Periodic shock with added clock

Rats were shocked every 6 min while responding was maintained on a variable-interval schedule of reinforcement. With some rats, shocks were interspersed with a sequence of three different stimulus conditions (S3→S2→S1), or clock cues, each lasting 2 min. For other rats, a single stimulus condition prevailed between shocks at the beginning of the experiment and clock cues were introduced later. Response rate decreased from S3 to S1. Response rate in S3, S2, and S1 was inversely related to shock intensity. When clock cues were added, response rate increased in all 2-min intershock periods. During clock cues, an index of curvature, indicating the degree of negative acceleration of response rate, was greatest for S1 and least for S3, and was directly related to shock intensity. The response-facilitating effect of shock and its relation to a possible discriminative function of shock and to behavioral contrast is discussed.     

Observing behavior during interval schedules

Experiment 1 showed that the three stimuli associated with three chained fixed-interval links could be used to maintain observing behavior. Experiment 2 showed that three stimuli correlated with the passage of time since the last reinforcement in a fixed-interval schedule could be used to maintain observing behavior. In both experiments most observing responses occurred midway between reinforcements. Few occurred just before or just after reinforcement. Experiment 3 showed that the decline in the rate of observing behavior just before reinforcement was reduced when more stimuli could be observed. The relatively high terminal rate of observing behavior that resulted was maintained even when at least 4 sec intervened between the reinforcement and the last observed stimulus.     

A program for fitting two-phase segmented-curve models with an unknown change point,with an application to the analysis of strategy shifts in a cognitive task

A program is described for fitting a regression model in which the relationship between the dependent and the independent variables is described by two regression equations, one for each of two mutually exclusive ranges of the independent variable. The point at which the change from one equation to the other occurs is often unknown, and thus must be estimated. In cognitive psychology, such models are relevant for studying the phenomenon of strategy shifts. The program uses a (weighted) least squares algorithm to estimate the regression parameters and the change point. The algorithm always finds the global minimum of the error sum of squares. The model is applied to data from a mental-rotation experiment. The program’s estimates of the point at which the strategy shift occurs are compared with estimates obtained from a nonlinear least squares minimization procedure in SPSSX.     

The experimental determination of unique green in the spectrum

The notion is gaining currency that observers who are distributed normally with respect to commonly measured indices of color vision, may be bimodally distributed with respect to the spectral locus of unique green. Experimental conditions which can produce such deviations from a normal distribution are explored, and it is concluded that the “bimodality” results reported in the literature may reflect differential chromatic adaptation effects. Experimental conditions which guarantee a neutral state of adaptation yield spectral unique green loci that show no evidence of bimodality.     

The variance of the number of mutual choices in sociometry

The variance of the number of mutual dyads in a sociometric situation where each member of a group chooses independently and at random is derived for unrestricted numbers of choices per group member, as well as for a fixed number of choices. The distribution of the number of mutuals is considered.We are indebted to Robert Bush and Hartley Rodgers of Harvard University for helpful criticisms.