Biomedical subjects

J Everatt

Publications and source records attributed to J Everatt.

6 recordsLinked to original sources

PubMed2001

Reflexive shifts of covert attention operate in an egocentric coordinate frame.

Covert shifts of attention have been shown to improve detection and discrimination thresholds for a range of visual stimuli. Although there is some evidence to suggest that the allocation of attention to a particular region of interest occurs in a retinotopic frame of reference, the importance of an allocentric, or object-based, framework has gained widespread empirical support. The current experiment investigates the nature of the spatial representation in which covert shifts of attention occur in response to a reflexive prime. Primes and targets were presented in four conditions designed to vary systematically the validity of the spatial relationship between the prime and target in egocentric or allocentric coordinate frameworks. A significant advantage, in terms of reaction time and correct identification, was found for targets located in positions previously primed in an egocentric (but not allocentric) framework whereas there was no advantage for locations primed in an allocentric (but not egocentric) framework. These results suggest that the allocation of covert spatial attention within an egocentric framework may be more important than previously thought.

Attention↗

PubMed1999

Visual processing and dyslexia.

Magnocellular-pathway deficits have been hypothesized to be responsible for the problems experienced by dyslexic individuals in reading. However, research has yet to provide a detailed account of the consequences of these deficits or to identify the behavioural link between them and reading disabilities. The aim of the present study was to determine the potential consequences of the magnocellular-pathway deficits for dyslexics in a comprehensive range of visual tasks. Dyslexics and nondyslexics were compared on their ability to (i) perform vernier-acuity and orientation-acuity tasks; (ii) perceive motion by using a range of measures common in the psychophysical literature (Dmin, Dmax, and global coherence); and (iii) perceive shapes presented in random-dot stereograms at a range of disparity pedestals, thereby dissociating stereopsis from vergence control. The results indicated no significant differences in performance between the dyslexic and nondyslexic subjects in terms of the visual-acuity measures. In general, dyslexics performed relatively poorly on measures of motion perception and stereopsis, although when considered individually some of the dyslexics performed better than some of the controls. The poor performance of the dyslexics in the stereo-gram tasks was attributable to a subgroup of dyslexics who also appeared to have severe difficulty with the motion-coherence task. These data are consistent with previous evidence that some dyslexics may have deficits within the magnocellular visual pathway.

Adolescent↗

PubMed1998

Pre-oxygenation using face mask or mouthpiece with and without nose clip: patient preferences and efficacy.

We assessed the effectiveness of mouthpieces for oxygenation before induction of anaesthesia. In part 1 of the study we asked 52 day case patients whether they would prefer mask, mouthpiece, or mouthpiece with nose clip, and which they would be willing to use. In part 2 we pre-oxygenated 18 volunteers using each of the three methods in a crossover study. We measured time to 90% end tidal oxygen concentration (FE'O2), or maximum FE'O2 after 3 min if less than 90%. Of the patients surveyed, 20 (39%) preferred mask, 23 (44%) mouthpiece, one mouthpiece with nose clip and nine (17%) expressed no preference. Only 88% would be willing to use the face mask, but all would accept either the face mask or the mouthpiece with nose clip. In part 2 of the study, the mouthpiece alone proved significantly worse than the mask or mouthpiece with nose clip. The latter two did not differ significantly. Offering the alternative of mouthpiece with nose clip would increase patient acceptance of effective pre-oxygenation.

Adolescent↗

PubMed1990

How do readers know where to look next? Local information distributions influence eye fixations.

Skilled readers' eye movements were recorded as they inspected sentences in preparation for comprehension questions. The sentences were written around target words that had uneven distributions of information, in that the words were predictable, given either the first few letters or the last few letters. Some parts of these words can be described as being more important than others for successful word recognition, and the experiments asked whether inspection patterns reflect the uneven distributions. Four types of ten-letter word were used: words with highly redundant endings (e.g. engagement), with moderately redundant endings (e.g. repatriate), with moderately redundant beginnings (e.g. superstore), and words with informative beginnings and endings (e.g. amalgamate). Redundancy was defined operationally in terms of the number of possible completions of a word given the first few or last few letters. A highly redundant ending is therefore one that occurs frequently and cannot be used to identify the word. Words gaining just one fixation received this fixation nearer to the word's centre than in the case of the first fixation upon words gaining two fixations. The single fixation also had a longer duration, giving support to the notion of a convenient viewing location, which, when achieved, can lead to a net saving in inspection time. In the case of words with redundant endings gaining just one fixation, the fixation was nearer to the beginning of the word than in the case of words with informative endings, and this influence of word type upon the location of the first fixation was interpreted in favour of the parafoveal processing hypothesis of eye guidance during reading.

Adult↗

PubMedDate not supplied

Dyslexia screening measures and bilingualism.

A series of measures used in a number of dyslexia screening tests was administered to groups of 7-8-year old English monolinguals and Sylheti/English bilinguals. Within these groups a subgroup of children was distinguished by poor spelling and reading in the absence of general ability, sensory, emotional or behavioural problems, i.e. specific literacy difficulties (SpLD). General ability (assessed by Raven's matrices), chronological age, male/female ratio and mono/bilingualism were controlled between SpLD and control groups. Screening measures assessed phonological skills, rapid naming, the ability to recite or repeat sequences of verbal and non-verbal stimuli, and visual and motor skills. Sample sizes were small owing to the selection criteria used and the small number of bilingual SpLD children identified. However, the results were encouraging in differentiating SpLD bilinguals from their peers, with the phonological measures in particular presenting consistent findings across bilingual and monolingual groupings. Those differences found between bilinguals and monolinguals are discussed in terms of a bilingual influence on the skills assessed or the reduced reliability of the measure.

Child↗

PubMedDate not supplied

Individual differences in reading subprocesses: relationships between reading ability, lexical access, and eye movement control.

This study examines the relationship between individual reading subprocesses and general reading ability in college students. The reading measures included eye movements while reading a passage, lexical decision latencies, comprehension, and vocabulary size. The results indicate that a distinct relation exists between reading speed and fixation behaviour associated with regressions through a text. About half the variability in comprehension scores can be predicted by subjects' performance on nonword lexical decisions, gaze durations, and vocabulary scores. These findings are discussed with reference to past studies using similar reading measures.

Eye Movements↗