The genetic aspects of developmental dyslexia.

Discusses evidence concerning genetic influences on developmental dyslexia, a disorder characterized by difficulty in learning to read despite adequate opportunity and intelligence. Research on familial incidence, concordance in twins, the influence of parental age at the child's birth, and the subtyping of dyslexics is summarized. It is concluded that there is strong evidence for the heritability of a subtype based on verbal/language deficiency, perhaps reflecting reversed cerebral asymmetry, for which a genetic marker has been found. It is uncertain whether this subtype is caused by left hemispheric impairment or immaturity. There is somewhat weaker evidence for the heritability of a subtype based on visual/spatial deficiencies and a mixed subtype. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual localization of the center of mass of compact, asymmetric, two-dimensional shapes.

This study aimed at understanding how visual information is used to locate the center of mass. The center of mass is an important physical property of objects that must be taken into account when grasping and/or manipulating them. Participants were instructed to identify the point of equilibrium of compact bidimensional, massless shapes displayed on a touch screen. The point of equilibrium was defined as the point on the face of the object that would allow one to balance the object in the horizontal position. Seven different triangles and 18 different quadrilaterals in different orientations were used as stimuli. It was found that participants can accurately and consistently estimate the position of the center of mass. The small observed errors were systematically influenced by the shape of the object. The participants tended to locate the center of mass at the center of an inscribed circle instead of the true center of mass. In general, the shape effect was impervious to the orientation of the figure and to the mode of response (left hand, right hand, or mouse). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of functions in developmental dyslexia and dyscalculia.

This work examines the association between symbols and their representation in adult developmental dyscalculia and dyslexia. Experiment 1 used comparative judgment of numerals, and it was found that in physical comparisons (e.g., 3-5 vs. 3-5) the dyscalculia group showed a significantly smaller congruity effect than did the dyslexia and the control groups. Experiment 2 used Navon figures (D. Navon, 1977) in Hebrew, and participants were asked to name the large or the small letters. Phoneme similarity modulated performance of the control and the dyscalculia groups and showed a very small effect in the dyslexia group. This suggests that the dyscalculia population has difficulties in automatically associating numerals with magnitudes but no problems in associating letters with phonemes, whereas the dyslexia population shows the opposite pattern. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

M-stream deficits and reading-related visual processes in developmental dyslexia.

Some visual processing deficits in developmental dyslexia have been attributed to abnormalities in the subcortical M stream and/or the cortical dorsal stream of the visual pathways. The nature of the relationship between these visual deficits and reading is unknown. The purpose of the present article was to characterize reading-related perceptual processes that may link the visual deficits to reading problems. We identified contrast sensitivity, position encoding, oculomotor control, visual attention, parafoveal/foveal interactions, and saccadic suppression as potential reading-related dorsal stream processes. We then evaluated the role of each process in reading and the status of each process in dyslexia. In theory, a number of dorsal stream processes (e.g., oculomotor control and visual attention) might contribute to reading problems in developmental dyslexia. More work is needed to demonstrate the connection empirically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory temporal coding in dyslexia

Developmental dyslexia is generally believed to result from impaired linguistic processing rather than from deficits in low-level sensory function. Challenging this view, we studied the perception of non-verbal acoustic stimuli and low-level auditory evoked potentials in dyslexic adults. Compared with matched controls, dyslexics were selectively impaired in tasks (frequency discrimination and binaural unmasking) which rely on decoding neural discharges phase-locked to the fine structure of the stimulus. Furthermore, this ability to use phase-locking was related to reading ability. In addition, the evoked potential reflecting phase-locked discharges was significantly smaller in dyslexics. These results demonstrate a low-level auditory impairment in dyslexia traceable to the brainstem nuclei.     

Rate and timing precision of motor coordination in developmental dyslexia.

Temporal characteristics of interlimb coordination were examined in adolescents and young adults with developmental dyslexia, matched normal control subjects, and matched learning disabled adolescent students without reading difficulties. Subjects were asked to tap in time to an entraining metronome at each of 3 prescribed rates by moving the index fingers of both hands in unison, in rhythmical alternation, or in more complex bimanual patterns. Dyslexic subjects showed significant deficits of timing precision on bimanual tasks that required the integration of asynchronous responses, but not when they moved the fingers in unison. Findings are discussed in terms of both the hypothesis that impaired temporal resolution in dyslexia reflects an underlying deficit of left-hemisphere function and an alternative hypothesis that functional deficits in developmental dyslexia are associated with impaired interhemispheric communication. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia.

The present study was conducted to examine the cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia. Thirty Chinese dyslexic children in Hong Kong were compared with 30 average readers of the same chronological age (CA controls) and 30 average readers of the same reading level (RL controls) in a number of rapid naming, visual, phonological, and orthographic tasks. Chinese dyslexic children performed significantly worse than the CA controls but similarly to the RL controls on most of the cognitive tasks. The rapid naming deficit was found to be the most dominant type of cognitive deficit in Chinese dyslexic children. Over half of the dyslexic children exhibited deficits in 3 or more cognitive areas, and there was a significant association between the number of cognitive deficits and the degree of reading and spelling impairment. The present findings support the multiple-deficit hypothesis in Chinese developmental dyslexia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Identical neural risk factors predict cognitive deficit in dyslexia and schizophrenia.

In previous work, the authors found that an anatomical risk index created from the combination of 7 neuroanatomical measures predicted reading and oral language skills in individuals with learning disabilities. Individuals with small auditory brain structures and reduced asymmetry had more deficits than those with large structures and exaggerated asymmetry. In the present study, the same anatomical index predicted reading and other cognitive abilities in 45 individuals with chronic schizophrenia. The anatomical risk index was significantly associated with broad cognitive ability (Pearson r = .53, p     

The neurology of dyslexia

Developmental dyslexia is a heterogeneous disorder in which the prominent manifestation is a discrepancy between reading achievement and intelligence. There is no serious auditory, visual, psychiatric, social or educational factor that could be responsible of the discrepancy. Males are more often affected than females. It is a pervasive condition but with adequate help and spontaneous compensation, reading ability may improve. Neuroimaging, mainly MRI, allows to demonstrate in two thirds, an absence of the usual symmetry of the planum temporale favoring the left side. Twenty to 25% of the remaining cases show asymmetry of the right side. Etiology is unknown but heredity plays an important role. The pathology of dyslexia has revealed abnormalities of the cerebral cortex focal four-layer microgyria, microdysgenesis and arteriovenous malformations. Galaburda hypothesises that a pre or perinatal adverse event produces a basic cognitive, progressive alteration, that eventually invades the perceptual elements (visual, phonological, semantic-syntaxic difficulties). Heilman, Voeller and Alexander propose a motor-articulatory feedback hypothesis.     

Word-recognition skills of adults with childhood diagnoses of dyslexia.

This study investigated whether the same pattern of reading deficits that characterize dyslexic children continue to characterize this population as it reaches adulthood. Standardized and experimental reading tasks were administered to college students with childhood diagnoses of dyslexia, and to age-matched and reading-matched control subjects. Despite relatively high levels of reading comprehension, dyslexics showed inaccurate and particularly slow word-recognition skills. Dyslexics did not use age-appropriate, and in some cases reading-level-appropriate word recognition processes. They relied heavily on the use of spelling–sound information, syllabic information, and context for word recognition. Word-recognition difficulties reflected poor knowledge of spelling–sound correspondences. Adult dyslexics' patterns of performance were most similar to those of beginning skilled readers and to dyslexic children. The term arrest rather than deviance or delay best characterizes the word-recognition skills of adult dyslexics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual depth discrimination in animals.

"The capacity to react discriminatively to the distance of visual stimulus appears to characterize a great many species, ranging from insects to primates. Especially in the case of insects, birds, and rats, it is evident that displacement of the images on the retinal mosaic is a very important factor in depth discrimination." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radial localization in the aged.

Elderly subjects were 41% less accurate than young subjects in localizing a point in the frontal plane. The decline could be ascribed neither to an age difference in image formation or skill acquisition nor to a difference in motivational level or trace retention. Evidently the "ambient" or "transient" visual system is compromised at an elementary level. Reasons why this deficit may not be compounded at more complex levels of spatial processing are suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual construction impairments in Parkinson's disease.

24 nondemented Parkinson's disease (PD) patients were asked to copy and then recall the Rey-Osterrieth Complex Figure, dividing the units of the figure into "main structural" and "detail" components. PD patients consistently omitted some main structural units from recall of the figure. When main structures were produced, PD patients were impaired at drawing these features in an organized fashion, and they produced these main units late in the course of their drawings. PD patients differed from control Ss in their recall of the figure's details, but there were no qualitatively unique features in their omission of details. Correlation and regression analyses suggest that compromised executive functioning contributed to the PD patients' constructional difficulties and that visual perception and motor functioning also played a modest role. It is concluded that visual construction impairments in PD are multifactorial in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual attention in HIV-1 infection.

27 nondemented HIV-seropositive men and 13 seronegative controls performed 2 versions of a spatial attention task that engaged either automatic or controlled attentional processing. Ss also performed a 3rd task requiring divided attention, which tested for potential deficits in attentional resources. HIV-seropositive symptomatic Ss were impaired on the automatic processing task, whereas asymptomatic Ss performed the task normally compared with controls. In contrast, no differences were observed among the 3 groups on the controlled attention task. However, both seropositive groups showed deficits on the divided attention task. These results suggest that deficits in selective attention are present early in the course of HIV-1 infection. The most prominent impairment is seen on tasks that are highly demanding of attentional resources, whereas deficits in automatic processing develop later in the disease process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel Processing in Visual Search Asymmetry.

The difficulty of visual search may depend on assignment of the same visual elements as targets and distractors-search asymmetry. Easy C-in-O searches and difficult O-in-C searches are often associated with parallel and serial search, respectively. Here, the time course of visual search was measured for both tasks with speed-accuracy methods. The time courses of the 2 tasks were similar and independent of display size. New probabilistic parallel and serial search models and sophisticated-guessing variants made predictions about time course and accuracy of visual search. The probabilistic parallel model provided an excellent account of the data, but the serial model did not. Asymptotic search accuracies and display size effects were consistent with a signal-detection analysis, with lower variance encoding of Cs than Os. In the absence of eye movements, asymmetric visual search, long considered an example of serial deployment of covert attention, is qualitatively and quantitatively consistent with parallel search processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual impairment in Swedish children. III. Diagnoses

PURPOSE: To gain an overview of the spectrum of diagnoses among Swedish visually impaired children. METHODS: An epidemiological study of all known visually impaired children was made by review of medical records. RESULTS AND CONCLUSION: In all we found 2373 children, 0-19 years of age, with an age-specific prevalence of 10.9/10,000. The two largest diagnostic groups included neuro-ophthalmological and retinal diseases. The most frequent disorders were cerebral visual impairment, non-hereditary optic atrophy, retinal dystrophy (when regarded as a general entity), congenital hypoplasia of the optic nerve and congenital cataract. Nystagmus secondary to brain disorder, albinism, congenital nystagmus, retinopathy of prematurity and high myopia were also found in a considerable number of patients. The leading diagnoses in children with WHO-defined childhood blindness were non-hereditary optic atrophy, cerebral visual impairment and retinopathy of prematurity. A large proportion of the children, especially in the groups with neuro-ophthalmological disorders and malformations of the posterior segment had additional impairments, emphasizing the importance of a multi-disciplinary approach when assessing multi-handicapped children.     

Visual lateralization during feeding in pigeons.

In a quasi-natural feeding situation, adult pigeons had to detect and consume 30 food grains out of about 1,000 pebbles of similar shape, size, and color within 30 s under monocular conditions. With the right eye seeing, the animals achieved a significantly higher discrimination accuracy and, consequently, a significantly higher proportion of grains grasped than with the left eye seeing. This result supports previous demonstrations of a left-hemisphere dominance for visually guided behavior in birds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual sensitivity to differences in velocity.

Applications of the Weber ratio, defined as the ratio of the differential speed threshold to the magnitude of the speed for comparison stimuli, to tracking and predictive behavior (prediction motion, prediction of future positions of a moving target) are examined. Experiments indicate that error in performance may be calculated for relatively simple tasks from the Weber ratio. For more complex tasks, constancy of the Weber ratio agrees with the linear relationship found between tracking error and speed of target motion. From Psyc Abstracts 36:02:2BI89B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual figural aftereffects in retarded adults.

A comparison of figural aftereffects (FAE) was made between 12 retarded and 10 normal adults. The response measure was figural displacement which was accurate to .0001 in. A careful attempt was made to control for eye movements which were considered as a possible artifact for previously noted differences between the 2 groups. The results clearly showed that retardates exhibit less immediate figural displacement than normal Ss. In addition, a significant proportion of retardates showed a "negative" FAE where the test figure was displaced toward the inspection figure. The significance of the negative effect was discussed in relation to the existing theories of FAE and a tentative explanation was offered within the framework of K?hler's satiation theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual perception of numerosity in infancy.

Numerosity was defined as an invariant property of a collection of objects specifying its numerical size. Infants looked at displays of small numerosities that changed optic structure such that size was not tied to certain static or dynamic configurational properties of the display but remained constant across patterns of optic motion. The displayed figures moved continuously and at a constant speed. The trajectories were irregular and could produce occlusion of objects. The task used involved infant-controlled habituation of visual looking time. At ages 5 mo, 8 mo, and 13 mo, 44 infants were tested for the numerosities 2, 3, and 4 in 3 randomly ordered sessions. The results demonstrated that infants from the age of at least 5 mo perceive small numerosities. It appears that discrimination of units, rather than discrimination of characteristic patterns, underlies numerosity perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)