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Biomedical subjects

R S Johnston

Publications and source records attributed to R S Johnston.

14 recordsLinked to original sources
PubMed1998

Memory span, naming speed, and memory strategies in poor and normal readers.

Eleven-year-old severely impaired poor readers failed to show a word length effect with pictorial presentation, but showed an effect of equal magnitude to that of reading age and chronological age controls with auditory presentation. The lack of a pictorial word length effect was unlikely to be due to slow speed of naming skills, as in one study these were at least as fast as those of the reading age controls. It is possible that the poor readers failed to verbally encode the pictures. However, they reported using verbal rehearsal, and lip movements were often observed during presentation, suggesting that they did verbally encode the items. Therefore they may have failed to show a word length effect because they did not retrieve information from the phonological store at recall. Although the poor readers had impaired naming speed skills for their age on both discrete item identification and articulation rate tasks, they could not be equated with their chronological age controls on memory span or reading when these naming speed differences were controlled. However, the groups were matched on the naming speed measures when differences in reading ability were controlled.

Child↗
PubMed1997

Children's arithmetical difficulties: contributions from processing speed, item identification, and short-term memory.

Children's arithmetical difficulties are often explained in terms of a short-term memory deficit. However, the underlying cause of this memory deficit is unclear, with some researchers suggesting a slow articulation rate and hence increased decay of information during recall, while others offer an explanation in terms of slow speed of item identification, indicating difficulty in retrieving information stored in long-term memory. General processing speed is also related to measures of short-term memory but has rarely been assessed in studies of children's arithmetic. Measures of short-term memory, processing speed, sequencing ability, and retrieval of information from long-term memory were therefore given to 7-year-old children. When reading ability was controlled for, arithmetic ability was best predicted by processing speed, with short-term memory accounting for no further unique variance. It was concluded that children with arithmetic difficulties have problems specifically in automating basic arithmetic facts which may stem from a general speed of processing deficit.

Analysis of Variance↗
PubMed1995

The functions of phonology in the acquisition of reading: lexical and sentence processing.

It has been claimed (V. Coltheart, Laxon, Rickard, & Elton, 1988) that learners as well as skilled readers use phonology for multiple functions in reading-for-meaning tasks. This claim was examined using lexical decision and sentence evaluation tasks. It was found in the first experiment that the type of instruction learners had received determined whether there was prelexical use of phonology in responding to items out of sentence context. Type of instruction had no effect when the items were in context. In the second experiment, performances on a homophone sentence evaluation task and a homophone semantic decision task, which excluded sentence processing, were examined. The results suggest that phonology served the function of access to lexical meanings in addition to any function in postlexical sentence processing. The obtained relationships between relative frequencies of the presented and unpresented homophone mates and item accuracy on these tasks were inconsistent with exclusive use of "direct access" but consistent with access of lexical meaning via phonology and application of a "spelling-check" procedure when multiple homophonic meanings are activated.

Attention↗
PubMed1991

Perception and action in 'visual form agnosia'.

A single case study of a patient with 'visual form agnosia' is presented. A severe visual recognition deficit was accompanied by impairments in discriminating shape, reflectance, and orientation, although visual acuity and colour vision, along with tactile recognition and intelligence, were largely preserved. Neuropsychological and behavioural investigations have indicated that the patient is able to utilize visual pattern information surprisingly well for the control of hand movements during reaching, and can even read many whole words, despite being unable to make simple discriminative judgements of shape or orientation. She seems to have no awareness of shape primitives through Gestalt grouping by similarity, continuity or symmetry. It is proposed that many of these perceptual disorders might be the combined result of (1) a selective loss of the cortical elaboration of the magnocellular visual processing stream, and (2) a selective output disconnection from a central processor of visual boundaries and shape primitives in the occipital cortex.

Adult↗
PubMed1990

Perceptual dysfunction in poor readers: evidence for visual and auditory segmentation problems in a sub-group of poor readers.

The purpose of this study was to consider reading disorders in children within the context of their general perceptual development. A review of the literature suggested that visual and auditory perceptual skills advance from a holistic to an analytical approach, and that reading skills also show this progression. It was proposed that poor readers might show impairments in visual and auditory segmentation tasks, if these skills are important factors in reading development. This hypothesis was tested on a sample (N = 20) of poor readers in the primary age range who were assessed against reading age and chronological age control groups. The hypothesis was partially borne out, a quarter of the sample performing very poorly on both types of tasks. It was argued that segmentation problems in perceptual tasks may underlie reading failure in some children, although the direction of the causation has yet to be determined.

Auditory Perceptual Disorders↗
PubMed1989

Is dependence on phonological information in children's reading a product of instructional approach?

Eight-year-old British children were found to be less accurate at rejecting pseudohomophones than ordinary nonwords in a lexical decision task, but 8-year-old New Zealand children did not show this effect. A subsequent homophone decision task showed that this difference was not due to the New Zealand children being unable to distinguish pseudohomophones from other nonwords. The New Zealand children, however, were less accurate than the British children in pronouncing the pseudohomophones they had identified. It was argued that the British children tended to sound out the items before making a choice in the lexical decision task, which gave salience to phonological rather than visual information, resulting in increased errors to the pseudohomophones. It was concluded that where the British children showed this dependency on use of phonological information it was a product of the teaching approach they had experienced.

Child↗
PubMed1987

Phonological similarity effects, memory span and developmental reading disorders: the nature of the relationship.

Eight-and 11-year-old poor readers of average and below average intelligence carried out a visually presented immediate memory task, recalling strings of similar- and dissimilar-sounding letters. Task difficulty was adjusted for each child by determining memory span for the dissimilar items prior to the memory task. All poor reader groups recalled significantly more dissimilar- than similar-sounding items, and the magnitude of these effects was comparable to those shown by their chronological and reading age controls. A close association was found between memory span and reading age, such that average intelligence poor readers had memory spans indistinguishable from those of their reading age controls. Furthermore, a highly significant correlation was found between memory span and reading age. However, it was concluded that this relationship could not be primarily due to a substantial immediate memory component in word recognition as the below average intelligence poor readers had poorer memory spans than the brighter poor readers, yet they had very similar reading ages. Additionally, a weaker association was found between memory span and non-word reading than between memory span and word reading. It was hypothesized that recognition difficulties may be the primary problem underlying both poor word recognition and immediate memory impairments in children with reading disorders.

Child↗
PubMed1983

Developmental deep dyslexia?

A detailed analysis was made of the errors of a developmental dyslexic who is now 18 years of age. It was found that her error pattern was very similar to that observed in a particular form of acquired dyslexia, i.e. deep dyslexia. She made semantic, visual, derivational and function word substitution errors, and was almost completely unable to read non-words. Although the possibility of brain damage cannot be completely ruled out, her case remains an unusual one as her reading disorder is a certain extent developmental in nature in that she has never achieved fluent reading.

Adolescent↗
PubMed1982

Phonological coding in dyslexic readers.

A study was made of the ability of 9-, 12-, and 14-year-old dyslexics to recall auditorily presented rhyming and non-rhyming letter strings. These children showed a normal phonemic confusability effect, although overall their recall was much poorer than that of their chronological age controls; their recall levels were in fact very similar to those of their reading age controls. It was concluded that although previous studies have argued that poor readers show a weak phonemic confusability effect, this finding does not appear to be generalizable to older poor readers.

Adolescent↗
PubMed1980

African swine fever in Malta, 1978.

In March 1978 an outbreak of African swine fever (ASF) occurred in Malta. The disease spread rapidly and by April 13, ASF had been found on 304 premises involving 25,100 pigs. A census carried out on April 15/16 showed that there were at least 1440 premises containing 70,700 pigs on the island. A slaughter policy was implemented and depopulation of known infected premises started on April 15. Pigs which appeared normal on these premises were stored in freezers for subsequent processing for human consumption and by the end of June more than 4500 carcases were in cold store. The most consistent clinical signs were fever, anorexia and reluctance to move. Haemorrhagic lymph nodes and petechial haemorrhages in the kidneys were the predominant macroscopic lesions. A serum survey, using the immunoelectroosmophoresis technique, was carried out on 2409 sera from 200 farms collected at the Government abattoir during a four-week period. Of these sera, 308 (12.8 per cent) from 65 (32.5 per cent) of the farms contained antibodies to ASF virus. By August the original pig population had been reduced to one-third and a second census taken on August 15/16 showed that a total of 501 owners and 13,975 pigs remained. The decision was taken to slaughter all the remaining pigs and by the end of January 1979 there were no pigs in Malta. The outbreak cost an estimated 5 million pounds and provided the first occasion when any country had slaughtered all members of a species of domestic animal in order to eliminate a disease.

Abattoirs↗