Alphabetic search: Comment on Klahr, Chase, and Lovelace (1983).

Response time (RT) curves were obtained from Ss who were instructed to search for following or preceding letters in the alphabet with respect to given stimulus letters. To describe the shape of these curves, D. Klahr et al (see record 1984-05777-001) proposed a search model. It was assumed that the alphabet was internally represented by a number of chunks of a few letters. Klahr et al assumed that serial searches occurred along 2 hierarchical levels: (1) a search for the correct chunk and (2) a search of the letters within the chunk. The Klahr et al model predicted an ascending sawtooth-shaped RT curve. However, according to the authors' analysis of the data, the RT curves did not show the expected sawtooth shapes. In order to find out whether the lack of empirical support for the model was an artifact of averaging the data, the experiment was replicated. It was found that individual RT curves did not show the shape characteristics that were predicted by the Klahr et al model either. The data supported the hypothesis that the access of letters was direct without any hierarchy, and that the retrieval of successive letters was determined by the variable associations between subsequent letters. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preference reversals: Violations of unidimensional procedure invariance.

Preference reversals have usually been explained by weighted additive models, in which different tasks give rise to different importance weights for the stimulus attributes, resulting in contradictory trade-offs. This article presents a preference reversal of a more extreme nature. Let (10, 5 Migr) denote living 10 years with a migraine for 5 days per week. Many participants preferred (10, 5 Migr) to (20, 5 Migr). However, when asked to equate these two options with a shorter period of good health, they usually demanded more healthy life years for (20, 5 Migr) than for (10, 5 Migr). This preference reversal within a single dimension cannot be explained by different importance weights and suggests irrationalities at a more fundamental level. Most participants did not change their responses after being confronted with their inconsistencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Large colour differences measured by spontaneous gestalt formation

Gestalt formation is used as a means to measure large colour differences. The stimulus is presented in the form of the Star of David, being made of two overlapping triangles of different colour, with the overlap being in a third colour. Through Gestalt formation the subjects perceive a triangle pointing to the left or to the right. Gestalt formation is assumed to occur for colour combinations with the smallest perceptual distance. We simulated responses at the ordinal level with several uniform-colour-distance models, derived from near-threshold colour-discrimination experiments. For isoluminant colours 84% of the responses, and for nonisoluminant colours 76% of the responses, are predicted correctly by the best model. We argue that the tritanopic direction is crucial for the understanding of large-colour-difference data.     

On the conditions affecting the contribution of color to brightness perception

Colored stimuli appear to be brighter than an achromatic stimulus of the same luminance as the colored stimuli. We have studied this effect using similarity judgments in a triadic scaling task. Several instructions and stimulus configurations were used. the color sets contained colors at three luminance levels. When subjects are instructed to attend to brightness differences, the contribution of the brightness axis is strongly increased relative to the contribution of the color channels. Moreover, a correction to the color input is necessary when subjects are instructed to attend to brightness similarities between saturated colors. For a fixed adaptation level, the chromatic input is relatively stronger for the lower luminance levels. This correction is absent in all other investigated conditions. the correction found here confirms an earlier report by Fairchild and Pirotta (1991).     

A review on family history of breast cancer: screening and counseling proposals for women with familial (non-hereditary) breast cancer

In a neural model of olfactory bulb processing, we demonstrate the putative role of the modulation of two types of inhibition, inspired by electrophysiological data on the effect of acetylcholine and noradrenaline on olfactory bulb synaptic transmission. Feedback regulation of modulation based on bulbar activity serves to 'normalize' the activity of output neurons in response to different levels of input activities. This mechanism also decreases the overlap between pairs of output patterns (Mitral cell activities), enhancing the discrimination between overlapping olfactory input patterns. The effect of the modulation at the two levels of interneurons is complementary: while an increase in periglomerular inhibition decreases the number of responding output neurons, a decrease in granule cell inhibition increases the firing frequencies of these neurons.