Modelling chromatic processes in human vision

This investigation programme has concentrated on a number of topics concerning visual function in humans, with particular emphasis on the processing of chromatic information. The programme included an investigation of colour constancy which was carried out using a computer - controlled colour display. A new dynamic colour matching method was developed and the experimental conditions arranged so as to test the constancy of colour appearance. The technigue makes possible the definition of an index of colour constancy which simplifies the interpretation of experimental results. Various spatial, temporal and chromatic parameters of the stimulus configuration were investigated and the results show the importance of the stimulus boundary and near surround in determining the magnitude of the constancy effects observed. Pupillary function was investigated in normal and amblyopic observers. The results suggest that the pupil light reflex is essentially of normal amplitude in amblyopic eyes, although a latency anomaly does exist. Pupillary responses to achromatic, sinusoidal grating stimuli were anomalous in the affected eyes of many amblyopic subjects. Interestingly, certain response parameters were found to be anomalous in the normal eyes of amblyopic observers. Pupillary responses in normal observers were measured following stimulation with isoluminant, red - green chromatic gratings. Responses were found to vary systematically with grating spatial frequency, and broadly reflect the way in which detection thresholds for the same stimuli vary with spatial frequency. Response latencies were approximately 80 ms longer than for equivalent responses to achromatic gratings. No responses were observed when the same experiments were carried out with a protanope. Chromatic discrimination thresholds were measured using a spatio - temporal luminance masking technique. The technique is implemented on a carefully calibrated colour monitor and obviates the requirement of stimulus isoluminance. Preliminary experiments employing psychophysical and pupillometric procedures illustrate the use of the technique in the subjective and objective assessment of colour vision. The rapid changes in visual sensitivity which occur following an intense flash of light were investigated by measuring increment thresholds for a small, brief test stimulus. Results are presented which show the dependence of the sensitivity changes on various spatial, temporal and chromatic parameters. An attempt is made to relate the experimental findings to the properties of retinal neurones

The use of silent substitution in measuring isolated cone- & rod- human electroretinograms. An electrophysiological study of human rod- and cone- photoreceptor activity derived using silent substitution paradigm

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG- recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time-consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation.Bradford School of Optometry and Vision Science

The use of Silent Substitution in measuring isolated cone- and rod- Human ERGs

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation.Bradford School of Optometry and Vision Sciences scholarshi

Vliv modré složky světelného spektra na vybrané aspekty lidského spánku a kognice

Úvod: Od objevu ipRGC buněk sítnice se rozšířily možnosti vědeckého zkoumání vlivu světla na regulaci širokého spektra behaviorálních a fyziologických funkcí nezávislých na tvorbě obrazu. Vzhledem k tomu, že jsou ipRGC nejvíce citlivé na světlo krátkých vlnových délek (460-480nm) se tato dizertace zaměří primárně na vliv modrého světla na cirkadiánní systém, spánek, kognitivní funkce, a možné využití v klinické i neklinické oblasti. Cíle: Cílem první studie bylo prozkoumat vliv 20-minutové expozice monochromatickému světlu různých vlnových délek na vybrané neuropsychologické a neurofyziologické parametry vigility u zdravých dobrovolníků. Druhá studie zkoumala efekt kombinace KBT-I a večerního nošení brýlí blokujících modré světlo na subjektivní a objektivní parametry spánku a denní symptomy (úzkost, deprese, hyperarousal). Cílem třetí studie bylo prozkoumat subjektivní kvalitu spánku u zdravé populace a její spojitost s večerním a nočním vystavováním se umělému světlu z obrazovek elektronických zařízení. Metodika: V první studii bylo 12 zdravých dobrovolníků vystaveno celkem třem 20-minutovým expozicím světlu různých vlnových délek (455, 508, and 629 nm, zářivost 14 μW/cm2), při nichž podstoupili měření EEG (vč. EP P300 a spektrálních charakteristik) a behaviorálních proměnných (subjektivní...Background: Since the discovery of ipRGCs (intrinsic photosensitive retinal ganglion cells) in the retina, new research possibilities for studying the effects of light on the regulation of various behavioral and physiological functions that are independent of image formation arose. As ipRGCs are most sensitive to light of short wavelengths (460-480nm), this dissertation focuses on current topics related to the use of blue light, emphasizing its influence on circadian rhythms, sleep and cognitive performance and possible applications in clinical and non-clinical settings. Aims: The first study aimed to explore the effects of 20 minutes of narrow-bandwidth light exposure of different wavelengths on various neuropsychological and neurophysiological parameters of vigilance in healthy volunteers. The objective of the second study was to assess the effect of combining CBT-I (cognitive-behavioral therapy for insomnia) with wearing blue-light blocking glasses 90 minutes before bedtime on subjective and objective sleep parameters and daily symptoms (anxiety, depression, hyperarousal). The third study aimed to examine subjective sleep quality in a population of healthy volunteers and its association with evening and night light exposure to screens of media devices. Methods: In the first study, twelve healthy...Department of Psychiatry and Medical Psychology 3FM CU and NIMHKlinika psychiatrie a lékařské psychologie 3. LF UK a NÚDZ3. lékařská fakultaThird Faculty of Medicin

Visual screening for blinding diseases in the community using computer controlled video perimetry

Detecting early visual impairment in a community-based approach is difficult because of the variety of light contrast in which measurements have to be made. Finding ways which are functionally efficient, and yet cost-effective, could lead to important improvements to health and quality of life. To select an appropriate visual screening test for use in multicontrast situations, requires an understanding of the interface between clinical epidemiology, visual field technology and the environment in the community where the tests are to take place. Four issues have been taken into account in the study: basic multicontrast characteristics; aspects of clinical application of motion stimuli; discriminative ability, reliability and validity to detect early visual loss, and the acceptability of the test. The study included the development of a group of software programmes called collectively Computer Controlled Video Perimetry (CCVP). The Motion Sensitivity Tests (MSTs) were developed as a part of CCVP in collaboration with Dr Fitzke for early glaucoma detection. The Motion Sensitivity Screening Test (MSST) was finally developed by using a low cost and portable notebook computer to assess acceptability. The tests were carried out on 2632 individuals, from whom 5129 CCVP tests were recorded. Testing was undertaken in a wide variety of situations that included a glaucoma clinic in an eye hospital; an eye health survey in inner city community; a glaucoma survey in an Irish rural community; mass screening for optic nerve disease in region of meso-endemic for onchocerciasis in Nigeria and a self-testing programme set up during a clinical meeting in the USA. CCVP showed that it was possible to detect early visual function loss in a wide variety of situations, whether in clinic or in the community. The results from my study provide a framework for clinical application of using CCVP technology and motion testing to be made with respect to glaucoma and optic nerve disease screening

Engineering Data Compendium. Human Perception and Performance, Volume 1

The concept underlying the Engineering Data Compendium was the product an R and D program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design of military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by system designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is Volume 1, which contains sections on Visual Acquisition of Information, Auditory Acquisition of Information, and Acquisition of Information by Other Senses

Spatial and temporal dynamics of retinal ganglion cells with different photoreceptor inputs

The retina must operate over a wide range of light levels. Two classes of input cells, rods and cones, specialised to different light conditions evolved to achieve this task. This thesis examines how interactions between these two classes shape retinal output as the light level changes, and the extent to which loss of one class can alter processing of the remaining class. Retinal ganglion cell (RGC) receptive elds were characterised using multielectrode array recordings performed during presentation of spatiotemporal white noise across a 4.5 log10 light level range. Receptive fi eld properties were compared between wild-type mice, mice lacking functional cones (cpfl1 model of achromatopsia), and mice lacking functional rods (rd17 model of congenital stationary night blindness). The response of RGCs to otherwise identical stimuli changed with ambient light level. In low light conditions, wild-type RGCs had a longer latency to spike and were shifted towards higher temporal and lower spatial frequency tuning. Of those RGCs characterised at multiple light levels, 28% changed the polarity of their receptive fields between ON and OFF. These polarity switches occurred between every possible pair of light levels, and several cells were observed to switch multiple times. RGCs which switched polarity were identi ed in both rd17 and cpfl1 mice, indicating that at least some circuit mechanisms responsible are driven by a single photoreceptor cell class. Loss of function in one photoreceptor cell class altered visual processing of inputs from the remaining class. In low light conditions, RGCs in cpfl1 mice showed shorter latency to spike and a marked shift towards higher temporal frequency tuning, a receptive field property that is often understood as indicating tuning to visual motion. This difference in visual processing could result in behavioural differences, for instance these mice may exhibit better contrast sensitivity at temporal frequencies in low light conditions