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931.
We confirm Craik's (1947) observation that the human manual1y tracking a visual target behaves like an intermittent servo-control1er. Such tracking responses are indicative of "sampled" negative-feedback control but could be the result of other, continuous, mechanisms. Tracking performance therefore was recorded in a task in which visual feedback of the position of the hand-held joystick could be eliminated. Depriving the subjects of visual feedback led to smoother tracking and greatly reduced the signal power of their responses between 0.5-1.8 Hz. Their responses remained intermittent when they used feedback of their own position but not of the target to track a remembered (virtual) target. Hence, intermittency in tracking behavior is not exclusively a signature of visual feedback control but also may be a sign of feedback to memorized waveforms. Craik's (1947) suggestion that the intermittency is due to a refractory period following each movement was also tested. The errors measured at the start of each intermittent response, during tracking of slow waveforms, showed evidence of a small error deadzone (measuring 0.7 cm on the VDU screen or 0.80 degrees at the eye). At higher target speeds, however, the mean size of starting errors increased, and the upper boundary of the distribution of starting error was close to that expected of a refractory delay of approximately 170 ms between responses. We consider a model of the control system that can fit these results by incorporating an error deadzone within a feedback control loop. We therefore propose that the initiation of intermittent tracking responses may be limited by a positional error deadzone and that evidence for a refractory period between successive corrective movements can be satisfied without evoking an explicit timing or sampling mechanism. 相似文献
932.
The motor system may use internal predictive models of the motor apparatus to achieve better control than would be possible by negative feedback. Several theories have proposed that the cerebellum may form these predictive representations. In this article, we review these theories and try to unify them by reference to an engineering control model known as a Smith Predictor. We suggest that the cerebellum forms two types of internal model. One model is a forward predictive model of the motor apparatus (e.g., limb and muscle), providing a rapid prediction of the sensory consequences of each movement. The second model is of the time delays in the control loop (due to receptor and effector delays, axonal conductances, and cognitive processing delays). This model delays a copy of the rapid prediction so that it can be compared in temporal register with actual sensory feedback from the movement. The result of this comparison is used both to correct for errors in performance and as a training signal to learn the first model. We discuss evidence that the cerebellum could form both of these models and suggest that the cerebellum may hold at least two separate Smith Predictors. One, in the lateral cerebellum, would predict the movement outcome in visual, egocentric, or peripersonal coordinates. Another, in the intermediate cerebellum, would predict the consequences in motor coordinates. Generalization of the Smith Predictor theory is discussed in light of cerebellar involvement in nonmotor control systems, including autonomic functions and cognition. 相似文献
933.
The LogicR4 is obtained by adding the axiom (A vB(AvB) to the modal relevant logicNR. We produce a model theory for this logic and show completeness. We also show that there is a natural embedding of a Kripke model forS4 in eachR4 model structure.We are indebted to several people for discussions relating to the topic of this paper, in particular, Kit Fine, John Slaney, J. M. Dunn, Jacques Riche, M. A. McRobbie, and Jill LeBlanc. We would also like to thank the Automated Reasoning Project for material assistance. Mares would like to thank The Social Sciences and Humanities Research Council of Canada for fellowships 456-89-0128 and 457-90-0081, which supported him while writing this paper. 相似文献
934.
Unit price as a useful metric in analyzing effects of reinforcer magnitude. 总被引:7,自引:6,他引:1 下载免费PDF全文
R J DeGrandpre W K Bickel J R Hughes M P Layng G Badger 《Journal of the experimental analysis of behavior》1993,60(3):641-666
In this paper, we applied the behavioral-economic concept of unit price to the study of reinforcer magnitude in an attempt to provide a consistent account of the effects of reinforcer magnitude on behavior. Recent research in the experimental analysis of behavior and in behavioral pharmacology suggests that reinforcer magnitude interacts with the schedule of reinforcement to determine response rate and total consumption. The utility of the unit-price concept thus stems from its ability to quantify this interaction as a cost-benefit ratio (i.e., unit price = characteristics of the schedule of reinforcement divided by magnitude of reinforcement). Research employing the unit-price concept has shown that as unit price increases, a positively decelerating function exists for consumption (i.e., a function with an increasingly negative slope, when plotted on log coordinates) and a bitonic function exists for response rate. Based on these findings, the present analysis applied the unit-price concept to those studies of reinforcer magnitude and drug self-administration that examined the effects of reinforcer magnitude on response rate using simple schedules of reinforcement (e.g., fixed-ratio schedule). This resulted in three findings: (a) Reinforcer-magnitude manipulations and schedule manipulations interact in a manner that can be quantified in terms of unit price as benefit and cost factors, respectively; (b) different reinforcer-magnitude manipulations are functionally interchangeable as benefit factors in the unit-price ratio; and (c) these conclusions appear warranted despite the differences in reinforcers (food or drug), species (dogs, monkeys, or rats), and schedules (interval or ratio), and despite the fact that these studies were not designed for a unit-price analysis. In methodological terms, these results provide further evidence that employing the unit-price concept is a parsimonious method for examining the effects of reinforcer magnitude. In theoretical terms, these results suggest that a single process may underlie the effect of combined reinforcer-magnitude and schedule manipulations. 相似文献
935.
TEMPORAL CONTROL ON INTERVAL SCHEDULES: WHAT DETERMINES THE POSTREINFORCEMENT PAUSE? 总被引:1,自引:1,他引:0 下载免费PDF全文
N K Innis S K Mitchell J E Staddon 《Journal of the experimental analysis of behavior》1993,60(2):293-311
On fixed-interval or response-initiated delay schedules of reinforcement, the average pause following food presentation is proportional to the interfood interval. Moreover, when a number of intervals of different durations occur in a programmed cyclic series, postreinforcement pauses track the changes in interval value. What controls the duration of postreinforcement pauses under these conditions? Staddon, Wynne, and Higa (1991), in their linear waiting model, propose control by the preceding interfood interval. Another possibility is that delay to reinforcement, signaled by a key peck and/or stimulus change, determines the subsequent pause. The experiments reported here examined the role of these two possible time markers by studying the performance of pigeons under a chained cyclic fixed-interval procedure. The data support the linear waiting model, but suggest that more than the immediately preceding interfood interval plays a role in temporal control. 相似文献
936.
John F. Horty 《Philosophical Studies》1993,72(2-3):223-263
Conclusion In contemporary work, the distinction between the proposition expressed by a sentence and its psychological significance is usually motivated by a familiar kind of counterfactual argument; and the discussion of these issues usually centers around the role of external factors in determining the meaning of our words. My primary goal in this paper has been to show that a similar, though not identical, distinction between two aspects of meaning can be developed entirely on the basis of considerations internal to language users — their cognitive limitations. To make this point, I have focused on symbols introduced through stipulative definitions. In a language containing such symbols, certain expressions and their definitional reductions will seem to differ in psychological significance for creatures with limited intellects, and so in any aspect of meaning that is supposed to correlate with psychological significance; but it seems also that there is some important aspect of meaning that they share.I have argued that a distinction in meaning like this — between sense and psychological significance — should be drawn even in the kind of languages of most concern to Frege, and that his failure to do so led to tensions in his thought. Of course, this observation only touches on the many issues involved in interpreting Frege's theory of definition more generally. I have not tried to describe here, for example, the ways in which the weak interpretation of fruitfulness might interact with the more robust interpretation mentioned earlier; I have only mentioned Frege's view on explicative definitions and the paradox of analysis, and failed even to mention either his treatment of contextual definition, or his peculiar objections to conditional definitions. I do want to emphasize, however, that the distinction drawn here is not simply a matter of Frege scholarship, but that it has some contemporary relevance as well. As we have seen, Frege's semantic goals often coincide with our own; and a number of contemporary writers are explicitly concerned, like Frege, to construct a semantic theory that is able to account for differences in meaning among logically equivalent expressions. Any such theorist should recognize a distinction like that drawn here between sense and psychological significance, and should avoid subjecting an account of one notion to constraints appropriate only for the other. 相似文献
937.
938.
Bailey and Gower examined the least squares approximationC to a symmetric matrixB, when the squared discrepancies for diagonal elements receive specific nonunit weights. They focussed on mathematical properties of the optimalC, in constrained and unconstrained cases, rather than on how to obtainC for any givenB. In the present paper a computational solution is given for the case whereC is constrained to be positive semidefinite and of a fixed rankr or less. The solution is based on weakly constrained linear regression analysis.The authors are obliged to John C. Gower for stimulating this research. 相似文献
939.
940.
Schedule-induced defecation by rats during ratio and interval schedules of food reinforcement. 下载免费PDF全文
Lever pressing in rats was maintained by continuous and intermittent schedules of food while defecation was monitored. In Experiment 1, reinforcement densities were matched across variable-ratio and variable-interval schedules for three pairs of rats. Defecation occurred in all 3 rats on the variable-ratio schedule and in all 3 rats on the yoked variable-interval schedule. In Experiment 2, fixed-ratio and fixed-interval schedules with similar reinforcement densities maintained lever pressing. Defecation occurred in 3 of 4 rats on the fixed-ratio schedule and in 4 of 4 rats on the fixed-interval schedule. Almost no defecation occurred during continuous reinforcement in either experiment. These results demonstrate that defecation may occur during both ratio and interval schedules and that the inter-reinforcement interval is more important than the behavioral requirements of the schedule in generating schedule-induced defecation. 相似文献