Biomedical subjects

J H Hogben

Publications and source records attributed to J H Hogben.

At least 19 recordsLinked to original sources

PubMed2005

Auditory frequency discrimination in children with specific language impairment: a longitudinal study.

It has been proposed that specific language impairment (SLI) is caused by an impairment of auditory processing, but it is unclear whether this problem affects temporal processing, frequency discrimination (FD), or both. Furthermore, there are few longitudinal studies in this area, making it hard to establish whether any deficit represents a developmental lag or a more permanent deficit. To address these issues, the authors retested a group of 10 children with SLI and 12 control children first tested 42 months previously. At Time 1, the children with SLI (between 9 and 12 years of age) had significantly elevated FD thresholds compared to the matched controls. At Time 2, the thresholds of both groups had improved, but the children with SLI still had poorer FD thresholds than those of the controls. To assess temporal resolution, auditory backward masking was measured and it was found that most of the children with SLI performed as well as the controls, but 2 children had exceptionally high thresholds. There was also greater variability among the children with SLI compared to that measured among the controls on the FD task. These studies indicate considerable heterogeneity in auditory function among children with SLI and suggest that, as with auditory temporal deficits, difficulties in FD discrimination are important in this population.

Adolescent↗

PubMed2001

Auditory backward recognition masking in children with a specific language impairment and children with a specific reading disability.

The auditory backward recognition masking (ABRM) and intensity discrimination (ID) thresholds of children with a specific language impairment and poor reading (SLI-poor readers), children with an SLI and average reading (SLI-average readers), children with a specific reading disability and average spoken language skills (SRD-average language), and children with normal spoken and written language (controls) were estimated with "child-friendly" psychophysical tasks. The pattern of ABRM and ID scores suggests that a subset of children with concomitant oral language and reading impairments has poor ABRM thresholds, and that a subgroup of children with an SLI or SRD has poorer ID thresholds than controls. The latter result warns against using rapid auditory processing tasks that do not actively control for auditory discrimination ability. Further, some unusually poor ABRM scores and ID scores question the validity of extreme scores produced by children on psychophysical tasks. Finally, the poor oral language scores of many of the children who had impaired reading highlight the need to test the oral language skills of SRD samples to ascertain how homogeneous and specifically disabled they really are.

Adolescent↗

PubMed2000

On the "specifics" of specific reading disability and specific language impairment.

The reading and oral language scores of 110 children with a specific reading disability (SRD) and 102 children with a specific language impairment (SLI) indicated that approximately 53% of children with an SRD and children with an SLI could be equally classified as having an SRD or an SLI, 55% of children with an SRD have impaired oral language, and 51% of children with an SLI have a reading disability. Finding that a large percentage of children can be equally classified as SRD or SLI has repercussions for the criteria used to define an SRD, for conceptualising subgroups of learning disability, and for estimates of the incidence of SRD. Further, it highlights the need for future studies to assess both the reading and oral language abilities of SRD and SLI participants to determine how specifically impaired and homogeneous samples really are.

Adolescent↗

PubMed1999

Spatial limitations of temporal segmentation.

We investigated the spatial parameters that permit temporal phase segmentation. Subjects identified a stimulus quadrant which was modulated 180 degrees out of phase with the rest of the stimulus at temporal frequencies between 2 and 30 Hz. We determined the modulation sensitivity for regular square lattices of Gaussian spots and a stimulus made from solid quadrants with varying separation. Sensitivity declined rapidly when spatial separation of the modulating areas was approximately 0.4 degree, but was relatively unchanged by further spatial separations. The results suggest that there are two systems that can detect temporal phase differences. The first is a segregation process that operates below 10 Hz, where phase can be consciously followed and compared across large retinal distances. The second system is a segmentation mechanism that operates at higher temporal frequencies but only over a short range.

Humans↗

PubMed1999

Blindsight in subjects with homonymous visual field defects.

Brain damage in the visual system can lead to apparently blind visual areas. However, more elaborate testing indicates that some visual ability may still exist for specific stimuli in the otherwise blind regions. This phenomenon is called 'blindsight' if subjects report no conscious awareness of visual stimuli but when forced to guess, nevertheless perform better than chance. It has mainly been suggested that secondary visual pathways are responsible for this phenomenon. However, no published study has clearly shown the neural mechanism responsible for blindsight. Furthermore, experimental artifacts may have been responsible for the appearance of the phenomenon in some subjects. In the present study, the visual fields of nine subjects were mapped and residual visual performance was examined in many areas using three different experimental procedures. Artifacts such as stray light or eye movements were well controlled. In addition, confidence ratings were required after each trial in the forced-choice tests. The results show that only one subject with a lesion in the optic radiation had blindsight in two discrete areas of the affected visual field. Spared optic radiation fibers of the main (primary) geniculo-striate visual pathway were most likely to account for this finding.

Adult↗

PubMed1999

Residual vision in a subject with damaged visual cortex.

It is well known that a lesion in the optic radiation or striate cortex leads to blind visual regions in the retinotopically corresponding portion of the visual field. However, various studies show that some subjects still perceive certain stimuli even when presented in the "blind" visual field. Such subjects either perceive stimuli abnormally or only certain aspects of them (residual vision) or, in some cases, deny perception altogether even though visual performance can be shown to be above chance (blindsight). Research on monkeys has suggested a variety of parallel extrastriate visual pathways that could bypass the striate cortex and mediate residual vision or blindsight. In the present study, we investigated a subject with perimetrically blind visual areas caused by bilateral brain damage. Black and white stimuli were presented at many locations in the intact and affected areas of the visual field. The subject's task was to state, using confidence levels, whether the target stimulus was black or white. The results revealed an area in the "blind" visual field in which the subject perceived a light flash when the experimental black stimulus was presented. We hypothesize that a spared region in the visual cortex most likely accounts for these findings.

Aged↗

PubMed1999

Auditory temporal processing in disabled readers with and without oral language delay.

Inferior auditory temporal processing has been postulated as causally linked to phonological processing deficits in disabled readers with concomitant oral language delay (LDRDs), and absent in specifically disabled readers with normal oral language (SRDs). This investigation compared SRDs, LDRDs and normal readers aged 7-10 years on measures of auditory temporal processing (temporal order judgement) and phonological decoding (nonword reading). LDRDs exhibited deficits in temporal order judgement compared with normal readers, from whom SRDs did not differ significantly. These findings suggest that auditory temporal processing and oral language are related; however, very large within-group variability in the auditory temporal processing data further suggests that this relationship prevails in only a proportion of disabled readers with concomitant oral language weakness. In nonword reading, LDRDs performed worst of all, but SRDs also exhibited significant deficits compared with normal readers. Taken together, our results preclude the conceptualisation of temporal processing deficits as the unitary cause of phonological and language deficits in disabled readers.

Analysis of Variance↗

PubMed1996

Effects of a red background on magnocellular functioning in average and specifically disabled readers.

Two experiments were conducted using metacontrast masking to examine responses in the magno system of adults, average reading adolescents and adolescents with specific reading disability. In Experiment 1 the effects of a red background field on the metacontrast functions of adult subjects were investigated. Results showed that a red, compared to a photometrically matched white background field, significantly attenuated metacontrast magnitude, supporting the interpretation of metacontrast as due to magno system suppression of parvo system responses. The finding of a red background effect was replicated in Experiment 2 with the two adolescent groups. The metacontrast functions of the adolescent groups also differed significantly, with those with specific reading disability exhibiting weaker metacontrast than the average readers. This result is consistent with a deficit in the magno system of individuals with specific reading disability and indicates the continuation of the deficit beyond childhood.

Adolescent↗

PubMed1996

Blurring the image does not help disabled readers.

Previous research has found that poor readers performed a visual search task more slowly than good readers, but that this difference was virtually eliminated by blurring of the search array. Whereas blurring had little effect on the performance of the good readers, it led to a dramatic improvement in the search rate of the poor readers. The present study set out to replicate this research with groups of 10-12 yr old disabled and average readers but with methodological improvements in the procedure and the analysis. It was found that the disabled readers performed the search task as well as the average readers, and that blurring of the display conferred no advantage on either group. The results are discussed in relation to the transient deficit theory of reading disability.

Child↗

PubMed1995

A comparison of temporal integration in children with a specific reading disability and normal readers.

Previous research has suggested that whereas some techniques show that subjects with a specific reading disability (SRD) have greater visible persistence than controls, a temporal integration of form technique does not. It has been suggested that the failure of the temporal integration task to show a difference results from the spatial separation between stimuli used in the technique. In this study SRD and control subjects were compared on a new version of a temporal integration task, under two conditions varying the spatial separation of elements in the display. It was predicted that there would be no difference between groups when spatial separation was large, but that the SRD subjects would show greater visible persistence at small separations. Neither prediction was confirmed, denying previous explanations of why the temporal integration task does not discriminate between groups. Analysis of errors showed that the result was not due to inattention nor to a general deficit on the part of the SRD subjects.

Afterimage↗

PubMed1994

Temporal integration and segregation of brief visual stimuli: patterns of correlation in time.

Two brief sequential displays separated by a brief interstimulus interval (ISI) are often perceived as a temporally integrated unitary configuration. The probability of temporal integration can be decreased by increasing the ISI or (counterintuitively) by increasing stimulus duration. We tested three hypotheses of the relative contributions of stimulus duration and ISI to the breakdown of temporal integration (the storage, processing, and temporal correlation hypotheses). In the first of two experiments, stimulus duration and ISI were varied factorially, and estimates of temporal integration were obtained with a form-part integration task. The second experiment was a replication of the first at two levels of stimulus intensity. The outcomes were inconsistent with the storage and processing options, but confirmed predictions from the temporal correlation hypothesis. Whether two sequential stimuli are perceived as temporally integrated or disjoint depends not on the availability of visible persistence, but on the emergence of a neural code that is based on the temporal correlation between the two visual responses.

Humans↗

PubMed1991

Visible persistence following a brief increment in stimulus luminance.

In previous studies, it has been demonstrated that visible persistence--the period for which the perceived duration of a stimulus exceeds its physical duration--can be extended by briefly incrementing the luminance of the stimulus immediately prior to offset. Using a two-component pattern integration task, we show that this effect is not an artifact of change in the total luminous flux within the stimulus. Visible persistence was unaffected by overall luminance of the stimulus. It was also time-locked to the luminance increment. Visible persistence is seen to result from a process that is initiated by stimulus onset and that can be either wholly or partially reinitiated by the onset of the luminance increment. The duration of this process (which determines the duration of stimulus visibility) can be modified in a graded fashion by stimulus events that occur after its initiation. We outline a single-process inhibitory feedback model of the persistence mechanism that accounts for the present findings.

Afterimage↗

PubMed1988