9 experimentally naive rhesus monkeys were tested on ambiguous-cue problems involving three stimuli: P, the positive or rewarded stimulus; N, the negative or nonrewarded stimulus; and A, the ambiguous stimulus which is nonrewarded when paired with P, but rewarded when paired with N. Either the NA pair or the PA pair was presented on every trial. All Ss were tested with two types of stimuli, planometric plaques and stereometric objects. The results corroborate apparently conflicting previous reports of performance by primates on ambiguous-cue problems with these two types of stimuli. That is, performance on PA trials was superior to performance on NA trials with plaque stimuli, but the converse was obtained with objects. A differential S-R spatial discontiguity inherent in only the plaque version of the problem was identified as one cause of the discrepant results.
In the method of constant stimulus differences, results obtained under two presentation orders (standard first and standard second) are commonly combined to eliminate time error. The present study shows that this technique is not adequate for controlling time error as the presentation orders have differential effects upon PSE. Using a two-handed technique, 96 subjects judged lifted weights on the comparative rating scale. The subjects lifted the standard before, with, or after the variable stimulus. They also either judged the standard in terms of the variable or the variable in terms of the standard (mode of judgment). Judgment mode, a previously uninvestigated confounding variable of presentation order was not an important factor in influencing the value of the PSE.In the method of constant stimulus differences, the observer is asked to judge if one member of a pair of stimuli is greater or less than the other member. One of the stimuli is the standard stimulus and the other is selected from a set of comparison stimuli. Each comparison stimulus is paired with the standard stimulus many times. From the judgments, a number of measures can be calculated. The point of subjective equality (PSE) specifies the value of the comparison stimulus which would be judged equal to the standard. Typically, the values of the PSE and standard stimulus are different and this difference is called the constant. error.Since the pair of stimuli are. separated in space or time, side effects of this separation can influence the judgments made by the observer. Space error is the aspect of constant error specifically related to changes in judgment caused by spatial separation. Space error is usually easily controlled by either counterbalancing conditions of presentation or by eliminating the spatial variable entirely. Time error (Fechner, 1860(Fechner, /1966 has to do with the influence on judgment of experiencing one stimulus before the other. Traditionally, a positive time error indicates underestimation of the second stimulus (PSE is greater than the standard); a negative time error indicates overestimation of the second stimulus (PSE is less than the standard) (Needham, 1934). Fechner suggested controlling for time error by using two presentation orders. For half the trials, present the standard stimulus first (S, presentation order), and in the other trials present the standard stimulus second (S2 presentation order). In this manner, the under-or overestimation of the second stimulus will affect both However, there is no reason that the variable and standard stimuli have to be equally affected by time error in the two presentation orders. In adaptation-level theory (Helson, 1964), the roles of the standard and variable are different, and consequently the presentation orders could well affect the two differentially. The Michels and Helson (1954) quantitative model of the effect of presentation order on PSE specifically allows for a differential effect as the usual state. Probably because presentation orders were a logical experim...
Almost all research in the behavioral sciences requires that the ordering of the presentation of conditions be suitably randomized. The process of developing a random ordering is tedious; computer assistance is available and frequently used. Most computer languages have a built-in procedure or command for generating pseudorandom orderings. In addition, the algorithms for producing pseudorandom orderings are becoming better known (Knuth, 1969; Sander-Cederlof, 1984a), as are methods oftesting the adequacy of specific implementationsof algorithms (Rasmussen, 1984; Sander-Cederlof, 1984b).Simply having a "random number" generator availaThis work was done while the author was on a semester sabbatical leave provided by Butler University. The author's mailing address is: Department of Psychology, Butler University, 4600 Sunset Avenue, Indianapolis, IN 46208. ble on a computer still leaves large sections of program code to be written for each application program. The UCSD Pascal unit described here makes two procedure calls available to an applications program: Randomorder and Reorder. These calls greatly reduce the coding overhead for providing random orderings of sequences. Randomorder produces a linked list of pseudorandomly ordered integers (l to n). Randomorder also returns a heap pointer so that the memory locations used in the list can be released when no longer needed. The second procedure, Reorder, randomizes a linked list of integers provided by the calling program. When Reorder returns control to the calling program, the heap has been restored to its state at the time of the procedure call.RANDOMTOOLS includes utility procedures making the creation, use, and maintenance of linked lists simple for those unfamiliar with this data structure. Heap management is left to the calling program. Table 1 contains a Pascal program that illustrates the use of RAN-DOMTOOLS by creating and then listing a random ordering of integers.RANDOMTOOLS does not use any other UCSD units.
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