John H. Hogben

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.

Perceptual integration and perceptual segregation of brief visual stimuli.

Abstract Six experiments are reported which employed a novel experimental task to investigate the perception of visual pattern when components of the pattern are distributed in time. The task required S to identify or guess the location of the missing dot when 24 of the 25 dots forming a 5 × 5 matrix were presented in random order, over some interval of time. In the first two experiments, dots were presented successively, at regular intervals in time: it was found that S s performance deteriorated as presentation of dots was strung out over greater intervals; most errors were the result of S s misidentifying one of the early-presented dots as missing. These results can be explained in terms of stimulus persistence. Experiments 3–6 examined the effect of inserting a temporal gap in the presentation sequence under conditions, as in the first two experiments, in which each dot was presented only once. When the temporal gap was greater than 30–50 msec., Ss reported the occurrence of two distinctly separate percepts, and the difficulty of the task was greatly increased. These results are interpreted on the basis of the concurrent operation of processes of stimulus persistence and of perceptual segregation.

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.

Short-term memory in stereopsis.

Abstract A new stochastic dot stereogram method for producing depth scenes from random point trains to each separate eye is used to measure the time for which information is held to enable stereopsis. The results indicate that one signal train may lag behind the other by 36–72 msec without affecting clear perception of form in depth. They suggest the existence of a visual memory system for stereopsis holding input to one eye for up to 50–70 msec but losing information about the input rapidly thereafter. The suggestion is confirmed by results with other less novel methods.

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.

The tale is in the tail: An alternative hypothesis for psychophysical performance variability in dyslexia

Dyslexic groups have been reported to display poorer mean performance than groups of normal readers on a variety of psychophysical tasks. However, inspection of the distribution of individual scores for each group typically reveals that the majority of dyslexic observers actually perform within the normal range. Differences between group means often reflect the influence of a small number of dyslexic individuals who perform very poorly. While such findings are typically interpreted as evidence for specific perceptual deficiencies in dyslexia, caution in this approach is necessary. In this study we examined how general difficulties with task completion might manifest themselves in group psychophysical studies. Simulations of the effect of errant or inattentive trials on performance produced patterns of variability similar to those seen in dyslexic groups. Additionally, predicted relationships between the relative variability in dyslexic and control groups, and the magnitude of group differences bore close resemblance to the outcomes of a meta-analysis of empirical studies. These results suggest that general, nonsensory difficulties may underlie the poor performance of dyslexic groups on many psychophysical tasks. Implications and recommendations for future research are discussed.

Short-term memory for symmetry

Abstract Symmetric cascades of dots were generated in a continuous random sequence such that each dot had a partner reflected about a vertical or horizontal axis, respectively. Between each point and its partner a temporal delay was introduced. While the brightness of the dots appeared constant within 120–140 msec, symmetry perception ceased at delays in the range of 50–90 msec, depending on observers, type of symmetry and plotting rate. These findings in conjuction with three control studies suggest that memory span for position Information is limited to 50–90 msec while memory for brightness information lasts for 120–140 msec. Perturbation experiments (with no delay) in which a certain proportion of dots had no symmetrical partner were compared with the delay experiments for equal performance, and equivalence curves between delay and perturbation rate were obtained. While performance depended on the type of symmetry and plotting rate, the shape of equivalence curves remained unchanged.

Suppression of visible persistence in apparent motion.

Moving stimuli produce less smear than would be expected on the basis of visible persistence lasting 100–150 msec. Two experiments examined the duration of smear as a function of background luminance, target velocity, and duration of the display. It was found that smear decreased as background luminance increased, smear increased with velocity, and, as display duration increased from 10 to 160 msec, duration of smear first increased and then decreased. Alternative explanations of the results are considered. It is suggested that smear is actively suppressed by stimulus-initiated inhibitory processes.

Attentional Modulation of Visual Processing in Adult Dyslexia: A Spatial-Cuing Deficit

A number of researchers have suggested that deficient visual attention may play a causal role in dyslexia. However, traditional methods for investigating this assertion have been limited by the conflation of sensory and attentional factors and the inability to isolate large attentional effects. In this study, we sought to overcome these problems by combining spatial cuing with a visual search task measuring psychophysical thresholds. In normal readers, uncued search performance was characterized by a strong dependence on the number of elements in the stimulus array. Cuing the location of the target removed much of this effect, suggesting attentional facilitation of performance. Although dyslexic participants performance in uncued search was nearly identical to that of normal readers, all dyslexic participants failed to gain the same effect of cuing that normal readers did. However, dyslexic participants did not differ from normal readers on tests of magnocellular function, suggesting that this spatial-cuing deficit is not merely a secondary consequence of magnocellular dysfunction.

Suppression of visible persistence as a function of spatial separation between inducing stimuli

In the first of two experiments, suppression of the visible persistence of a temporally leading stimulus by a trailing stimulus was studied as a joint function of stimulus onset asynchrony (SOA) and of spatial proximity between the two stimuli. In agreement with earlier work, temporal integration between the two successive stimuli was progressively impaired as SOA was increased. In addition, degree of suppression of visible persistence was found to increase markedly with proximity. This confirms the outcome of earlier research that employed trains of successive stimuli seen in apparent motion. However, the present finding suggests that neither a seriated mode of display nor the appearance of coherent motion are necessary for the suppressive effect of spatial proximity. The results favor an account based on inhibitory interactions, rather than one based on spatiotemporal summation. Further predictions from inhibition theory-bearing on the luminance of the component stimuli-were tested and confirmed in a second experiment.