Functional Assessment of Magno, Parvo and Konio-Cellular Pathways; Current State and Future Clinical Applications

The information generated by cone photoreceptors in the retina is compressed and transferred to higher processing centers through three distinct types of ganglion cells known as magno, parvo and konio cells. These ganglion cells, which travel from the retina to the lateral geniculate nucleus (LGN) and then to the primary visual cortex, have different structural and functional characteristics, and are organized in distinct layers in the LGN and the primary visual cortex. Magno cells are large, have thick axons and usually collect input from many retinal cells. Parvo cells are smaller, with fine axons and less myelin than mango cells. Konio cells are diverse small cells with wide fields of input consisting of different cells types. The three cellular pathways also differ in function. Magno cells respond rapidly to changing stimuli, while parvo cells need time to respond. The distinct patterns of structure and function in these cells have provided an opportunity for clinical assessment of their function. Functional assessment of these cells is currently used in the field of ophthalmology where frequency-doubling technology perimetry selectively assesses the function of magno cells. Evidence has accrued that the three pathways show characteristic patterns of malfunctions in multiple sclerosis, schizophrenia, Parkinson’s and Alzheimer’s diseases, and several other disorders. The combination of behavioral assessment with other techniques, such as event related potentials and functional magnetic resonance imaging, seems to bear promising future clinical applications

Neural correlates of boredom in music perception

Introduction: Music can elicit powerful emotional responses, the neural correlates of which have not been properly understood. An important aspect about the quality of any musical piece is its ability to elicit a sense of excitement in the listeners. In this study, we investigated the neural correlates of boredom evoked by music in human subjects. Methods: We used EEG recording in nine subjects while they were listening to total number of 10 short-length (83 sec) musical pieces with various boredom indices. Subjects evaluated boringness of musical pieces while their EEG was recording. Results: Using short time Fourier analysis, we found that beta2 rhythm was (16-20 Hz) significantly lower whenever the subjects rated the music as boring in comparison to nonboring. Discussion: The results demonstrate that the music modulates neural activity of various parts of the brain and can be measured using EEG

A Glance at Psychophysics Software Programs

Visual stimulation with precise control of stimulus has transformed the field of psychophysics since the introduction of personal computers. Luminance and chromatic features of stimulus, timing, and position of the stimulus are the main features that could be defined using programs written specifically for psychophysical experiments. In this manuscript, software used for the psychophysical experiments have been reviewed and evaluated for ease of use, license, popularity, and expandability

Motion parallax-defined segmentation and depth perception in human vision

Relative retinal image motion from active observer movement in the environment, often called motion parallax, provides an important source of information both for segmentation and depth perception. Two distinct boundary types occur as a result of such movement: boundaries that are parallel to the direction of movement give rise to a shearing motion, whereas boundaries orthogonal to the direction of movement create dynamic occlusion. This dissertation examines the role and importance of such types of motion boundaries in motion parallax, and how head and eye movements influence them. We psychophysically measured segmentation and depth performance from shear and dynamic occlusion-based motion parallax across different conditions, accompanied by head and eye movement recordings. Segmentation was measured with an orientation judgment, whereas depth ordering was measured using a 2AFC task. Perceived depth magnitude was assessed with a task in which observers matched the amount of perceived depth in the stimulus to a number, using a series of rendered images as a guide. We found that depth perception largely benefits from active observer movement, whereas segmentation performance seemed to be unaffected or even somewhat negatively affected. Shear and dynamic occlusion yielded similar performance for segmentation, whereas dynamic occlusion provided superior depth perception. Perceived depth magnitude was linearly correlated with rendered depth for small values of depth, but did not grow with further increase in rendered depth for both shear and dynamic occlusion. We also measured eye movements during segmentation and depth tasks with motion parallax. Eye movements only partially compensated to maintain fixation during translational head movements. Furthermore, eye movements were independent of the actual stimulus motion for shear, whereas they showed some dependence in dynamic occlusion. Psychophysical performance was significantly correlated with the accuracy of eye movements, primarily in the mid-range values of rendered depth. Taken together, these studies demonstrated distinct patterns of results for segmentation and depth performance across different ranges of rendered depth. These findings suggest that motion parallax information might be processed by distinct mechanisms, perhaps in separate areas of the visual cortex, depending upon the amount of depth in the visual stimulus.Le mouvement relatif d'une image sur la rétine dû au mouvement actif de l'observateur dans son environnement, souvent appelé mouvement de parallaxe, fournit une importante source d'informations pour la segmentation et la perception de la profondeur. Deux types de contours peuvent résulter d'un tel mouvement : les contours parallèles à la direction du mouvement génèrent un mouvement de cisaillement, alors que les contours orthogonaux à la direction du mouvement créent une occlusion dynamique. Cette dissertation étudie le rôle et l'importance de ces contours définis par le mouvement de parallaxe, et comment les mouvements de la tête et des yeux les influencent. Nous avons effectué des mesures psychophysiques de la segmentation et de la détection de profondeur issues du mouvement de parallaxe par cisaillement et par occlusion dynamique dans différentes conditions, tout en enregistrant les mouvements des yeux et de la tête. La segmentation a été mesurée par jugement d'orientation, alors que l'ordre de profondeur a été mesuré en utilisant une tâche de choix forcé d'alternative. L'amplitude de la profondeur perçue a été étudiée avec une tâche dans laquelle les observateurs jugeaient la profondeur du stimulus en lui attribuant un nombre choisi grâce à un guide d'images de références.Nous avons observé que la perception de la profondeur bénéficie énormément du mouvement actif de l'observateur alors que la performance de segmentation semble peu affectée, voire même réduite. Le mouvement de cisaillement et l'occlusion dynamique induisent la même performance pour la segmentation, alors que l'occlusion dynamique fournit une meilleure perception de la profondeur. Pour les faibles valeurs, l'amplitude de la profondeur perçue est linéairement corrélée avec la profondeur rendue, mais m'augmente plus après un certain point, pour à la fois le cisaillement et l'occlusion dynamique.Nous avons également mesuré les mouvements des yeux pendant les tâches de profondeur et de segmentation par mouvement de parallaxe. Les mouvements des yeux ne compensent que partiellement le maintient de la fixation pendant les mouvements de tête translationnels. De plus, les mouvements des yeux sont indépendants du mouvement du stimulus pour le cisaillement alors qu'ils montrent une certaine dépendance pour l'occlusion dynamique. La performance psychophysique est significativement corrélée avec la précision du mouvement des yeux, particulièrement pour les valeurs moyennes de profondeur rendue. Ces résultats suggèrent que l'information du mouvement de parallaxe pourrait être traitée par des mécanismes distincts, peut-être dans des aires différentes du cortex visuel, selon la quantité de profondeur dans le stimulus visuel

Efficiency of Information Coding in Various L/M Retinal Cone Ratios

Previous evidence has shown that the number of L and M cones in retina varies significantly between subjects. However, it is not clear how the variation of L/M ratio changes the behavioral performance of the subject. A model of transformation of data from retina to visual cortex for evaluation of various L/M cones ratios is presented. While L/M cone ratios close to 1 brings the best performance for one of postreceptoral (magnocellular) channels, we showed that the performance in the second channel (parvocells) will improve when the ratio furthers away from 1. Effects of different ratios of S were also explored

Psychophysical evidence for impaired Magno, Parvo, and Konio-cellular pathways in dyslexic children

Purpose: Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring luminance and color perception. Methods: Visual stimuli consisted of a series of natural images, divided into layers of luminance, red-green and blue-yellow, which probed magnocellular, parvocellular, and koniocellular pathways, respectively. Thirteen children with dyslexia and 13 sex- and age- matched controls performed three psychophysical tasks. In the first task, subjects were instructed to match the contrast of luminance (magno) and red-green (parvo) images to that of the blue-yellow (konio) images. In the second task, subjects detected the isoluminant point of red-green images to probe parvocellular pathway. In the third task, temporal processing was assessed by measuring reaction time and percentage of correct responses in an identification task using four categories of images, activating all three pathways. Results: The dyslexic group had significantly elevated luminance and color contrast thresholds and higher isoluminant point ratio in comparison to the control group. Furthermore, they had significantly less correct responses than the control group for the blue-yellow images. Conclusion: We may suggest that dyslexic subjects might suffer from both magnocellular and parvocellular deficits. Moreover, our results show partial impairment of the koniocellular pathway. Thus, dyslexia might be associated with deficits in all three visual pathways

Neural Correlates of Craving in Methamphetamine Abuse

Introduction: Methamphetamine is a powerful psychostimulant that causes significant neurological impairments with long-lasting effects and has provoked serious international concerns about public health. Denial of drug abuse and drug craving are two important factors that make the diagnosis and treatment extremely challenging. Here, we present a novel and rapid noninvasive method with potential application for differentiation and monitoring methamphetamine abuse. Methods: Visual stimuli comprised a series of images with neutral and methamphetamine-related content. A total of 10 methamphetamine abusers and 10 age-gender matched controls participated in the experiments. Event-related potentials (ERPs) were recorded and compared using a time window analysis method. The ERPs were divided into 19 time windows of 100 ms with 50 ms overlaps. The area of positive sections below each window was calculated to measure the differences between the two groups. Results: Significant differences between two groups were observed from 250 to 500 ms (P300) in response to methamphetamine-related visual stimuli and 600 to 800 ms in response to neutral stimuli. Conclusion: This study presented a novel and noninvasive method based on neural correlates to discriminate healthy individuals from methamphetamine drug abusers. This method can be employed in treatment and monitoring of the methamphetamine abuse