The effect of signaled reinforcement availability on concurrent performances in humans

During Phase I, three female human subjects pressed a button for monetary reinforcement in two-component concurrent variable-interval schedules. Five different reinforcement frequencies were used in component A, whereas the reinforcement frequency in component B was held constant. Absolute rates of responding conformed to equations proposed by Herrnstein to describe concurent performances, and the ratios of the response rates and the times spent in the two components conformed to the matching law. During Phase II, the availability of reinforcement in component A was signaled by the illumination of a lamp. This resulted in suppression of response rates in component A and elevation of response rates in component B, these changes being reflected in a distortion of the matching relationship which took the form of a bias in favor of component B.     

Effect of variable-interval punishment on the behavior of humans in variable-interval schedules of monetary reinforcement

One male and three female human subjects pressed a button for monetary reinforcement under a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtraction of money) according to a variable-interval 170-second schedule. In the absence of punishment, the rate of responding was an increasing negatively accelerated function of reinforcement frequency, as predicted by Herrnstein's equation. The effect of the punishment schedule was to suppress responding under lower frequencies of reinforcement; responding under higher reinforcement frequencies was much less affected. This was reflected in an increase in the value of K_H (the constant expressing the reinforcement frequency corresponding to the half-maximal response rate), whereas there was no significant change in the value of R_max (the constant expressing the maximum response rate). Previous results had shown that variable-ratio punishment resulted in a change in the values of both constants (Bradshaw, Szabadi, and Bevan, 1977). The results of the present study were consistent with the concept that the suppressive effects of punishment on responding depend on the nature of the punishment schedule.     

Pupil size and problem solving

Pupil size changes were monitored during the solution of various types of problems. A number of solution and response strategies were required of the subject. There was strong confirmation of the theory that this autonomic index can provide a sensitive measure of the fluctuating levels of attention and arousal, which are associated with the various aspects of information processing and response.     

Effect of punishment on human variable-interval performance

Three female human subjects pressed a button for monetary reinforcement in a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtracting money) according to a variable-ratio 34 schedule. In the absence of punishment, rate of responding was an increasing negatively accelerated function of reinforcement frequency; the relationship between response rate and reinforcement frequency conformed to Herrnstein's equation. The effect of the punishment schedule was to suppress responding at all frequencies of reinforcement. This was reflected in a change in the values of both constants in Herrnstein's equation: the value of the theoretical maximum response-rate parameter was reduced, while the parameter describing the reinforcement frequency corresponding to the half-maximal response rate was increased.     

Attention and hemispheric differences in reaction time during simultaneous audio-visual tasks

The effect of different types of competing auditory tasks on laterality differences in visual perception was investigated. Right-handed subjects were presented with digits which occurred randomly in the left or right visual fields. They responded vocally to previously specified digits in a go, no-go reaction time situation. In the absence of any competing auditory task, digits presented in the right visual field were processed more quickly. This visual field difference in reaction time was in the same direction while subjects performed a secondary musical task. However, when a secondary verbal task had to be performed, digits in the left visual field received faster responses. The results support the view that the right hemisphere is capable of some language functions, and that hemispheric differences in performance have at their basis a quantitative asymmetry, which can be reversed even in normal subjects by overloading their limited capacity.     

2-D tilt and 3-D slant illusions in perception and action tasks

There is now a well established dissociation between perception and action based primarily on neuropsychological evidence [Milner and Goodale, 1995 The Visual Brain in Action (Oxford: Oxford University Press)]. Although equivocal, an important source of evidence from normal observers is that 'perceptual illusions' may affect the systems differently. We investigated the relative effects of 2-D tilt and 3-D slant illusions in the two domains, using similar tasks to those employed originally by Milner and Goodale. Subjects were required to either post a card through, or set a paddle to match the orientation of, a plane that was presented in two conditions: surrounded by a striped surface tilted between +90 degrees and -90 degrees (2-D tilt contrast), or surrounded by a disparity defined surface slanted in depth between +60 degrees and -60 degrees (3-D depth contrast). For 2-D tilt, action and perception were equally affected by the illusion, whereas in the 3-D condition they were not. Here, the illusion appeared greater in the posting than in the perceptual task. We conclude that, although no qualitative differences exist, there were quantitative differences between perception and action tasks in the binocular condition.     

The ability to orient attention in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome is characterised by tics, although patients also commonly present with attentional problems. This experiment aimed to ascertain whether TS patients have problems in orienting attention, via the use of a vibrotactile choice reaction time task. Participants were required to push a button in response to a faint vibration delivered to the index finger. Prior to each stimulus vibration, a pre-cue (valid, neutral or invalid) was administered to the finger. The performance benefits and costs participants gained from valid and invalid precues were calculated. Contrary to our prediction TS patients did not show significantly different costs or benefits. Furthermore, both patients and controls showed an equal and increased benefit in the crossed arm posture, compared to the uncrossed. These results suggest TS patients do not generally have problems in orienting attention. In addition, in the tactile modality, both patients and controls may benefit from directed attention when difficulty levels are maximal.     

Directed attention in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (TS) is a basal ganglia (BG) disorder, associated not only with hyperkinetic movements but also with attentional impairments. This experiment sought to ascertain whether overt direct visual attention would influence tactile attentional performance in TS, via the use of a vibrotactile choice reaction time procedure involving biased probabilities of event occurrence. Participants were required to look (i.e., direct gaze) either at the hand receiving the most (expected) vibrations, or the hand less often stimulated (the unexpected), for both crossed and uncrossed arm postures. Contrary to our predictions, gaze did not influence attentional performance in TS patients. Furthermore, patients were found not to be sensitive to distributions of event probability; that is, they did not demonstrate normal expectancy effects like controls. Attentional deficits in TS (as in Parkinson's disease, another BG disorder) may pertain more to difficulties in holding rather than in shifting the focus of attention. Moreover, directing attention towards the unexpected locus in the crossed arm posture improved overall performance in both patients and controls, suggesting that increased task demands (e.g., crossed arm posture), and/or unexpected stimulus location, may be alleviated by directed attention. These impairments may stem from dysfunction in the circuits linking the frontal lobes with the BG.