Jacqueline Liederman

Greater plasticity in lower-level than higher-level visual motion processing in a passive perceptual learning task.

Simple exposure is sufficient to sensitize the human visual system to a particular direction of motion, but the underlying mechanisms of this process are unclear. Here, in a passive perceptual learning task, we found that exposure to task-irrelevant motion improved sensitivity to the local motion directions within the stimulus, which are processed at low levels of the visual system. In contrast, task-irrelevant motion had no effect on sensitivity to the global motion direction, which is processed at higher levels. The improvement persisted for at least several months. These results indicate that when attentional influence is limited, lower-level motion processing is more receptive to long-term modification than higher-level motion processing in the visual cortex.

Male Vulnerability to Reading Disability Is Not Likely to Be a Myth A Call for New Data

Whether boys are more vulnerable than girls to reading disabilities (RD) is controversial. We review studies that were designed to minimize ascertainment bias in the selection of individuals with RD. These include population-based studies that identified children with RD by objective, unbiased methods and studies that examined the gender ratios among the affected relatives of those diagnosed with RD. We conclude that even when ascertainment biases are minimized, there is still a significant preponderance of boys with RD, although the gender ratio of the affected relatives of those with RD manifests the weakest male bias. Furthermore, we demonstrate that potentially confounding factors such as attentional or neurological problems, race, IQ, and severity of RD cannot account for the observed gender bias. We end with a clarion call to future researchers to (a) consider analyzing gender differences by means of more than one definition of RD, (b) compare gender ratios when boys and girls are ranked against the performance of their own gender as opposed to an average across genders, and (c) report group differences in variability and effect sizes of obtained gender ratios.

Male prevalence for reading disability is found in a large sample of Black and White children free from ascertainment bias

Male vulnerability to neurodevelopmental disorders remains controversial. For one disorder, reading disability, this sex bias has been interpreted as an artifact of referral bias. We investigated sex differences for the incidence of reading disability within a large prospective sample of White (N = 16,910) and Black (N = 15,313) children derived from the National Collaborative Perinatal Project (NCPP). Children were classified as having either moderate or severe reading disability when they had reading scores lower than 1.5 or 2.0 standard errors of prediction, respectively, given their age and intelligence. Reading disability was about twice as common in boys than girls (p < .001), irrespective of race, severity of disability, or exclusion of children with attentional disturbances or high activity levels. We conclude that there is a clear sex bias toward males for the incidence of reading disabilities.

Interhemispheric collaboration in response to simultaneous bilateral input

Two experiments tested whether processing is speeded when inputs are divided between the hemispheres rather than projected to a single hemisphere. Bilateral (bihemispheric) vs unilateral (single hemisphere) word pairs were tachistoscopically presented. Subjects responded when the words semantically matched. Irrespective of distance, visual angle and compatibility with reading biases, bilateral/bihemispheric performance was as fast as the better of the two individual unilateral/single hemisphere conditions and faster than their average. This pattern occurred only at the beginning of each experiment. With practice, performance significantly improved in the single but not the bihemispheric conditions. The excellent initial performance during the bihemispheric condition and its lack of improvement with practice are discussed with reference to models of interhemispheric collaboration.

Splenium Microstructure is Related to Two Dimensions of Reading Skill

Inconsistent differences in the corpus callosum (CC) structure between dyslexic readers (DRs) and typical readers (TRs) have been reported. We examine differences in CC splenium microstructure and the association of splenium microstructure with reading-related skills. Nine DRs and 18 TRs completed a reading skills battery and diffusion tensor imaging. DRs had higher splenium fractional anisotropy (FA) and axial diffusivity (LA) as compared with TRs. Retrieval of orthographic information from the language lexicon was negatively associated with FA and LA within both reading groups. Phonological awareness was positively associated with splenium FA and LA in TRs but not DRs. This study suggests two white matter pathways that may be differentially associated with reading skills in the CC splenium.

Surface Area Accounts for the Relation of Gray Matter Volume to Reading-Related Skills and History of Dyslexia

It is unknown whether the abnormalities in brain structure and function observed in dyslexic readers are congenital or arise later in development. Analyzing the 2 components of gray matter volume separately may help in differentiating these possibilities. Gray matter volume is the product of cortical surface area, determined during prenatal brain development, and cortical thickness, determined during postnatal development. For this study, 16 adults with a history of phonological dyslexia and 16 age- and gender-matched controls underwent magnetic resonance imaging and an extensive battery of tests of reading-related skills. Cortical surface area and gray matter volume measures of the whole brain, the inferior frontal gyrus, and the fusiform gyrus were similarly related to phonological skills and a history of dyslexia. There was no relationship between cortical thickness and phonological skills or history of dyslexia. Because cortical surface area reflects cortical folding patterns determined prenatally, this suggests that brain differences in dyslexia are rooted in early cortical development and are not due to compensatory changes that occur during postnatal development and would be expected to influence cortical thickness. This study demonstrates the importance of examining the separate components of gray matter volume when studying developmental abnormalities.

The mechanism of neonatal rightward turning bias: A sensory or motor asymmetry?*

The earliest behavioral asymmetry in humans is a rightward bias in the direction of head turning, a measure which relates to subsequent hand preference and possibly lateralization of cognitive function. Are newborns more responsible to right sided than left sided stimulation, or is the bias motoric and evident not only in orienting (turning toward) but also in withdrawal (turning away) behavior? In the first study, 62 newborns were presented with aversive and non-aversive stimuli within three modalities (visual, tactile and gustatory). A right turning bias was present, across modalities and was strongest during withdrawal from aversive midline stimulation. In the second study, of 72 newborns, only unilateral, aversive stimuli were used, and the infants prior body position (left or right) was controlled. Right sided aversive touch did not result in faster withdrawal or more irritable behavior than left (as expected if sensitivity were greater on the right). Prior position biased turning toward the same side for both aversive touch and aversive taste, but an overall right-turning bias was still evident. These findings suggest that the motor act of turning is biased rightward in these newborn offspring of righthanded parents, independent of any lateralized differential in sensory sensitivity.

Subtraction in addition to addition: dual task performance improves when tasks are presented to separate hemispheres.

This research links neuro- and cognitive psychology by asking whether performance of two concurrent cognitive tasks is facilitated by presentation of each task to a different cerebral hemisphere. Subjects were required to perform two arithmetic problems which were presented simultaneously. One problem required addition; the other subtraction. In Experiment I, briefly exposed numbers were exposed for 100 ms and were arranged so that a digit at fixation had to be added to a top number and subtracted from a bottom number. In Experiment II, the numbers were reversed so that the addition task was below the subtraction task. During Bilateral/bihemispheric trials, the addition problem was presented to one visual field and the subtraction problem to the other visual field. During Unilateral/single hemisphere trials, the addition and subtraction problems were projected to only one visual field. Results indicated that a higher proportion of problems were correctly solved during the Bilateral/bihemispheric trials than during the Unilateral/single hemisphere trials. These data suggest that dividing simultaneous inputs so that each hemisphere is confronted with a task requiring only one kind of cognitive operation facilitates performance, perhaps by minimizing intertask interference. This study illustrates one kind of hemispheric cooperation which facilitates dual task performance.

Rightward motor bias in newborns depends upon parental right-handedness ☆

Abstract Direction of head turning in response to symmetrically placed stimulation was rightward-biased in newborn infants with two right-handed parents but not in those with one non-right-handed parent. The data suggested that lateral preference is transmitted genetically, and implied that the left side of the brain is predominant for motor function even at birth.

The Effect of Task Difficulty Upon the Extent to which Performance Benefits from Between-Hemisphere Division of Inputs

The means by which the two hemispheres coordinate processing of information are not well understood. By means of a tachistoscopic paradigm, we have shown repeatedly that performance is better when two conflicting tasks are presented to separate hemispheres than when both tasks are presented to a single hemisphere. The present study examines whether this effect is restricted to a specific range of task difficulty. Adult right-handers viewed two conflicting naming tasks by means of a tachistoscope. Task difficulty was lowered by reducing processing load (Experiment I: N = 32). Task difficulty was raised by projecting a visual mask 40 ms after offset of the visual displays (Experiment II: N = 10). At lower levels of processing load, dividing conflicting tasks between the hemispheres was beneficial, but not significantly so. At higher levels of load, and at either higher or lower loads with a visual mask, there were significant benefits associated with dividing conflicting tasks between the hemispheres. Three alternative explanations are discussed for the absence of an advantage associated with between-hemisphere division of inputs when task difficulty is reduced.