A test of the assumptions of multidimensional scaling by separating sensitivity and response bias

Summary This study investigates one of the main assumptions underlying multidimensional scaling models. It is tested whether the violation of decomposability found in previous studies can be explained by variation in sensitivity or in response bias. Rectangles of different shape served as stimuli in an experiment using a matching procedure. In addition the probability for presenting pairs of identical stimuli was varied. The data were analysed by a model separating response bias and sensitivity. Six versions of the model with different numbers of parameters were applied. The results suggest that the violation of decomposability comes from variation in sensitivity and not in response bias.This research was supported by a grant from the Deutsche Forschungsgemeinschaft to the first author. All computing was done on the Telefunken TR 440 of the Deutsches Rechenzentrum Darmstadt.     

On counteradaptation

Often adaptation to artificially altered stimulation takes place because veridical stimulation that produces the same perceptual property that is produced by the altered stimulation is also received. In these cases, an assimilation of the two perceptual processes produced by the two different stimulations (the altered and the veridical) is supposed to be responsible for the adaptation that is achieved. This hypothesis, which was formulated by Wallach and Karsh (1963), would be confirmed by demonstrating a modification of the perceptual process produced by veridical stimulation rather than the one produced by the altered stimulation. We demonstrated this by having S observe in the dark for 20 min a luminous figure that objectively expanded as it moved toward S and contracted as it moved away. But instead of testing for changes in size perception as such, we tested for a change in the relation between accommodation and convergence on the one hand and registered distance on the other. In one experiment, such a change was measured by obtaining estimates of perceived size and depth before and after the adaptation period. Highly significant changes of size and significantly greater changes of stereoscopic depth were obtained. Inasmuch as stereoscopic vision was totally absent from the adaptation conditions, the change in stereoscopic depth that was larger than the size change can only be ascribed to a change in registered distance. In another experiment, we tested for a change in distance by having S point from the side to a vertical line, before and again after the adaptation period, under conditions where only accommodation and convergence could serve as distance cues. Significant changes in the pointing distance were measured, indicating more directly a change in the relation between these oculomotor adjustments and perceived distance. We propose the term counteradaptation for such modification of a perceptual process away from veridicality.     

The relationship between binocular brightness matches and luminance difference discriminability of successively presented light flashes1

Measurements of monocular ΔI and PSE as a function of the ISI between two 2-deg foveal fields successively presented to the same retinal area were obtained for two Standard durations, using the method of constant stimuli. Binocular brightness matches of the stimuli revealed that detection of a difference occurred whenever a constant difference (in log mL) in matching luminance existed. The implication of the results was that ΔI is related to the rate of change of brightness with changes in test-field luminance.     

Influence and Selection In the Friend-adolescent Relationship: Findings from Studies of Adolescent Smoking and Drinking1

The importance of friend influence as a determinant of adolescent behavior has primarily been inferred from research that has repeatedly demonstrated the behavior of friends to be similar. Homogeneity among peers, however, could also be due to a selection process whereby adolescents choose and keep friends whose behavior is similar to their own. Most previous studies have used cross-sectional designs that cannot delineate the source of peer homogeneity; this study employed sociometric data from longitudinal research on adolescent smoking and drinking to separate and examine the selection and influence processes. Although the findings indicate some support for the friend influence model, the acquisition hypothesis from the selection model accounts for substantially more of the adolescent-friend relationship. The implications of these results for past and future research concerning the role of peers in adolescence are discussed.     

DADTA VI: A minicomputer-based video control system for the analysis of behavioral and electrophysiological data

A computer-automated testing apparatus for monkey and human subjects is described. This dual-computer system generates programmable color video displays and permits on-line collection of behavioral and electrophysiological data. Video displays are generated by an Apple II minicomputer linked via a serial transmission port to a general-purpose laboratory computer (DEC PDP-11/34). Control of event sequences is determined by serial interaction between the two computers. Software (programs) for the collection and analysis of event-related brain potentials data is described, and the experimental and clinical applications of this DADTA VI (Discrimination apparatus for discrete-trial analysis, Version 6) for neuropsychology are discussed.