Silverman, and Charlotte Christner assisted in collecting the data here reported.

assisted in collecting the data here reported. ' Theorem 17 states that "the capacity of a channel of band W perturbed by white thermal noise of power N when the average transmitter poser is limited to P is given by P+N" C-W log-^-(22, p. 67). W is in cycles per second and takes the form of the reciprocal of some value of time. The power of a band of noise is equivalent to the variance of its amplitude distribution around its mean value.

The effects of response amplitude and terminal accuracy on 2-choice reaction time (RT) and on movement time (MT) were studied. Both the required amplitude (A) of a movement, and the width (W) of the target that S was required to hit, had a large and systematic effect on MT, whereas they had a relatively small effect on RT. Defining an index of movement difficulty as ID = log^B2)2A/W, the correlation between ID and MT was found to be above .99 over the ID range from 2.6 to 7.6 bits per response. Thus the times for discrete movements follow the same type of law as was found earlier to hold for serial responses. The relative independence of RT and MT is interpreted as pointing to the serial and independent nature of perceptual and motor processes. (17 ref.)

The hypothesis that information transfer in a perceptual-motor task is in a large measure a function of the matching sets of stimuli and sets of responses was tested. The results, analyzed in terms of reaction time, errors, and information lost, support the hypothesis. A further experiment was run to test the performance of three selected S-R compatibility effects. It was found that in making a particular set of responses to each of three sets of stimuli, differences in reaction time, movement time, and frequency of errors persisted over the entire 32 days of testing.

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This study examines the capacity of Os to adapt to changes in the relative emphasis on speed vs. accuracy of responses. 3 matched groups of 6 Os each were trained for 3 days in a choice reaction-time (RT) task, with feedback indicating both speed and accuracy. Emphasis on speed decreased mean RT but increased errors. A control group, working without an exact payoff or immediate feedback, showed somewhat greater within-and between-S variability than did either the speed or accuracy groups and was at an intermediate level on all performance measures. Similar distributions of RTs were found for correct responses and for errors as was predicted by a sequential sampling and decision model of choice RT. RT distributions for all Os were approximately normal under a set for speed, but under accuracy instructions some Os gave highly skewed distributions.

The present paper is the second dealing with the usefulness of the concept of S-R compatibility for behavior theory. This concept concerns the effects of a class of variables that influence task difficulty in experiments in which learning, complexity (amount of information), and discriminability are controlled. Compatibility effects are conceived as resulting from hypothetical information transformation processes (encoding and/or decoding) that intervene between receptor and effector activity. The rate of processing information is assumed to be maximum when these receding processes are at a minimum.The objective of the study of compatibility effects is to discover conditions under which these effects occur, and to establish principles that will permit specification of the nature and difficulty of perceptual-motor tasks in terms of (hypothetical) intervening information transformation processes. Such processes must be inferred, just as do constructs such as habit strength, from measures of performance obtained in appropriate experiments. The type of experiment of greatest interest for the present purpose is one in which it is possible to measure the rate of information trans-

No abstract