Computer-based training of stimulus detection improves color and simple pattern recognition in the defective field of hemianopic subjects

Training with optic flow stimuli promotes recovery in cortical blindness

BACKGROUND

Cortical blindness is a form of severe vision loss that is caused by damage to the primary visual cortex (V1) or its afferents. This condition has devastating effects on quality of life and independence. While there are few treatments currently available, accumulating evidence shows that certain visual functions can be restored with appropriate perceptual training: Stimulus sensitivity can be increased within portions of the blind visual field. However, this increased sensitivity often remains highly specific to the trained stimulus, limiting the overall improvement in visual function.

OBJECTIVE

Recent advances in the field of perceptual learning show that such specificity can be overcome with training paradigms that leverage the properties of higher-level visual cortical structures, which have greater capacity to generalize across stimulus positions and features. This targeting can be accomplished by using more complex training stimuli that elicit robust responses in these visual structures.

METHODS

We trained cortically blind subjects with a complex optic flow motion stimulus that was presented in a location of their blind field. Participants were instructed to train with the stimulus at home for approximately 30 minutes per day. Once performance plateaued, the stimulus was moved deeper into the blind field. A battery of pre- and post-training measures, with careful eye tracking, was performed to quantify the improvements.

RESULTS

We show that 1) optic flow motion discrimination can be relearned in cortically blind fields; 2) training with an optic flow stimulus can lead to improvements that transfer to different tasks and untrained locations; and 3) such training leads to a significant expansion of the visual field. The observed expansion of the visual field was present even when eye movements were carefully controlled. Finally, we show that regular training is critical for improved visual function, as sporadic training reduced the benefits of training, even when the total numbers of training sessions were equated.

CONCLUSIONS

These findings are consistent with the hypothesis that complex training stimuli can improve outcomes in cortical blindness, provided that patients adhere to a regular training regimen. Nevertheless, such interventions remain limited in their ability to restore functional vision.

Individualized Visual Reality Training Improves Visual Acuity and Visual Field Defects in Patients with Glaucoma: A Preliminary Study Report

To explore whether individualized visual training improves the visual acuity and visual field defects of patients with glaucoma. Patients with established primary glaucoma who visited the glaucoma clinic of Beijing Shijitan Hospital, Capital Medical University from January 2018 to April 2018 were recruited. The binocular visual perception examination was performed by using the visual perception examination system, and a personalized training program was developed according to the relevant threshold conditions between the eyes of the patients. The binocular visual perception training session for 20 minutes for two sessions was completed at home by using a virtual reality helmet. The visual function, intraocular pressure, and Octopus visual field were examined, before and at the first month and the third month after training. Seven patients completed the study. None of the seven patients has fine stereopsis, four of them have large stereopsis, and two patients are without large stereopsis. The visual acuity at 3 months after training was significantly improved compared with that before training. The mean defect value after 1 month of training was significantly lower than that before training, and it was further decreased after 3 months. Similarly, the mean sensitivity value was significantly increased in both follow-ups after training. There was no significant difference in loss variance after 1 and 3 months of training when compared with that before training (p > 0.05). Our small prospective observational study indicated that individualized visual perception training can improve the visual function and improve the visual field in patients with glaucoma, and a large sample size study is warranted to further assess the value of this novel treatment.

Telerehabilitation for people with low vision

BACKGROUND

Low vision affects over 300 million people worldwide and can compromise both activities of daily living and quality of life. Rehabilitative training and vision assistive equipment (VAE) may help, but some visually impaired people have limited resources to attend in-person visits at rehabilitation clinics to receive training to learn to use VAE. These people may be able to overcome barriers to care through remote, Internet-based consultation (i.e. telerehabilitation).

OBJECTIVES

To compare the effects of telerehabilitation with face-to-face (e.g. in-office or inpatient) vision rehabilitation services for improving vision-related quality of life and near reading ability in people with visual function loss due to any ocular condition. Secondary objectives were to evaluate compliance with scheduled rehabilitation sessions, abandonment rates for VAE devices, and patient satisfaction ratings.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2019, Issue 6); Ovid MEDLINE; Embase.com; PubMed; ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not use any language restriction or study design filter in the electronic searches; however, we restricted the searches from 1980 onwards because the Internet was not introduced to the public until 1982. We last searched the electronic databases on 24 June 2019.

SELECTION CRITERIA

We planned to include randomized controlled trials (RCTs) or controlled clinical trials (CCTs) in which participants diagnosed with low vision were undergoing low vision rehabilitation using an Internet, web-based technology compared with an approach involving in-person consultations.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened titles and abstracts and then full-text articles against the eligibility criteria. We planned to have two review authors independently abstract data from the included studies. Any discrepancies were resolved by discussion.

MAIN RESULTS

We identified two ongoing studies, but did not find any completed RCTs and CCTs that met the inclusion criteria for this review. We did not conduct a quantitative analysis. We discussed review articles on telemedicine for facilitating communication with elderly individuals or for providing remote ophthalmological care.

AUTHORS' CONCLUSIONS

We did not find any evidence from RCTs or CCTs on the efficacy of using telerehabilitation for remote delivery of rehabilitation services to individuals with low vision. Given the disease burden and the growing interest in telemedicine, the two ongoing studies, when completed, may provide evidence in understanding the potential for telerehabilitation as a platform for providing services to people with low vision.

Transcranial direct current stimulation (tDCS) combined with blindsight rehabilitation for the treatment of homonymous hemianopia: a report of two-cases

[Purpose] Homonymous hemianopia is one of the most common symptoms following neurologic damage leading to impairments of functional abilities and activities of daily living. There are two main types of restorative rehabilitation in hemianopia: "border training" which involves exercising vision at the edge of the damaged visual field, and "blindsight training," which is based on exercising the unconscious perceptual functions deep inside the blind hemifield. Only border effects have been shown to be facilitated by transcranial direct current stimulation (tDCS). This pilot study represents the first attempt to associate the modulatory effects of tDCS over the parieto-occipital cortex to blindsight treatment in the rehabilitation of the homonymous hemianopia. [Subjects and Methods] Patients TA and MR both had chronic hemianopia. TA underwent blindsight treatment which was combined with tDCS followed by blindsight training alone. MR underwent the two training rounds in reverse order. [Results] The patients showed better scores in clinical-instrumental, functional, and ecological assessments after tDCS combined with blindsight rehabilitation rather than rehabilitation alone. [Conclusion] In this two-case report parietal-occipital tDCS modulate the effects induced by blindsight treatment on hemianopia.

Review of rehabilitation and habilitation strategies for children and young people with homonymous visual field loss caused by cerebral vision impairment

Partial and homonymous visual field loss (HVFL) is a common consequence of post-chiasmatic injury to the primary visual pathway or injury to the primary visual cortex. Different approaches to rehabilitation have been reported for older adults with HVFL and there is evidence to support the use of compensatory training over other proposed therapies. We reviewed the literature to investigate the current state of the art of rehabilitation and habilitation strategies for children and young people with HVFL, and whether there is enough evidence to support the use of these strategies in the paediatric population. We have provided an overview of the existing literature on children and young people with HVFL, a brief overview of rehabilitation strategies for adults with HVFL, and evidence on whether these different interventions have been applied with children and young people effectively. We found that there have been very few studies to investigate these strategies with children and young people, and the quality of evidence is currently low. New research is required to evaluate which strategies are effective for children and young people with HVFL and whether new strategies need to be developed.

Relearning to See in Cortical Blindness

The incidence of cortically induced blindness is increasing as our population ages. The major cause of cortically induced blindness is stroke affecting the primary visual cortex. While the impact of this form of vision loss is devastating to quality of life, the development of principled, effective rehabilitation strategies for this condition lags far behind those used to treat motor stroke victims. Here we summarize recent developments in the still emerging field of visual restitution therapy, and compare the relative effectiveness of different approaches. We also draw insights into the properties of recovered vision, its limitations and likely neural substrates. We hope that these insights will guide future research and bring us closer to the goal of providing much-needed rehabilitation solutions for this patient population.

Bernhard Sabel and 'Residual Vision Activation Theory': a History Spanning Three Decades

This review has the purpose of retracing the work of Professor Bernard Sabel and his group over the last 2-3 decades, in order to understand how they achieved formulation of the 'Residual Vision Activation Theory'. The methodology proposed is described, from the first studies in 1995 with High Resolution Perimetry requiring a six-months training period, to the new technologies, such as repetitive transorbital Alternating Current Stimulation, that require ten days of training. Vision restoration therapy has shown improvement in visual responses irrespective of age at the training, lesion aetiology and site of lesion. The hypothesis that visual training may induce network plasticity, improving neuronal networks in cortical and subcortical areas of both hemispheres, appears to be confirmed by recent studies including observation of the cerebral activity by fMRI and EEG. However, the results are quite variable and the mechanisms that influence cerebral activity are still unclear. The residual vision activation theory has been much criticized, both for its methodology and analysis of the results, but it gave a new impulse to the research in this area, stimulating more studies on induced cerebral plasticity.

Telerehabilitation for people with low vision

BACKGROUND

Low vision affects over 300 million people worldwide and can compromise both activities of daily living and quality of life. Rehabilitative training and vision assistive equipment (VAE) may help, but some visually impaired people have limited resources to attend in-person visits at rehabilitation clinics. These people may be able to overcome barriers to care through remote, Internet-based consultation (i.e., telerehabilitation).

OBJECTIVES

To compare the effects of telerehabilitation with face-to-face (e.g., in-office or inpatient) vision rehabilitation services for improving vision-related quality of life and reading speed in people with visual function loss due to any ocular condition. Secondary objectives are to evaluate compliance with scheduled rehabilitation sessions, abandonment rates for visual assistive equipment devices, and patient satisfaction ratings.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015 Issue 5), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1980 to June 2015), EMBASE (January 1980 to June 2015), PubMed (1980 to June 2015), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any language restriction or study design filter in the electronic searches; however, we restricted the searches from 1980 onwards because the Internet was not introduced to the public until 1982. We last searched the electronic databases on 15 June 2015.

SELECTION CRITERIA

We planned to include randomized controlled trials (RCTs) or controlled clinical trials (CCTs) in which participants were diagnosed with low vision and were undergoing low vision rehabilitation using an Internet, web-based technology compared with an approach based on in-person consultations.

DATA COLLECTION AND ANALYSIS

Two authors independently screened titles and abstracts, and then full-text articles against the eligibility criteria. We planned to have two authors independently abstract data from included studies. We resolved discrepancies by discussion.

MAIN RESULTS

We did not find any study that met the inclusion criteria for this review and, hence, we did not conduct a quantitative analysis. As a part of the background, we discussed review articles on telemedicine for facilitating communication with elderly individuals or for providing remote ophthalmological care.

AUTHORS' CONCLUSIONS

We did not find any evidence on whether the use of telerehabilitation is feasible or a potentially viable means to remotely deliver rehabilitation services to individuals with low vision. Given the disease burden and the growing interest in telemedicine, there is a need for future pilot studies and subsequent clinical trials to explore the potential for telerehabilitation as a platform for providing services to people with low vision.

Visual rehabilitation: visual scanning, multisensory stimulation and vision restoration trainings

Neuropsychological training methods of visual rehabilitation for homonymous vision loss caused by postchiasmatic damage fall into two fundamental paradigms: “compensation” and “restoration”. Existing methods can be classified into three groups: Visual Scanning Training (VST), Audio-Visual Scanning Training (AViST) and Vision Restoration Training (VRT). VST and AViST aim at compensating vision loss by training eye scanning movements, whereas VRT aims at improving lost vision by activating residual visual functions by training light detection and discrimination of visual stimuli. This review discusses the rationale underlying these paradigms and summarizes the available evidence with respect to treatment efficacy. The issues raised in our review should help guide clinical care and stimulate new ideas for future research uncovering the underlying neural correlates of the different treatment paradigms. We propose that both local “within-system” interactions (i.e., relying on plasticity within peri-lesional spared tissue) and changes in more global “between-system” networks (i.e., recruiting alternative visual pathways) contribute to both vision restoration and compensatory rehabilitation, which ultimately have implications for the rehabilitation of cognitive functions.

Visual Field Preservation in Surgery of Occipital Arteriovenous Malformations: A Prospective Study

OBJECTIVE

We reviewed our prospective study of patients with occipital arteriovenous malformations (AVMs) to assess whether the display of optic radiation diffusion tensor imaging (DTI) during neuronavigation-guided surgery can reduce the severity of postoperative visual field deficits (VFDs) and to evaluate the factors associated with visual field preservation.

METHODS

Forty-six consecutive patients with occipital AVMs were randomized in our study. DTI of the optic radiation was displayed during neuronavigation surgery in 24 patients. The other 22 patients were treated surgically without neuronavigation. Modified Rankin Scale (mRS) scores and visual fields were evaluated preoperatively, immediately after surgery, and at the last follow-up.

RESULTS

The patients' baseline characteristics and AVM features were statistically similar between the 2 surgical groups. The postoperative obliteration rate was 100%. The postoperative mRS scores did not differ between the 2 groups (P > 0.05). Preexisting VFDs were more common (P = 0.00004) in patients who bled than in those with unruptured AVMs. The application of DTI-incorporated neuronavigation reduced the frequency and severity of postoperative VFDs (P = 0.013 and 0.001, respectively). Visual fields were more likely to be preserved in patients with an AVM >5 mm from the optic radiation (P = 0.025).

CONCLUSIONS

A history of hemorrhage is an independent risk factor for VFDs associated with occipital AVMs. Although not showing superiority in postoperative mRS, functional MRI navigation-guided surgery may help to radically resect occipital AVMs and preserve patient visual fields. A 5-mm distance from the optic radiation may be a suitable safety margin for visual field preservation.

A matter of time: improvement of visual temporal processing during training-induced restoration of light detection performance

The issue of how basic sensory and temporal processing are related is still unresolved. We studied temporal processing, as assessed by simple visual reaction times (RT) and double-pulse resolution (DPR), in patients with partial vision loss after visual pathway lesions and investigated whether vision restoration training (VRT), a training program designed to improve light detection performance, would also affect temporal processing. Perimetric and campimetric visual field tests as well as maps of DPR thresholds and RT were acquired before and after a 3 months training period with VRT. Patient performance was compared to that of age-matched healthy subjects. Intact visual field size increased during training. Averaged across the entire visual field, DPR remained constant while RT improved slightly. However, in transition zones between the blind and intact areas (areas of residual vision) where patients had shown between 20 and 80% of stimulus detection probability in pre-training visual field tests, both DPR and RT improved markedly. The magnitude of improvement depended on the defect depth (or degree of intactness) of the respective region at baseline. Inter-individual training outcome variability was very high, with some patients showing little change and others showing performance approaching that of healthy controls. Training-induced improvement of light detection in patients with visual field loss thus generalized to dynamic visual functions. The findings suggest that similar neural mechanisms may underlie the impairment and subsequent training-induced functional recovery of both light detection and temporal processing.

Transient increase of intact visual field size by high-frequency narrow-band stimulation

Three patients with visual field defects were stimulated with a square matrix pattern, either static, or flickering at frequencies that had been found to either promote or not promote blindsight performance. Comparison between pre- and post-stimulation perimetric maps revealed an increase in the size of the intact visual field but only for flicker frequencies previously found to promote blindsight. These changes were temporary but dramatic - in two instances the intact field was increased by an area of ∼30 deg(2) of visual angle. These results indicate that not only does specific high-frequency stimulus flicker promote blindsight, but that intact visual field size may be increased by stimulation at the same frequencies. Our findings inform speculation on both the brain mechanisms and the potency of temporal modulation for altering the functional visual field.

Spontaneous recovery and treatment effects in patients with homonymous visual field defects: a meta-analysis of existing literature in terms of the ICF framework

Homonymous visual field defects (HVFDs) are a common consequence of posterior brain injury. Most patients do not recover spontaneously and require rehabiliation. To determine whether a certain intervention may help an individual patient, it is necessary to predict the patient's level of functioning and the effect of specific training. We provide an overview of both the existing literature on HVFDs in terms of the International Classification of Functioning, Disability, and Health (ICF) components and the variables predicting the functioning of HVFD patients or the effect of treatment. We systematically analyzed 221 publications on HVFD. All variables included in these articles were classified according to the ICF, as developed by the World Health Organization, and checked for their predictive value. We found that ICF helps to clarify the scope of the existing literature and provides a framework for designing future studies, which should consider including more outcome measures related to Activities and Participation. Although several factors have been described that predict HVFD patients' level of functioning or the effects of training, additional research is necessary to identify more.

Evaluation of two treatment outcome prediction models for restoration of visual fields in patients with postchiasmatic visual pathway lesions

Visual functions of patients with visual field defects after acquired brain injury affecting the primary visual pathway can be improved by means of vision restoration training. Since the extent of the restored visual field varies between patients, the prediction of treatment outcome and its visualization may help patients to decide for or against participating in therapies aimed at vision restoration. For this purpose, two treatment outcome prediction models were established based on either self-organizing maps (SOMs) or categorical regression (CR) to predict visual field change after intervention by several features that were hypothesized to be associated with vision restoration. Prediction was calculated for visual field changes recorded with High Resolution Perimetry (HRP). Both models revealed a similar predictive quality with the CR model being slightly more beneficial. Predictive quality of the SOM model improved when using only a small number of features that exhibited a higher association with treatment outcome than the remaining features, i.e. neighborhood activity and homogeneity within the surrounding 5° visual field of a given position, together with its residual function and distance to the scotoma border. Although both models serve their purpose, these were not able to outperform a primitive prediction rule that attests the importance of areas of residual vision, i.e. regions with partial visual field function, for vision restoration.

[Disorders of visual perception]

Disorders of visual perception are frequent and disabling functional consequences of acquired brain injury (20-40%). They also have adverse effects on the assessment, diagnosis and treatment of other functional disorders. Most frequent are visual field disorders followed by disorders of visual acuity and contrast sensitivity, visual adaptation, color and visual space perception as well as of visual recognition. Multiple visual and/or additional cognitive disorders are most common. The differential diagnosis of cerebral visual disorders and an individually tailored and specific approach in the rehabilitation are therefore of great importance. Compensatory treatment methods are to be preferred because of their efficacy, ecological validity as well as a good cost-benefit ratio.

Adaptive neuroplastic responses in early and late hemispherectomized monkeys

Behavioural recovery in children who undergo medically required hemispherectomy showcase the remarkable ability of the cerebral cortex to adapt and reorganize following insult early in life. Case study data suggest that lesions sustained early in childhood lead to better recovery compared to those that occur later in life. In these children, it is possible that neural reorganization had begun prior to surgery but was masked by the dysfunctional hemisphere. The degree of neural reorganization has been difficult to study systematically in human infants. Here we present a 20-year culmination of data on our nonhuman primate model (Chlorocebus sabeus) of early-life hemispherectomy in which behavioral recovery is interpreted in light of plastic processes that lead to the anatomical reorganization of the early-damaged brain. The model presented here suggests that significant functional recovery occurs after the removal of one hemisphere in monkeys with no preexisting neurological dysfunctions. Human and primate studies suggest a critical role for subcortical and brainstem structures as well as corticospinal tracts in the neuroanatomical reorganization which result in the remarkable behavioral recovery following hemispherectomy. The non-human primate model presented here offers a unique opportunity for studying the behavioral and functional neuroanatomical reorganization that underlies developmental plasticity.

Temporal profile of functional visual rehabilitative outcomes modulated by transcranial direct current stimulation

OBJECTIVES

We have previously reported that transcranial direct current stimulation (tDCS) delivered to the occipital cortex enhances visual functional recovery when combined with three months of computer-based rehabilitative training in patients with hemianopia. The principal objective of this study was to evaluate the temporal sequence of effects of tDCS on visual recovery as they appear over the course of training and across different indicators of visual function.

METHODS

Primary objective outcome measures were 1) shifts in visual field border and 2) stimulus detection accuracy within the affected hemifield. These were compared between patients randomized to either vision restoration therapy (VRT) combined with active tDCS or VRT paired with sham tDCS. Training comprised two half-hour sessions, three times a week for three months. Primary outcome measures were collected at baseline (pretest), monthly interim intervals, and at posttest (three months). As secondary outcome measures, contrast sensitivity and reading performance were collected at pretest and posttest time points only.

RESULTS

Active tDCS combined with VRT accelerated the recovery of stimulus detection as between-group differences appeared within the first month of training. In contrast, a shift in the visual field border was only evident at posttest (after three months of training). tDCS did not affect contrast sensitivity or reading performance.

CONCLUSIONS

These results suggest that tDCS may differentially affect the magnitude and sequence of visual recovery in a manner that is task specific to the type of visual rehabilitative training strategy employed.

Restoration of vision after optic nerve lesions with noninvasive transorbital alternating current stimulation: a clinical observational study

BACKGROUND

Non-invasive current stimulation can induce neuroplastic changes in the normal brain, including visual system structures. Because it is not known if such plasticity is of clinical value, we wished to learn if vision restoration can be induced after optic nerve damage.

METHODS

In an open-label, clinical observational study 446 patients with optic nerve lesions were treated with non-invasive repetitive transorbital alternating current stimulation (rtACS). Current bursts (<1000 μA, 5-20 Hz) were applied to induce phosphenes for one or two 10-day stimulation periods. Efficacy was assessed by monocular measurements of visual acuity and visual field (VF) size. EEG recordings at rest (n = 68) were made before and after treatment and global power spectra changes were analyzed.

RESULTS

rtACS improved VF size in the right and left eye by 7.1% and 9.3% (p < 0.001), respectively. VF enlargements were present in 40.4% of right and 49.5% of left eyes. Visual acuity (VA) significantly increased in both eyes (right = 0.02, left = 0.015; p < 0.001). A second 10-day course was conducted 6 months in a subset of 62 patients and resulted in additional significant improvements of VA. Analysis of EEG power spectra revealed that VA and VF improvements were associated with increased alpha power. Increased theta power was observed in patients that had only VF enlargements but no VA change. In contrast, non-responders had increased delta power spectra in frontal and occipital areas.

CONCLUSIONS

rtACS leads to long-lasting improvements in VA and VF size and after-effects in EEG power spectra. Because physiological and clinical parameters are correlated we hypothesize that rtACS enhances plasticity by inducing synchronization in different cortical regions, but the precise mechanisms needs further clarification. These encouraging results require confirmation by controlled clinical trials.

Clinical treatment options for patients with homonymous visual field defects

The objective of this review is to evaluate treatments for homonymous visual field defects (HVFDs). We distinguish between three treatments: visual restoration training (VRT), optical aids, and compensatory training. VRT is both the most ambitious and controversial approach, aiming to restore portions of the lost visual field. While early studies suggested that VRT can reduce the visual field defect, recent studies using more reliable means of monitoring the patients’ fixation could not confirm this effect. Studies utilizing modern optical aids have reported some promising results, but the extent to which these aids can reliably reduce the patients’ visual disability has yet to be confirmed. Compensatory approaches, which teach patients more effective ways of using their eyes, are currently the only form of treatment for which behavioral improvements have been demonstrated. However, with the exception of one study using a reading training, placebo-controlled clinical evaluation studies are lacking. It is also not yet clear whether the training benefits found in laboratory tasks lead to reliable improvements in activities of daily living and which of the various forms of compensatory training is the most promising. It is therefore too early to recommend any of the currently available treatment approaches.

Effects of vision restoration training on early visual cortex in patients with cerebral blindness investigated with functional magnetic resonance imaging

Cerebral blindness is a loss of vision as a result of postchiasmatic damage to the visual pathways. Parts of the lost visual field can be restored through training. However, the neuronal mechanisms through which training effects occur are still unclear. We therefore assessed training-induced changes in brain function in eight patients with cerebral blindness. Visual fields were measured with perimetry and retinotopic maps were acquired with functional magnetic resonance imaging (fMRI) before and after vision restoration training. We assessed differences in hemodynamic responses between sessions that represented changes in amplitudes of neural responses and changes in receptive field locations and sizes. Perimetry results showed highly varied visual field recovery with shifts of the central visual field border ranging between 1 and 7°. fMRI results showed that, although retinotopic maps were mostly stable over sessions, there was a small shift of receptive field locations toward a higher eccentricity after training in addition to increases in receptive field sizes. In patients with bilateral brain activation, these effects were stronger in the affected than in the intact hemisphere. Changes in receptive field size and location could account for limited visual field recovery (± 1°), although it could not account for the large increases in visual field size that were observed in some patients. Furthermore, the retinotopic maps strongly matched perimetry measurements before training. These results are taken to indicate that local visual field enlargements are caused by receptive field changes in early visual cortex, whereas large-scale improvement cannot be explained by this mechanism.

Compensatory strategies following visual search training in patients with homonymous hemianopia: an eye movement study

A total of 29 patients with homonymous visual field defects without neglect practised visual search in 20 daily sessions, over a period of 4 weeks. Patients searched for a single randomly positioned target amongst distractors displayed for 3 s. After training patients demonstrated significantly shorter reaction times for search stimuli (Pambakian et al. in J Neurol Neurosurg Psychiatry 75:1443-1448, 2004). In this study, patients achieved improved search efficiency after training by altering their oculomotor behaviour in the following ways: (1) patients directed a higher proportion of fixations into the hemispace containing the target, (2) patients were quicker to saccade into the hemifield containing the target if the initial saccade had been made into the opposite hemifield, (3) patients made fewer transitions from one hemifield to another before locating the target, (4) patients made a larger initial saccade, although the direction of the initial saccade did not change as a result of training, (5) patients acquired a larger visual lobe in their blind hemifield after training. Patients also required fewer saccades to locate the target after training reflecting improved search efficiency. All these changes were confined to the training period and maintained at follow-up. Taken together these results suggest that visual training facilitates the development of specific compensatory eye movement strategies in patients with homonymous visual field defects.

Plasticity of the visual system after early brain damage

The aim of this review is to discuss the existing evidence supporting different processes of visual brain plasticity after early damage, as opposed to damage that occurs during adulthood. There is initial evidence that some of the neuroplastic mechanisms adopted by the brain after early damage to the visual system are unavailable at a later stage. These are, for example, the ability to differentiate functional tissue within a larger dysplastic cortex during its formation, or to develop new thalamo-cortical connections able to bypass the lesion and reach their cortical destination in the occipital cortex. The young brain also uses the same mechanisms available at later stages of development but in a more efficient way. For example, in people with visual field defects of central origin, the anatomical expansion of the extrastriatal visual network is greater after an early lesion than after a later one, which results in more efficient mechanisms of visual exploration of the blind field. A similar mechanism is likely to support some of the differences found in people with blindsight, the phenomenon of unconscious visual perception in the blind field. In particular, compared with people with late lesions, those with early brain damage appear to have stronger subjective awareness of stimuli hitting the blind visual field, reported as a conscious feeling that something is present in the visual field. Expanding our knowledge of these mechanisms could help the development of early therapeutic interventions aimed at supporting and enhancing visual reorganization at a time of greatest potential brain plasticity.

New approaches to visual rehabilitation for cortical blindness: outcomes and putative mechanisms

Cortical blindness is a chronic loss of vision following damage to the primary visual cortex (V1) or its postchiasmal afferents. Such damage is followed by a brief period of spontaneous plasticity that rarely lasts beyond 6 months. Following this initial phase, the visual deficit is thought to be stable, intractable, and permanent. Cortically blind subjects demonstrate spontaneous oculomotor adaptations to their deficits that can be further improved by saccadic localization training. However, saccadic training does not improve visual sensitivity in the blind field. In contrast, recent studies by a number of independent groups suggest that localized, repetitive perceptual training can improve visual sensitivity in the blind field, although mechanisms underlying the observed recovery remain unclear. This review discusses the current literature on rehabilitative strategies used for cortical blindness with emphasis on the use of perceptual training methods. The putative mechanisms that underlie the resulting, training-induced visual improvements are then outlined, along with the special challenges posed to their elucidation by the great variability in the extent and sometimes nature of the V1 damage sustained in different individuals.

Perceptual plasticity in damaged adult visual systems

Plasticity appears to be a ubiquitous property of nervous systems, regardless of developmental stage or complexity. In the visual system of higher mammals, perceptual plasticity has been intensively studied, both during development and in adulthood. However, the last few years have seen some significant controversies arise about the existence and properties of visual plasticity after permanent damage to the adult visual system. The study of perceptual plasticity in damaged, adult visual systems is of interest for several reasons. First, it is an important means of unmasking the relative contribution of individual visual areas to visual learning, adaptation and priming, among other plastic phenomena. Second, it can provide knowledge that is essential for the development of effective therapies to rehabilitate the increasing number of people who suffer the functional consequences of damage at different levels of their visual hierarchy. This review summarizes the available evidence on the subject and proposes that visual plasticity may be just as ubiquitous after damage as it is in the intact visual system. However, damage may alter visual plasticity in ways that are still being defined.

Kompensatorische und restitutive Methoden des Gesichtsfeldtrainings

Gesichtsfelddefekte sind eine häufige Folge von Hirnschäden. Es existieren zwei Behandlungsansätze: 1. Kompensation durch Spiegelbrillen, Prismen, sakkadische Augenbewegungen, exzentrisches Lesetraining und 2. Gesichtsfeldvergrößerung durch ein spezielles visuelles Restitutionstraining. Spiegelbrillen und Prismen wurden vielfach kritisiert, tauchen aber auch in aktuellen Studien immer wieder auf. Kompensation durch ein Training sakkadischer Augenbewegungen in den blinden Bereich führt rasch zu Alltagsverbesserungen und ist als Methode weitgehend unumstritten. Für ein exzentrisches Lesetraining wurde aktuell ein computergestütztes System entwickelt. Erste Forschungsergebnisse des Restitutionstrainings wurden positiv bewertet, seit der Jahrtausendwende tauchte jedoch zunehmende Kritik auf – insbesondere bezüglich mangelnder Fixationskontrolle. Der Artikel setzt sich mit diesen Kritikpunkten auseinander und gibt einen Überblick über aktuelle Forschungsergebnisse, die zeigen, dass eine Gesichtsfelderweiterung zwar klein, aber durchaus möglich ist. Alternativerklärungen wie z. B. sakkadische Augenbewegungen und Veränderungen der Aufmerksamkeit konnten in neuen Studien weitgehend ausgeräumt werden. Hinsichtlich der Fahreignung können offenbar viele Patienten den Defekt gut kompensieren; Studien hierzu sind aber widersprüchlich. Empfohlen wird die bessere Verquickung von restitutiven und kompensatorischen Behandlungsstrategien, um Patienten optimale Hilfe zu geben.

Visual restoration in cortical blindness: Insights from natural and TMS-induced blindsight

Unilateral damage to visual cortex of the parietal or occipital lobe can cause the patient to be unaware of contralesional visual information due to either hemispatial neglect or hemianopia. It is now known that both neglect and hemianopia result from the disruption of a dynamic interaction between cortical visual pathways and more phylogenetically primitive visual pathways to the midbrain. We consider the therapeutic implications of these cortical-subcortical interactions in the rehabilitation of hemianopia. We start with the pheonmenon of "blindsight", in which patients with hemianopia can be shown, by implicit measures of visual detection or discrimination, to process visual information without conscious awareness. Some variants of blindsight have been postulated to recruit subcortical processes, while others may reflect compensatory optimisation of processing of spared visual cortex. Both mechanisms may offer opportunities for innovative strategies for rehabilitation of visual field defects. We relate the neural mechanisms that have been proposed to underlie blindsight to those that have been suggested to underlie the recovery of visual function after rehabilitation. It is suggested that the similarity and overlap of the neural processes supporting blindsight and recovery of visual function might provide insights for effective rehabilitation strategies for restoring visual functions.

Acquiring long-term representations of visual classes following extensive extrastriate damage

Different areas of human visual cortex are thought to play different roles in the learning of visual information: whereas in low/intermediate cortical areas, plasticity may be manifested by enhanced selectivity to learned visual features, in higher-level areas, plasticity may result in generalization and development of tolerance to degraded versions of the learned stimuli. The most effective tolerance to degraded information is presumably achieved in the case of cooperation between the different forms of plasticity. Whether this tolerance to degraded information also applies when the visual input is degraded as a result of a lesion to lower levels of the visual system remains an open question. To address this, we studied visual classification learning in a patient with an extensive bilateral lesion affecting intermediate/low-level visual areas but sparing higher-level areas. Despite difficulty in perceiving the stimuli, the patient learned to classify them, albeit not as quickly as control participants. Moreover, the patient's learning was maintained over the long term and was accompanied by improved discrimination of individual stimuli. These findings demonstrate that degraded output from lesioned, lower areas can be exploited in the service of a new visual task and the results likely implicate a combination of bottom-up and top-down processing during visual learning.

Saccadic visual search training: a treatment for patients with homonymous hemianopia

OBJECTIVES

We describe a novel rehabilitation tool for patients with homonymous hemianopia based on a visual search (VS) paradigm that is portable, inexpensive, and easy to deploy. We hypothesised that by training patients to improve the efficiency of eye movements made in their blind field their disability would be alleviated.

METHODS

Twenty nine patients with homonymous visual field defects (HVFD) without neglect practised VS paradigms in 20 daily sessions over one month. Search fields comprising randomly positioned target and distracter elements, differing by a single feature, were displayed for three seconds on a dedicated television monitor in the patients' homes. Improvements were assessed by examining response time (RT), error rates in VS, perimetric visual fields (VFs) and visual search fields (VSFs), before and after treatment. Functional improvements were measured using objective visual tasks which represented activities of daily living (ADL) and a subjective questionnaire.

RESULTS

As a group the patients had significantly shorter mean RT in VS after training (p<0.001) and demonstrated a variety of mechanisms to account for this. Improvements were confined to the training period and maintained at follow up. Three patients had significantly longer RT after training. They had high initial error rates which improved with training. Patients performed ADL tasks significantly faster after training and reported significant subjective improvements. There was no concomitant enlargement of the VF, but there was a small but significant enlargement of the VSF.

CONCLUSION

Patients can improve VS with practice. This usually involves shorter RTs, but occasionally a longer RT in a complex speed-accuracy trade-off. These changes translate to improved overall visual function, assessed objectively and subjectively, suggesting that they represent robust training effects. The underlying mechanism may involve the adoption of compensatory eye movement strategies.

Reaching Out to See: Arm Position Can Attenuate Human Visual Loss

Electrophysiological recordings in monkeys have now revealed several brain regions that contain bimodal visuotactile neurons capable of responding to either tactile or visual stimuli placed on or near the hands, arms, and face. These cells have now been found in frontal, parietal, and subcortical areas of the monkey brain, suggesting a cortical network of neurons that preferentially represent near peripersonal space. The degree to which the visual responses of such cells rely on input from the primary visual cortex and the extent to which they may contribute to visual perception is not completely understood. Nonetheless, recent neuropsychological studies suggest that a similar representation of near space may be bimodally coded in humans as well. Given the accumulating evidence for specialized processing of visual stimuli placed near the hands and arms, we hypothesized that arm position may be capable of modulating human visual ability. Here we report the case of WM, who lost his ability to see in his left visual hemifield after sustaining damage to his right primary visual cortex. Interestingly, the placement of WM's left arm into his “blind” field resulted in significantly better detection of left visual field stimuli compared to when his hand was placed in his lap at midline. Moreover, we found this attenuation to be confined to stimuli presented within reaching distance (unless a tool that extended WM's reach was held while he performed the test). These findings are highly consistent with the characteristics of the bimodal visuo-tactile neurons that have been described in monkeys. Thus, it seems that arm position can modulate human visual ability, even after damage to the primary visual cortex. This study provides an exciting bridge between monkey neurophysiology and human visual capacity while also offering a novel approach for improving visual defects acquired via cortical injury.

Grundlagen und Empirie der Neuropsychologischen Therapie: Neuropsychotherapie oder Hirnjogging?

Zusammenfassung: Dieser Beitrag beschäftigt sich mit dem theoretischen Fundament und den empirischen Grundlagen neuropsychologischer Interventionen. Nach einem kurzen historischen Rückblick werden die konzeptionellen Grundlagen einer neuropsychologischen Behandlung dargestellt und erläutert. Neuropsychologische Interventionen werden drei Therapiesäulen zugeordnet: Restitution, Kompensation und integrierten Verfahren. Restitution bezieht sich auf Maßnahmen, mit denen gestörte neuronale Systeme wieder reaktiviert werden sollen. Kompensation beinhaltet den aktiven oder passiven Ausgleich von Funktionsdefiziten durch vorhandene Fähigkeiten. Hierzu zählt nicht nur das Lernen neuer Strategien und der Einsatz von Hilfsmitteln, sondern auch die Veränderung von Erwartungen, Lebenszielen und andere kognitive Anpassungen. Integrierte Verfahren stellen Verfahren (z. B. operante Techniken) anderer Psychotherapierichtungen dar, die bei einer neuropsychologischen Behandlung Anwendung finden können und auf die Bedürfnisse von Patienten mit organisch bedingten psychischen Störungen zugeschnitten sind. Die in dem Beitrag referierten Studien unterstreichen die Bedeutung der drei postulierten Therapiesäulen.