Visual Perception In Patients Research Articles

Effects of visual neuroplasticity training on visual perception, visual quality, and macular blood flow in patients with strabismus.

To observe the effects of visual neuroplasticity training on visual perception, visual quality, and macular blood flow in patients with concomitant strabismus postoperatively. In total, 108 patients underwent binocular strabismus correction operation, and some patients underwent neuroplasticity training. All patients underwent clinical ophthalmic examination, including measurement of best-corrected visual acuity, spherical equivalent, axis length, optical coherence tomography angiography, optical quality analysis system, and visual perception examinations. A total of 78 patients received neuroplasticity training for 1 month postoperatively, and 30 patients did not receive training. All patients underwent a visual perception examination preoperatively and at 1 day, 1 week, and 1 month postoperatively. Macular blood flow and visual quality were examined preoperatively and at 1 month postoperatively. Postoperative visual perception was better than preoperative visual perception (P < 0.05). After neuroplasticity training, the visual perception of the trained subjects was better than that of the untrained subjects (P < 0.05), and the blood flow in the macular area of the trained patients was lower than that of the untrained subjects (P < 0.05). The visual quality of the untrained subjects was lower than that of the trained patients (P < 0.05). Visual inspection system could accurately evaluate binocular visual perception in patients with concomitant strabismus. After surgical alignment of the strabismus patient, training can stimulate and integrate the formation of stereovision in a short period of time, maintain the visual quality of patients after surgery, and provide conditions for the formation of binocular visual signals and binocular stereovision, but in the short term, it will lead to the decrease of macular blood vessel density and perfusion density. However, the long-term effects of training have not been proven.

Visual perception of facial expressions of emotions and alexithymia among people suffering from schizophrenia

Aim of the studyThe aim of the study is to find out whether there is a relationship between the severity of alexithymia and the visual perception of facial expressions of emotions among people suffering from schizophrenia.Subject or material and methods41 people suffering from schizophrenia and 41 healthy people participated in the study. In the first stage, the subjects completed the Toronto Alexithymia Scale (TAS-20) questionnaire. The second stage was based on eye-tracking measurements made during a computer experiment of recognising facial expressions.ResultsPeople with schizophrenia showed significantly higher intensity of alexithymia than healthy people. In the group of patients with schizophrenia, a negative correlation between alexithymia and the length of saccades on the nose was found.DiscussionIn the group of people with schizophrenia, alexithymia is associated with less intensive exploration of the nasal area. A wrinkled nose is an important area, first of all, in the manifestation of negative emotions, in recognition of which the sick people make the most mistakes.ConclusionsProblems with recognising emotions in people suffering from schizophrenia are associated with neuronal dysfunction and abnormalities in the eye movement. These factors disrupt the early stages of sensory processing. The relationship of alexithymia with the visual perception of patients with schizophrenia suggests that top-down processes may also contribute to the development of these deficits.

Optogenetic targeting of AII amacrine cells restores retinal computations performed by the inner retina

Most inherited retinal dystrophies display progressive photoreceptor cell degeneration leading to severe visual impairment. Optogenetic reactivation of inner retinal neurons is a promising avenue to restore vision in retinas having lost their photoreceptors. Expression of optogenetic proteins in surviving ganglion cells, the retinal output, allows them to take on the lost photoreceptive function. Nonetheless, this creates an exclusively ON retina by expression of depolarizing optogenetic proteins in all classes of ganglion cells, whereas a normal retina extracts several features from the visual scene, with different ganglion cells detecting light increase (ON) and light decrease (OFF). Refinement of this therapeutic strategy should thus aim at restoring these computations. Here we used a vector that targets gene expression to a specific interneuron of the retina called the AII amacrine cell. AII amacrine cells simultaneously activate the ON pathway and inhibit the OFF pathway. We show that the optogenetic stimulation of AII amacrine cells allows restoration of both ON and OFF responses in the retina, but also mediates other types of retinal processing such as sustained and transient responses. Targeting amacrine cells with optogenetics is thus a promising avenue to restore better retinal function and visual perception in patients suffering from retinal degeneration.

Facial emotion recognition deficits in schizophrenia - a review of research and a model of pathogenesis

Objective: The aim of the paper is to describe in detail the problems in the field of recognising emotional facial expressions in patients with schizophrenia. This paper also analyses studies and theoretical literature on the potential connections between deficits in recognition of emotional facial expressions and neuronal dysfunctions and attachment styles. Materials and method: The literature review was performed using the following databases: EBSCO, PsycINFO, PubMed, and Google Scholar. The databases were searched using the following keywords: ‘emotion’, ‘facial emotion’, ‘facial expression’. Those terms were combined with the words 'recognition', 'perception', 'genetic', 'attachment style' and each time with the term 'schizophrenia'. Results: The literature review clearly confirms that among people suffering from schizophrenia there are problems with recognising emotional facial expressions. Studies suggest that the visual perception of patients is related to the recognition of facial expressions. Studies also confirm the relationship of neuronal dysfunctions and genetic factors with the recognition of emotional facial expressions. Discussion and conclusions: The genesis of problems in recognising emotional facial expressions in patients with schizophrenia is multifactorial in nature. The influence of attachment styles on epigenetic mechanisms and the development of neural structures related to emotion recognition remains unverified. In the future, this study will allow for the creation of more accurate models of the pathogenesis of these deficits.

Visual temporal discrimination is impaired in patients with migraine without aura.

Dysfunctional sensory processing is described in migraine. This study aimed to evaluate visual perception in patients with migraine without aura using the visual temporal discrimination (VTD) test. A total of 45 participants were enrolled in this prospective exploratory study. In all, 15 patients had migraine without aura and 15 healthy volunteers were analyzed in the study. The VTD threshold (VTDT) was measured using light-emitting diode lights to perceive two separate visual stimuli as clearly distinct. VTD was tested during the attack and the interictal period. The disease duration, attack side, visual analog scale for pain, accompanying symptoms, and allodynia were recorded during the attack. The VTDT of each visual field in both attack (mean [SD] 102.3[38.4]ms for the right visual field and 106.3[52.2]ms for the left) and the interictal periods (mean [SD] 75.2[27.9]ms for the right and 78.2[27.9]ms for the left) were significantly higher than in the control group (mean [SD] 45.3[9.9]ms for the right and 48.2[11.9]ms for the left) (p < 0.001, p < 0.001, p=0.003, p < 0.001, respectively). The ipsilateral threshold during the attack was significantly prolonged compared to the interictal period (mean [SD] 143.8[53.8] vs. 78[19.6]ms, p=0.025) and the contralateral threshold during the attack (mean [SD] 143.8[53.8] vs. 71.9[14.1]ms, p=0.025). The ipsilateral threshold was significantly correlated with the visual analog score (r=0.894, p < 0.001) and frequency of the attacks (r=0.696, p=0.004), but not correlated with photophobia. The VTDTs are prolonged both ictally and interictally in patients with migraine without aura attacks. Ipsilateral threshold prolongation is more pronounced during lateralized migraine attacks. The results suggest dysfunctional visual perception is not limited to the migraine attack period, and a defective sensory processing/modulation in the visual pathways may involve the superior colliculus.

Changes in early visual perception in patients with minimal hepatic encephalopathy

Minimal Hepatic Encephalopathy (MHE) is characterized by very subtle cognitive changes that are diagnosed with the Psychometric hepatic encephalopathy score (PHES) and critical flickering frequency (CFF). Patients with MHE are slower in attention tests evaluated with visual cognitive evocative potentials, which are late indicators. However, it is unknown whether there is also slowness in automatic responses of early visual perception, such as those of stationary visual potential P100. This study aimed to detect early visible changes in patients with minimal hepatic encephalopathy. Cirrhotic patients who went to the Liver Clinic of the Gastroenterology Service of the General Hospital of Mexico "Eduardo Liceaga" were included. The PHES, CFF test was applied and the electroencephalogram (EEG) was recorded while repeated visual stimuli were presented to obtain the stationary visual potential P100. The trial was approved by the research ethics committee, and informed consent was obtained. Eighty-nine patients with hepatic cirrhosis participated, 54 women (60.7%) with 53 ± 7.9 years of age and 8.3 ± 3.4 years of schooling. 57 patients (64.0%) and 64 FCP-positive (71.9%) were PHES-positive. MHE (PHES and CFF positive) was detected in 53 patients (59.6%). 29 MHE patients and 10 patients with cirrhosis agreed to do the perceptual tests. P100 latency of the visual potential was quantified lower in patients with MHD 113 ± 9 milliseconds than in cirrhotic 94 ± 14 milliseconds. Patients with MHE showed slowness in early perceptual processes that preceded cognitive processes. Donation by the volunteer ladies of the Hospital General de México “Dr. Eduardo Liceaga.” The authors declare no potential conflicts of interest.

High Brightness, Highly Directional Organic Light‐Emitting Diodes as Light Sources for Future Light‐Amplifying Prosthetics in the Optogenetic Management of Vision Loss

AbstractOptogenetic control of retinal cells transduced with light‐sensitive channelrhodopsins can enable restoration of visual perception in patients with vision loss. However, a light intensity orders of magnitude higher than ambient light conditions is required to achieve robust cell activation. Relatively bulky wearable light amplifiers are currently used to deliver sufficient photon flux (&gt;1016 photons/cm2/s in a ±10° emission cone) at a suitable wavelength (e.g., 600 nm for channelrhodopsin ChrimsonR). Here, ultrahigh brightness organic light‐emitting diodes (OLEDs) with highly directional emission are developed, with the ultimate aim of providing high‐resolution optogenetic control of thousands of retinal cells in parallel from a compact device. The orange‐emitting phosphorescent OLEDs use doped charge transport layers, generate narrowband emission peaking at 600 nm, and achieve a luminance of 684 000 cd m–2 at 15 V forward bias. In addition, tandem‐stack OLEDs with a luminance of 1 152 000 cd m–2 and doubled quantum efficiency are demonstrated, which greatly reduces electrical and thermal stress in these devices. At the photon flux required to trigger robust neuron firing in genetically modified retinal cells and when using heat sinking and realistic duty cycles (20% at 12.5 Hz), the tandem‐stack OLEDs therefore show a greatly improved half‐brightness lifetime of 800 h.

Prestimulus Low-Alpha Frontal Networks Are Associated with Pareidolias in Parkinson's Disease.

Background: Pareidolias are visual phenomena wherein ambiguous, abstract forms or shapes appear meaningful due to incorrect perception. In Parkinson's disease (PD), patients susceptible to visual hallucinations experience visuo-perceptual deficits in the form of pareidolias. Although pareidolias necessitate top-down modulation of visual processing, the cortical dynamics of internally generated perceptual priors on these visual misperceptions is unknown. Objectives: To study prestimulus-related electroencephalography (EEG) spectral and network abnormalities in PD patients experiencing pareidolias. Methods: Twenty-one PD in-patients and 10 age-matched controls were evaluated. Neuropsychological assessments included tests for cognition, attention, and executive functions. Pareidolias were quantified by using the "noise pareidolia test" with simultaneous EEG recording. The PD patients were subdivided into two groups-those with high pareidolia counts (n = 10) and those without (n = 11). The EEG was analyzed 1000 msec before stimulus presentation in the spectral domain (theta, low-alpha, and high-alpha frequencies) with corresponding graph networks to evaluate network properties. Statistical analysis included analysis of variance and multiple regression to evaluate the differences. Results: The PD patients with high pareidolia counts were older with lower scores on neuropsychological tests. Their prestimulus EEG low-alpha band showed a tendency toward higher frontal activity (p = 0.07). Graph networks showed increased normalized clustering coefficient (p = 0.05) and lower frontal degree centrality (p = 0.005). These network indices correlated positively to patients' pareidolia scores. Discussion: We suggest that pareidolias in PD are a consequence of an abnormal top-down modulation of visual processing; they are defined by their frontal low-alpha spectral and network alterations in the prestimulus phase due to a dissonance between patients' internally generated mental processing with external stimuli. Impact statement Pareidolias in Parkinson's disease (PD) are considered to be promising early markers of visual hallucinations and an indicator of PD prognosis. In certain susceptible PD patients, pareidolias can be evoked and studied. Here, via electroencephalography, we aimed at understanding this visual phenomenon by studying how neural information is processed before stimulus presentation in such patients. Using spectral and graph network measures, we revealed how top-down modulated internally generated processes affect visual perception in patients with pareidolias. Our findings highlight how prestimulus network alterations in the frontal cortex shape poststimulus pareidolic manifestations in PD.

The threshold and semantic characteristics of fast transient visual-perceptive processes in patients with affective disorders

The article is devoted to the currently topical problem of modern medical psychology, namely the study of conscious and unconscious perceptual-information processes in patients with affective disorders. The aim of the work was to determine the thresholds and semantic components of visual perception in patients with various forms of affective disorders. The latest method of ultrafast (tachistoscopic) demonstration of visual verbal stimuli was used to examine 23 patients with depression and anxiety-depressive disorders. The obtained results are compared with similar indicants of the control group, which consisted of 15 mentally healthy individuals, and analyzed using Student's criterion, one-way and multifactor models of analysis of variance. It has been shown that in the presence of an affective disorder, the threshold exposure time required for reliable identification of visual verbal stimuli is on average more than three times higher, i.e. is much worse than a similar perceptual threshold in individuals without mental disorders. Thus, in affective disorders there is inhibition and suppression of not only emotional and psychomotor, but visual-perceptual processes as well. It is proved that the time thresholds of visual perception significantly depend not only on the presence of emotional disorders, but also on their psychopathological structure, as well as on the age factor. In depressed patients, visual-perceptual disorders are much more pronounced than in patients with anxiety-depressive disorders, namely: in depression, the minimal absolute sensory thresholds are significantly higher, more attempts are made to adapt the visual analyzer, and this deficit is significantly increased depending on age. In patients with depressive and anxiety-depressive disorders also revealed significant features of psychosemantic components of the mechanisms of recognition of verbal stimuli, which consists in a kind of unconscious filtering of the latter with a predominant perception of words with negative emotional loading. The obtained results might be meaningful in the process of developing the new diagnostic methods for affective disorders and in creating the personalized psycho-correctional programs based on the methodological principles of subsensory stimulation.

Real-Time Optimization of Retinal Ganglion Cell Spatial Activity in Response to Epiretinal Stimulation.

Retinal prostheses aim to improve visual perception in patients blinded by photoreceptor degeneration. However, shape and letter perception with these devices is currently limited due to low spatial resolution. Previous research has shown the retinal ganglion cell (RGC) spatial activity and phosphene shapes can vary due to the complexity of retina structure and electrode-retina interactions. Visual percepts elicited by single electrodes differ in size and shapes for different electrodes within the same subject, resulting in interference between phosphenes and an unclear image. Prior work has shown that better patient outcomes correlate with spatially separate phosphenes. In this study we use calcium imaging, in vitro retina, neural networks (NN), and an optimization algorithm to demonstrate a method to iteratively search for optimal stimulation parameters that create focal RGC activation. Our findings indicate that we can converge to stimulation parameters that result in focal RGC activation by sampling less than 1/3 of the parameter space. A similar process implemented clinically can reduce time required for optimizing implant operation and enable personalized fitting of retinal prostheses.

What do patients with glaucoma see: a novel iPad app to improve glaucoma patient awareness of visual field loss

PurposeGlaucoma patients with peripheral vision loss have in the past subjectively described their field loss as ‘blurred’ or ‘no vision compromise’. We developed an iPad app for patients to self-characterise...

Effect of Home-Based Activities of Daily Living (ADL) on Cognition and Visual Perception in Patients With Stroke: A Randomized Controlled Pilot Study

Abstract Date Presented 03/26/20 We investigated whether using ADLs as a means of treatment in the home environment for six weeks could improve cognition and visual perception in patients with stroke. Twenty-four patients were randomized to receive home-based ADL and hospital-based traditional rehabilitation. Our findings showed that there was a statistically significant improvement and small effect size in visual perception. No significant improvement was found in cognition, but small effect size was noticed. Primary Author and Speaker: En-Chi Chiu Contributing Authors: Fang-Chi Chi

Transcranial Direct Current Stimulation in Poststroke Hemianopia

Introduction. Development of the new approaches to the rehabilitation of patients with poststroke hemianopia is of great importance, given the high prevalence of that disorder and its negative impact on patients’ quality of life. This study aimed to investigate the effect of transcranial direct current stimulation (tDCS) on the quality of life and the quality of visual perception in patients with poststroke hemianopia, as well as to study the safety and tolerability of this technique. Materials and methods. The study included ten patients with poststroke hemianopia. Patients underwent ten tDCS sessions (2 mA, 20 min with anode placed over Oz, cathode — over Cz for a unilateral lesion, and anode — over O1 and O2, cathode — over Fp1 and Fp2 for bilateral lesions). The tolerability of tDCS was evaluated after each session using a standardized questionnaire. Clinical assessment before and after tDCS was performed using the Visual Function Questionnaire (VFQ-25) and the 36-item Short Form Survey (SF-36). Functional MRI using a visual paradigm was performed in 5 patients before and after the course of tDCS. Results. Adverse effects were recorded during 9.9% of the sessions and had low severity in most cases. There was one withdrawal from the study because of increased pain in the hand and leg, in a patient with central post-stroke pain syndrome, which was likely unrelated to the biological effects of stimulation. Data of 9 patients were included in the analysis. There was a statistically significant increase in the overall score on the VFQ-25 (p = 0.02) after tDCS with improvements in the social activity (p = 0.02), mental health (p = 0.02), dependence on others (p = 0.04), and peripheral vision (p = 0.04) sections. A statistically significant improvement was also found in the psychological component of quality of life (p = 0.04), vitality (p = 0.03), social functioning (p = 0.02), role functioning due to physical health (p = 0.04), and general health (p = 0.008). In 3 cases, increased activation of the occipital cortex after tDCS was identified using functional MRI with a visual paradigm. Conclusion. tDCS is a safe, well-tolerated, and potentially effective method in patients with poststroke hemianopia. Larger, controlled, and randomized studies are needed to clarify the efficacy of this method in hemianopia.

Development and Testing of Experimental Psychological Techniques for the Study of Unconscious Visual-Perceptual Processes

The work is devoted to the actual problem of research of visual-perceptual processes that take place on an unconscious level. There is a shortage of reliable and informative psychodiagnostic tools, specially designed to study unconscious perceptual and mnestic phenomena in mentally healthy people and in the persons with affective disorders. It is emphasized that when creating such techniques, it is necessary to take into account the influence of emotional disorders on the course of basic mental processes. Three new experimental psychological techniques have been developed, aimed at research and objectification of transient conscious and unconscious perceptual-informational processes. The technique of forming a subsensory stimulus is a step-by-step determination of the exact threshold time of exposure, in which one verbal stimulus out of three demonstrated ones remains unidentified at the conscious level, i.e. subsensory. The technique of psychophysiological confirmation of the significance of a subsensory stimulus is an automated registration-analytical procedure, which involves the use of a serial digital polygraph "Rheocom-stress" and allows you to identify the words most significant to the subject, regardless of the level of subjective awareness of that significance. The technique of detecting unconscious perceptual-mnestic fixation of subsensory stimuli is a method of studying the effect of involuntary memorization, retention and reproduction of subsensory stimuli. Approbation of the developed experimental psychological techniques was performed on the sample of 38 people, including 23 patients with affective disorders and 15 mentally healthy people. It is shown that the thresholds of visual perception in patients with affective disorders are almost three times higher than in the control group. The effect of perceptual-mnestic fixation was confirmed by one or more methods in 100% of the cases. The results of the approbation conclusively testify to the high sensitivity and informativeness of the approach used.

Review of the main colour vision clinical assessment tests

Abstract Introduction Congenital colour vision deficiencies affect 8% of the male and 0.5% of the female population. The study of colour vision is a complex process due to several factors: the psychophysics of vision itself, the difficulty to establish mathematical models for its analysis, the vague correlation of results between different tests, and the influence of external factors such as lighting, the tests condition, or the experience of the examiner and the patient. In the present document, a simplified review was carried out on the main colour vision tests available in clinical practice. Material and methods Once a filtered preliminary review was made of the bibliography related to the study of colour vision using the PubMed search tool, the most used tests in clinical practice were selected according to their frequency of use and the purpose for which they were applied. A bibliographic study was then carried out on each particular test according to the design of the shown stimuli, its target population, and its sensitivity and specificity. Results From the 95 publications found using the PubMed search tool, in 41 of them, colour tests were used by researchers in their methodology. From the 64 colour tests used, 19 of them were different (with 4 of them being different tests adapted by research groups, and 2 of them carried out online). The most used tests were the following: Ishihara test (10.88%), Farnsworth–Munsell (7.04%), Farnsworth–Munsell 100 Hue (6.4%), Cambridge Colour Test (3.84%), Hardy–Rand–Rittler (3.2%), tests developed by the groups (2.56%), the Anomaloscope (1.28%), the online tests (1.28%) and, finally, Colour Assessment and Diagnosis (0.64%), Pfluger Trident Colour Plates (0.64%), Toothguide Training Box (0.64%), Lanthony Desaturated D-15 (0.64%), City University Test (0.64%), Universal Colour Discrimination Test (0.64%), and Rabin Cone Contrast Test (0.64%). Conclusions The Anomaloscope is the “gold standard” in terms of colour vision testing, despite its incompatibility with daily clinical practice. It is fairly complex to use, difficult to understand for children, and its practice requires having the time available. Nevertheless, it is possible to reach an accurate approximation through the combination of some of the tests listed in this article. The above mentioned tests are a good alternative to determine the presence of dyschromatopsia in settings closer to daily clinical practice or in less controlled settings than a clinical study. The major drawback among the wide range of tests available for the study of colour vision is the difficulty to compare results between tests, since units of the reported data are usually different, and experience is required for its correct interpretation. Currently, there is no consensus on which colour test is the most complete. It is, therefore, advisable to use at least 2 tests in order to ensure diagnoses, and have more extensive information about the visual perception of patients.

Chromatic and achromatic visual fields in relation to choroidal thickness in patients with high myopia: A pilot study

To analyse the relationship between the choroidal thickness and the visual perception of patients with high myopia but without retinal damage. All patients underwent ophthalmic evaluation including a slit lamp examination and dilated ophthalmoscopy, subjective refraction, best corrected visual acuity, axial length, optical coherence tomography, contrast sensitivity function and sensitivity of the visual pathways. We included eleven eyes of subjects with high myopia. There are statistical correlations between choroidal thickness and almost all the contrast sensitivity values. The sensitivity of magnocellular and koniocellular pathways is the most affected, and the homogeneity of the sensibility of the magnocellular pathway depends on the choroidal thickness; when the thickness decreases, the sensitivity impairment extends from the center to the periphery of the visual field. Patients with high myopia without any fundus changes have visual impairments. We have found that choroidal thickness correlates with perceptual parameters such as contrast sensitivity or mean defect and pattern standard deviation of the visual fields of some visual pathways. Our study shows that the magnocellular and koniocellular pathways are the most affected, so that these patients have impairment in motion perception and blue-yellow contrast perception.

Microfluidics-Based Subretinal Chemical Neuromodulation of Photoreceptor Degenerated Retinas.

Retinal prostheses can restore rudimentary vision in cases of photoreceptor degeneration through electrical stimulation, but face difficulties achieving high spatial resolution because electrical current is an inherently unnatural stimulus. We investigated the therapeutic feasibility of using patterned delivery of the glutamate neurotransmitter, a primary agent of natural synaptic communication of the retina, as a biomimetic chemical alternative to electrical current for neuromodulation of photoreceptor degenerate retina. We injected small quantities of the neurotransmitter glutamate into the subretina of 20 explanted photoreceptor degenerated S334ter-3 rat retinas using glass micropipettes and a prototype multiport microfluidic device to accomplish single- and multisite stimulation in vitro. The effects of chemical stimulation were characterized by recording neural responses from retinal ganglion cells (RGCs) using a multielectrode array. Subretinally injected exogenous glutamate activates RGCs, despite the substantial anatomic and physiologic changes caused by retinal remodeling, eliciting robust neural responses. The presence of excitatory and inhibitory RGC responses provides evidence that exogenous glutamate differentially activated neurons presynaptic to RGCs, likely inner retinal neurons belonging to the OFF and ON pathways. We also demonstrate that glutamate injections can evoke focal RGC responses with spatial resolutions comparable to or better than current generation electrical prostheses and, when applied at multiple sites simultaneously with the multiport microfluidic device, can produce spatially patterned neural responses. These significant results establish that chemical stimulation of degenerated retinas with neurotransmitters is an effective neuromodulation strategy with the potential of restoring high-resolution visual perception in patients rendered blind through photoreceptor degeneration.

Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro.

Photoreceptor degenerative diseases cause irreparable blindness through the progressive loss of photoreceptor cells in the retina. Retinal prostheses are an emerging treatment for photoreceptor degenerative diseases that seek to restore vision by artificially stimulating the surviving retinal neurons in the hope of eliciting comprehensible visual perception in patients. Current retinal prostheses have demonstrated success in restoring limited vision to patients using an array of electrodes to electrically stimulate the retina but face substantial physical barriers in restoring high acuity, natural vision to patients. Chemical neurostimulation using native neurotransmitters is a biomimetic alternative to electrical stimulation and could bypass the fundamental limitations associated with retinal prostheses using electrical neurostimulation. Specifically, chemical neurostimulation has the potential to restore more natural vision with comparable or better visual acuities to patients by injecting very small quantities of neurotransmitters, the same natural agents of communication used by retinal chemical synapses, at much finer resolution than current electrical prostheses. However, as a relatively unexplored stimulation paradigm, there is no established protocol for achieving chemical stimulation of the retina in vitro. The purpose of this work is to provide a detailed framework for accomplishing chemical stimulation of the retina for investigators who wish to study the potential of chemical neuromodulation of the retina or similar neural tissues in vitro. In this work, we describe the experimental setup and methodology for eliciting retinal ganglion cell (RGC) spike responses similar to visual light responses in wild-type and photoreceptor-degenerated wholemount rat retinas by injecting controlled volumes of the neurotransmitter glutamate into the subretinal space using glass micropipettes and a custom multiport microfluidic device. This methodology and protocol are general enough to be adapted for neuromodulation using other neurotransmitters or even other neural tissues.

Validation of the Test of Visual Perceptual Skills-Third Edition in patients with stroke

Purpose: The Test of Visual Perceptual Skills-Third Edition (TVPS-3) with seven subscales has been used to assess visual perception in patients with stroke. The purpose of this study was to investigate ecological validity, convergent validity, and discriminative validity of the TVPS-3 in patients with stroke.Methods: One hundred patients were assessed with the TVPS-3, two measures of activities of daily living, and two cognitive measures. To examine ecological validity, we calculated correlations (Pearson’s r) among the TVPS-3 and two measures of activities of daily living. To examine convergent validity, correlations (r) were estimated among the TVPS-3 and two cognitive measures. To examine discriminative validity, independent t-test was used to compare the two groups with different levels of disability and to detect whether there were statistically significant differences in the TVPS-3 between these groups.Results: The correlations were 0.21–0.48 among the TVPS-3 and two measures of activities of daily living. The correlations were 0.29–0.68 among the TVPS-3 and two cognitive measures. Between the two groups, the t-test results showed statistically significant difference (p < 0.05) for the overall scale and the five subscales of the TVPS-3.Conclusions: The TVPS-3 has acceptable convergent validity, ecological validity, and discriminative validity and is useful to assess the visual perception in patients with stroke.Implications for rehabilitationThe Test of Visual Perceptual Skills-Third Edition is a motor free visual perception test, which is an adequate tool for use in patients with stroke.The Test of Visual Perceptual Skills-Third Edition showed acceptable ecological validity, convergent validity, and discriminative validity in patients with stroke.

Topographic prominence discriminator for the detection of short-latency spikes of retinal ganglion cells

Objective. Direct stimulation of retinal ganglion cells in degenerate retinas by implanting epi-retinal prostheses is a recognized strategy for restoration of visual perception in patients with retinitis pigmentosa or age-related macular degeneration. Elucidating the best stimulus-response paradigms in the laboratory using multielectrode arrays (MEA) is complicated by the fact that the short-latency spikes (within 10 ms) elicited by direct retinal ganglion cell (RGC) stimulation are obscured by the stimulus artifact which is generated by the electrical stimulator. Approach. We developed an artifact subtraction algorithm based on topographic prominence discrimination, wherein the duration of prominences within the stimulus artifact is used as a strategy for identifying the artifact for subtraction and clarifying the obfuscated spikes which are then quantified using standard thresholding. Main results. We found that the prominence discrimination based filters perform creditably in simulation conditions by successfully isolating randomly inserted spikes in the presence of simple and even complex residual artifacts. We also show that the algorithm successfully isolated short-latency spikes in an MEA-based recording from degenerate mouse retinas, where the amplitude and frequency characteristics of the stimulus artifact vary according to the distance of the recording electrode from the stimulating electrode. By ROC analysis of false positive and false negative first spike detection rates in a dataset of one hundred and eight RGCs from four retinal patches, we found that the performance of our algorithm is comparable to that of a generally-used artifact subtraction filter algorithm which uses a strategy of local polynomial approximation (SALPA). Significance. We conclude that the application of topographic prominence discrimination is a valid and useful method for subtraction of stimulation artifacts with variable amplitudes and shapes. We propose that our algorithm may be used as stand-alone or supplementary to other artifact subtraction algorithms like SALPA.