Illusory conjunctions and the cerebral hemispheres

Two visual half-field experiments tested Moscovitch’s (1979) proposition that cerebral asymmetry does not concern the earliest perceptual stages but only later processing. Subjects were briefly shown displays that included one (Experiment 1) or two (Experiment 2) types of forms differing in size and which, according to previous evidence, might lead to opposite laterality effects. Laterality effects were assessed for correct detections and for illusory conjunctions, both in terms of raw detection scores and in terms of perceptual discriminability (dr scores). In Experiment 1, displays included either rectangles or triangles. In the first case, the target was a cross; in the second case, it was a Star of David. A hemifield x size interaction was observed both on correct detections and on associated discriminability. Yet, no such interaction was obtained for illusory conjunctions or for associated d’ scores. In Experiment 2, the two types of forms were presented simultaneously, with the small ones either inside or outside the large ones. No laterality effects were observed. Some implications of these data for both hemispheric asymmetry and feature integration issues are discussed. The results suggest that early preattentive processes of feature extraction are not lateralized, whereas some integrative mechanisms, such as Treisman’s (1988) focal attention, may operate differently in the two hemispheres.     

An alternating least squares method for the weighted approximation of a symmetric matrix

Bailey and Gower examined the least squares approximationC to a symmetric matrixB, when the squared discrepancies for diagonal elements receive specific nonunit weights. They focussed on mathematical properties of the optimalC, in constrained and unconstrained cases, rather than on how to obtainC for any givenB. In the present paper a computational solution is given for the case whereC is constrained to be positive semidefinite and of a fixed rankr or less. The solution is based on weakly constrained linear regression analysis.The authors are obliged to John C. Gower for stimulating this research.     

On becoming a leader: Effects of gender and cultural differences on power distance reduction

The present research focused on power processes in a simulated organizational structure consisting of three hierarchical levels occupied by different numbers of mules and females. Subjects were presented with a chart showing the organizational hierarchy of which they were a member placed at the lowest level, and asked to nominate any person for the leader position vacated by the current incumbent. The results of Experiment I (n = 88 Dutch male and female university students) showed that male subjects strongly overnominated themselves, whereas a majority of the female subjects nominated either self or another female. Of the others that were nominated by both males and females, almost all were occupants of positions immediately below the leader position, indicating the normative influence of a bureaucratic rule of leader succession. Experiment 2 was a replicational study carried out in a different culture (n = lOl Polish male and female university students). Polish subjects adhered to the bureaucratic rule more strongly than their Dutch counterparts, and both females and males nominated mostly males. Results are discussed with reference to gender self-stereotypes and cultural differences.     

Medical expertise asa function of task difficulty

This paper is concerned with factors that disrupt the pattern of forward reasoning characteristic of experts with accurate performance. Two experiments are described. In the first, the performances of cardiologists, psychiatrists, and surgeons in diagnostic explanation of a clinical problem in cardiology were examined. In the second, the performances of cardiologists and endocrinologists in diagnostic explanation of clinical problems within and outside their domains of expertise were examined. The performances of researchers and practicing physicians are also compared. The results of Experiment 1 replicated earlier results regarding the relationship between forward reasoning and accurate diagnosis. There were no differences in recall as a function of expertise. Experts did not show any bias toward using specific knowledge from their own areas of expertise. The results of Experiment 2 showed that the breakdown of forward reasoning was related to the structure of the task. In particular, nonsalient cues induced some backward reasoning even in subjects with accurate diagnoses. Some differences were also found between the types of explanation used by researchers and practitioners. The practitioners referred more to clinical components in their explanations, whereas the researchers focused more on the biomedical components.     

Effects of Level of Processing on Implicit and Explicit Memory in Depressed Mood

Recently, several studies have addressed the question of whether depression affects priming in implicit memory tasks. The main aim of this experiment was to assess the presence of a bias for negative information in explicit memory (free recall) and implicit memory (word-stem completion) tasks among subclinically depressed subjects compared to nondepressed subjects, using the typical levels of processing manipulation. The results of this study show the existence of a mood-congruent memory bias for both implicit and explicit memory in depressed subjects. The theoretical implications of these findings for implicit and explicit memory biases associated with depressed mood are discussed.     

TheP system: A scheme for organizing Pavlovian procedures

The present paper introduces theP system as a scheme for organizing Pavlovian procedures in an orderly and comprehensive manner. The system is defined by three temporal variables and three restrictions on their possible values. It can be used to define all standard temporal variables—namely, stimulus duration, interstimulus interval, trace interval, and intertrial interval—as well as variables C and T of scalar expectancy theory. The system also permits the definition of new independent variables through combinations of the basic temporal parameters. We exemplify this possibility by defining two ratios of temporal intervals. These ratios lead to a space where traditional Pavlovian arrangements (viz., simultaneous, forward-trace, forward-delay, backward) become points on a continuum, and optimal conditions across different experimental preparations become equivalent. Finally, the system can be used to define contingency variables such asp(US/CS),p(US/～CS), and the phi coefficient (φ). In this manner, an organization of different kinds of Pavlovian procedures is achieved on the basis of a single parametric scheme. Such an organization facilitates establishing procedural and theoretical relationships between temporal and contingency variables. The paper concludes with a discussion of certain limitations of the system and other related issues     

Comparing Locomotion With Lever-press Travel In An Operant Simulation Of Foraging

An operant model of foraging was studied. Rats searched for food by pressing on the left lever, the patch, which provided one, two, or eight reinforcers before extinction (i.e., zero reinforcers). Obtaining each reinforcer lowered the probability of receiving another reinforcer, simulating patch depletion. Rats traveled to another patch by pressing the right lever, which restored reinforcer availability to the left lever. Travel requirement changed by varying the probability of reset for presses on the right lever; in one condition, additional locomotion was required. That is, rats ran 260 cm from the left to the right lever, made one response on the right lever, and ran back to a fresh patch on the left lever. Another condition added three hurdles to the 260-cm path. The lever-pressing and simple locomotion conditions generated equivalent travel times. Adding the hurdles produced longer times in patches than did the lever-pressing and simple locomotion requirements. The results contradict some models of optimal foraging but are in keeping with McNair's (1982) optimal giving-up time model and add to the growing body of evidence that different environments may produce different foraging strategies.     

The functional role of attention for spatial coding in the Simon effect

Summary Two experiments investigated relative spatial coding in the Simon effect. It was hypothesized that relative spatial coding is carried out with reference to the position of the focus of visual attention. The spatial code for an imperative stimulus presented exactly at the position of focal attention should be neutral on the horizontal plane, and therefore no Simon effect should be observed. However, when the imperative stimulus is presented to the left or to the right of the current position of focal attention, the spatial code should not be neutral, thus producing a Simon effect. In both experiments, focal attention was manipulated either by a peripherally presented onset precue (Experiment 1) or by a centrally presented symbolic precue (Experiment 2). Results showed that the Simon effect was substantially reduced in both experiments when a valid precue preceded the imperative stimulus just in time to conclude refocusing of attention to the position of the imperative stimulus before it was presented. However, conditions with neutral precues yielded a normally sized Simon effect. In both experiments, the Simon effect decreased as the SOA grew when the precue was valid. At least for the Simon effect, the results can be interpreted as evidence that relative spatial coding is functionally related to the position of the focus of attention.