Duration comparison: relative stimulus differences stimulus age, and stimulus predictiveness.

Under a psychophysical trials procedure, pigeons were presented with a red light of one duration followed by a green light of a second duration. Eight geometrically spaced base durations were paired with one of four shorter and four longer durations as the alternate member of a duration pair, with different pairs randomly intermixed. One choice was reinforced if red had lasted longer than green, and a second choice was reinforced if green had lasted longer. Performance was compared when all the base durations and their pair members were included (entire-range condition) or when only the four longest base durations and their comparison durations (restricted-range condition) were used. Discrimination sensitivity decreased for longer duration pairs under both conditions, supporting a memory-based account. Sensitivity was lower under the restricted-range condition. Under both conditions, a bias to report "green as longer" increased as the second green duration increased. Bias changed as a matching function of the green-duration predictiveness of the correct choice. The results are related to a quantitative model of timing and remembering proposed by Staddon.     

An empirical look at the Defence Mechanism Test (DMT) Stimulus effects

Based on a sample of non-clinical subjects (N=74) the study examines the Defence Mechanism Test (DMT) by focusing on when perceptual distortions, called ‘signs of defence’ in DMT terminology, occur (distribution in exposure duration), which part of the picture is involved (distribution in localisation), and which ‘signs’ go together (using correlation and factor analyses). The results disclosed that the occurrence of perceptual distortions (‘signs of defence’) was related to exposure duration (some ‘defences’ are more frequent at brief exposures, some others at longer exposure durations), and to localisation on the picture. The location of misperceptions to the central person (hero) or the peripheral person (pp) of the picture was the major explanatory principle for the distribution of ‘signs’ on factors. Rather than capturing psychodynamic defence mechanisms, which is the theoretical basis of the test, the analyses imply that the DMT seems to measure misperceptions which are a function of the localisation of persons on the stimulus picture and of exposure durations.     

Depression,self-focus,and social interaction

The accuracy of depressed and nondepressed subjects' perceptions of their own and a social interactional partner's performance was investigated. Twenty depressed and twenty nondepressed college students participated in dyadic interactions and then rated their own and their partner's social behavior. The interactions were also rated by objective coders. Depressed subjects were differentiated from nondepressed subjects on several measures by both the coders and the subjects. Depressed subjects' self-ratings were correlated with the coders' ratings more often than were the nondepressives' ratings, suggesting depressives provided more accurate self-observations. Contrary to prediction, depressives were also more accurate in judging their partner's behavior. Depressives experienced heightened levels of self-focused attention, but this attentional focus did not mediate the relationship between depression level and self-accuracy. Finally, an analysis of the verbal statements suggests that performance differences between depressives and nondepressives may be a function of the quantity, rather than the quality, of the verbal production.     

Cognitive components in risk perception: Natural versus manmade risks

In a questionnaire study 106 Norwegian students rated natural and manmade hazards according to risk magnitude and public versus private responsibility for risk management. Another group of 50 subjects judged 36 natural hazards on nine risk dimensions used in previous psychometric studies of ‘manmade risks’. When ratings on nine risk characteristics for natural hazards were factor analyzed a three-dimensional solution was found, with one active/passive dimension, one potency dimension, and one novelty dimension. This contrasts with the two-dimensional solution found for manmade hazards. Responsibility for risk management was found to be related to the type of risk in focus, and different risk characteristics seem to play different roles for manmade and natural hazards.     

Evaluating performance in continuous experiments with feedback to subjects

Consider an experiment in which a subject guesses repeatedly at a randomly chosen target on a continuum. To guarantee a positive probability of success, the continuum is partitioned into a finite but large number of segments. The subject is given directional feedback. General guessing strategies are characterized, and an optimal strategy is identified. The hypothesis that the subject's performance can be explained by chance alone is of interest in such experiments. A test is developed based on comparing the subject's performance to expected performance using the optimal strategy. A skill-scoring procedure is developed for assessing a subject's performance in light of the strategy used, and a test based on skill-scoring is advanced.Research by the first author is supported in part by the Air Force Office of Scientific Research under grant AFOSR 77-3180.The authors wish to thank the referees for remarks that led to improvements in both content and clarity.     

Nonmetric maximum likelihood multidimensional scaling from directional rankings of similarities

A maximum likelihood estimation procedure is developed for multidimensional scaling when (dis)similarity measures are taken by ranking procedures such as the method of conditional rank orders or the method of triadic combinations. The central feature of these procedures may be termed directionality of ranking processes. That is, rank orderings are performed in a prescribed order by successive first choices. Those data have conventionally been analyzed by Shepard-Kruskal type of nonmetric multidimensional scaling procedures. We propose, as a more appropriate alternative, a maximum likelihood method specifically designed for this type of data. A broader perspective on the present approach is given, which encompasses a wide variety of experimental methods for collecting dissimilarity data including pair comparison methods (such as the method of tetrads) and the pick-M method of similarities. An example is given to illustrate various advantages of nonmetric maximum likelihood multidimensional scaling as a statistical method. At the moment the approach is limited to the case of one-mode two-way proximity data, but could be extended in a relatively straightforward way to two-mode two-way, two-mode three-way or even three-mode three-way data, under the assumption of such models as INDSCAL or the two or three-way unfolding models.The first author's work was supported partly by the Natural Sciences and Engineering Research Council of Canada, grant number A6394. Portions of this research were done while the first author was at Bell Laboratories. MAXSCAL-4.1, a program to perform the computations described in this paper can be obtained by writing to: Computing Information Service, Attention: Ms. Carole Scheiderman, Bell Laboratories, 600 Mountain Ave., Murray Hill, N.J. 07974. Thanks are due to Yukio Inukai, who generously let us use his stimuli in our experiment, and to Jim Ramsay for his helpful comments on an earlier draft of this paper. Confidence regions in Figures 2 and 3 were drawn by the program written by Jim Ramsay. We are also indebted to anonymous reviewers for their suggestions.     

Auditorily elicited EEG desynchronization and synchronization: A review of Christina M. Krause's doctoral thesis

The present paper reviews the doctoral dissertation of Christina M. Krause, in which auditorily elicited EEG desynchronization (ERD) and synchronization (ERS) was studied in five experiments. These experiments which were conducted by Krause and co-workers are the first in which the ERD-method was systematically applied to the analysis of the perception and processing of complex auditory stimuli. The main conclusion is that listening to sounds elicits ERS, whereas cognitive and/or memory processes elicit ERD.     

Postural stabilization for the control of touching

We attempted to distinguish between task-related (supra-postural) and perceptual influences on postural motions. Two groups of participants had to make very light tactile contact with an adjacent pliable surface while standing with their eyes closed. In the absence of vision, such light touching with a finger is known to reduce sway. For one group, tactile contact with the surface was merely the result of extending the right forearm. For the other group, variability in the point of tactile contact had to be kept to a minimum. Touching reduced postural sway relative to non-touching only for participants in the latter group. The present results, in combination with others addressing similar task differences, question the assumption that information detected haptically and/or visually is used solely to reduce postural fluctuations. It seems that postural fluctuations are modulated to facilitate performance of tasks over and above the task of standing upright and still.