Hierarchical diffusion models for two-choice response times.

Two-choice response times are a common type of data, and much research has been devoted to the development of process models for such data. However, the practical application of these models is notoriously complicated, and flexible methods are largely nonexistent. We combine a popular model for choice response times—the Wiener diffusion process—with techniques from psychometrics in order to construct a hierarchical diffusion model. Chief among these techniques is the application of random effects, with which we allow for unexplained variability among participants, items, or other experimental units. These techniques lead to a modeling framework that is highly flexible and easy to work with. Among the many novel models this statistical framework provides are a multilevel diffusion model, regression diffusion models, and a large family of explanatory diffusion models. We provide examples and the necessary computer code. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A diffusion model analysis of the effects of aging on letter discrimination.

The effects of aging on accuracy and response time were examined in a letter discrimination experiment with young and older subjects. Results showed that older subjects (ages 60-75) were generally slower and less accurate than young subjects. R. Ratcliff's (1978) diffusion model was fit to the data, and it provided a good account of response times, their distributions, and response accuracy. The results produce similar age effects on the nondecision components of response time (about 50 ms slowing) and the response criteria (more conservative settings) to those from R. Ratcliff, A. Thapar, and G. McKoon (2001), but also show a reduced rate of accumulation of evidence for older subjects. The model-based approach has the advantage of allowing the separation of aging effects on different components of processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Application of the diffusion model to two-choice tasks for adults 75-90 years old.

The effects of aging on simple 2-choice decision making was investigated with the diffusion model (R. Ratcliff, 1978). Data for 75- to 90-year-olds were collected and compared with previous data from 60- to 75-year-olds and college students for 5 tasks: a signal detection-like task, letter and brightness discrimination with masking, recognition memory, and lexical decision. The model fit the data well and therefore allows components of processing to be examined as a function of age. Compared with decision-making processes in college students, decision criteria and nondecision components of processing increased with participants' age. However, the quality of the evidence on which decisions were based decreased with age only for letter and brightness discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An interactive activation model of context effects in letter perception: I. An account of basic findings.

Describes a model in which perception results from excitatory and inhibitory interactions of detectors for visual features, letters, and words. A visual input excites detectors for visual features in the display and for letters consistent with the active features. Letter detectors in turn excite detectors for consistent words. It is suggested that active word detectors mutually inhibit each other and send feedback to the letter level, strengthening activation and hence perceptibility of their constituent letters. Computer simulation of the model exhibits the perceptual advantage for letters in words over unrelated contexts and is considered consistent with basic facts about word advantage. Most important, the model produces facilitation for letters in pronounceable pseudowords as well as words. Pseudowords activate detectors for words that are consistent with most active letters, and feedback from the activated words strengthens activations of the letters in the pseudoword. The model thus accounts for apparently rule-governed performance without any actual rules. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structures in two-choice reaction-time data.

This study served (a) to illustrate a maximum likelihood estimation procedure for metric multidimensional scaling applied to speeded same–different judgments, (b) to compare the spatial representations of various stimulus sets derived from dissimilarity data obtained in conditions of data- and resource-limitations with the spatial representations of the same stimulus sets derived from dissimilarity measures collected in conditions of unlimited viewing and/or responding, and (c) to examine the concepts of integrality and separability as they apply to the dimensional decomposability of stimuli. The results showed that although the same spatial metrics best represented perceived dissimilarities for each subject within each stimulus set, individual differences and divergence with results obtained on similar stimulus sets in different conditions were apparent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A set-intersection model of letter recognition in the spatial probe task.

Proposes a dual-process model involving 2 interacting identification processes. The set-intersection model can explain the predominance of mislocations, but, contrary to independent dual-process models, predicts that mislocations and intrusions can be affected by the same variable. Results of 2 experiments conducted with 24 undergraduates support the set-intersection model but are difficult to explain using independent dual-process models. Computer simulations comparing a single-process identification model to the set-intersection model isolated the advantages of a new identification process in the set-intersection model. Only the set-intersection model successfully reproduced the results of the 2 experiments. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory span development: A time-based resource-sharing model account.

The time-based resource-sharing model (P. Barrouillet, S. Bernardin, & V. Camos, 2004) assumes that during complex working memory span tasks, attention is frequently and surreptitiously switched from processing to reactivate decaying memory traces before their complete loss. Three experiments involving children from 5 to 14 years of age investigated the role of this reactivation process in developmental differences in working memory spans. Though preschoolers seem to adopt a serial control without any attempt to refresh stored items when engaged in processing, the reactivation process is efficient from age 7 onward and increases in efficiency until late adolescence, underpinning a sizable part of developmental differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The masking account of attentional capture: A reply to Yantis and Jonides (1996).

B. S. Gibson (see record 1997-06229-001) has recently argued that stimulus-driven attentional capture by abrupt onsets (or new objects) may be due to forward masking of the no onsets (or old objects) by preceding figure-eight placeholders. Three experiments are reported in the present article that address recent arguments and evidence offered by S. Yantis and J. Jonides (see record 1997-06254-001) against the masking account of attentional capture. Contrary to Yantis and Jonides's claims, the present study provides strong support for the masking account of attentional capture. Thus, the masking account appears to provide the best explanation of the existing data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Priming and response selection processes in letter classification and identification tasks.

The processing of isolated visual letters was studied by means of a priming paradigm. In alphabetic (letter vs nonletter) classification, any letter prime reduced response times to letter targets. Additional facilitation occurred only with primes physically identical to the target. In letter naming, facilitation was seen with primes nominally identical to the target even when they were physically different. This result is not due to phonological priming because phonologically similar primes had no effect on naming times. Primes nominally different from the target but physically similar to it increased naming times. The classification task seems to be performed through the global monitoring of stored visual knowledge of letters. In contrast, the absolute identification of letters appears to rest on a signal-to-noise statistic derived from an abstract encoding of letter identities. Connectionist simulations provide support for these proposals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Bayesian model for implicit effects in perceptual identification.

Retrieving effectively from memory (REM; R. M. Shiffrin & M. Steyvers, 1997), an episodic model of memory, is extended to implicit memory phenomena, namely the perceptual identification studies reported in R. Ratcliff and G. McKoon (1997). In those studies, the influence of prior study was greatest when words were presented most briefly and when forced-choice targets and foils were most similar. R. Ratcliff and G. McKoon use these data to argue against models in which prior study changes a word's representation. A model in which prior study changes a word's representation by adding context information is fit to their data; at test, the model uses a Bayesian decision process to compare the perceptual and context features associated with the test flash to stored traces. The effects of prior study are due to matching extra context information and are larger when alternatives share many features, thereby reducing noise that attenuates these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the functional relationship between word identification and letter probability.

Investigated whether words made up of probable letters and probable letter combinations are more accurately recognized than words made up of improbable letters and improbable letter combinations. The experimental method corrected shortcomings in previous research which has shown accuracy of word recognition to be affected only by word probability and not by letter probability. The shortcomings were the confounding of different letter probability dimensions within one another. In the present investigation with 40 19-43 yr old adults, 100 words were assessed with respect to the probabilities of their letters and, independently, the conditional probabilities of their letters. Subsequent tests of recognition accuracy in a brief presentation showed accuracy to be greatest for words made up of letters having either high simple probabilities or high conditional probabilities. It is concluded that word recognition is an active, perhaps serial, process which makes liberal use of individual letter statistics to facilitate accurate recognition. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A multinomial model for short-term priming in word identification.

A simple multinomial model for short-term priming in perceptual word identification is presented. In the experiments to which the model is applied, prime words are presented just prior to a flashed target word, and subjects must decide which of 2 alternative words matches the target. The model assumes that on some proportion of trials, confusion among the words leads to the decision being based on 1 of the prime words instead of the target. In addition, it is assumed that subjects sometimes discount a prime that matches 1 of the test alternatives and so choose the alternative that does not match. With these assumptions, the model fits the data from 5 experiments (including 4 used to develop the model known as ROUSE [responding optimally with unknown sources of evidence]; D. E. Huber, R. Shiffrin, K. Lyle, & K. Ruys, 2001). The multinomial model fits the data about as well as the ROUSE model and so should lead to further development and critical testing of both models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A letter from the publisher.

In this letter, the editor-in-chief announces that the Guilford Press will become the publisher of School Psychology Quarterly, previously titled Professional School Psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A childhood letter of Sigmund Freud.

Analyzes a childhood letter written by Freud in an attempt to discover early evidence of lasting personality characteristics. It is deduced that the letter was written when Freud was between 11 and 12 yrs old. Aspects of the letter reveal Freud's neatness and exactness, general conservatism, egocentricity, and deep emotional attachments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A counter model for implicit priming in perceptual word identification.

A model for the identification of briefly presented words is presented. The model accounts for data from naming and forced-choice experiments in which factors such as similarity of alternatives and stimulus presentation time are varied. The model assumes that counts are accumulated in counters that correspond to words and that a word is chosen as a response when the number of counts in its counter exceeds the maximum of the numbers of counts in other counters by a criterial value. Prior exposure to a word causes its counter to attract more counts than it otherwise would, and this yields priming effects. Ten experiments are presented, and the model provides correct predictions for the data. Implications of the model for research in implicit memory are considered. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Metacontrast masking in amblyopia.

Measured the time course of visual signals arising from each eye of 4 strabismic and/or anisometropic amblyopes and 2 visually normal Ss using monoptic metacontrast masking. The amblyope Ss had 1 nonamblyopic eye, clear ocular media, and normal fundi. The method involved the brightness estimation of a high-contrast disk target whose visibility varied as a function of the stimulus onset asynchrony (SOA) of a subsequent annular mask. Results indicate that the SOA of optimal masking was delayed in the amblyopic eye compared to that of the fellow nonamblyopic eye or with normal eyes. The smaller the target, the greater was this SOA difference and the broader was the amblyopic U-shaped masking function. This finding is discussed in terms of the current model of metacontrast and represents the differential effect of the amblyopic process on human sustained and transient neurons. (French abstract) (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A memory-based account of retrospective revaluation.

We adapt an instance model of human memory, Minerva 2, to simulate retrospective revaluation. In the account, memory preserves the events of individual trials in separate traces. A probe presented to memory contacts all traces in parallel and causes each to become active. The information retrieved from memory is the sum of the activated traces. Learning is modelled as a process of cued-recall; encoding is modelled as a process of differential encoding of unexpected features in the probe (i.e., expectancy-encoding). The model captures three examples of retrospective revaluation: backward blocking, recovery from blocking, and backward conditioned inhibition. The work integrates an understanding of human memory and complex associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A multiprocess account of hindsight bias in children.

In hindsight, that is, after receiving the correct answers to difficult questions, people's recall of their own prior answers tends to be biased toward the correct answers. We tested 139 participants from 3 age groups (9- and 12-year-olds and adults) in a hindsight-bias paradigm and found that all groups showed hindsight bias. Multinomial model-based analyses indicated that all age groups used the correct answers to reconstruct their original answers. In addition, the youngest group showed memory impairment caused by the presentation of the correct answers as well as an increased belief that they knew the correct answers all along. These results support a multiprocess explanation of hindsight bias in children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A diffusion model for tungsten powder carburization

A mathematical model describes the carburization kinetics of tungsten powders mixed with carbon and heated in hydrogen. It is based on diffusion of carbon through a shell of WC growing into particles which are modeled as spheres. The activation energy is 58 kcal/mole in the temperature range 1056 to 1833 °C. Hydrogen gas is important to transport carbon as methane or acetylene, but increased hydrogen pressure increases the rate of carburization so little that an adsorbed species such as CH probably controls the carbon concentration at the particle surface.     

A diffusion model for tungsten powder carburization

Metallurgical and Materials Transactions A - A mathematical model describes the carburization kinetics of tungsten powders mixed with carbon and heated in hydrogen. It is based on diffusion of...