The time course of visual afterimages: data and theory

Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern (Vidyasagar et al, 1999 Nature 399 422-423; Francis and Rothmayer, 2003 Perception and Psychophysics 65 508-522). We investigated how the timing between the first stimulus (a vertical bar grating) and the second stimulus (a horizontal bar grating) affected the visibility of the afterimage (a perceived vertical grating). As the duration from offset of the first stimulus increased, reports of afterimages decreased. Holding fixed the total time from offset of the first stimulus and increasing the duration from offset of the second stimulus while decreasing the time between the first and second stimuli, caused a decrease in afterimage reports. We interpret this finding in terms of Grossberg's BCS - FCS (boundary contour system--feature contour system) theory. In this theory, the afterimage percept is the result of color complement after-responses in the FCS system interacting with orientation after-responses in the BCS system. The two types of after-responses interact at a stage of neural filling-in to produce the afterimage percept. As the duration between the stimuli increases, the color after-responses weaken so that visible filling-in is less likely to occur. A similar effect occurs for the orientation after-responses but at a faster time scale. Simulations of the model match the experimental data.     

Discrepancies between premorbid and current IQ as a function of progressive mental deterioration

The declining cognitive functioning typically found in patients with Alzheimer's disease presents an opportunity to study that decline. The changing magnitude of ever widening discrepancies between premorbid estimators of IQ and observed IQ increases as severity of the disease increases. Premorbid IQs estimated by these scores (the National Adult Reading Test-Revised, the reading tests of the Revised and Third Editions of the Wide Range Achievement Test, and a demographically based regression index for the Wechsler Adult Intelligence Scale-Revised) had relatively similar discrepancies from obtained WAIS-R Full Scale IQs in samples of normal elderly (n = 30), and elderly patients diagnosed with mild (n = 30) and moderate Alzheimer's disease (n = 30) dementia. The discrepancies became larger, regardless of premorbid estimator, as disease severity progressed from none to mild to moderate across the samples.     

Two interpretations of the discrimination parameter

In this paper we propose two interpretations for the discrimination parameter in the two-parameter logistic model (2PLM). The interpretations are based on the relation between the 2PLM and two stochastic models. In the first interpretation, the 2PLM is linked to a diffusion model so that the probability of absorption equals the 2PLM. The discrimination parameter is the distance between the two absorbing boundaries and therefore the amount of information that has to be collected before a response to an item can be given. For the second interpretation, the 2PLM is connected to a specific type of race model. In the race model, the discrimination parameter is inversely related to the dependency of the information used in the decision process. Extended versions of both models with person-to-person variability in the difficulty parameter are considered. When fitted to a data set, it is shown that a generalization of the race model that allows for dependency between choices and response times (RTs) is the best-fitting model.     

The General Health Questionnaire and Eysenck's three-dimensional model of personality

A sample of 115 men and women between the ages of 20 and 60 completed the 30-item General Health Questionnaire together with the short-form Revised Eysenck Personality Questionnaire. The data indicate psychological distress so assessed is correlated .43 (p <.001) with Neuroticism and -.26 (p <.01) with Introversion but is unrelated to Psychoticism scores.     

Fragment memories mark the end of childhood amnesia

Adults described and dated two kinds of first remembrances: a personal event memory (the recollection of a personal episode that had occurred at some time in some place) and a memory fragment (an isolated memory moment having no event context and remembered, perhaps, as an image, a behavior, or an emotion). First fragment memories were judged to have originated substantially earlier in life than first event memories--approximately 3 1/3 years of age for first fragment memories versus roughly 4 years of age for first event memories. We conclude that the end of childhood amnesia is marked not by our earliest episodic memories, but by the earliest remembered fragments of childhood experiences.     

Decision-bound theory and the influence of familiarity

In this article, we derive a nonparametric prediction from decision-bound theory (DBT). The crucial aspect that is tested is whether or not familiarity of a stimulus affects response time in categorization. We show that, for our design, DBT, extended with some reasonable and testable assumptions, predicts no familiarity effect. Our prediction is nonparametric in that, rather than fit a specific instantiation of general DBT, we posit only some general assumptions of this theory and derive the prediction from these assumptions. It is found that familiarity did have a strong impact on response time for at least half of our participants. We suggest that DBT is in itself incomplete and should be extended to account for the full range of available data.     

Interactions of afterimages for orientation and color: experimental data and model simulations

Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern. We report an experiment that quantifies some properties of this type of afterimage. It is shown that it is important for the two patterns to have orthogonal orientations and that the appearance of the afterimage does not depend on the spatial frequency of the second pattern. We then show that Grossberg's model of interacting boundary and feature contour systems can account for the observed properties of these afterimages.     

On the (non)categorical perception of lexical tones

Identification and discrimination of lexical tones in Cantonese were compared in the context of a traditional categorical perception paradigm. Three lexical tone continua were used: one ranging from low level to high level, one from high rising to high level, and one from low falling to high rising. Identification data showed steep slopes at category boundaries, suggesting that lexical tones are perceived categorically. In contrast, discrimination curves generally showed much weaker evidence for categorical perception. Subsequent investigation showed that the presence of a tonal context played a strong role in the identification of target tones and less of a role in discrimination. The results are consistent with the hypothesis that tonal category boundaries are determined by a combination of regions of natural auditory sensitivity and the influence of linguistic experience.     

A nonlinear mixed model framework for item response theory

Mixed models take the dependency between observations based on the same cluster into account by introducing 1 or more random effects. Common item response theory (IRT) models introduce latent person variables to model the dependence between responses of the same participant. Assuming a distribution for the latent variables, these IRT models are formally equivalent with nonlinear mixed models. It is shown how a variety of IRT models can be formulated as particular instances of nonlinear mixed models. The unifying framework offers the advantage that relations between different IRT models become explicit and that it is rather straightforward to see how existing IRT models can be adapted and extended. The approach is illustrated with a self-report study on anger.