Search results for " Vision"
showing 10 items of 2709 documents
Changes in pattern induced flicker colors are mediated by the blue-yellow opponent process.
1992
The colors of Benham's Top [pattern induced flicker colors (PIFCs)] were matched with color stimuli provided by a computer aided color mixer. Subjects viewed a series of specifically modified black and white disks and matched the resulting subjective color with a comparison field containing the color generated by additive mixing. Different phase relations between the apparently colored ring and the surround were tested. The color loci of all PIFCs were found to lie on a plane in receptor three-space which is given by the axis of the shortwave receptor excitation and a vector given by combining the middle and long wave receptor excitation directions in a fixed ratio of nearly 1:1. From the o…
Color and lightness constancy in different perceptual tasks
1998
Color and lightness constancy with respect to changing illumination was studied with three different perceptual tasks: ranking of colored papers according (1) to their lightness and (2) to their chromatic similarity in photopic, mesopic, and scotopic states of adaptation, and (3) recognition of remembered colored papers after changes of illumination in photopic vision. Constancy was found in the second task, only. Excitations of light receptors and luminance channels were computed to simulate the empirical rank orders. Results of the first task can be predicted with the hypothesis that luminance channels are activated, if lightness is asked for. Sequences arranged with respect to chromatic …
Effect of luminance on photopic visual acuity in the presence of laser speckle
1988
Visual acuity in coherent and incoherent light has been determined by using square-wave gratings of 100% contrast. Luminance was varied from 3 to 400 cd/m2. Coherent illumination resulted in a 40% loss of visual acuity. This is probably due to the masking effect of coherent spatial noise (speckle). However, the most interesting finding is the change in shape of the photopic visual-acuity-luminance function. With coherent illumination, the function is vertically displaced and of a different gradient. An increase in luminance produces a decrease in visual acuity. This indicates that the masking effect of the speckle is dependent on luminance. Two observers were used, and similar results were …
Haptic information differentially interferes with visual analysis in reaching-grasping control and in perceptual processes.
1998
We used an interference paradigm in order to study integration between haptic and visual information in motor control and in perceptual analysis. Subjects either reached and grasped a visually presented sphere or matched its size with their left hand while manipulating with their right hand another sphere whose size could be smaller or greater. In four experiments haptic analysis of the manipulated sphere could be either automatically incorporated with or explicitly dissociated from visual analysis. In a fifth experiment reaching-grasping and matching were executed with the right hand, whereas manipulation was executed with the left hand. Manipulation with the right hand influenced finger s…
Does matching of internal and external facial features depend on orientation and viewpoint?
2009
Although it is recognized that external (hair, head and face outline, ears) and internal (eyes, eyebrows, nose, mouth) features contribute differently to face recognition it is unclear whether both feature classes predominately stimulate different sensory pathways. We employed a sequential speed-matching task to study face perception with internal and external features in the context of intact faces, and at two levels of contextual congruency. Both internal and external features were matched faster and more accurately in the context of totally congruent/incongruent facial stimuli compared to just featurally congruent/ incongruent faces. Matching of totally congruent/incongruent faces was no…
Visual inference of arm movement is constrained by motor representations
2015
International audience; Several studies support the idea that motion inference is strongly motor dependent. In the present study, we address the role of biomechanical constraints in motion prediction and how this implicit knowledge can interfere in a spatial prediction task. Right-handed (RHS) and left-handed subjects (LHS) had to estimate the final position of a horizontal arm movement in which the final part of the trajectory was hidden. Our study highlighted a direction effect: end point prediction accuracy was better to infer the final position of horizontal motion directed toward the median line of human body. This finding suggests that the spatial prediction of end point is mapped ont…
Image quality and visual performance in the peripheral visual field following photorefractive keratectomy.
2002
ABSTRACT PURPOSE: A theoretical and experimental study was performed to assess the possible effects of photorefractive keratectomy (PRK) on retinal image quality and thresholds in the peripheral visual field. METHODS: Simple optical calculations suggest that although the quality of the retinal image at the fovea of the postoperative PRK eye may be comparable to that in an emmetropic eye, images in the peripheral field may be markedly worse, since peripheral ray bundles may pass partly through ablated and partly through unablated cornea, giving a simultaneous-vision bifocal effect. This would be expected to create an annular zone of confusion, so that light from two different directions in o…
Prevalence and causes of blindness and low vision in the Casteldaccia Eye Study.
1994
In a population-based survey performed on the middle-aged and elderly population of Casteldaccia, Sicily, we found that the prevalence of blindness was 0.47% and the prevalence of low vision 1.22%. Unilateral blindness affected 2.81% of the population and unilateral low vision 4.12%. Visual impairment was much more frequently seen in subjects aged 70 years or more than in younger persons. The main cause of visual impairment was cataract, followed by amblyopia, which was responsible for many cases of unilateral low vision.
Feasibility and reproducibility of electroencephalography-based corticokinematic coherence
2020
Corticokinematic coherence (CKC) is the phase coupling between limb kinematics and cortical neurophysiological signals, reflecting cortical processing of proprioceptive afference, and it is reproducible when estimated with magnetoencephalography (MEG). However, feasibility and reproducibility of CKC based on electroencephalography (EEG) is still unclear and is the primary object of the present report. Thirteen healthy right-handed volunteers (seven females, 21.7 ± 4.3 yr) participated in two combined MEG/EEG sessions 12.6 ± 1.3 mo apart. Participants' dominant and nondominant index finger was continuously moved at 3 Hz for 4 min separately using a pneumatic-movement actuator. Coherence was …
Axis Rotation and Visually Induced Motion Sickness: The Role of Combined Roll, Pitch, and Yaw Motion
2011
A well-known phenomenon in aviation and in virtual environments such as simulators or computer games is motion sickness (MS). The amount of sensory conflict is thought to be responsible for the severity of MS, which should increase with the complexity of the simulated motion. The focus of the present study is on the direction and complexity of simulated body rotations in the genesis and severity of visually induced MS. The methods utilized for this study are as follows: Three simulated rollercoaster rides including translational movement in the fore-aft axis and additional rotational motion either in pitch only, along the pitch and roll axes, or in pitch, roll, and yaw were generated. The a…