Perceived contrast explains asymmetries in visual-search tasks with shaded stimuli

Shaded stimuli have traditionally been used in the context of three-dimensional (3-D) shape perception. Many studies have shown a persistent asymmetry in that a circle filled with a shaded gradient that is dark at the top and bright at the bottom (top-dark circle) is much easier to locate among top-bright circles than in the opposite arrangement (a top-bright circle among top-dark circles). The immediate 3-D interpretation of top-dark and top-bright circles as hollows and protuberances, respectively, and the asymmetry just described have been explained in terms of 3-D percepts. The work described here challenges this view: the results of the first experiment show that top-dark circles are perceived as having 10% higher contrast than top-bright circles of the same physical contrast. Experiment 2 replicates classical visual-search experiments but adding a new condition where target and distractors were subjectively equated in contrast. For five of six subjects, the ubiquitous asymmetry disappears in this condition.     

The role of parametric assumptions in adaptive Bayesian estimation

Variants of adaptive Bayesian procedures for estimating the 5% point on a psychometric function were studied by simulation. Bias and standard error were the criteria to evaluate performance. The results indicated a superiority of (a) uniform priors, (b) model likelihood functions that are odd symmetric about threshold and that have parameter values larger than their counterparts in the psychometric function, (c) stimulus placement at the prior mean, and (d) estimates defined as the posterior mean. Unbiasedness arises in only 10 trials, and 20 trials ensure constant standard errors. The standard error of the estimates equals 0.617 times the inverse of the square root of the number of trials. Other variants yielded bias and larger standard errors.     

Accuracy in discriminating blood glucose levels in a sample of children with type 1 diabetes

The present study explores accuracy in estimating blood glucose levels (BGL) in children with type 1 diabetes and analyzes the kinds of symptoms and cues which they use to estimate their BGL. Forty two children with type 1 diabetes completed a SI/IC-3 scale consisting of 28 items (22 symptoms and 6 feelings), indicating those which they perceived at the time and their intensity. They estimated their BGL and gave reasons for their estimation, before having a blood glucose level analysis performed. The results indicated great variability in the accuracy of estimating BGL. They showed failures in the correct discrimination of symptoms of hypoglycemia as well as the presence of false beliefs regarding indicative symptoms of hyperglycemia, and the absence of symptoms as an indicator for euglycemia, beliefs which provoke different and frequent errors in the estimation of BGL. Correct use of external signs is shown to be related to correct estimations of normal BGL, as well as hypoglycemia and hyperglycemia. We discuss the implications these results could have on designing psychological intervention procedures for diabetics in the form of training programs to discriminate BGL accurately, taking into account these findings and previous studies completed in the same field.     

Deficit of preparatory attention in frontotemporal dementia

We studied preparatory attention in patients suffering from frontotemporal dementia in the beginning stages of the disease, using an experimental test developed by LaBerge, Auclair, and Siéroff (2000). In this experimental test, a distracter can appear while subjects have to prepare to respond to a simple target. The probability that a distracter can appear in a trial is varied across three blocks. Normal controls show an increase of response times to targets (slope) as a function of the distracter probability, preparatory attention to the target is reduced by the increase of the distracter probability. Patients suffering from frontotemporal dementia show a slope of response times which is more than twice as large as the slope obtained by their matched controls. Such an abnormal increase of response times to targets is interpreted as a deficit in preparatory attention. Patients also show more omissions than controls. We suggest that this deficit in preparatory attention is related to the frontal lesion presented by the patients and can result in higher distractibility, a symptom frequently encountered in these patients.     

Toward a behavioral analysis of joint attention

Joint attention (JA) initiation is defined in cognitive-developmental psychology as a child's actions that verify or produce simultaneous attending by that child and an adult to some object or event in the environment so that both may experience the object or event together. This paper presents a contingency analysis of gaze shift in JA initiation. The analysis describes reinforcer-establishing and evocative effects of antecedent objects or events, discriminative and conditioned reinforcing functions of stimuli generated by adult behavior, and socially mediated reinforcers that may maintain JA behavior. A functional analysis of JA may describe multiple operant classes. The paper concludes with a discussion of JA deficits in children with autism spectrum disorders and suggestions for research and treatment.     

Sexual risk as an outcome of social oppression: data from a probability sample of Latino gay men in three U.S. cities

Based on data from a probability sample of 912 Latino gay men in 3 U.S. cities, a multivariate model of sexual risk was tested, including experiences of homophobia, racism, and poverty as predictors. Participants reported multiple instances of verbal and physical abuse, rude mistreatment, and discrimination on account of their sexual orientation and their race or ethnicity. Many reported experiences of poverty, such as inability to pay for basic necessities of food or shelter. Men who reported more instances of social discrimination and financial hardship were more psychologically distressed and more likely to participate in "difficult" sexual situations, as predicted. Participation in difficult sexual situations mediates the effects of social oppression and psychological distress on sexual risk behavior.     

Repetition priming effects from attended vs. ignored single words in a semantic categorization task

The present research examines priming effects from a centrally presented single-prime word to which participants were instructed to either attend or ignore. The prime word was followed by a single central target word to which participants made a semantic categorization (animate vs. inanimate) task. The main variables manipulated across experiments were attentional instructions (attend vs. ignore the prime word), presentation duration of the prime word (20, 50, 80 or 100 ms), prime-target stimulus onset asynchrony (SOA; 300 vs. 800 ms), and temporal presentation of instructions (before vs. after the prime word). The results showed (a) a consistent interaction between attentional instructions and repetition priming and (b) a qualitatively different ignored priming pattern as a function of prime duration: reduced positive priming (relative to the attend instruction) for prime exposures of 80 and 100 ms, and reliable negative priming for the shorter prime exposures of 20 and 50 ms. In addition (c), the differential priming pattern for attend and ignore trials was observed at a prime-target SOA of 800 ms (but not at a shorter 300-ms SOA) and only when instructions were presented before the prime word. Methodological and theoretical implications of the present findings for the extant negative priming literature are discussed.     

Processing of temporal information: Evidence from eye movements

In two experiments, we recorded eye movements to study how readers monitor temporal order information contained in narrative texts. Participants read short texts containing critical temporal information in the sixth sentence, which could be either consistent or inconsistent with temporal order information given in the second sentence. In Experiment 1, inconsistent sentences yielded more regressions to the second sentence and longer refixations of it. In Experiment 2, this pattern of eye movements was shown only by readers who noticed the inconsistency and were able to report it. Theoretical and methodological implications of the results for research on text comprehension are discussed.     

Visuomotor adaptation in normal aging

Visuomotor adaptation to a gradual or sudden screen cursor rotation was investigated in healthy young and elderly subjects. Both age groups were equally divided into two subgroups; one subgroup was exposed to 11.25° step increments of visual feedback rotation, every 45 trials (up to a total of 90°), whereas a second subgroup was subjected to 90° rotation from the onset of exposure. Participants performed discrete, horizontal hand movements to virtual targets in four randomized directions. Targets appeared on a computer screen in front of them, and a board prevented vision of the hand at all times. Differential effects of aging on visuomotor adaptation were found, depending on the time course of the visual distortion. In both age groups, early exposure to the sudden visual feedback distortion resulted in typical spiral-like trajectories, which became straighter by late exposure. However, the final adaptation level was reduced in the aged group, although the aftereffects were similar. When subjects were exposed to the gradual distortion, no statistically significant differences in measures of adaptation with advancing age were found. In this case, both age groups appeared to adapt equally. However, after removal of the distortion, elderly subjects showed reduced aftereffects as compared with the young group. These findings suggest differential effects of aging on adaptation to gradual versus sudden visual feedback distortions, and may help to explain the conflicting results obtained in previous visuomotor adaptation studies.     

Influence of prime-target relationship on semantic priming effects from words in a lexical-decision task

The present research examines the influence of prime-target relationship (associative and categorical versus categorical only) on priming effects from attended and ignored parafoveal words. Participants performed a lexical-decision task on a single central target, which was preceded by two parafoveal prime words, one of which (the attended prime) was spatially precued. The results showed reliable positive and negative priming effects from attended and ignored words, respectively. However, this priming pattern was observed only for the "associative and categorical", but not for the "categorical only" relationship condition. These results suggest that the lack of semantic priming effects from words in some prior studies may be attributed to the kind of material used (i.e. weakly-associated word pairs).