Imperative Signals Research Articles

Face/Agent Interference in Individual and Social Context

Two experiments studied the impact of irrelevant background faces on Go responses to imperative signals superimposed on them. Two major results were obtained. The first concerns a response time advantage of one's own face and a related advantage of familiar over unfamiliar faces. When the imperative signal was superimposed on the responding agent's own face, or the face of a sibling or friend, Go responses were faster as compared to unfamiliar faces. The second concerns the impact of social context. A slight increase of the own-face advantage was observed when the task was performed together with a co-actor. Importantly, this increase was only observed for unfamiliar, not familiar co-actors. The implications of these results are discussed in a framework for stimulus-based response selection which relies on two factors, face familiarity and face/agent compatibility.

Relation of Locus Coeruleus Neurons in Monkeys to Pavlovian and Operant Behaviors

Noradrenaline is released throughout the forebrain from locus coeruleus (LC) projections in close temporal proximity to emotional and goal-directed events. To examine interactive influences of these processes on LC neuronal activity, we used a task where Pavlovian and operant processes vary and can be easily identified. We recorded 69 single LC neurons from two monkeys performing a task where cues indicate the progression through schedules of one, two, or three operant trials. Pavlovian responses and phasic LC activations occur following the appearance of conditioned visual cues (54/69 neurons), especially those at the beginning of new schedules, whether the current trial will be rewarded (single trial schedule) or not (2 or 3 trial schedules), and after visual imperative signals eliciting the operant response (64/69 neurons), whether the current trial will be rewarded or not. The modulation of LC responses seems to be relatively independent of attention or motivation, because the responses do not covary with operant performance in the task. The magnitude of LC responses across the schedules varied in close relation to the intensity of Pavlovian behavior but these responses were also modulated by operant processes. Our conclusion is that LC activation occurs when task-relevant stimuli evoke a conditioned instinctive (Pavlovian) response, with the strength of the activation also being modulated by goal-directed processes. Thus locus coeruleus neurons broadcast information about stimulus-elicited primitive and goal-directed behaviors to forebrain structures important for executive functions and emotions.

Knowing when to respond and the efficiency of the cortical motor command: A Laplacian ERP study

The objective was to test whether motor preparation can modulate the efficiency of the cortical motor command. The electroencephalogram (EEG) was recorded from electrodes located over the primary sensorimotor cortices during the performance of a between-hand choice reaction time task in which foreperiod duration (the interval between the warning and the imperative signals, 800 vs. 2800 ms) was varied across blocks of trials. In order to increase the spatial resolution of the EEG traces, surface Laplacian was estimated. The amplitude of the negative wave developing over the hemisphere contralateral to the response was smaller for the short foreperiod associated with the best performance level. These results indicate that the activation of the primary sensorimotor cortex involved in the response is less pronounced for the short foreperiod, suggesting that temporal advance information increases the efficiency of the cortical motor command.

Event-related beta desynchronization in human subthalamic nucleus correlates with motor performance.

Although the basal ganglia play an important role in self-generated movement, their involvement in externally paced voluntary movement is less clear. We recorded local field potentials (LFPs) from the region of the subthalamic nuclei of eight patients with Parkinson's disease during the performance of a warned reaction time task in which an imperative cue instructed the subject to move or not to move. In 'go' trials, LFP activity in the beta frequency band ( approximately 20 Hz) decreased prior to movement, with an onset latency that strongly correlated with mean reaction time across patients. This was followed by a late post-movement increase in beta power. In contrast, in 'nogo' trials the beta power drop following imperative signals was prematurely terminated compared with go trials and reversed into an early beta power increase. These differences were manifest as power increases when go trials were subtracted from nogo trials. In six patients these relative beta power increases in nogo-go difference trials were of shorter latency than the respective reaction time. The findings suggest that, firstly, the subthalamic nucleus is involved in the preparation of externally paced voluntary movements in humans and, secondly, the degree of synchronization of subthalamic nucleus activity in the beta band may be an important determinant of whether motor programming and movement initiation is favoured or suppressed.

Parametric coupling and generalized decoupling revealed by concurrent and successive isometric contractions of distal muscles

In two experiments we examined the hypothesis of transient parametric coupling during the specification of peak forces of isometric contractions produced by the left and right hand. In the first experiment participants had to produce bimanual contractions with same and different target forces as rapidly as possible in response to an auditory signal; target forces were cued visually with variable cueing intervals. At short cueing intervals reaction times were longer when different peak forces had to be specified than when same peak forces were cued, and this reaction-time difference declined as the cueing interval was increased. Independent of the cueing interval intermanual correlations of peak forces, rise times, and reaction times were smaller in conditions with different peak forces than in those with same peak forces. In the second experiment imperative signals for left-hand and right-hand contractions were separated in time. Target forces for the first response were cued with variable cueing intervals, while for the second response the cues were presented simultaneously with the second imperative signal. Reaction time of the second response was longer when target forces for the two successive responses were different rather than same, and this reaction-time difference declined when the delay of the second signal was increased as well as when the cueing interval for the first response became longer. These results are consistent with the hypothesis of a transient cross-talk between concurrent processes of peak-force specifications; in addition they indicate generalization of the decoupling required to specify different peak forces concurrently to the specification of temporal response characteristics and to processes of response initiation.

Mechanisms of cardiac risk among professional drivers.

This literature review indicates that professional drivers have excess cardiac risk that is not fully explained by standard risk factors. The contribution of occupation is suggested by two independent methods and by psychophysiological studies during on the job driving. Driving has been conceptualized as a threat-avoidance task. Stimuli encountered in traffic are not inherently aversive but become so by association with driving experience, a formulation corroborated by laboratory studies in which stimuli such as car headlights elicit cardiovascular hyperreactivity and electroencephalographic signs of arousal in professional drivers. More-advanced neurophysiological methods (event-related potentials) show higher cortical electronegativity to imperative signals among professional drivers than among non-driver referents. These data are viewed in light of reports of possible associations between event-related slow potentials and cardiac risk. A clinically and ecologically relevant neurocardiological model is proposed, and preventive strategies, including workplace interventions, are suggested.

Physiological changes in a reaction time task: Further problems with Sokolov’s dimension of stimulus “significance”

Sokolov placed attentional and response requirements in the same dimension of stimulus significance, and proposed that these produced similar effects upon the magnitude and habituation rate of the OR. In a previous study, subjects were required to focus attention on stimulus events; here, the same stimuli served as imperative signals in a simple RT task. The effect of this manipulation upon several indices of the OR (GSR, respiration, HR, PPV, CPV, and EEG) failed to support Sokolov's position. The data obtained were used to further develop a hypothetical structure tentatively offered as a replacement of the unitary OR concept. The orienting response (OR) of Sokolov (1963) may be described as a unitary response system sensi­ tive to stimulus variation in three dimensions: novelty, intensity, and significance. Upon this response system has been built, by Sokolov and others, an elaborate theoretical structure concerned with the psychophysiological basis of perception and attentive processes. Barry (1975, 1976, 1977a, 1977b) has critically examined the foundations of this theoretical structure by comparing Sokolov's detailed predictions regarding stimulus-response relationships with experimental findings from parametric inves­ tigations. These have centered upon six psycho­ physiological indices: electroencephalographic (EEG) alpha rhythm levels, galvanic skin response (GSR), heart rate (HR), respiration, and cephalic and peripheral pulse volumes (CPV and PPV, respec­ tively). Changes in these measures have been inves­ tigated as a function of stimulus intensity (using auditory stimulation of from 20 to 50 dB SPL), novelty (by providing repeated cycles of the stimulus complex), and significance (indifferent stimuli vs. instructions to attend). Barry (l977a) reported that the dependent variables listed above exhibited such markedly different behav­ iors in response to manipulation of stimulus intensity and novelty that the concept of a unitary OR appeared untenable: only two of the six measures examined covaried to the extent of having similar relationships with these two independent variables. It would thus appear that the simple OR concept which has been widely accepted in western psychophysiology may be an extreme oversimplification, having little empirical basis. Barry (l977b) varied stimulus significance,

Contingent negative variation and evoked responses recorded by radio-telemetry in free-ranging subjects

1. 1. Using an 8-channel radio-telemetry system (RTE) records were obtained of the EEG, pulse rate, respiration, evoked responses and Contingent Negative Variation (CNV) in four normal subjects and three patients with intracerebral electrodes. The subjects were free to move about within 30 m of the receiving aerial. Two RTE channels were modified to provide time constants of 7 sec. 2. 2. Auditory stimuli, synchronized with the operation of average response computers, were transmitted to the subjects by a separate radio-control link. These were used as conditional and imperative signals to the subjects to perform various tasks: pressing a button to arrest the imperative signals, turning the pages of a book, inserting pegs in a peg-board and coming to a stop on a bicycle. 3. 3. Responses to the signals were averaged on line with two barrier-grid tubes and a 2-channel Enhancetron and the intrinsic rhythms were analysed with a 2-channel frequency analyser. The pulse rate was indicated by a cardiotachometer. 4. 4. The initil responses and CNV during the reception of paired auditory signals were similar to those seen with direct connection, provided that the subjects were engaged in some task related to the signals. The CNV was attenuated during exercise or conversation only while the subject was inattentive to the signals. 5. 5. The amplitude of the intracerebral responses to the conditional and imperative stimuli in the patients with implanted electrodes was reduced when the scalp CNV was attenuated by isolation or distraction. 6. 6. During the performance of fairly complex tasks following the auditory signals, the CNV terminated only at the completion of the task, not at the moment of muscular effort. 7. 7. The radio-control link was also used to instruct an experimenter when to loss a ball to a subject or to feint. In this situation also the CNV developed only when the subject was sure the ball was in the air and terminated when it was caught. 8. 8. These observations suggest that the interactions of evoked responses and CNV seen in laboratory conditions also accompany normal activity and the performance of everyday tasks.