Lapses of concentration and dyslexic performance on the Ternus task

Saccade Latency Provides Evidence for Reduced Face Inversion Effects With Higher Autism Traits

Individuals on the autism spectrum are reported to show impairments in the processing of social information, including aspects of eye-movements towards faces. Abnormalities in basic-level visual processing are also reported. In the current study, we sought to determine if the latency of saccades made towards social targets (faces) in a natural scene as opposed to inanimate targets (cars) would be related to sub-clinical autism traits (ATs) in individuals drawn from a neurotypical population. The effect of stimulus inversion was also examined given that difficulties with processing inverted faces are thought to be a function of face expertise. No group differences in saccadic latency were established for face or car targets, regardless of image orientation. However, as expected, we found that individuals with higher autism-like traits did not demonstrate a saccadic face inversion effect, but those with lower autism-like traits did. Neither group showed a car inversion effect. Thus, these results suggest that neurotypical individuals with high autism-like traits also show anomalies in detecting and orienting to faces. In particular, the reduced saccadic face inversion effect established in these participants with high ATs suggests that speed of visual processing and orienting towards faces may be associated with the social difficulties found across the broader autism spectrum.

Behavioral and electrophysiological investigation of speech perception deficits in silence, noise and envelope conditions in developmental dyslexia

The present study investigated whether children with developmental dyslexia showed specific deficits in the perception of three phonetic features (voicing, place, and manner of articulation) in optimal (silence) and degraded listening conditions (envelope-coded speech versus noise), using both standard behavioral and electrophysiological measures. Performance of children with dyslexia was compared to that of younger typically developing children who were matched in terms of reading age. Results showed no significant group differences in response accuracy except for the reception of place-of-articulation in noise. However, dyslexic children responded more slowly than typically developing children across all conditions with larger deficits in noise than in envelope than in silence. At the neural level, dyslexic children exhibited reduced N1 components in silence and the reduction of N1 amplitude was more pronounced for voicing than for the other phonetic features. In the envelope condition, the N1 was localized over the right hemisphere and it was larger for typically developing readers than for dyslexic children. Finally, in stationary noise, the N1 to place of articulation was clearly delayed in children with dyslexia, which suggests a temporal de-organization in the most adverse listening conditions. The results clearly show abnormal neural processing to speech sounds in all conditions. They are discussed in the context of recent theories on perceptual noise exclusion, neural noise and temporal sampling.

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.

Visual Illusions: An Interesting Tool to Investigate Developmental Dyslexia and Autism Spectrum Disorder

A visual illusion refers to a percept that is different in some aspect from the physical stimulus. Illusions are a powerful non-invasive tool for understanding the neurobiology of vision, telling us, indirectly, how the brain processes visual stimuli. There are some neurodevelopmental disorders characterized by visual deficits. Surprisingly, just a few studies investigated illusory perception in clinical populations. Our aim is to review the literature supporting a possible role for visual illusions in helping us understand the visual deficits in developmental dyslexia and autism spectrum disorder. Future studies could develop new tools - based on visual illusions - to identify an early risk for neurodevelopmental disorders.

Encoding order and developmental dyslexia: a family of skills predicting different orthographic components

We investigated order encoding in developmental dyslexia using a task that presented nonalphanumeric visual characters either simultaneously or sequentially--to tap spatial and temporal order encoding, respectively--and asked participants to reproduce their order. Dyslexic participants performed poorly in the sequential condition, but normally in the simultaneous condition, except for positions most susceptible to interference. These results are novel in demonstrating a selective difficulty with temporal order encoding in a dyslexic group. We also tested the associations between our order reconstruction tasks and: (a) lexical learning and phonological tasks; and (b) different reading and spelling tasks. Correlations were extensive when the whole group of participants was considered together. When dyslexics and controls were considered separately, different patterns of association emerged between orthographic tasks on the one side and tasks tapping order encoding, phonological processing, and written learning on the other. These results indicate that different skills support different aspects of orthographic processing and are impaired to different degrees in individuals with dyslexia. Therefore, developmental dyslexia is not caused by a single impairment, but by a family of deficits loosely related to difficulties with order. Understanding the contribution of these different deficits will be crucial to deepen our understanding of this disorder.

Subjective criteria and illusions in visual testing: some methodological limitations

It is argued that illusions cannot generally be investigated with criterion-independent methods. This limits the value of the data obtained from them. This is particularly important when the results are compared between groups of subjects, for example, between dyslexic readers and controls, since it is possible that the differences between the groups reflect differences with regard to criteria rather than real perceptual differences.

Attention modulates spatio-temporal grouping

Dynamic stimuli are ubiquitous in natural viewing conditions implying that grouping operations need to operate, not only in space, but also jointly in space and time. Moreover, in natural viewing, attention plays an important role in controlling how resources are allocated. We investigated how attention interacts with spatio-temporal perceptual grouping by using a bistable stimulus, called the Ternus-Pikler display. Ternus-Pikler displays can give rise to two different motion percepts, called Element Motion (EM) and Group Motion (GM), the former dominating at short Inter-Stimulus Intervals (ISIs) and the latter at long ISIs. Our results indicate that GM grouping requires more attentional resources than EM grouping. Different theoretical accounts of perceptual grouping and attention are discussed and evaluated in the light of the current results.

Reading-Related Skills, Reading Achievement, and Inattention: A Correlational Study

Here we investigated the psychological texture of a literacy-related disability, specific reading disability (SRD, also referred to as dyslexia), as it is manifested in Russian and defined in the Russian Federation. Specifically, we attempted to understand the emerging properties of this deficit among 96 students in grades 2 and 3 (38 girls and 58 boys, aged 7.90–10.42 years, mean = 8.87, SD = 0.56) attending a public primary school in St. Petersburg, Russia. Based on the linguistic properties of the Russian language, we designed a literacy-skills assessment battery that incorporates both internationally common (i.e., the traditional IQ-achievement discrepancy-based) and Russia-specific (i.e., typology-based) approaches to identifying reading difficulties in emergent readers. In addition, we measured children’s levels of general intelligence, inattention, and hyperactivity (i.e., the symptomatology related to attention deficit and hyperactivity disorders, ADHD). Multi-trait-multi-method methodology was employed in that data were collected both from teachers and students for multiple reading-related processes, using both self-report and maximum performance assessments. The results are interpreted in terms of the convergence (and lack of such) between the common and country/language-specific approaches to the identification of reading difficulties, and the relevance of the general level of intelligence to diagnosing specific reading difficulties in Russian and in Russia.

Speech perception abilities of adults with dyslexia: is there any evidence for a true deficit?

PURPOSE

This study investigated whether adults with dyslexia show evidence of a consistent speech perception deficit by testing phoneme categorization and word perception in noise.

METHOD

Seventeen adults with dyslexia and 20 average readers underwent a test battery including standardized reading, language and phonological awareness tests, and tests of speech perception. Categorization of a pea/bee voicing contrast was evaluated using adaptive identification and discrimination tasks, presented in quiet and in noise, and a fixed-step discrimination task. Two further tests of word perception in noise were presented.

RESULTS

There were no significant group differences for categorization in quiet or noise, across- and within-category discrimination as measured adaptively, or word perception, but average readers showed better across- and within-category discrimination in the fixed-step discrimination task. Individuals did not show consistent poor performance across related tasks.

CONCLUSIONS

The small number of group differences, and lack of consistent poor individual performance, suggests weak support for a speech perception deficit in dyslexia. It seems likely that at least some poor performances are attributable to nonsensory factors like attention. It may also be that some individuals with dyslexia have speech perceptual acuity that is at the lower end of the normal range and exacerbated by nonsensory factors.

Auditory and visual stream segregation in children and adults: an assessment of the amodality assumption of the 'sluggish attentional shifting' theory of dyslexia

Among the hypotheses relating dyslexia to a temporal processing disorder, Hari and Renvall (Hari, R., Renvall, H., 2001. Impaired processing of rapid stimulus sequences in dyslexia. Trends. Cognit. Sci. 5, 525-532.) argued that dyslexic individuals would show difficulties at an attentional level, through sluggish attentional shifting (SAS) in all sensory modalities. However, the amodality assumption of the SAS theory was never straightforwardly assessed in the same group of dyslexic participants using similar paradigms in both the visual and auditory modalities. Here, the attentional sequential performance of control and dyslexic participants was evaluated using rapid serial presentation paradigms measuring individual stream segregation thresholds in the two modalities. The first experiment conducted on French dyslexic children with a phonological disorder revealed an SAS only in the auditory modality only which was strongly related to reading performance. The second experiment carried out on British dyslexic young adults with a phonological disorder using the same auditory segregation task but a different visual paradigm revealed an SAS in both the visual and the auditory modalities. In addition, a relationship was found in this group between SAS, poor reading and poor phonological skills. Two further control experiments showed that differences in task design or participants' language between Experiments 1 and 2 could not account for the differences in terms of visual segregation patterns. Overall, our results support the view that the auditory SAS plays a role in developmental dyslexia via its impact on phonological abilities. In addition, a visual temporal disorder in dyslexia might emerge at a later developmental stage, when the visual system normally becomes more expert at rapid temporal processing.

The role of visual and auditory temporal processing for Chinese children with developmental dyslexia

This study examined temporal processing in relation to Chinese reading acquisition and impairment. The performances of 26 Chinese primary school children with developmental dyslexia on tasks of visual and auditory temporal order judgement, rapid naming, visual-orthographic knowledge, morphological, and phonological awareness were compared with those of 26 reading level ability controls (RL) and 26 chronological age controls (CA). Dyslexic children performed worse than the CA group but similar to the RL group on measures of accurate processing of auditory and visual-order stimuli, rapid naming, morphological awareness, and phonological awareness and a minority performed worse on the two temporal processing tasks. However, hierarchical regression analyses revealed that visual but not auditory temporal processing contributed unique variance to Chinese character recognition even with other cognitive measures controlled, suggesting it may be as important a correlate of reading ability in Chinese as in alphabetic scripts.

Dyslexia: sensory deficits or inattention?

An important question in regard to dyslexia is whether or not this condition is the result of sensory deficits. A number of studies have indeed found sensory deficiencies in dyslexic readers. However, it has been proposed that these are due simply to inattention. If so, this would be expected to produce either (i) a general reduction or (ii) random reductions in performance. On the basis of published data, it seems that neither of these is in fact the case. Rather the data indicate reproducible non-random patterns of deficiencies with regard to stimulus conditions. The stimulus specificity of the deficits represents, therefore, an important issue which needs to be addressed by any attempt to account for the sensory deficiencies of dyslexic readers in terms of inattention.

Attention, dyslexia, and the line-motion illusion

Dyslexic readers have been found to have a reduced line-motion illusion. This has been interpreted as evidence for an attention deficit of magnocellular origin. We show that this interpretation has severe problems: 1) to link reduced line-motion illusion to attention overlooks other factors, 2) to link the line-motion illusion specifically to the magnocellular system is problematic because the illusion can be obtained with isoluminant stimuli, 3) reduced illusory motion in dyslexic individuals may reflect sensory deficits, and 4) to link dyslexia specifically to the magnocellular system is in general problematic.

Attention, reading and dyslexia

It has been proposed that magnocellular deficits cause dyslexia through reduced attention. According to one model (Vidyasagar, Clinical and Experimental Optometry 2004; 87: 4-10), attention is shifted from letter to letter during fixations and magnocellular deficits are hypothesised to cause reading problems by interfering with the ability to control the attention. The present report points out several problems in this model. 1. It requires dissociation of eye movements and attention, which may be problematic within the framework of reading. 2. There is direct evidence to indicate that reading is not carried out in a letter-to-letter manner during fixations. 3. There are aspects of the visual performance of dyslexic readers, which are difficult to attribute to inattention. 4. There are indications that attentional deficiencies of dyslexic readers are not associated with magnocellular deficits. 5. The evidence for linking magnocellular deficits to dyslexia in general is weak.

Funções neuropsicológicas em crianças com dificuldades de leitura e escrita

Nos estudos sobre a relação entre dificuldades de leitura e escrita e fatores neuropsicológicos associados, controvérsias giram em torno de hipóteses de um possível desvio ou atraso de desenvolvimento. Para examinar esta polêmica, o presente estudo comparou o desempenho em tarefas neuropsicológicas de crianças de 2ª série com dificuldades de leitura e escrita (n=14) com o de dois grupos: um contrastando competência de leitura e escrita, mas não idade (n=15) e outro contrastando idade, mas não competência de leitura e escrita (1ª série; n=9). Os resultados revelaram que o grupo de 2ª série, com dificuldade de leitura e escrita, apresentou escores estatisticamente inferiores aos do grupo de 2ª série competente em leitura e escrita em consciência fonológica, linguagem oral e memória fonológica, não diferindo significativamente do grupo de 1ª série. Tais achados favorecem a hipótese de atraso de desenvolvimento destas funções neuropsicológicas em crianças com dificuldades de leitura e escrita.

Parietal function in good and poor readers

BACKGROUND

While there are many psychophysical reports of impaired magnocellular pathway function in developmental dyslexia (DD), few have investigated parietal function, the major projection of this pathway, in good and poor readers closely matched for nonverbal intelligence. In view of new feedforward-feedback theories of visual processing, impaired magnocellular function raises the question of whether all visually-driven functions or only those associated with parietal cortex functions are equally impaired and if so, whether parietal performance is more closely related to general ability levels than reading ability.

METHODS

Reading accuracy and performance on psychophysical tasks purported to selectively activate parietal cortex such as motion sensitivity, attentional tracking, and spatial localization was compared in 17 children with DD, 16 younger reading-age matched (RA) control children, and 46 good readers of similar chronological-age (CA) divided into CA-HighIQ and a CA-LowIQ matched to DD group nonverbal IQ.

RESULTS

In the age-matched groups no significant differences were found between DD and CA controls on any of the tasks relating to parietal function, although performance of the DD group and their nonverbal IQ scores was always lower. As expected, CA and RA group comparisons indicated purported parietal functioning improves with age. No difference in performance was seen on any of the parietally driven tasks between the DD and age-nonverbal IQ matched groups, whereas performance differentiated the DD group from the age-matched, higher nonverbal IQ group on several such tasks. An unexpected statistical difference in performance between lower reading age (DD and RA children) and all higher reading age (CA) children was seen on a test of chromatic sensitivity, whereas when high and low nonverbal IQ normal readers were compared performance was not different

CONCLUSION

The results indicate that performance on purported parietal functions improves with age and may be more associated with nonverbal mentation than reading accuracy. Performance on a cognitively demanding task, traditionally considered to rely on ventral stream functions, was more related to reading accuracy.

Dorsal stream associations with orthographic and phonological processing

Several studies have indicated a key role for dorsal stream processing in lexical decoding. To examine this relationship further, performance on orthographic and phonological reading tests was compared with both steady-state visual evoked potentials and a putative behavioral measure of dorsal stream processing, coherent motion detection. Frequency analysis of the visual evoked potential data showed power at the second harmonic to be largely confined to dorsal stream regions, and significantly correlated with motion detection thresholds. Regression analyses showed that orthographic processing was significantly associated with the second harmonic power. Although consistent with previous reports, there remains a question as to why the orthographic visual evoked potential power relationship did not extend to include the coherent motion detection measures.

Categorical perception of speech sounds in illiterate adults

Children affected by dyslexia exhibit a deficit in the categorical perception of speech sounds, characterized by both poorer discrimination of between-category differences and by better discrimination of within-category differences, compared to normal readers. These categorical perception anomalies might be at the origin of dyslexia, by hampering the set up of grapheme-phoneme correspondences, but they might also be the consequence of poor reading skills, as literacy probably contributes to stabilizing phonological categories. The aim of the present study was to investigate this issue by comparing categorical perception performances of illiterate and literate people. Identification and discrimination responses were collected for a /ba-da/ synthetic place-of-articulation continuum and between-group differences in both categorical perception and in the precision of the categorical boundary were examined. The results showed that illiterate vs. literate people did not differ in categorical perception, thereby suggesting that the categorical perception anomalies displayed by dyslexics are indeed a cause rather than a consequence of their reading problems. However, illiterate people displayed a less precise categorical boundary and a stronger lexical bias, both also associated with dyslexia, which might, therefore, be a specific consequence of written language deprivation or impairment.

The effect of script on poor readers' sensitivity to dynamic visual stimuli

The current research examined performance of good and poor readers of Thai on two tasks that assess sensitivity to dynamic visual displays. Readers of Thai, a complex alphabetic script that nonetheless has a regular orthography, were chosen in order to contrast patterns of performance with readers of Korean Hangul (a similarly regular language but one that has a simple visual format, see ). Thai poor readers were less sensitive than good readers on the two measures of dynamic visual processing; they had higher thresholds for detecting coherent movement and required longer ISIs to report group movement in the Ternus task. These results differ from those for poor readers of Korean Hangul that found no relationship between visual processing thresholds and reading skill. This contrast suggests that the expression of visual processing problems in dyslexia is mediated by the format properties of the writing system and points to the need to consider such factors in formulating brain-behavior relationships.

Auditory temporal pattern discrimination and reading ability

The relation between reading ability and performance on an auditory temporal pattern discrimination task was investigated in children who were either good or delayed readers. The stimuli in the primary task consisted of sequences of tones, alternating between high and low frequencies. The threshold interstimulus interval (ISI) for discrimination of differences in the temporal properties of the sequences was measured. An ISI threshold was also measured in a control task that was identical to the primary task, except all tones in a control sequence had the same frequency. Delayed readers and good readers were equally able to discriminate the timing of the sequences at short ISIs, for both the primary and control tasks. Furthermore, the ISI thresholds were not correlated with the ability to read either irregular words or nonwords. These results suggest that reading ability is not related to the ability to track large and rapid frequency changes in auditory temporal patterns.

Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction?

Dyslexia research now faces an intriguing paradox. It is becoming increasingly clear that a significant proportion of dyslexics present sensory and/or motor deficits; however, as this 'sensorimotor syndrome' is studied in greater detail, it is also becoming increasingly clear that sensory and motor deficits will ultimately play only a limited role in a causal explanation of specific reading disability.

Contrast sensitivity in subgroups of developmental dyslexia

It has been proposed that developmental dyslexia is associated with a deficit in the magnocellular pathway of the visual system. Other research focuses upon the heterogeneous nature of developmental dyslexia, and evidence that subgroups of dyslexia may be identified based on selective deficits in specific component reading skills. This study tested the hypothesis that visual processing deficits may be present in different subgroups of developmental dyslexia by comparing the visual contrast sensitivity of three subgroups of dyslexic children (phonological, surface and mixed) and controls. The stimulus designed to measure magnocellular visual function was a low spatial frequency Gaussian blob, flickered sinusoidally at a temporal frequency of 8.33 Hz. The control stimulus, designed to measure parvocellular visual function, was a relatively high spatial frequency Gaussian windowed grating (8 c/deg) slowly ramped on and off. There were no significant differences between the groups of dyslexic and control children in contrast sensitivity to either stimulus. The findings do not support the existence of a magnocellular system deficit in dyslexia.

On the use of the Ternus test to assess magnocellular function

Ternus stimuli give rise to two mutually exclusive visual experiences: with long interstimulus intervals (ISIs) the elements in the stimulus are perceived as moving together as a group ('group movement'), while at shorter ISIs only a single element appears to be moving ('element movement' or 'end-to-end movement'). It has been hypothesized that group and element movements, respectively, reflect magnocellular and parvocellular activity. On this basis, Ternus tests have been used to assess magnocellular function in dyslexic individuals. This use of Ternus stimuli is examined in the present report. On the basis of amplitude spectra of the stimuli and of a review of previous studies it is concluded that to use Ternus tests to assess magnocellular function is problematic.