A series of experiments examined the effects of lesions of the dorsal noradrenergic bundle (DNAB), induced by 6-hydroxydopamine (6-OHDA), on the behavioural response to systemic and intra-accumbens amphetamine, using a rat analogue of Leonard's 5-choice serial reaction time task for humans. Although the 6-OHDA DNAB lesion produced a profound depletion of cortical noradrenaline (NA) (to around 5% of control levels) it did not impair any aspect of performance on this task. Both systemic and intra-accumbens amphetamine increased behavioural measures of impulsivity of responding, but neither impaired discriminative accuracy in the sham-operated control rats. However, the DNAB lesioned rats did show a discriminative impairment following both low doses of systemic amphetamine, and intra-accumbens amphetamine. The latter effect was antagonised by systemic administration of the specific dopaminergic (DA) antagonist alpha-flupenthixol. The DNAB lesion did not alter the effect of amphetamine on any other behavioural measure, including speed and impulsivity of responding. These results suggest that although DA and NA participate in qualitatively different behavioural processes, the effects of DNAB lesions on attentional processes depend on the level of DA activity within the nucleus accumbens.
Experiments were performed to investigate the retardation of motor reactions, triggered immediately after saccadic eye movements, by comparing VEP latencies and manual reaction times. As visual stimuli grating patterns of different spatial frequencies were used. They were presented during continuous fixation (“resting eye” condition) as well as shortly after a saccade (“saccadic” condition) with different onset delays (25, 50, 100, 150 msec), in order to determine the influence of saccades on VEP latencies and on manual reaction times. Compared with the reaction times in the “resting eye” condition, the postsaccadic reaction times were much prolonged whereas the respective VEP latencies are almost unchanged. Thus an inhibitory interaction of different motor responses (i.e. saccadic eye movements and manual reactions in this study) at higher levels of the afferent system or at the motor control site is postulated. This result has been confirmed for stimuli of different spatial frequencies.
Thirty-six subjects were each tested in three sessions on separate days, in which they were given 0, 0.33 or 1.0 ml alcohol per kg body weight (the order of administration being counterbalanced across subjects). Performance on two tasks requiring both speed and accuracy was studied in all three sessions. The first was a four-choice serial reaction time task in which the subject had to press one of four keys in response to four stimuli ( A, B, C and D) presented in a random order. The second was a visual search task requiring the cancellation of two targets (the digits ‘0’ and ‘1’) from a random sequence of letters. Compared to no alcohol, the small dose did not affect speed but improved accuracy in both tasks, while the large dose impaired speed in the first task and accuracy in the second. The results therefore demonstrate that the effects of alcohol on performance are dependent upon both the quantity ingested and the particular task required.
Ten patients with Parkinson's disease performed a simple reaction time task in which, on hearing a tone, they pressed a button with the left thumb. In the first experiment tones sometimes occurred unannounced and at other times were preceded (by between 0 and 3200 ms) by a warning signal. The second experiment was identical to the first except that the subject had simultaneously to perform a simple continuous task with his right hand. Patients had slower reaction times than controls under all circumstances. In general, however, the effect of a warning signal and the effect of a second task were the same for both groups. In the control group the effect of a warning signal depended on whether or not a second task was being performed. Specifically, the advantage of a warning signal for reaction time was lost after long intervals (greater than 200 ms) when a second task was being performed. Parkinson's disease patients lost this advantage even when they were not performing a second task. Animal studies have suggested that dopamine deficiency results in an increase in neural "noise" in the basal ganglia. The behavioural consequences of this may be that Parkinson's disease patients always perform as if they were carrying out another task at the same time. In contrast, their ability to benefit from a warning signal and to allocate attentional resources are unimpaired.
Subjects identified as electrodermally labile or stabile ( n = 10 per group) on the basis of non-specific electrodermal fluctuations and a trials-to-criterion measure of habituation were compared in a simple reaction time (RT) task that employed long, variable foreperiods (from 8 to 19 s). Labiles had significantly faster RTs across all foreperiods, but there were no differences in RT variability between the groups. Phasic heart rate responses recorded concurrently through the foreperiod showed a characteristic pattern of acceleratory and deceleratory activity, which was similar among both labiles and stabiles. The findings indicate that labiles and stabiles show a consistent difference in the speed of processing of a target imperative stimulus, which is not due to differences in response preparation processes. Overall, the results support the use of RT paradigms for evaluating individual differences in information-processing associated with electrodermal lability.
Laboratory measures of visual reaction time suggest that some aspects of high-speed ball games such as cricket are ‘impossible’ because there is insufficient time for the player to respond to unpredictable movements of the ball. Given the success with which some people perform these supposedly impossible acts, it has been assumed by some commentators that laboratory measures of reaction time are not applicable to skilled performers. An analysis of high-speed film of international cricketers batting on a specially prepared pitch which produced unpredictable movement of the ball is reported, and it is shown that, when batting, highly skilled professional cricketers show reaction times of around 200 ms, times similar to those found in traditional laboratory studies. Furthermore, professional cricketers take roughly as long as casual players to pick up ball flight information from film of bowlers. These two sets of results suggest that the dramatic contrast between the ability of skilled and unskilled sportsmen to act on the basis of visual information does not lie in differences in the speed of operation of the perceptual system. It lies in the organisation of the motor system that uses the output of the perceptual system.
Three experiments investigated the nature of the single‐item visual recency effect in the serial choice reaction‐time task (Rabbitt & Vyas, 1979; Walker & Marshall, 1982). The first experiment demonstrated that, like single letters varying in case, pictorial stimuli yield visual priming that is limited to consecutive stimuli and is unaffected by the presentation of an irrelevant stimulus in the response‐stimulus interval. The second experiment confirmed that repeating a picture produces facilitation over and above repeating the object that it portrays. In addition, it was observed that name priming, but not visual or object priming, decreases with practice. This indicated that visual priming and object priming occur during identification. Finally, in Expt 3, an irrelevant picture was presented unpredictably in the response‐stimulus interval. Previous results had suggested that this manipulation would provide evidence for distinct visual and object codes. Although the results were inconclusive, they do indicate that time intervals and presence of intervening information per se do not explain the loss of visual and object priming effects. It was suggested that the unpredictable irrelevant stimulus may have been disrupting a process whereby memory and perception interact directly at the level of a visual code.
A neurophysiological technique that quantifies drowsiness as the speed of falling asleep at intervals across a day is used to identify patterns of sleepiness/alertness. The Multiple Sleep Latency Test (MSLT) reveals a daily biphasic organization of sleepiness that is affected in predictable ways by the length and continuity of nocturnal sleep on one or several nights, and by maturation, aging, sleep pathology, and drug ingestion. The systematic nature of these relationships provides impetus to efforts examining the neurobiological mechanisms subserving the delicate balance of sleep and wakefulness.
Stimuli presented in a non-attended location are responded to much slower than stimuli presented in an attended one. The hypptheses proposed to explain this effect make reference to covert movement of attention, hemifield inhibition, or attentional gradients. The experiment reported here was aimed at discriminating among these hypotheses. Subjects were cued to attend to one of four possible stimulus locations, which were arranged either horizontally or vertically, above, below, to the right or left of a fixation point. The instructions were to respond manually as fast as possible to the occurence of a visual stimulus, regardless of whether it occurred in a cued or in a non-cued location. In 70% of the cued trials the stimulus was presented in the cued location and in 30% in one of the non-cued locations. In addition there were trials in which a non-directional cue instructed the subject to pay attention to all four locations. The results showed that (a) the correct orienting of attention yielded a small but significant benefit; (b) the incorrect orienting of attention yielded a large and significant cost; (c) the cost tended to increase as a function of the distance between the attended location and the location that was actually stimulated; and (d) an additional cost was incurred when the stimulated and attended locations were on opposite sides of the vertical or horizontal meridian. We concluded that neither the hypothesis postulating hemifield inhibition nor that postulating movement of attention with a constant time can explain the data. The hypothesis of an attention gradient and that of attention movements with a constant speed are tenable in principle, but they fail to account for the effect of crossing the horizontal and vertical meridians. A hypothesis is proposed that postulates a strick link between covert orienting of attention and programming explicit ocular movements. Attention is oriented to a given point when the oculomotor programme for moving the eyes to this point is ready to be executed. Attentional cost is the time required to erase one ocular program and prepare the next one.