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John R. Skoyles - One of the best experts on this subject based on the ideXlab platform.
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The Frequency Doubling Illusion and Testing of Magnocellular Sensitivity
Neuro-Ophthalmology, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:The frequency doubling illusion has been claimed to be a useful test of Magnocellular integrity. This claim is examined. It is found that since the temporal frequency of the stimuli is very high, it is plausible that they are detected by Magnocellular neurons. This, however, does not make frequency doubling by itself into an appropriate test of Magnocellular sensitivity. This is because it involves testing sensitivity under only one stimulus condition and so does not allow Magnocellular deficits to be differentiated from general visual impairments. Further limitations on the use of the frequency doubling illusion to assess Magnocellular sensitivity are also discussed.
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On the prevalence of Magnocellular deficits in the visual system of non-dyslexic individuals.
Brain and Language, 2020Co-Authors: John R. Skoyles, Bernt C. SkottunAbstract:Numerous studies have found visual deficits associated with dyslexia. This has made it important to understand how these deficits may be related to reading difficulties. A widely held theory is that dyslexia is the result of a deficit in the Magnocellular part of the visual system (earlier called the transient system). In support for this theory, the prevalence of Magnocellular deficits has been reported to be high among dyslexic readers and very low among non-dyslexic ones. This creates the impression that in the population as a whole dyslexic individuals have Magnocellular deficits and non-dyslexic individuals do not. However, we show that because the prevalence of dyslexia itself is low this need not be the case. On the basis of previously published data we have estimated the number of non-dyslexic and dyslexic individuals with Magnocellular deficits. Our estimates indicate that there should be a large number of non-dyslexic individuals with Magnocellular deficits. Paradoxically more individuals without dyslexia have Magnocellular deficits than individuals with dyslexia. This poses a challenge to the view that dyslexia is the result of a Magnocellular deficit.
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L- and M-cone ratios and Magnocellular sensitivity in reading
International Journal of Neuroscience, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:It has been proposed that Magnocellular deficits cause the reading problems in dyslexia. However, how Magnocellular deficiencies are supposed to cause these problems is unclear. Recently it has been proposed that reading performance is limited by the L-/M-cone inputs to the Magnocellular system. However, as explained in this review, this is problematic for a number of reasons. Particularly difficult is the linking of L- and M-cone sensitivity specifically to the Magnocellular system.
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YELLOW FILTERS, Magnocellular RESPONSES, AND READING
International Journal of Neuroscience, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:It has been suggested that yellow filters may increase Magnocellular responsivity. This suggestion was, in large part, based on the assumption that the S-cones inhibit the Magnocellular system. However, the evidence invoked to justify this assumption is only indirect. A previously reported direct electrophysiological investigation of this issue has found that S-cone input to the Magnocellular system actually sum with L-and M-cone inputs. Therefore, the notion that yellow filters enhance Magnocellular responses by reducing inhibition from S-cones cannot be maintained.
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Vernier Acuity as a Test of Magnocellular Sensitivity
Neuro-Ophthalmology, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:Vernier acuity has been argued to provide a means to measure the integrity of the Magnocellular visual pathway. This proposal is reviewed here and found to be inadequately supported for the following reasons: (1) the conditions under which Vernier acuity corresponds to Magnocellular resolution differ from those used in psychophysical tests; (2) Vernier offsets can be induced by adaptation of cortical neurons; (3) factors other than the Magnocellular system have the ability to interfere with Vernier acuity. Taken together, this review argues that Vernier acuity is at best limited as a selective test of Magnocellular sensitivity.
John H R Maunsell - One of the best experts on this subject based on the ideXlab platform.
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visual response latencies of Magnocellular and parvocellular lgn neurons in macaque monkeys
Visual Neuroscience, 1999Co-Authors: John H R Maunsell, Geoffrey M Ghose, John A Assad, Carrie J Mcadams, C E Boudreau, Brett D NoeragerAbstract:Signals relayed through the Magnocellular layers of the LGN travel on axons with faster conduction speeds than those relayed through the parvocellular layers. As a result, Magnocellular signals might reach cerebral cortex appreciably before parvocellular signals. The relative speed of these two channels cannot be accurately predicted based solely on axon conduction speeds, however. Other factors, such as different degrees of convergence in the Magnocellular and parvocellular channels and the retinal circuits that feed them, can affect the time it takes for Magnocellular and parvocellular signals to activate cortical neurons. We have investigated the relative timing of visual responses mediated by the Magnocellular and parvocellular channels. We recorded individually from 78 Magnocellular and 80 parvocellular neurons in the LGN of two anesthetized monkeys. Visual response latencies were measured for small spots of light of various intensities. Over a wide range of stimulus intensities the fastest Magnocellular response latencies preceded the fastest parvocellular response latencies by about 10 ms. Because parvocellular neurons are far more numerous than Magnocellular neurons, convergence in cortex could reduce the Magnocellular advantage by allowing parvocellular signals to generate detectable responses sooner than expected based on the responses of individual parvocellular neurons. An analysis based on a simple model using neurophysiological data collected from the LGN shows that convergence in cortex could eliminate or reverse the Magnocellular advantage. This observation calls into question inferences that have been made about ordinal relationships of neurons based on timing of responses.
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Magnocellular and parvocellular contributions to the responses of neurons in macaque striate cortex
The Journal of Neuroscience, 1994Co-Authors: Tara A Nealey, John H R MaunsellAbstract:Anatomical and physiological studies of the primate visual system have suggested that the signals relayed by the Magnocellular and parvocellular subdivisions of the LGN remain segregated in visual cortex. It has been suggested that this segregation may account for the known differences in visual function between the parietal and temporal cortical processing streams in extrastriate visual cortex. To test directly the hypothesis that the temporal stream of processing receives predominantly parvocellular signals, we recorded visual responses from the superficial layers of V1 (striate cortex), which give rise to the temporal stream, while selectively inactivating either the Magnocellular or parvocellular subdivisions of the LGN. Inactivation of the parvocellular subdivision reduced neuronal responses in the superficial layers of V1, but the effects of Magnocellular blocks were generally as pronounced or slightly stronger. Individual neurons were found to receive contributions from both pathways. We furthermore found no evidence that Magnocellular contributions were restricted to either the cytochrome oxidase blobs or interblobs in V1. Instead, Magnocellular signals made substantial contributions to responses throughout the superficial layers. Thus, the regions within V1 that constitute the early stages of the temporal processing stream do not appear to contain isolated parvocellular signals. These results argue against a direct mapping of the subcortical Magnocellular and parvocellular pathways onto the parietal and temporal streams of processing in cortex.
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does primate motion perception depend on the Magnocellular pathway
The Journal of Neuroscience, 1991Co-Authors: William H Merigan, C E Byrne, John H R MaunsellAbstract:This study examined the importance of the primate Magnocellular retinocortical pathway in the perception of moving stimuli. A portion of the Magnocellular pathway was permanently and selectively interrupted by ibotenic acid injections in the LGN of macaque monkeys. We then tested contrast sensitivity for detecting moving stimuli, as well as two indices of motion perception, contrast sensitivity for opposite direction discrimination and speed difference thresholds, in the affected portion of the visual field. Magnocellular lesions greatly reduced detection contrast sensitivity at high temporal and low spatial frequencies and had a similar effect on contrast sensitivity for opposite direction discrimination under these same stimulus conditions. Consequently, opposite direction discriminations could be made at contrast threshold, suggesting that Magnocellular lesions reduced the visibility of stimuli used to test direction perception, but did not act directly on direction perception. Magnocellular lesions also elevated speed difference thresholds under some stimulus conditions. However, this deficit was reduced or eliminated by raising the contrast of the test stimulus. Together, these findings suggest that Magnocellular lesions reduce the visibility of stimuli used to test motion perception but that they do not appear to alter motion perception otherwise.
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macaque vision after Magnocellular lateral geniculate lesions
Visual Neuroscience, 1990Co-Authors: William H Merigan, John H R MaunsellAbstract:Ibotenic-acid lesions of the magnocelluar portion of the macaque lateral geniculate nucleus were used to examine the role of the M-cell pathway in spatio-temporal contrast sensitivity. A lesion was place in layer 1 of the lateral geniculate of each of two monkeys. Physiological mapping in one animal demonstrated that the visual-field locus of the lesion was on the horizontal meridian, approximately 6 deg in the temporal field. Visual thresholds were tested monocularly in the contralateral eye, and fixation locus was monitored with a scleral search coil to control the retinal location of the test target. Three threshold measures were clearly disrupted by the Magnocellular lesions. Contrast sensitivity for a 1 cycle/deg grating that drifted at 10 Hz was reduced from about twofold greater than, to about the same as, that for 10-Hz counterphase modulated gratings. Sensitivity for a very low spatial frequency (Gaussian blob), 10-Hz flickering stimulus was reduced so severely that no threshold could be measured. In addition, flicker resolution was greatly reduced at lower modulation depths (0.22), but not at higher depths (1.0). Two of the measured thresholds were unaffected by the lesions. Contrast sensitivity for 2 cycle/deg stationary gratings remained intact, and little or no effect on sensitivity was found for 1 cycle/deg, 10-Hz counterphase modulated gratings. Together, these results suggest that the Magnocellular pathway makes little contribution to visual sensitivity at low to moderate temporal frequencies. On the other hand, some contribution to detection sensitivity is evident at lower spatial and high temporal frequencies, especially for drifting stimuli. It appears that a major role of the Magnocellular pathway may be to provide input to cortical mechanisms sensitive to rapid visual motion.
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Magnocellular and parvocellular contributions to responses in the middle temporal visual area mt of the macaque monkey
The Journal of Neuroscience, 1990Co-Authors: John H R Maunsell, Tara A Nealey, Derryl D DepriestAbstract:Many lines of evidence suggest that the visual signals relayed through the Magnocellular and parvocellular subdivisions of the primate dorsal LGN remain largely segregated through several levels of cortical processing. It has been suggested that this segregation persists through to the highest stages of the visual cortex, and that the pronounced differences between the neuronal response properties in the parietal cortex and inferotemporal cortex may be attributed to differential contributions from Magnocellular and parvocellular signals. We have examined this hypothesis directly by recording the responses of cortical neurons while selectively blocking responses in the Magnocellular or parvocellular layers of the LGN. Responses were recorded from single units or multiunit clusters in the middle temporal visual area (MT), which is part of the pathway leading to parietal cortex and thought to receive primarily Magnocellular inputs. Responses in the MT were consistently reduced when the Magnocellular subdivision of the LGN was inactivated. The reduction was almost always pronounced and often complete. In contrast, parvocellular block rarely produced striking changes in MT responses and typically had very little effect. Nevertheless, unequivocal parvocellular contributions could be demonstrated for a minority of MT responses. At a few MT sites, responses were recorded while Magnocellular and parvocellular blocks were made simultaneously. Responses were essentially eliminated for all these paired blocks. These results provide direct evidence for segregation of Magnocellular and parvocellular contributions in the extrastriate visual cortex and support the suggestion that these signals remain largely segregated through the highest levels of cortical processing.
J F Stein - One of the best experts on this subject based on the ideXlab platform.
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the current status of the Magnocellular theory of developmental dyslexia
Neuropsychologia, 2019Co-Authors: J F SteinAbstract:Abstract Some people doubt that the concept of developmental dyslexia (DD) is useful at all because the phonological weaknesses seen in DD cannot be distinguished from those found in every person with poor reading skills, whatever their cause. Here I argue that true DD is characterised by poor temporal processing, hence impaired visual and auditory sequencing, that is caused by impaired development of transient/Magnocellular (M-) systems throughout the brain. These deficits can be measured in order to distinguish the causes of the phonological weaknesses in DD from those causing similar deficits in other types of poor reading. Importantly this knowledge can be exploited to develop effective improvements in treatment. The evidence for impaired visual Magnocellular function in many, if not all, people with dyslexia is now overwhelming; it is supported not only by psychophysical tests of M- function, but also by electrophysiological, eye movement, attentional, imaging, interventional and genetic findings. Analogously, auditory temporal processing is mediated by auditory transient, 'Magnocellular', processing systems, and evidence is accumulating persuasively that this system is also impaired in dyslexics. I briefly introduce the idea that 'motor Magnocellular systems' may also be impaired in dyslexia, then consider genetic, immunological and nutritional factors that interact to cause the impaired Magnocellular phenotype. I then discuss why the dyslexic phenotype is so common by speculating about what strengths it might confer that would maintain the responsible genes in the human genome.
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Magnocellular based visual motion training improves reading in persian
Scientific Reports, 2019Co-Authors: Leila Ebrahimi, Hamidreza Pouretemad, Ali Khatibi, J F SteinAbstract:The visual Magnocellular system is thought to play a crucial role in learning to read. Here therefore, we examined whether Magnocellular based training could improve reading in children with visual reading problems. The participants were 24 male primary school students aged between 9–11 (Mean = 9.76, SD = 0.59) with specific reading difficulty. Experimental and control groups were matched for age, sex, educational level, IQ, reading abilities (measured by APRA), Magnocellular performance as assessed by a random dot kinematogram (RDK) paradigm and recordings of their saccadic eye movements. The experimental group received twelve Magnocellular based visual motion training sessions, twice a week over 6 weeks. During the same period, the control group played a video game with the help of a practitioner. All measures were made just prior to the training and were repeated at the 6th, 12th training session and one month later. The experimental group showed significant improvements in Magnocellular function, visual errors and reading accuracy during the course of intervention. Follow-up assessment confirmed that these effects persisted one month later. Impaired Magnocellular functioning appeared to be an important cause of poor reading in Persian. Hence Magnocellular based training could help many children with specific reading difficulties. Also testing Magnocellular function could be used as screening tool for detecting dyslexia before a child begins to fail at school.
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yellow filters can improve Magnocellular function motion sensitivity convergence accommodation and reading
Annals of the New York Academy of Sciences, 2005Co-Authors: S Fowler, J F SteinAbstract:The Magnocellular system plays an important role in visual motion processing, controlling vergence eye movements, and in reading. Yellow filters may boost Magnocellular activity by eliminating inhibitory blue input to this pathway. It was found that wearing yellow filters increased motion sensitivity, convergence, and accommodation in many children with reading difficulties, both immediately and after three months using the filters. Motion sensitivity was not increased using control neutral density filters. Moreover, reading-impaired children showed significant gains in reading ability after three months wearing the filters compared with those who had used a placebo. It was concluded that yellow filters can improve Magnocellular function permanently. Hence, they should be considered as an alternative to corrective lenses, prisms, or exercises for treating poor convergence and accommodation, and also as an aid for children with reading problems.
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impaired neuronal timing in developmental dyslexia the Magnocellular hypothesis
Dyslexia, 1999Co-Authors: J F Stein, Joel B TalcottAbstract:Developmental dyslexia is not just a literacy problem. Dyslexics' reading and spelling difficulties are but two of a much larger number of differences between dyslexic and normal readers. The condition is a wide-ranging, genetically based, neurodevelopmental syndrome. Reading requires fast and accurate processing of transient visual and auditory stimuli, functions for which large neurones, known as Magnocellular, are specialized. We review the evidence that many dyslexics have impaired function of the visual Magnocellular system, which correlates with their reading impairment, whereas good readers have high Magnocellular sensitivity. We discuss possible mechanisms for this relationship. Although there is no such clearly defined Magnocellular pathway in the auditory system as there is for vision, there is an analogous set of large auditory neurones which are specialized for following changes in the frequency or amplitude of sounds. We review evidence that the sensitivity of this auditory transient system is reduced in many dyslexics and that this reduction correlates with, hence may cause, their impaired phonological ability. As for the visual Magnocellular system we show that auditory transient sensitivity predicts phonological and reading ability not only in dyslexics but also in good readers. Thus the Magnocellular hypothesis postulates that dyslexics have lower sensitivity to dynamic visual and auditory stimuli as a result of slightly impaired development of large neurones and that this may explain not only their visual problems when attempting to read, but also their phonological deficit. Copyright © 1999 John Wiley & Sons, Ltd.
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Magnocellular visual function and children s single word reading
Vision Research, 1998Co-Authors: Piers L Cornelissen, Peter C Hansen, J L Hutton, V Evangelinou, J F SteinAbstract:Abstract Recent research has shown that reading disabled children find it unusually difficult to detect flickering or moving visual stimuli, consistent with impaired processing in the Magnocellular visual stream. Yet, it remains controversial to suggest that reduced visual sensitivity of this kind might affect children's reading. Here we suggest that when children read, impaired Magnocellular function may degrade information about where letters are positioned with respect to each other, leading to reading errors which contain sounds not represented in the printed word. We call these orthographically inconsistent nonsense errors “letter” errors. To test this idea we assessed Magnocellular function in a sample of 58 unselected children by using a coherent motion detection task. We then gave these children a single word reading task and found that their “letter” errors were best explained by independent contributions from motion detection (i.e., Magnocellular function) and phonological awareness (assessed by a spoonerism task). This result held even when chronological age, reading ability, and IQ were controlled for. These findings suggest that impaired Magnocellular visual function, as well as phonological deficits may affect how children read.
Bernt C. Skottun - One of the best experts on this subject based on the ideXlab platform.
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L- and M-cone ratios and Magnocellular sensitivity in reading
International Journal of Neuroscience, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:It has been proposed that Magnocellular deficits cause the reading problems in dyslexia. However, how Magnocellular deficiencies are supposed to cause these problems is unclear. Recently it has been proposed that reading performance is limited by the L-/M-cone inputs to the Magnocellular system. However, as explained in this review, this is problematic for a number of reasons. Particularly difficult is the linking of L- and M-cone sensitivity specifically to the Magnocellular system.
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On the use of the Ternus Test to Assess Magnocellular Function
Perception, 2020Co-Authors: Bernt C. SkottunAbstract: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.
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Stereopsis and Magnocellular sensitivity in schizophrenia
World Journal of Biological Psychiatry, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:There is evidence to indicate that schizophrenic individuals, in addition to cognitive deficiencies, also suffer from visual deficits. These deficits, it has been proposed, are the result of a deficiency in the Magnocellular portion of the early visual system. A number of approaches have been used in attempts to assess the sensitivity of the Magnocellular system in individuals with schizophrenia. It has recently been proposed that Magnocellular sensitivity can be tested by measuring stereo acuity, i.e. by measuring the accuracy with which visual depth can be detected based on differences in the retinal images in the two eyes. This suggestion was based on early claims which linked stereopsis, i.e. the visual perception of depth generated from differences in the two retinal images, to the Magnocellular system. We here review more recent results which indicate that stereopsis and stereo acuity are more closely linked to the parvocellular system. It is concluded that stereo acuity is not an appropriate test f...
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YELLOW FILTERS, Magnocellular RESPONSES, AND READING
International Journal of Neuroscience, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:It has been suggested that yellow filters may increase Magnocellular responsivity. This suggestion was, in large part, based on the assumption that the S-cones inhibit the Magnocellular system. However, the evidence invoked to justify this assumption is only indirect. A previously reported direct electrophysiological investigation of this issue has found that S-cone input to the Magnocellular system actually sum with L-and M-cone inputs. Therefore, the notion that yellow filters enhance Magnocellular responses by reducing inhibition from S-cones cannot be maintained.
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Vernier Acuity as a Test of Magnocellular Sensitivity
Neuro-Ophthalmology, 2020Co-Authors: Bernt C. Skottun, John R. SkoylesAbstract:Vernier acuity has been argued to provide a means to measure the integrity of the Magnocellular visual pathway. This proposal is reviewed here and found to be inadequately supported for the following reasons: (1) the conditions under which Vernier acuity corresponds to Magnocellular resolution differ from those used in psychophysical tests; (2) Vernier offsets can be induced by adaptation of cortical neurons; (3) factors other than the Magnocellular system have the ability to interfere with Vernier acuity. Taken together, this review argues that Vernier acuity is at best limited as a selective test of Magnocellular sensitivity.
Daniel C. Javitt - One of the best experts on this subject based on the ideXlab platform.
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impaired Magnocellular dorsal stream activation predicts impaired reading ability in schizophrenia
NeuroImage: Clinical, 2013Co-Authors: Antigona Martinez, Daniel C. Javitt, Nadine Revheim, Pamela D Butler, David N Guilfoyle, Elisa C DiasAbstract:In healthy humans, passage reading depends upon a critical organizing role played by the Magnocellular/dorsal visual pathway. In a recent study, we found a significant correlation between orthographic reading deficits in schizophrenia and deficits in contrast sensitivity to low spatial frequency stimuli, suggesting an underlying Magnocellular processing abnormality. The interrelationship between Magnocellular dysfunction and passage reading impairments in schizophrenia was investigated in 21 patients with schizophrenia and 17 healthy control volunteers using behavioral and functional MRI (fMRI) based measures. fMRI activation patterns during passage- and single-word reading were evaluated in relation to cortical areas with differential sensitivity to low versus high spatial frequency cortical regions indentified using a phase-encoded fMRI paradigm. On average, patients with schizophrenia read at the 6th grade level, despite completion of more than 12 years of education and estimated normal pre-morbid IQ. Schizophrenia patients also showed significantly impaired contrast sensitivity to low spatial frequencies and abnormal neural activity in response to stimulation with low spatial frequencies, consistent with dysfunction of Magnocellular processing. Further, these Magnocellular deficits were predictive of poor performance on a standardized psychoeducational test of passage reading. These findings suggest that reading is an important index of cognitive dysfunction in schizophrenia and highlight the contribution of Magnocellular dysfunction to overall cognitive impairments in schizophrenia.
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Magnocellular training improves visual word recognition.
Frontiers in Human Neuroscience, 2012Co-Authors: Tara Chouake, Tamar Levy, Daniel C. Javitt, Michal LavidorAbstract:Current research has shown that the Magnocellular system may play a crucial role in reading deficits related to dyslexia. The current study explored the relationship between Magnocellular activity and reading abilities; we examined the hypothesis that a repeated usage of the Magnocellular stream may improve reading by strengthening crucial neural pathways. Visual training was conducted for five consecutive days using a motion detection task (Magnocellular training) and a control task of pattern detection (parvocellular training). Reading abilities of skilled readers were measured before and after the training using a lexical decision task. It was found that low grade visual training overall can improve speed of lexical decision, but only Magnocellular training selectively improved accuracy. Improvement in the Magnocellular training task predicted performance on adjacent anagram and word recognition after training. In contrast, in the control group (parvocellular training) degree of improvement in training did not predict lexical decision performance after training. This result lends support to the role of the Magnocellular system in reading, and has potential implications for neuro-rehabilitation of reading related deficits.
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Magnocellular contributions to impaired motion processing in schizophrenia
Schizophrenia Research, 2006Co-Authors: Glenn Wylie, Daniel C. Javitt, Pamela D Butler, Roey PasternakAbstract:Patients with schizophrenia show impairments in motion processing, along with deficits in lower level processing primarily involving the Magnocellular visual pathway. The present study investigates potential Magnocellular contributions to impaired motion processing in schizophrenia using a combined neurophysiological and behavioral approach. As compared to prior motion studies in schizophrenia, thresholds were determined for both incoherent and coherent visual motion. In this study, velocity discrimination thresholds were measured for schizophrenia patients (n = 14) and age-matched normal control subjects (n = 16) using a staircase procedure. Early visual processing was evaluated using steady-state visual evoked potentials (ssVEP), with stimuli biased toward activation of either the Magnocellular or parvocellular visual pathways through luminance contrast manipulation. Patients with schizophrenia showed poor velocity discrimination for both incoherent and coherent motion, with no significant group × task interaction. Further, when coherent motion performance was measured at individually determined incoherent motion thresholds, accuracy levels for patients were similar to controls, also indicating similarity of deficit for incoherent vs. coherent motion discrimination. Impairments in velocity discrimination correlated significantly with reduced amplitude of ssVEP elicited by Magnocellular – but not parvocellular – selective stimuli. This study demonstrates that deficits in motion processing in schizophrenia are significantly related to reduced activation of the Magnocellular visual system. Further, this study supports and extends prior reports of impaired motion processing in schizophrenia, and indicates significant bottom-up contributions to higher-order cognitive impairments.