The role of visual information in control of a constrained locomotor task

The nature of visually guided locomotion was examined in an experiment where subjects had to walk to targets under various conditions. Target distance was manipulated so that subjects had to (a) lengthen their paces in order to hit the target; (b) shorten their paces; (c) make no adjustments to their standard pace length at all. They did this under four visual conditions: (a) normal vision; (b) with vision restricted to a "snapshot" each time the foot that was to be placed on the target was on the ground; (c) with a snapshot each time the foot to be placed was in the swing phase; and (d) no vision after departure fro the target. The results show that the subjects succeed in reaching the target in most cases. However, the smoothness and fluidity of their movements vary significantly between conditions. Under normal vision or where visual snapshots are delivered when the pointing foot is on the ground, locomotion is smoothly regulated as the subjects approach the target. where snapshots are delivered when the pointing foot is in the swing phase, regulation becomes clumsy and ill coordinated. Where no vision is available at all during the approach, adjustments are made, but these are least coordinated of all. The results show that well-coordinated visual regulation does not require continuous visual guidance but depends on intermittent information being available at the appropriate times in the action sequence. Such timing is often more important than the total amount of information that is available for guidance.     

Choice between repleting/depleting patches: A concurrent-schedule procedure

Six pigeons responded on two concurrently available keys that defined patches with the following characteristics. Reinforcer stores repleted on a patch as a linear function of time when the bird had last responded to the other patch, or else did not replete. Repletion schedules thus timed only when the bird was absent from the patch. Reinforcer stores on a patch could be depleted and reinforcers obtained, again as a linear function of time, when the bird responded on a key. Depletion schedules thus timed only when the birds were present at a patch. Experiment 1 investigated changing relative depletion rates when repletion rates were constant and equal (Part 1) and changing relative repletion rates when the depletion rates were constant and equal (Part 2). Response- and time-allocation ratios conformed to a generalized matching relation with obtained reinforcer ratios, and there appeared to be no control by the size of the reinforcer stores. In Experiment 2, absolute depletion rates were varied with a pair of unequal repletion rates (Part 3), and absolute repletion rates were varied with a pair of unequal depletion rates (Part 4). Dwell times in the patches were not affected by either variation. Melioration theory predicted the results of Experiment 1 quite closely but erroneously predicted changing dwell times in Experiment 2. Molar maximization theory did not accurately predict the results of either experiment.     

A quantitative analysis of chain-schedule performance

Six pigeons were trained with a chain variable-interval variable-interval schedule on the left key and with reinforcers available on the right key on a single variable-interval schedule arranged concurrently with both links of the chain. All three schedules were separately and systematically varied over a wide range of mean intervals. During these manipulations, the obtained reinforcer rates on constant arranged schedules also frequently changed systematically. Increasing reinforcer rates in Link 2 of the chain increased response rates in both links and decreased response rates in the variable-interval schedule concurrently available with Link 2. Increasing Link-1 reinforcer rates increased Link-1 response rates and decreased Link-2 response rates. Increasing reinforcer rates on the right-key schedule decreased response rates in Link 1 of the chain but did not affect the rate in Link 2. The results extend and amplify previous analyses of chain-schedule performance and help define the effects that a quantitative model must describe. However, the complexity of the results, and the fact that constant arranged reinforcer schedules did not necessarily lead to constant obtained reinforcer rates, precluded a quantitative analysis.     

Task-dependent compensatory responses to perturbations applied during rhythmic movements in humans

Modulation of the responses to perturbation applied during different phases of three rhythmic movements in humans-running, cycling, and hopping-was studied. The perturbation was an electrical stimulus. The results showed gating and modulation of the responses in both ipsi- and contralateral limb muscles. The responses during running and cycling were only excitatory in nature, while during hopping an inhibitory response was observed. These responses were not correlated with the normal activity during the movement. The latency of the response in general was not altered for different stimulation phases. The alterations in the step cycle demonstrated overt behavioral changes due to the responses. There were differences between the responses observed during these movements and walking. In running, the major adaptation to perturbations appears to be in the contralateral side as seen in the changes in the step cycle. During cycling (except for one phase) and hopping, the same set of muscles was activated in response to perturbation. This represents a simplifying strategy in response organization. The dependency of the response on the task characteristics, postural stability requirement, and external constraints imposed on the subject is discussed. These studies provide insights into task-dependent strategies adopted by the nervous system to meet unexpected perturbation during rhythmic movements in humans.     

运动心理学的历史和当前的研究课题

一、历史运动心理学的基础在于运动学习和动作操作。1920年之前,就有少数人单独地进行一些零星分散的调查。这些调查推动了各种心理变量影响动作操作的研究。首先在美国发表的是观众对自行车比赛的影响。在1918年,伊利诺斯大学的心理学家C·R·格里菲斯对足球运动员和篮球运动员的反应时进行了比较,这仅仅为以后的研究播下了一些种子。在此期间,其它国家(苏联、德国和日本)也有类似的研究。 1920—1940年间,有些人对运动心理学的研究发生了特殊的兴趣。美国的运动心理学之父 C·R·     

Harming future people

Hanser examines Derek Parfit's contention in his treatise on rationalism, Reasons and Persons (Oxford University Press; 1984) that acts that are not reproductive in nature can nonetheless predictably affect the identities of future people, and that this fact has unexpected and important consequences for ethical theory. Hanser argues tht this fact is not as significant as Parfit believes it to be. The arguments of both scholars concern the morality of choices that, while causing future persons to be badly off, do not make them worse off than they would have been if the choices had not been made. Hanser concludes his essay with a discussion of responsibility for acts that will affect the health of future offspring.     

Natural ways are better: Adolescents and the ‘anti-obesity’ gene

Empirical research with young people in Finland, Germany, Spain and Britain was carried out as part of the BIOCULT project funded by the European Union. The project focused on their attitudes to biotechnology and, in particular, the formation of arguments about risk and safety. This paper looks at the responses of 14–18 year olds to a story about the so called anti-obesity gene, in the form of advice to a friend who is taking it. The majority advised against taking it with some differences by gender and country. Most reservations were on grounds of safety and the feeling that ‘natural’ ways to lose weight are better: A minority questioned the idea of striving for a ‘perfect’ body. The types of arguments used by the young people reveal underlying perspectives on the place of human beings in the world and whether they have a right to manipulate nature and their own bodies. Marie Levitt is a sociologist with research interests in attitudes and values in relation to biotechnology, health and religion.