We report research on different phasic evoked cardiac responses associated with differences in cogintive activity.These were examined in relation to a stable individual difference variable, mean simple reaction time (RT). Individual means on RT were found to be sufficiently stable over a 10 month period to consider them as individual functional characteristics. Subjects were divided into two subgroups on the basis of the first measure of their individual mean RT (above and below the group median). Each subject received 10 innocuous auditory stimuli with randomly varying interstimulus intervals. Stimuli were presented in one of two conditions defined by instructions allowing them to ignore (irrelevant condition), or requiring them to count the stimuli (relevant condition). A main effect of instruction was obtained in the evoked cardiac response. The initial heart rate deceleration was significantly larger in the relevant condition. Short-RT subjects had smaller heart rate changes to the irrelevant stimuli. The data are discussed in terms of the intensity of stimulus processing (both physical and cognitive) as a factor which may be related fundamentally to stable individual differences in RT.
A reaction time study with normal human subjects was conducted to obtain support for one or the other model of interhemispheric relations - referred to as the one-system and the two-systems hypotheses. 12 subjects were extensively trained in a complex reaction time task consisting of a "priming sub-task" which introduced interhemispheric interference and two different "test sub-tasks" measuring the generalization of interference. The interference priming produced visible slowing of RT's on subsequent trials. Interestingly, the deterioration of the two test sub-tasks was alike, despite the marked difference in the amount of the interhemispheric communication they required. This result is more in line with the one-system hypothesis, as the two-systems hypothesis predicts deterioration proportional to the amount of the required interhemispheric communication.
The main topics of time and timing in psychology, cognitive neuroscience and biology have been formulated already in the nineteenth century. Unfortunately, time and timing as a challenging topic has been put to rest for quite some time, but has become a central issue again during the last years. It has become clear, that perceptual or cognitive processes can only be understood if the dimension of time is taken more seriously. The reduction of complexity in neuronal systems is for instance, achieved by temporal integration mechanisms which are independent of the content of a percept or a cognitive act but are presemantical operations. It is essential to distinguish between content functions and logistical functions that provide presemantically defined temporal frames for mental activity.
Based on previous work indicating different neural substrates, two aspects of energetic state, 'arousal' and 'activation', have been conceptualized separately in our laboratory. 'Arousal' has been defined as the energetic state at any particular time, and task-related 'activation' as the task-related change in state from resting baseline to the task situation. Both are reflected in electrodermal activity and measured by skin conductance level. Our previous studies in this area have indicated that physiological responses to stimuli in a task are dependent on the arousal level at the time of stimulus presentation, rather than the task-related activation. In contrast, performance on the task is dependent on the task-related activation, rather than the current arousal level. That is, different aspects of the individual's state determine physiological and behavioral responses. Those studies had examined between-subjects differences in arousal and activation. The present study investigated the relevance of this separation in an across-subjects examination of fluctuations in arousal and activation, and their effects on physiological and behavioral responses, during a continuous performance task. It was found that the magnitude of the phasic orienting reflex to the targets during the task was dependent mainly on arousal, rather than task-related relative activation. Reaction time improved with increasing relative activation, but not with arousal. These findings support our earlier conclusions relating to the usefulness of arousal and activation as distinguishable features of the energetics of physiological and behavioral functions.
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