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Biomedical subjects

G Chastain

Publications and source records attributed to G Chastain.

At least 37 records · Page 2Linked to original sources
PubMed1988

Target letter inclusion in single and multiple word substrings and identification accuracy.

In experiment 1, target letter discrimination in quadrigrams containing multiple subwords was found to be no more accurate than target letter discrimination in strings of four unrelated letters. Discrimination in quadrigrams, each including the target letter and a one-word trigram of which the target was not a part, was significantly poorer than discrimination in either of the other two types. In Experiment 2, a possible explanation of the latter result involving capacity limitations was eliminated by presenting the target above or below the other letters, which were presented in the same order as in corresponding strings in Experiment 1. The results are explained with respect to the interactive activation model of context effects in letter perception, with a modification proposed involving inhibitory connections between word nodes.

Form Perception↗
PubMed1987

Visually-presented letter strings typically are encoded phonologically: some converging evidence.

Three experiments were conducted to show that phonological encoding is typical for visually-presented letter strings, and that an interactive activation model with a phonological route to the mental lexicon accounts adequately for the word-superiority effect. In Experiment 1, pseudohomophones produced a word-superiority effect that was as great as that produced by words. More accurate target discrimination in homophones than in nonhomophones in Experiment 2 was interpreted to mean that excitability of entries in the mental lexicon increases with frequency of access. Target discrimination accuracy was inversely related to the phonological complexity of strings containing targets in Experiment 3, supposedly because lexical access through which target discrimination is enhanced becomes more difficult as phonological complexity increases.

Attention↗
PubMed1986

Neurologic complications in oral polio vaccine recipients.

Between April 1982 and June 1983 four children 3 to 24 months of age were referred for evaluation of neurologic abnormalities found to be compatible with vaccine-related poliovirus infection, which had not been suspected by referring physicians. Patients were epidemiologically unrelated residents of Indiana, and none had prior symptoms suggestive of immunodeficiency. All had received poliovirus vaccine orally (first dose in three, fourth dose in one) and a diphtheria-tetanus-pertussis injection in the left anterior thigh within 30 days of symptoms. A vaccine-like strain of poliovirus was isolated from each patient, and each had symptoms (left leg paralysis in three; developmental regression, spasticity, and progressive fatal cerebral atrophy in one) persisting for at least 6 months. Immune function was normal in two with poliovirus type 3 infection, and abnormal (hypogammaglobulinemia, combined immunodeficiency) in two with type 1 and type 2 infection, respectively. The incidence of observed vaccine-related poliovirus infection in Indiana recipients of orally administered poliovirus vaccine was 0.058 per 100,000 per year, significantly greater (P less than 0.001) than predicted.

Atrophy↗
PubMed1986

Facilitation in letter detection with sequentially presented homophonic strings.

A consistent phonology between sequentially presented pseudoword quadrigrams was found to improve performance in a letter-detection task. Each of 8 subjects was required to judge whether an M appeared in either the initial or terminal position of letter strings. The letter N was used as a foil. For each presentation, two quadrigrams appeared sequentially, the first for 20 ms and the second for a duration that allowed approximately 75% overall accuracy. The strings differed only by the letter next to the one on the opposite end of the string from the M or N. Subjects were not told that two strings were exposed on each presentation, and when asked, none reported having been aware of this. Nevertheless, detection was significantly better when the two strings were homophones (e.g., SERM, SIRM) than when they were not (e.g., SARM, SORM). Results are discussed in terms of phonological access to the mental lexicon.

Discrimination Learning↗
PubMed1985

Positional differences in performance on members of confusable and nonconfusable letter pairs.

A parafoveally presented letter is more accurately identified when flanked by a letter to its foveal side than when flanked by one to its peripheral side, but only if the two letters are nonconfusable. With confusable letters there is no such relative position effect. Four experiments indicated that the basis for this confusability-asymmetry interaction is not criterion or response bias, but rather that it occurs earlier in visual processing. In Experiment 1 the interaction was found when only one pair member was reported, thus eliminating response bias requiring the report of both letters as the source of the effect. In Experiment 2 the data were subjected to signal detection analysis, and the interaction persisted. In Experiment 3 pair members were presented simultaneously or in rapid sequence, and the interaction was found only with simultaneous presentations. In Experiment 4 letters were used with upper- and lowercase counterparts that were quite different in shape. Uppercase letters that were most and least confusable for each subject were paired for presentation in their upper case form or in mixed-case form. The interaction occurred only with upper-case pairs.

Attention↗
PubMed1984

Phonological access to the mental lexicon in a target discrimination task.

A phonological route to the mental lexicon was demonstrated in two experiments. Each involved a target discrimination task in which the target was the first or last letter of a quadrigram. Half the quadrigrams were pseudohomophones (identical in sound but not in spelling to an English word) and the other half were nonhomophones (pronounceable but neither spelled like nor sounding like any English word). In Experiment 1 each pseudohomophone had a nonhomophone counterpart produced by changing only the letter on the opposite end of the string from the target. In Experiment 2 the nonhomophone counterparts were produced by changing only the letter next to the one on the opposite end of the string from the target; thus the extreme letters were the same for both types of quadrigrams. Performance was significantly better on pseudohomophones than on nonhomophones in both experiments.

Form Perception↗
PubMed1983

Parafoveal identification asymmetry in a lateral masking effect.

The degree to which the identification of a parafoveally presented letter target was impaired by being flanked by a foveal or peripheral nontarget at a target-mask interval of zero, 75, or 150 msec, was examined. Peripheral placement of the nontarget was more disruptive than foveal placement, and this asymmetry was significantly more pronounced at a 75-msec interval than at either of the other two. This finding is consonant with explanations of the asymmetry based on target visibility rather than on criterion or response factors.

Attention↗