Peripheral ocular monochromatic aberrations

Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.

Effects of Prochlorperazine on Normal Vestibular Ocular and Perceptual Responses: A Randomised, Double-Blind, Crossover, Placebo-Controlled Study

Background: The present study investigated whether prochlorperazine affects vestibular-ocular reflex (VOR) and vestibulo-perceptual function. Methods: We studied 12 healthy naïve subjects 3 hours after a single dose of oral prochlorperazine 5mg in a randomised, placebo-controlled, double-blind, cross-over study in healthy young subjects. Two rotational tests in yaw were used: 1) a Threshold task investigating perceptual motion detection and nystagmic thresholds (acceleration steps of 0.5deg/s/s) and 2) Suprathreshold responses to velocity steps of 90deg/s in which vestibulo-ocular (VO) and vestibulo-perceptual (VP) time constants of decay, as well as VOR gain, were measured. Results: Prochlorperazine had no effect upon any measure of nystagmic or perceptual vestibular function compared to placebo. This lack of effects on vestibular-mediated motion perception suggests that the drug is likely to act more as an antiemetic than as an anti-vertiginous agent.

Mouvement biologique et entraînement perceptivo-cognitif chez les personnes âgées

Lorsque nous cherchons un ami dans une foule ou attendons un proche sur le quai d’une gare, l’identification de cette personne nous est souvent possible grâce à la reconnaissance de sa démarche. Plusieurs chercheurs se sont intéressés à la façon de se mouvoir de l’être humain en étudiant le mouvement biologique. Le mouvement biologique est la représentation, par un ensemble structuré de points lumineux animés, des gestes d’un individu en mouvement dans une situation particulière (marche, golf, tennis, etc.). Une des caractéristiques du patron de mouvement biologique peu étudiée et néanmoins essentielle est sa taille. La plupart des études concernées utilisent des patrons de petite taille correspondant à une personne située à 16 mètres de l’observateur. Or les distances d’interaction sociale, chez l’humain, sont généralement inférieures à 16 mètres. D’autre part, les résultats des études portant sur la perception des patrons de mouvement biologique et le vieillissement demeurent contradictoires. Nous avons donc, dans un premier temps, évalué, dans une voûte d’immersion en réalité virtuelle, l’importance de la distance entre l’observateur et le patron de mouvement biologique, chez des adultes jeunes et des personnes âgées. Cette étude a démontré que l’évaluation de la direction de mouvement d’un patron devient difficile pour les personnes âgées lorsque le patron est situé à moins de 4 mètres, alors que les résultats des jeunes sont comparables pour toutes distances, à partir d’un mètre et au-delà. Cela indique que les gens âgés peinent à intégrer l’information occupant une portion étendue de leur champ visuel, ce qui peut s’avérer problématique dans des espaces où les distances d’interaction sont inférieures à 4 mètres. Nombre de recherches indiquent aussi clairement que les gens âgés s’adaptent difficilement à des situations complexes. Nous avons donc cherché, dans un second temps, à minimiser ces altérations liées à l’âge de l’intégration des processus complexes, en utilisant une tâche adaptée à l’entraînement et à l’évaluation de l’intégration de ces processus : la poursuite multiple d’objets dans l’espace ou 3D-MOT (3 Dimensions Multiple Object Tracking). Le 3D-MOT consiste à suivre simultanément plusieurs objets d’intérêt en mouvement parmi des distracteurs également en mouvement. Nous avons évalué les habiletés de participants jeunes et âgés à une telle tâche dans un environnement virtuel en 3D en déterminant la vitesse maximale de déplacement des objets à laquelle la tâche pouvait être exécutée. Les résultats des participants âgés étaient initialement inférieurs à ceux des jeunes. Cependant, après plusieurs semaines d’entraînement, les personnes âgées ont obtenu des résultats comparables à ceux des sujets jeunes non entraînés. Nous avons enfin évalué, pour ces mêmes participants, l’impact de cet entraînement sur la perception de patrons de mouvement biologique présentés à 4 et 16 mètres dans l’espace virtuel : les habiletés des personnes âgées entraînées obtenues à 4 mètres ont augmenté de façon significative pour atteindre le niveau de celles obtenues à 16 mètres. Ces résultats suggèrent que l’entraînement à certaines tâches peut réduire les déclins cognitivo-perceptifs liés à l’âge et possiblement aider les personnes âgées dans leurs déplacements quotidiens.

Internal representation of movement in children with developmental coordination disorder : a mental rotation task

Recent studies show that children with developmental coordination disorder (DCD) have difficulties in generating an accurate visuospatial representation of an intended action, which are shown by deficits in motor imagery. This study sought to test this hypothesis further using a mental rotation paradigm. It was predicted that children with DCD would not conform to the typical pattern of responding when required to imagine movement of their limbs. Participants included 16 children with DCD and 18 control children; mean age for the DCD group was 10 years 4 months, and for controls 10 years. The task required children to judge the handedness of single-hand images that were presented at angles between 0° and 180° at 45° intervals in either direction. Results were broadly consistent with the hypothesis above. Responses of the control children conformed to the typical pattern of mental rotation: a moderate trade-off between response time and angle of rotation. The response pattern for the DCD group was less typical, with a small trade-off function. Response accuracy did not differ between groups. It was suggested that children with DCD, unlike controls, do not automatically enlist motor imagery when performing mental rotation, but rely on an alternative object-based strategy that preserves speed and accuracy. This occurs because these children manifest a reduced ability to make imagined transformations from an egocentric or first-person perspective.

Maternity

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Luxe

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Lust

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Glance

Fruiting bodies represents human engagement with and consciousness of a corresponding presence in our landscape. ʻFruiting Bodiesʼ is an instance of the application of this practice employed to ask the viewer to consider how strange is the phenomenon of the fruiting tree. Is it promiscuous to offer your seed openly to the elements, to any who will take it. Is this forbidden? Is it profligate to hide your progeny inside gifts so tempting in their appeal to that most primitive desire, hunger? Is this wholly mere biological expedience evolved to ensure the widest migration of your offspring? Or does it derive from some boundless cosmic generosity? These images invite you to come close to the tree, where within its arms you will find shelter from the sun at its zenith and from the autumnal rains. Fruit is the focus of Jamesʼs lens as it circles deep into the embrace of limbs and leaves.

Gyration

European Renaissance and Romantic landscape appeared in vistas. The conditions of the industrial revolution and, according to Patrick Maynard and Jonathon Crary, the film camera especially, led to a Modernist re-vision vividly recorded in Xavier Herbert’s contrary Modernist vision, prompted by seeing the Australian bush, its ‘... stunted trees, the mulga and the wilga and the gimlet gum, doing a kind of dance, spinning past, seeming to swing away from the train to the horizon and race ahead, to come back...the same set of trees in endless gyration’.

Aprendizagem motora baseada em demonstrações de movimento biológico

O objetivo deste estudo foi avaliar o processo de aprendizagem motora de uma habilidade complexa da Ginástica Artística a partir da observação de demonstrações de modelos de pontos de luz e vídeo. Dezesseis participantes divididas em grupos dos respectivos modelos executaram um pré-teste, seguido de 100 tentativas de uma parada de mãos, igualmente distribuídas em blocos de 10 tentativas em dois dias, alternando períodos de demonstração e prática, com um teste de retenção após um dia. Cinemática de braço, tronco e perna das participantes possibilitaram análise da semelhança entre a coordenação de cada participante e do modelo e do tempo de movimento; a performance das participantes também foi avaliada por duas especialistas em Ginástica Artística. Ambas as análises indicaram que os grupos não diferiram. Os resultados são discutidos em termos da hipótese de suficiência de informação nos modelos de movimento biológico particularmente aplicada ao processo de aprendizagem de habilidades motoras complexas.

Seeking one's heading through eye movements

A study of eye movements during simulated travel toward a grove of four stationary trees revealed that observers looked most at pairs of trees that converged or decelerated apart. Such pairs specify that one's direction of travel, called heading, is to the outside of the near member of the pair. Observers looked at these trees more than those that accelerated apart; such pairs do not offer trustworthy heading information. Observers also looked at gaps between trees less often when they converged or diverged apart, and heading can never be between such pairs. Heading responses were in accord with eye movements. In general, if observers responded accurately, they had looked at trees that converged or decelerated apart; if they were inaccurate, they had not. Results support the notion that observers seek out their heading through eye movements, saccading to and fixating on the most informative locations in the field of view.

Exploration time of static images implying different body movements causes time distortions

Studies of subjective time have adopted different methods to understand different processes of time perception. Four sculptures, with implied movement ranked as 1.5-, 3.0-, 4.5-, and 6.0-point stimuli on the Body Movement Ranking Scale, were randomly presented to 42 university students untrained in visual arts and ballet. Participants were allowed to observe the images for any length of time (exploration time) and, immediately after each image was observed, recorded the duration as they perceived it. The results of temporal ratio (exploration time/time estimation) showed that exploration time of images also affected perception of time, i.e., the subjective time for sculptures representing implied movement were overestimated.\

Untersuchung zum Beitrag des ON-Kanals zu zeitlichen und chromatischen Verarbeitungsmechanismen in der Retina

Ziel der vorliegenden Arbeit war es, mithilfe von Dressurexperimenten in Kombination mit dem Einsatz von Neuropharmaka die Bedeutung des retinalen ON-Kanals für zwei visuelle Leistungen des Goldfisches – das kontrastabhängige zeitliche Auflösungsvermögen sowie die Wellenlängenunterscheidungsfähigkeit - zu untersuchen. Da die Tiere nach der pharmakologischen Blockade keinerlei verändertes Verhalten zeigten, kann davon ausgegangen werden, dass der retinale ON-Kanal weder für die Prozessierung des kontrastabhängigen zeitlichen Auflösungsvermögens noch für die Wellenlängenunterscheidungsfähigkeit eine maßgebliche Rolle spielt. Aus den Versuchen zur Wellenlängenunterscheidungsfähigkeit kann des Weiteren abgeleitet werden, dass der ON-Kanal auch für die spektrale Empfindlichkeit der Tiere bei der gegebenen Beleuchtungs- und Dressurbedingungen (L+-Dressur) keine Bedeutung zu haben scheint. Nach den Versuchen zum kontrastabhängigen zeitlichen Auflösungsvermögen kann festgehalten werden, dass das zeitliche Auflösungsvermögen des Goldfisches sich mit abnehmendem Stimuluskontrast verändert: Der für die Tiere wahrnehmbare Flickerfrequenzbereich wird mit abnehmendem Kontrast geringer. Die Flimmerfusionsfrequenz wird im oberen Frequenzbereich früher erreicht; im unteren Flickerfrequenzbereich tritt mit abnehmendem Kontrast auch eine untere Grenze des zeitlichen Auflösungsvermögens auf. Des Weiteren zeigen die Ergebnisse aus den Verhaltensversuchen zu den kontrastabhängigen zeitlichen Übertragungseigenschaften eine gute Vergleichbarkeit zu elektrophysiologisch gewonnenen Antworten von ON bzw. OFF-Bipolarzellen. Ebenso ähneln sich die Kurvenverläufe zum kontrastabhängigen zeitlichen Auflösungsvermögen und die aus den Versuchen zur kontrastabhängigen Ganzfeldbewegungswahrnehmung – einer visuellen Leistung, deren Prozessierung eines ON-Kanal-Beitrages bedarf. Diese Ergebnisse deuten darauf hin, dass das zeitliche Auflösungsvermögen wie auch die Ganzfeldbewegungswahrnehmung hauptsächlich von retinalen Verarbeitungsprozessen abhängen.

Influence of optic flow on postural control

The study of optic flow on postural control may explain how self-motion perception contributes to postural stability in young males and females and how such function changes in the old falls risk population. Study I: The aim was to examine the optic flow effect on postural control in young people (n=24), using stabilometry and surface-electromyography. Subjects viewed expansion and contraction optic flow stimuli which were presented full field, in the foveral or in the peripheral visual field. Results showed that optic flow stimulation causes an asymmetry in postural balance and a different lateralization of postural control in men and women. Gender differences evoked by optic flow were found both in the muscle activity and in the prevalent direction of oscillation. The COP spatial variability was reduced during the view of peripheral stimuli which evoked a clustered prevalent direction of oscillation, while foveal and random stimuli induced non-distributed directions. Study II was aimed at investigating the age-related mechanisms of postural stability during the view of optic flow stimuli in young (n=17) and old (n=19) people, using stabilometry and kinematic. Results showed that old people showed a greater effort to maintain posture during the view of optic flow stimuli than the young. Elderly seems to use the head stabilization on trunk strategy. Visual stimuli evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stabilizes postural sway, while random and foveal stimuli provoke larger sway variability similar to those evoked in baseline. Postural control uses different mechanisms within each leg to produce the appropriate postural response to interact with extrapersonal environment. Ageing reduce the effortlessness to stabilize posture during optic flow, suggesting a neuronal processing decline associated with difficulty integrating multi-sensory information of self-motion perception and increasing risk of falls.

Imagery of a moving object: the role of occipital cortex and human MT/V5+

Visual imagery – similar to visual perception – activates feature-specific and category-specific visual areas. This is frequently observed in experiments where the instruction is to imagine stimuli that have been shown immediately before the imagery task. Hence, feature-specific activation could be related to the short-term memory retrieval of previously presented sensory information. Here, we investigated mental imagery of stimuli that subjects had not seen before, eliminating the effects of short-term memory. We recorded brain activation using fMRI while subjects performed a behaviourally controlled guided imagery task in predefined retinotopic coordinates to optimize sensitivity in early visual areas. Whole brain analyses revealed activation in a parieto-frontal network and lateral–occipital cortex. Region of interest (ROI) based analyses showed activation in left hMT/V5+. Granger causality mapping taking left hMT/V5+ as source revealed an imagery-specific directed influence from the left inferior parietal lobule (IPL). Interestingly, we observed a negative BOLD response in V1–3 during imagery, modulated by the retinotopic location of the imagined motion trace. Our results indicate that rule-based motion imagery can activate higher-order visual areas involved in motion perception, with a role for top-down directed influences originating in IPL. Lower-order visual areas (V1, V2 and V3) were down-regulated during this type of imagery, possibly reflecting inhibition to avoid visual input from interfering with the imagery construction. This suggests that the activation in early visual areas observed in previous studies might be related to short- or long-term memory retrieval of specific sensory experiences.