378 research outputs found
PEC886247 Supplemetal Material - Supplemental material for What Color Was It? A Psychophysical Paradigm for Tracking Subjective Progress in Continuous Tasks
No full textSupplemental material, PEC886247 Supplemetal Material for What Color Was It? A Psychophysical Paradigm for Tracking Subjective Progress in Continuous Tasks by Anna Kosovicheva and Peter J. Bex in Perception</p
Simulated disparity and peripheral blur interact during binocular fusion
No full textWe have developed a low-cost, practical gaze-contingent display in which natural images are presented to the observer with dioptric blur and stereoscopic disparity that are dependent on the three-dimensional structure of natural scenes. Our system simulates a distribution of retinal blur and depth similar to that experienced in realworld viewing conditions by emmetropic observers. We implemented the system using light-field photographs taken with a plenoptic camera which supports digital refocusing anywhere in the images. We coupled this capability with an eye-tracking system and stereoscopic rendering. With this display, we examine how the time course of binocular fusion depends on depth cues from blur and stereoscopic disparity in naturalistic images. Our results show that disparity and peripheral blur interact to modify eye-movement behavior and facilitate binocular fusion, and the greatest benefit was gained by observers who struggled most to achieve fusion. Even though plenoptic images do not replicate an individual's aberrations, the results demonstrate that a naturalistic distribution of depth-dependent blur may improve 3-D virtual reality, and that interruptions of this pattern (e.g., with intraocular lenses) which flatten the distribution of retinal blur may adversely affect binocular fusion.</p
A Space-Variant Model for Motion Interpretation across the Visual Field
No full textWe implement a neural model for the estimation of the focus of radial motion (FRM) at different retinal locations and we assess the model by comparing its results with respect to the precision with which human observers can estimate the FRM in naturalistic, moving dead leaves stimuli. The proposed neural model describes the deep hierarchy of the first stages of the dorsal visual pathway [Solari et al., 2014]. Such a model is space-variant, since it takes into account the retino-cortical transformation of the primate visual system through log-polar mapping that produces a cortical representation of the visual signal to the retina. The log-polar transform of the retinal image is the input to the cortical motion estimation stage where optic flow is computed by a three-layer population of cells. A population of spatio-temporal oriented Gabor filters approximates the simple cells of area V1 (first layer), which are combined into complex cells as motion energy units (second layer). The responses of the complex cells are pooled (third layer) to encode the magnitude and direction of velocities as in the extrastriate motion pathway between area MT and MST. The sensitivity to complex motion patterns that has been found in area MST is modeled through a population of adaptive templates, and from the responses of such a population the first order description of optic flow is derived. Information about self-motion (e.g. direction of heading) is estimated by combining such first-order descriptors computed in the cortical domain
Three-dimensional binocular eye–hand coordination in normal vision and with simulated visual impairment
No full textSensorimotor coupling in healthy humans is demonstrated by the higher accuracy of visually tracking intrinsically—rather than extrinsically—generated hand movements in the fronto-parallel plane. It is unknown whether this coupling also facilitates vergence eye movements for tracking objects in depth, or can overcome symmetric or asymmetric binocular visual impairments. Human observers were therefore asked to track with their gaze a target moving horizontally or in depth. The movement of the target was either directly controlled by the observer’s hand or followed hand movements executed by the observer in a previous trial. Visual impairments were simulated by blurring stimuli independently in each eye. Accuracy was higher for self-generated movements in all conditions, demonstrating that motor signals are employed by the oculomotor system to improve the accuracy of vergence as well as horizontal eye movements. Asymmetric monocular blur affected horizontal tracking less than symmetric binocular blur, but impaired tracking in depth as much as binocular blur. There was a critical blur level up to which pursuit and vergence eye movements maintained tracking accuracy independent of blur level. Hand–eye coordination may therefore help compensate for functional deficits associated with eye disease and may be employed to augment visual impairment rehabilitation.</p
Monocular and Binocular Contributions to Oculomotor Plasticity
No full textMost eye movements in the real-world redirect the foveae to objects at a new depth and thus require the co-ordination of monocular saccade amplitudes and binocular vergence eye movements. Additionally to maintain the accuracy of these oculomotor control processes across the lifespan, ongoing calibration is required to compensate for errors in foveal landing positions. Such oculomotor plasticity has generally been studied under conditions in which both eyes receive a common error signal, which cannot resolve the long-standing debate regarding whether both eyes are innervated by a common cortical signal or by a separate signal for each eye. Here we examine oculomotor plasticity when error signals are independently manipulated in each eye, which can occur naturally owing to aging changes in each eye’s orbit and extra-ocular muscles, or in oculomotor dysfunctions. We find that both rapid saccades and slow vergence eye movements are continuously recalibrated independently of one another and corrections can occur in opposite directions in each eye. Whereas existing models assume a single cortical representation of space employed for the control of both eyes, our findings provide evidence for independent monoculomotor and binoculomotor plasticities and dissociable spatial mapping for each eye
A Gaussian scenario for unsupervised learning
No full textA Gaussian scenario for unsupervised learning / Peter Reimann ; Chris Van den Broeck ; Geert-Jan Bex. - In: Journal of physics. A. 29. 1996. S. 3521-353
Evaluation of the Tobii EyeX Eye tracking controller and Matlab toolkit for research
No full textThe Tobii Eyex Controller is a new low-cost binocular eye tracker marketed for integration in gaming and consumer applications. The manufacturers claim that the system was conceived for natural eye gaze interaction, does not require continuous recalibration, and allows moderate head movements. The Controller is provided with a SDK to foster the development of new eye tracking applications. We review the characteristics of the device for its possible use in scientific research. We develop and evaluate an open source Matlab Toolkit that can be employed to interface with the EyeX device for gaze recording in behavioral experiments. The Toolkit provides calibration procedures tailored to both binocular and monocular experiments, as well as procedures to evaluate other eye tracking devices. The observed performance of the EyeX (i.e. accuracy < 0.6°, precision < 0.25°, latency < 50 ms and sampling frequency ≈55 Hz), is sufficient for some classes of research application. The device can be successfully employed to measure fixation parameters, saccadic, smooth pursuit and vergence eye movements. However, the relatively low sampling rate and moderate precision limit the suitability of the EyeX for monitoring micro-saccadic eye movements or for real-time gaze-contingent stimulus control. For these applications, research grade, high-cost eye tracking technology may still be necessary. Therefore, despite its limitations with respect to high-end devices, the EyeX has the potential to further the dissemination of eye tracking technology to a broad audience, and could be a valuable asset in consumer and gaming applications as well as a subset of basic and clinical research settings
The perceptual quality of the Oculus Rift for immersive virtual reality
No full textThe recent release of the Oculus Rift, originally developed for entertainment applications, has reignited the interest of researchers and clinicians toward the use of head-mounted-displays in basic behavioral research and physical and psychological rehabilitation. However, careful evaluation of the Oculus Rift is necessary to determine whether it can be effectively used in these novel applications. In this article we address two issues concerning the perceptual quality of the Oculus Rift. (a) Is the Oculus able to generate an acceptable degree of immersivity? In particular, is it possible to elicit the sensation of presence via the virtual stimuli rendered by the device? (b) Does the Virtual Reality experienced through the Oculus Rift induce physical discomfort? To answer these questions, we employed four virtual scenarios in three separate experiments and evaluated performance with objective and subjective outcomes. In Experiment 1 we monitored observers’ heart rate and asked them to rate their Virtual Reality experience via a custom questionnaire. In Experiment 2 we monitored observers’ head movements in reaction to virtual obstacles and asked them to fill out the Simulator Sickness Questionnaire (Kennedy et al., 1993) both before and after experiencing Virtual Reality. In Experiment 3 we compared the Oculus Rift against two other low-cost devices used in immersive Virtual Reality: the Google cardboard and a standard 3DTV monitor. Observers’ heart rate increased during exposure to Virtual Reality, and they subjectively reported the experience to be immersive and realistic. We found a strong relationship between observers’ fear of heights and vertigo experienced during one of the virtual scenarios involving heights, suggesting that observers felt a strong sensation of presence within the virtual worlds. Subjects reacted to virtual obstacles by moving to avoid them, suggesting that the obstacles were perceived as real threats. Observers did not experience simulator sickness when the exposure to Virtual Reality was short and did not induce excessive amounts of vection. Compared to the other devices the Oculus Rift elicited a greater degree of immersivity. Thus our investigation suggests that the Oculus Rift head-mounted-display is a potentially powerful tool for a wide array of basic research and clinical applications.</p
The Perceptual Quality of the Oculus Rift for Immersive Virtual Reality
No full textThe recent release of the Oculus Rift, originally developed for entertainment applications, has re-ignited the interest of researchers and clinicians toward the use of head-mounted-displays (HMDs) in basic behavioral research and physical and psychological rehabilitation. However, careful evaluation of the Oculus Rift is necessary to determine whether it can be effectively used in these novel applications. In this paper, we address two issues concerning the perceptual quality of the Oculus Rift. (i) Is the Oculus able to generate an acceptable degree of immersivity? In particular, is it possible to elicit the sensation of presence via the virtual stimuli rendered by the device? (ii) Does the Virtual Reality experienced through the Oculus Rift induce physical discomfort? To answer these questions, we employed four virtual scenarios in three separate experiments and evaluated performance with objective and subjective outcomes. In Experiment 1 we monitored observers’ heart rate and asked them to rate their Virtual Reality experience via a custom questionnaire. In Experiment 2 we monitored observers’ head movements in reaction to virtual obstacles and asked them to fill out the Simulator Sickness Questionnaire (Kennedy et al., 1993) both before and after experiencing Virtual Reality. In Experiment 3 we compared the Oculus Rift against two other low-cost devices used in immersive Virtual Reality: the Google cardboard and a standard 3DTV monitor. Observers’ heart rate increased during exposure to Virtual Reality, and they subjectively reported the experience to be immersive and realistic. We found a strong relationship between observers’ fear of heights and vertigo experienced during one of the virtual scenarios involving heights, suggesting that observers felt a strong sensation of presence within the virtual worlds. Subjects reacted to virtual obstacles by moving to avoid them, suggesting that the obstacles were perceived as real threats. Observers did not experience simulator sickness when the exposure to virtual reality was short and did not induce excessive amounts of vection. Compared to the other devices the Oculus Rift elicited a greater degree of immersivity. Thus, our investigation suggests that the Oculus Rift HMD is a potentially powerful tool for a wide array of basic research and clinical applications
Near-optimal combination of disparity across a log-polar scaled visual field
No full textThe human visual system is foveated: we can see fine spatial details in central vision, whereas resolution is poor in our peripheral visual field, and this loss of resolution follows an approximately logarithmic decrease. Additionally, our brain organizes visual input in polar coordinates. Therefore, the image projection occurring between retina and primary visual cortex can be mathematically described by the log-polar transform. Here, we test and model how this space-variant visual processing affects how we process binocular disparity, a key component of human depth perception. We observe that the fovea preferentially processes disparities at fine spatial scales, whereas the visual periphery is tuned for coarse spatial scales, in line with the naturally occurring distributions of depths and disparities in the real-world. We further show that the visual system integrates disparity information across the visual field, in a near-optimal fashion. We develop a foveated, log-polar model that mimics the processing of depth information in primary visual cortex and that can process disparity directly in the cortical domain representation. This model takes real images as input and recreates the observed topography of human disparity sensitivity. Our findings support the notion that our foveated, binocular visual system has been moulded by the statistics of our visual environment.</div
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