Control of responding by sounds of different quality: an evolutionary analysis.

Two experiments investigated the acquisition of discriminations between two acoustic stimuli of different quality (noise bursts vs. a 2-kHz pulsed signal) when features of the everyday environment were incorporated into the experiments. In Experiment 1, rats were trained, using food, to press a lever. Throughout all sessions, 5-s trials of noise bursts (the random stimulus) were presented, after variable intertrial intervals, through a remote speaker mounted outside the experimental enclosure. The noise burst occurred randomly with respect to reinforcement of lever pressing and had no programmed relationship to the animal's behavior. When lever pressing was established, the 2-kHz signal was presented through a speaker adjacent to the response lever according to a different set of variable intertrial intervals. A response in the presence of the 2-kHz signal terminated the trial and was reinforced. The 2-kHz signal acquired control of responding within the first few trials, whereas the random stimulus exerted no control of responding. In Experiment 2, rats were trained to press the lever in the presence of the 2-kHz signal presented through the adjacent speaker on a variable intertrial interval. After 14 sessions, 5-s trials of noise bursts (random stimulus) were presented through the remote speaker on the second variable intertrial interval. The random stimulus initially elicited exploratory behavior, which then rapidly declined. Subsequently, the random stimulus exerted no or weak control of responding. The introduction of the random stimulus had no effect on responding in the presence of the adjacent stimulus. In Experiments 3 and 4 the random stimulus was presented through the adjacent speaker, and the stimulus correlated with reinforcement was presented through the remote speaker. In both experiments, there was persistent control of responding by the random stimulus and slow development of control by the stimulus correlated with reinforcement. In Experiment 5, both stimuli were presented through the adjacent speaker. There was persistent control of responding by the random stimulus.     

Acute neuropsychological consequences of coronary artery bypass surgery

This study examines a series of coronary artery bypass patients (CABS) for neuropsychological and regional cerebral blood flow (RCBF) changes at 8 days and 8 weeks post surgery. Seventy-three percent were found to have moderate or severe neuropsychological deficits at 8 days post operation and 37% at 8 weeks post surgery. A comparison group of major vascular and thoracic surgery patients was also found to have a significant proportion of neuropsychological deficit following surgery. The RCBF assessments indicated a significant drop in mean RCBF at 8 days post surgery in the coronary artery bypass group which did not persist to 8 weeks. The comparison group showed no changes in RCBF following surgery. The findings suggest different patterns of recovery and origins of the neuropsychological deficit in the two groups and emphasize the need for appropriate control groups in studies examining the cortical effects of extracorporeal circulation. In addition, the project received generous support from the special trustees of the Middlesex Hospital.     

The component awareness and accuracy of dual- and single-jointed actions

The accuracy with which people execute wrist and elbow movements were measured using three main conditions: (i) single-jointed (wrist or elbow) movements to targets, (ii) dual-jointed (wrist and elbow) movements to targets, and (iii) components of dual-jointed movements to targets, when the task for the subject was to perform the elbow or wrist constituent of the action in isolation, without displacing the second joint. Elbow precision was significantly worse under component than dual conditions, which is compatible with the notion that wrist and elbow activity are conjugately, rather than independently, programmed when a dual-jointed action is performed. The pattern of wrist accuracy was divergent, but possible reasons for this were discussed. In all cases, error was measured in terms of deviation from perfect posture; using this index, the hypothesis that incorporating more moving joints into an action serves to increase movement complexity and jeopardise precision was tested, but the results were ambiguous. Discussion also centered on the problems of using performance data to infer changes in motor programming, and the need for rigorous conceptualisation and research in this area.     

Control of responding by the location of an auditory stimulus: role of rise time of the stimulus

The control of responding by the location of tone bursts of 0.2- or 50-msec rise time was investigated in three albino rats. The apparatus consisted of an enclosure with two levers, two loudspeakers (in different locations), and a dipper feeder. The animal was exposed to tone bursts from either one or the other of the two speakers, and the speaker through which the tone bursts were delivered on any particular trial alternated in an irregular manner. Responses on one lever were reinforced with food in the presence of tone bursts from one speaker; responses on the second lever were reinforced with food in the presence of tone bursts from the second speaker. Responding came under the control of the location of 4-kHz tone bursts of 0.2-msec rise time within the first session. At this rise time, animals maintained a stable level of correct responding of greater than 95%. When the rise time was increased to 50 msec the percentage of correct responding fell to an average of 80 to 85%. It was concluded that location of an auditory stimulus is a powerful controller of responding in rats and that the degree of control is dependent upon rise time.     

Loss of negative priming following sleep deprivation

It has been argued that one night of sleep loss in young healthy adults produces changes similar to that associated with normal, healthy ageing—in particular, that young sleep-deprived adults perform similarly to 60-year-old sleep-satiated adults on some tasks of frontal lobe function. This proposition was examined using a protocol viewed by many to be a direct probe of nonvolitional attention mechanisms associated with frontal lobe function. A negative priming (NP) procedure was used to compare performance between non-sleep-deprived (NSD) and sleep-deprived (SD, 34 hr) young, healthy adults. This protocol allowed for exploration of two theories of the NP effect based on inhibitory or memorial processes. Under conditions believed to facilitate inhibitory processes a normal NP effect was found for NSD(16 ms) and SD (9 ms) participants. Under conditions believed to rely on memorial processes there was no NPeffect following SD, compared with a normal NP effect for NSD participants (11 ms). Distractor interference was also greater following SD. These findings do not suggest a similar pattern of change following sleep loss in healthy young adults to that of normal, healthy, non-sleep-deprived aged groups.