designed to announce the beginning of each trial. Following that signal there is a delay of preparatory interval during which the subject has been asked to wait vigilantly for the second stimulus which serves as a signal-to-respond. The response is generally a finger lift or a retraction from a telegraph key. These task features have been studied to learn how procedural variation interacts with schizophrenic pathology. The latency of response, recorded in milliseconds, is generally used to assess experimental and subject variation. Maximum attention has been given in the literature to the study of two of these features. The signal-to-respond or imperative signal has been investigated in terms of the intensity,2 the modality,3 and the modality relationship among trials.4 The delay interval, or preparatory interval, has been investigated in relation to the length of the delay and the predictability of the various delays used across trials. 5 Studies of these two features have provided support for various theoretical constructions of schizophrenic pathology, for example, SHAKOW~ and ZUBIN.6.

Event-related cortical desynchronization detected by power measurements of scalp EEG

Changes in the background EEG activity occurring at the same time as visual and auditory evoked potentials, as well as during the interstimulus interval in a CNV paradigm were analysed in human subjects, using serial power measurements of overlapping EEG segments. The analysis was focused on the power of the rhythmic activity within the alpha band (RAAB power). A decrease in RAAB power occurring during these event-related phenomena was indicative of desynchronization. Phasic, i.e. short lasting, localised desynchronization was present during sensory stimulation, and also preceding the imperative signal and motor response (motor preactivation) in the CNV paradigm.

Event-related brain potentials in selective response

Event-related potentials were recorded during performance of a simple reaction task and two selective response tasks differing in the intensity of the non-key stimulus. Known differences in reaction time between these tasks were confirmed, but there were no corresponding differences in amplitude of the slow potential shift which develops in the EEG in anticipation of the imperative signal. Since this anticipatory potential is not affected by event uncertainty, it seems to be related to motor preparation rather than to expectancy. Performance differences between simple and selective response tasks appear to depend not upon differential preparation, but upon selective processing of the imperative signal, which is reflected in the N120 component of the visual evoked response to that signal.

Sex differences in performance and associated cardiac activity during a reaction time task

Measures of reaction time and cardiac activity were recorded from 10 males and 10 female subjects during a variable foreperiod reaction time task. Males showed faster reaction times, greater cardiac decelerations, and higher levels of heart-rate variability during the foreperiod. Trend analyses revealed sex differences in the heart-rate response to the onset of the warning signal, but not in the response to the imperative signal. These results indicate that those measures of cardiac activity which have been shown previously to predict performance tend to differentiate between the sexes when there are sex differences in performance.

The impact of warning signal intensity on reaction time and components of the contingent negative variation

Slow EEG potentials were recorded during performance of a simple reaction task in which warning signal intensity was varied from trial to trial under foreperiod durations of 1, 3 and 8 sec. As shown by speed of reaction, the warning signal had an activating effect which increased with its intensity and decreased with foreperiod duration. This effect was related to the amplitude of a slow potential which appears in the EEG shortly after presentation of the warning signal. This potential is interpreted as a component of the orienting response regulating sensitivity to subsequent stimulation, so that reaction time is affected through change in the effective intensity of the imperative signal.

Slow potential changes and choice reaction time as a function of interstimulus interval

Slow potential changes were recorded over the vertex (C z) during a choice reaction task. The constant interstimulus interval (ISI) between the visual warning (S 1) and the visual imperative signal (S 2) was either 200, 400, 1000 or 2000 msec. The contingent negative variation (CNV) was not only measured between S 1 and S 2 (CNV 2), but also before S 1 (CNV 1). The main results were: (1) The CNV 2 amplitude showed significant variation as a function of ISI. It reached its maximum with an ISI of 1000 msec. (2) CNV 1 developed only before the short ISIs (200 and 400 msec). (3) When CNV 1 and CNV 2 were summed the differences in CNV amplitudes and durations between different ISIs became smaller. (4) The peak-to-peak amplitude P 1-N 1 of the potential evoked by S 1 was enhanced with short ISIs. (5) The correlations between mean CNV and median reaction time (RT) were low but significant for ISIs of 400, 1000 and 2000 msec. When, however, the effect of subjects was partialized out these correlations were drastically reduced, whereas the partialization of session and block effects had no noticeable influence on these correlations. (6) The correlations between single RT and single CNV (measured for the ISI of 1000 msec, individually for two subjects) were weak or even completely lacking. The main conclusion was that CNV coincides with preparedness to react to a stimulus in a choice RT-task, but its amplitude at the moment of onset of the imperative stimulus does not reflect, or reflects weakly, the degree of preparedness (as indicated by RTs) at that moment.

Orientating responses of mentally retarded and normal subjects to word-signals.

GSRs of normal and retarded children of comparable CA were recorded during a 30‐min. vigilance task, which consisted of two signal and four non‐signal words. One of the signal words served as a warning signal, preceding the other, which was an imperative signal for buttton‐pressing. The warning signal evoked a greater number of GSRs in the normals than the imperative one; this was reversed for the retardates. GSR adaptation to signal words occurred at the same rate and level for both groups; but in adaptation to the non‐signal words the retardates maintained a higher level of GSR frequencies than the normals. These results were not congruent with an attentional deficit model of retardation.

Brain responses to semantic stimuli

IN A foregoing communication (Black and Walter, 1965) the probabilistic relation between stimulus association and anterior brain responses has been demonstrated. In particular (Walter, 1965), the development of the Contingent Negative Variation or “Expectancy Wave” has been found to follow very closely alterations in the significance of conditional stimuli, whether objective or subjectively manipulated by direct suggestion under hypnosis. While these experiments were in progress similar observations were being made on a large number of normal subjects and patients in order to ascertain the origin of the E-wave and its relation to physical and mental activity. Altogether, over 600 complete polygraphic records have been obtained from 320 people, including 190 children. In the early series of experiments the sensory stimuli were essentially “physiological” in the sense that they were fairly loud clicks or bright flashes of light, with no intrinsic meaning or interest. The “significance” of the conditional or warning stimuli was acquired by repeated experience of their association with the unconditional or imperative stimuli to which the subject had been instructed to respond by an operant action such as pressing a button. The circuit arrangements were such that this action would terminate the imperative stimuli only if the action were deferred until their onset; if the subject “jumped the gun” the operant action was ineffective. The inclusion of some action by the subject is an essential condition for the development and maintenance of the E-wave, which can persist through thousands of trials as long as the subject retains his interest. The abbreviation of the motor reaction time when the E-wave appears suggested that the cortical state is modified by the change of potential so as to defer the response until the correct moment, but accelerate its development when triggered by the arrival of the imperative signal. However, several chance observations during the early experiments indicated that although some response was necessary this did not have to be a simple motor action; in several subjects a purely mental event, amounting to a simple decision, was adequate to sustain an E-wave. The procedure was accordingly modified to permit the study of responses to stimuli intended to evoke a change in mental rather than motor state. At the same time it was also observed that the amplitude of the stimuli could be reduced to threshold level without affecting the E-wave, provided, again, that the subject maintained his interest and engagement. Even “negative” stimuli, that is the termination of a tone or light, were found to be adequate to evoke an E-wave when such an event was assigned conditional significance by association. In such conditions the primary responses in non-specific frontal regions are often small and long delayed but the subsequent E-wave is as large as when the stimuli are maximal. These observations corroborated the conclusion drawn from the early experiments, that the E-wave reflects only the subjective estimation of significance. Experiments were therefore made to analyse the brain responses to purely semantic stimuli in which the intrinsic significance or “amount of information” could be varied with only trivial