Biomedical subjects

D J K Mewhort

Publications and source records attributed to D J K Mewhort.

10 recordsLinked to original sources

PubMed2005

The influence of grammatical, local, and organizational redundancy on implicit learning: an analysis using information theory.

People behave as if they know the structure of their environment. Because people rarely study that structure explicitly, several theorists have postulated an implicit learning system that abstracts that structure automatically. An alternative view is that people respond to local structure that derives from global structure. Measures are developed that quantify structure in a set of stimuli, in individual stimuli, and in encoded stimuli. The authors apply the measures to examine serial recall for sequences of colors generated using a stationary Markov grammar. They demonstrate that the 3 kinds of redundancy are confounded and show that the memorial advantage for grammatical stimuli reflects participants' use of local expressions of grammatical structure to aid learning.

Humans↗

PubMed2005

A comparison of the randomization test with the F test when error is skewed.

I compared the randomization/permutation test and the F test for a two-cell comparative experiment. I varied (1) the number of observations per cell, (2) the size of the treatment effect, (3) the shape of the underlying distribution of error and, (4) for cases with skewed error, whether or not the skew was correlated with the treatment. With normal error, there was little difference between the tests. When error was skewed, by contrast, the randomization test was more sensitive than the F test, and if the amount of skew was correlated with the treatment, the advantage for the randomization test was both large and positively correlated with the treatment. I conclude that, because the randomization test was never less powerful than the F test, it should replace the F test in routine work.

Humans↗

PubMed2004

Tracking attention with the focus-window technique: the information filter must be calibrated.

Many researchers have recommended the focus-window tracking (FWT) technique to study the course of information acquisition and visual attention. In FWT, the stimulus is blurred, and the subject scans for information by moving a clear window with a computer mouse. We show that poor calibration of the blur filter will bias search behavior in FWT because diagnostically useful information may leak through a filter even though the subjects are unaware of it. To provide a valid index of information acquisition, FWT requires an information filter that is calibrated to the task.

Adolescent↗

PubMed2004

Case-sensitive letter and bigram frequency counts from large-scale English corpora.

We tabulated upper- and lowercase letter frequency using several large-scale English corpora (approximately 183 million words in total). The results indicate that the relative frequencies for upper- and lowercase letters are not equivalent. We report a letter-naming experiment in which uppercase frequency predicted response time to uppercase letters better than did lowercase frequency. Tables of case-sensitive letter and bigram frequency are provided, including common nonalphabetic characters. Because subjects are sensitive to frequency relationships among letters, we recommend that experimenters use case-sensitive counts when constructing stimuli from letters.

Cues↗

PubMed2003

Do conjunction errors in auditory recognition imply feature migration?

It has recently been proposed that the feature values (e.g., pitch, duration, etc.) of tones are processed in separate perceptual channels and are later reintegrated to form the experience of a unitary percept. Patterns of errors in recognizing combinations of auditory features have been taken as failures of, and thus evidence for, an auditory feature-integration process. We outline an alternative interpretation of these effects based on similarity structure of the stimuli.

Humans↗

PubMed2003

The effect of feature frequency on short-term recognition memory.

We report two experiments using Sternberg's (1969) multitrial recognition-memory paradigm. We used colored shapes as stimuli and manipulated the frequency of the shapes (but not of the colors) across trials. For lures containing an extralist shape (i.e., a shape not studied in the current study list), responses were faster if the shape had occurred infrequently than if it had occurred frequently in the preceding trials. For lures containing an extralist color and a studied shape, by contrast, the frequency of the shape in the preceding trials was irrelevant. We conclude that correct rejections depend solely on contradictory evidence. Furthermore, low-frequency target items were recognized more easily than high-frequency targets. Both the interaction of frequency with the features of the lures and the main effect of frequency for the targets are problematic for current accounts of recognition.

Form Perception↗

PubMed2002

Letter encoding in visual word identification: more evidence for a word-integration explanation for parafoveal preview effects in reading.

A letter string presented briefly in the parafovea facilitates naming a foveally presented word provided that the two stimuli are orthographically similar. The facilitation (called priming) is asymmetrical in that to obtain it, both letter strings must have the first letters in common. One possible explanation, a letter-integration hypothesis, proposes that readers only identify the letters at the beginning of the parafoveal stimulus, an action that facilitates processing the target. Another explanation, a word-integration hypothesis, postulates that all the letters of the parafoveal stimulus are identified and that the asymmetry occurs because the first letters of the parafoveal stimulus are weighted more heavily than the later ones. The two accounts differ in the way the position of the first letter is determined: The first postulates that readers know the side to identify first without reference to the stimulus; the second postulates that readers establish an order on the stimuli postcategorically. To distinguish the views, we presented English and Hebrew stimuli to bilingual readers. Readers could not anticipate the position of the first letters; hence, if the letter-integration explanation is correct, the asymmetry in the priming should be attenuated. Consistent with the word-integration explanation, however, priming occurred when the target shared the beginning letters with the prime in both languages.

Adult↗

PubMed2002

What information underlies correct rejections in short-term recognition memory?

We propose that correct rejections are based on information that contradicts the study set, rather than on insufficient familiarity. Using two-dimensional stimuli, we varied the featural overlap between lures and the study set so that one feature of the lure had occurred during study and the second feature of the lure had not occurred. Familiarity varied with the number of times the studied feature had occurred, whereas detectability of the extralist feature varied with the number of studied alternatives on the same dimension. Lures increased in difficulty with familiarity only when familiarity of the studied feature was confounded with the number of alternatives to the extralist feature. Hence, the difficulty in rejecting the lure was controlled by the number of alternatives to the extralist feature, not by the familiarity of the lure. Current theory requires additional representation assumptions and a new comparison process to accommodate these data.

Adult↗

PubMed2002

Quantile maximum likelihood estimation of response time distributions.

We introduce and evaluate via a Monte Carlo study a robust new estimation technique that fits distribution functions to grouped response time (RT) data, where the grouping is determined by sample quantiles. The new estimator, quantile maximum likelihood (QML), is more efficient and less biased than the best alternative estimation technique when fitting the commonly used ex-Gaussian distribution. Limitations of the Monte Carlo results are discussed and guidance provided for the practical application of the new technique. Because QML estimation can be computationally costly, we make fast open source code for fitting available that can be easily modified to use QML in the estimation of any distribution function.

Data Interpretation, Statistical↗

PubMedDate not supplied

Sharpening the echo: an iterative-resonance model for short-term recognition memory.

We present an iterative-resonance model for recognition memory. On successive iterations, the probe is compared against a feature-by-feature profile of the study set. Yes decisions depend on the similarity of the probe to the profile; No decisions depend on a count of elements in the probe that are not in the profile. Successive iterations sharpen the evidence, and response latency is a function of the number of iterations needed to obtain a sufficiently clear result. The model successfully simulates classic data as well as recent data problematic for alternate models.

Algorithms↗