Experimental note on fading of briefly flashed lines

A peripheral uniform stimulus on a uniform background tends to fade when a ring enclosing the stimulus is flashed briefly, indicating that neural signals external to the stimulus such as those from the ring or those from the background tend to inhibit the onset-response or after-discharge of the stimulus. In this study, a peripheral achromatic line was flashed briefly on an achromatic background while the subject was steadily fixating on a point on the background. It was predicted that the stimulus line would fade due to background inhibition of the onset-response or afterdischarge of the stimulus. On a reference line, subjects indicated two points delimiting the part of the stimulus line which looked uniform in intensity of color. These points converged toward the center of the reference line as the luminance of the stimulus line approached that of the background. Compared to the central uniform part, the nonuniform parts near the endpoints of the stimulus line looked more faded. These results support the idea that the background surrounding a stimulus tends to inhibit the onset-response of after-discharge of the stimulus.     

Ask and you might receive: The actor–partner interdependence model approach to estimating cultural and gender variations in social support

As an essential part of close relationships, social support is a dynamic interactive process. This paper aims to simultaneously investigate social support‐seeking and provision behaviours using the Actor–Partner Interdependence Model (APIM). Ninety‐two friendship dyads participated in this study. Supportive versus negative friendship qualities were used to predict different support‐seeking and support‐provision behaviours during an experimental task. Cultural and gender variations were also examined. Results showed that self‐reported friendship qualities influence support‐seeking and provision behaviours intrapersonally and interpersonally. Female participants were more likely to provide emotion‐focused support than were male participants. After accounting for friendship qualities in the dyads, there was no evidence of cultural group differences on support‐seeking or provision behaviours among same‐sex friends. These results demonstrate the conceptual and empirical advantages of using APIM to unpack cultural and gender variations in social support processes.     

On the syndrome of the "spare limb": one case

We describe a case of a brain-damaged patient who had a peculiar bodily illusion which could not be labelled an hallucination but seemed somatognosically and phenomenologically similar to the phantom limb without amputation. The patient, who showed left hemiplegia, felt a third upper limb (without seeing it) which he himself defined as "spare." The spare limb was not deformed; it could be moved and controlled by the patient, and there was no sensation of pain. The patient did not show psychopathological or cognitive disorders. A possible interpretation of the phenomenon is as a "phantom movement" of the paralysed limb: the mental representation of the movement of the limb was dissociated from the bodily representation of his own limb and so was still present in his consciousness despite the paralysis.     

Absolute and relative effects of similarity and distance on grouping

Four experiments are reported, the aim of which was to explore the achromatic-colour and distance relations that determine the probability of achromatic surfaces grouping perceptually. The first two experiments were performed to test Wertheimer's conjecture that similarity and dissimilarity of achromatic colours jointly determine grouping. The results indicate that only similarity of achromatic colours determines grouping. Data from the other two experiments show that grouping is determined by absolute, relative, and Gillam's distances. These findings agree with previous literature showing that different algorithms or mechanisms determine grouping by similarity and grouping by distance. Additionally, these findings show that the single factor of grouping by distance also depends on multiple algorithms or mechanisms.     

On the determinants of surface brightness

The brightness of an achromatic surface with luminance S on an achromatic background with luminance B varies with S, with B, and with the luminance step deltaL at the border of the surface. In agreement with previous findings indicating that the visual system can perform as a photometer, the results of the two experiments reported here show that S and B determined surface brightness independently of deltaL when the surface was adjacent to and when it was separated from the background. This finding suggests that surface brightness depends on the integration of neural signals representing magnitudes of absolute luminance. A weighted-average model of this integration is proposed.     

Working memory and updating processes in reading comprehension

In this study, we examine the relation between reading comprehension ability and success in working memory updating tasks. Groups of poor and good comprehenders, matched for logical reasoning ability, but different in reading comprehension ability, were administered various updating tasks in a series of experiments. In the first experiment, the participants were presented with lists of words, the length of which (4-10 words) was unknown beforehand, and were required to remember the last 4 words in each series. In this task, we found a decrease in performance that was related to longer series and poor reading ability. In the second experiment, we presented lists of nouns referring to items of different sizes, in a task that simulated the selection and updating of relevant information that occurs in the on-line comprehension process. The participants were required to remember a limited, predefined number of the smallest items presented. We found that poor comprehenders not only had a poorer memory, but also made a greater number of intrusion errors. In the third and fourth experiments, memory load (number of items to be selected) and suppression request (number of potentially relevant items) were manipulated within subjects. Increases in both memory load and suppression requests impaired performance. Furthermore, we found that poor comprehenders produced a greater number of intrusion errors, particularly when the suppression request was increased. Finally, in a fifth experiment, a request to specify the size of presented items was introduced. Poor comprehenders were able to select the appropriate items, although their recall was poorer. Altogether, the data show that working memory abilities, based on selecting and updating relevant information and avoiding intrusion errors, are related to reading comprehension.     

Cognitive and neuronal processes involved in sequential generation of general and specific mental images

Mental image generation is a complex process mediated by dynamically interrelated components, e.g. image generation and image enrichment of details. This study investigated the cognitive and neural correlates of sequential image generation. An event-related fMRI experiment was carried out in which general and specific images had to be generated sequentially in two different positions. Participants had to generate either a general image first and then a specific one or a specific image first and then a general one, in response to the same word-stimulus. Generation times showed that specific images took shorter to be produced if they had been preceded by the generation of a general image. The fMRI results showed that position of generation and type of image was associated with different patterns of neurofunctional change. When an image was generated as first, areas of activation were found in the parahippocampal, fusiform and occipital regions. These are areas associated with memory retrieval and visual processing. When an image was generated as second, significant activations were found in superior temporal and precuneus areas, brain structures that are involved in the storage of visual memory for object shapes and imagery, respectively. The generation of a general image was supported by frontal areas and by the precuneus. The generation of a specific image involved frontal and thalamic areas (structures associated with visual processing of details) and the posterior cingulate cortex. When shifting from a specific image to a general one, a higher level of activity was found in the middle frontal gyrus involved in global visuo-spatial processing, suggesting that the generation of specific images required the retrieval of an object’s global shape. Altogether, these data suggest that the sequential generation of different types of image is associated with discrete processes but also shares common cognitive and neural components.     

Computing finite models by reduction to function-free clause logic

Recent years have seen considerable interest in procedures for computing finite models of first-order logic specifications. One of the major paradigms, MACE-style model building, is based on reducing model search to a sequence of propositional satisfiability problems and applying (efficient) SAT solvers to them. A problem with this method is that it does not scale well because the propositional formulas to be considered may become very large.We propose instead to reduce model search to a sequence of satisfiability problems consisting of function-free first-order clause sets, and to apply (efficient) theorem provers capable of deciding such problems. The main appeal of this method is that first-order clause sets grow more slowly than their propositional counterparts, thus allowing for more space efficient reasoning.In this paper we describe our proposed reduction in detail and discuss how it is integrated into the Darwin prover, our implementation of the Model Evolution calculus. The results are general, however, as our approach can be used in principle with any system that decides the satisfiability of function-free first-order clause sets.To demonstrate its practical feasibility, we tested our approach on all satisfiable problems from the TPTP library. Our methods can solve a significant subset of these problems, which overlaps but is not included in the subset of problems solvable by state-of-the-art finite model builders such as Paradox and Mace4.     

Early alternative derivations of Fechner's law

Historians of psychology, notably Boring, fostered Fechner's idea that Weber's law is the indispensable basis for the derivation of the logarithmic psychophysical law. However, it is shown here that Bernoulli in 1738 and Thurstone in 1931 derived the logarithmic law using principles other than Weber's law and that Fechner and Thurstone based their derivations on the principles originally employed by Bernoulli. It is concluded that awareness of researchers about Bernoulli's and Thurstone's derivations could expand the directions of research on the form of the psychophysical law. © 2009 Wiley Periodicals, Inc.