查看更多>>摘要：Motion parallax and binocular disparity contribute to the perceived depth of three-dimensional (3D) objects. However, depth is often misperceived, even when both cues are available. This may be due in part to conflicts with unmodelled cues endemic to computerized displays. Here we evaluated the impact of display-based cue conflicts on depth cue integration by comparing perceived depth for physical and virtual objects. Truncated square pyramids were rendered using Blender and 3D printed. We assessed perceived depth using a discrimination task with motion parallax, binocular disparity, and their combination. Physical stimuli were presented with precise control over position and lighting. Virtual stimuli were viewed using a head-mounted display. To generate motion parallax, observers made lateral head movements using a chin rest on a motion platform. Observers indicated if the width of the front face appeared greater or less than the distance between this surface and the base. We found that accuracy was similar for virtual and physical pyramids. All estimates were more precise when depth was defined by binocular disparity than motion parallax. Our probabilistic model shows that a linear combination model does not adequately describe performance in either physical or virtual conditions. While there was inter-observer variability in weights, performance in all conditions was best predicted by a veto model that excludes the less reliable depth cue, in this case motion parallax.
查看更多>>摘要：Motion parallax and binocular disparity contribute to the perceived depth of three-dimensional (3D) objects. However, depth is often misperceived, even when both cues are available. This may be due in part to conflicts with unmodelled cues endemic to computerized displays. Here we evaluated the impact of display-based cue conflicts on depth cue integration by comparing perceived depth for physical and virtual objects. Truncated square pyramids were rendered using Blender and 3D printed. We assessed perceived depth using a discrimination task with motion parallax, binocular disparity, and their combination. Physical stimuli were presented with precise control over position and lighting. Virtual stimuli were viewed using a head-mounted display. To generate motion parallax, observers made lateral head movements using a chin rest on a motion platform. Observers indicated if the width of the front face appeared greater or less than the distance between this surface and the base. We found that accuracy was similar for virtual and physical pyramids. All estimates were more precise when depth was defined by binocular disparity than motion parallax. Our probabilistic model shows that a linear combination model does not adequately describe performance in either physical or virtual conditions. While there was inter-observer variability in weights, performance in all conditions was best predicted by a veto model that excludes the less reliable depth cue, in this case motion parallax.
查看更多>>摘要：Little is known about how perceived gaze direction and head orientation may influence human categorization of visual stimuli as faces. To address this question, a sequence of unsegmented natural images, each containing a random face or a non-face object, was presented in rapid succession (stimulus duration: 91.7 ms per image) during which human observers were instructed to respond immediately to every face presentation. Faces differed in gaze and head orientation in 7 combinations - full-front views with perceived gaze (1) directed to the observer, (2) averted to the left, or (3) averted to the right, left '/, side views with (4) direct gaze or (5) averted gaze, and right '/, side views with (6) direct gaze or (7) averted gaze - were presented randomly throughout the sequence. We found highly accurate and rapid behavioural responses to all kinds of faces. Crucially, both perceived gaze direction and head orientation had comparable, non-interactive effects on response times, where direct gaze was responded faster than averted gaze by 48 ms and full-front view faster than '/, side view also by 48 ms on average. Presentations of full-front faces with direct gaze led to an additive speed advantage of 96 ms to '/, faces with averted gaze. The results reveal that the effects of perceived gaze direction and head orientation on the speed of face categorization probably depend on the degree of social relevance of the face to the viewer.
查看更多>>摘要：Little is known about how perceived gaze direction and head orientation may influence human categorization of visual stimuli as faces. To address this question, a sequence of unsegmented natural images, each containing a random face or a non-face object, was presented in rapid succession (stimulus duration: 91.7 ms per image) during which human observers were instructed to respond immediately to every face presentation. Faces differed in gaze and head orientation in 7 combinations - full-front views with perceived gaze (1) directed to the observer, (2) averted to the left, or (3) averted to the right, left '/, side views with (4) direct gaze or (5) averted gaze, and right '/, side views with (6) direct gaze or (7) averted gaze - were presented randomly throughout the sequence. We found highly accurate and rapid behavioural responses to all kinds of faces. Crucially, both perceived gaze direction and head orientation had comparable, non-interactive effects on response times, where direct gaze was responded faster than averted gaze by 48 ms and full-front view faster than '/, side view also by 48 ms on average. Presentations of full-front faces with direct gaze led to an additive speed advantage of 96 ms to '/, faces with averted gaze. The results reveal that the effects of perceived gaze direction and head orientation on the speed of face categorization probably depend on the degree of social relevance of the face to the viewer.
Hughes, Rohan P. J.Read, Scott A.Collins, Michael J.Vincent, Stephen J....
11页
查看更多>>摘要：Changes in higher order aberrations (HOA's) and retinal image quality during accommodation have not previ-ously been examined in children. This study measured ocular HOA's in ninety non-myopic, school-aged children during short-term accommodation tasks at 0, 3, 6, and 9 D demands presented via a Badal optometer mounted to a Hartmann-Shack wavefront aberrometer (COAS-HD, Wavefront Sciences). Eighty-four participants who exhibited active accommodation were included in the analyses. An eighth order Zernike polynomial was fit across a 2.3 mm, 4 mm, and natural pupil diameter to evaluate changes in refractive power vectors (M, J(180), and J(45)), accommodation errors (lags and leads), HOA root mean square (RMS) variables, individual Zernike co-efficients, and the visual Strehl ratio based on the optical transfer function (VSOTF). All HOA RMS variables changed significantly with accommodation, with the greatest change observed for the 9 D demand. Of the in-dividual Zernike coefficients, primary (C-4(0)) and secondary spherical aberration (C-6(0)) exhibited the greatest magnitude of change, becoming negative and positive with increasing accommodation, respectively. The VSOTF changed significantly with greater accommodation for both the 4 mm and natural pupil size, becoming signif-icantly worse for the 9 D demand. HOA's increase and retinal image quality decreases significantly during higher levels of accommodation in children, similar to adults. These findings provide a greater understanding of the optical properties of children's eyes and insights into possible mechanisms for the association between accom-modation, near work, and refractive error development.
Hughes, Rohan P. J.Read, Scott A.Collins, Michael J.Vincent, Stephen J....
11页
查看更多>>摘要：Changes in higher order aberrations (HOA's) and retinal image quality during accommodation have not previ-ously been examined in children. This study measured ocular HOA's in ninety non-myopic, school-aged children during short-term accommodation tasks at 0, 3, 6, and 9 D demands presented via a Badal optometer mounted to a Hartmann-Shack wavefront aberrometer (COAS-HD, Wavefront Sciences). Eighty-four participants who exhibited active accommodation were included in the analyses. An eighth order Zernike polynomial was fit across a 2.3 mm, 4 mm, and natural pupil diameter to evaluate changes in refractive power vectors (M, J(180), and J(45)), accommodation errors (lags and leads), HOA root mean square (RMS) variables, individual Zernike co-efficients, and the visual Strehl ratio based on the optical transfer function (VSOTF). All HOA RMS variables changed significantly with accommodation, with the greatest change observed for the 9 D demand. Of the in-dividual Zernike coefficients, primary (C-4(0)) and secondary spherical aberration (C-6(0)) exhibited the greatest magnitude of change, becoming negative and positive with increasing accommodation, respectively. The VSOTF changed significantly with greater accommodation for both the 4 mm and natural pupil size, becoming signif-icantly worse for the 9 D demand. HOA's increase and retinal image quality decreases significantly during higher levels of accommodation in children, similar to adults. These findings provide a greater understanding of the optical properties of children's eyes and insights into possible mechanisms for the association between accom-modation, near work, and refractive error development.
Boehm, Alexandra E.Bosten, JennyMacLeod, Donald I. A.
11页
查看更多>>摘要：In anomalous trichromacy, the color signals available from comparing the activities of the two classes of cone sensitive in the medium and long wavelength parts of the spectrum are much reduced from those available in normal trichromacy, and color discrimination thresholds along the red-green axis are correspondingly elevated. Yet there is evidence that suprathreshold color perception is relatively preserved; this has led to the suggestion that anomalous trichromats post-receptorally amplify their impoverished red-green signals. To test this idea, we measured chromatic discrimination from white and from saturated red and green pedestals. If there is no postreceptoral compensation, the anomalous trichromat's loss of chromatic contrast will apply equally to the pedestal and to the test color. Coupled with a compressively nonlinear neural representation of saturation, this means that a given pedestal contrast will cause a smaller than normal modulation of discrimination sensitivity. We examined cases where chromatic pedestals impair the color discrimination of normal trichromatic observers. As predicted, anomalous observers experienced less impairment than normal trichromats, though they remained less sensitive than normal trichromats. Although the effectiveness of chromatic pedestals in impairing color discrimination was less for anomalous than for normal trichromats, the chromatic pedestals were more effective for anomalous observers than would be expected if the anomalous post-receptoral visual system were the same as in normal trichromacy; the hypothesis of zero compensation can be rejected. This might suggest that the effective contrast of the pedestal is post-receptorally amplified. But on closer analysis, the results do not support candidate simple models involving post-receptoral compensation either.
Boehm, Alexandra E.Bosten, JennyMacLeod, Donald I. A.
11页
查看更多>>摘要：In anomalous trichromacy, the color signals available from comparing the activities of the two classes of cone sensitive in the medium and long wavelength parts of the spectrum are much reduced from those available in normal trichromacy, and color discrimination thresholds along the red-green axis are correspondingly elevated. Yet there is evidence that suprathreshold color perception is relatively preserved; this has led to the suggestion that anomalous trichromats post-receptorally amplify their impoverished red-green signals. To test this idea, we measured chromatic discrimination from white and from saturated red and green pedestals. If there is no postreceptoral compensation, the anomalous trichromat's loss of chromatic contrast will apply equally to the pedestal and to the test color. Coupled with a compressively nonlinear neural representation of saturation, this means that a given pedestal contrast will cause a smaller than normal modulation of discrimination sensitivity. We examined cases where chromatic pedestals impair the color discrimination of normal trichromatic observers. As predicted, anomalous observers experienced less impairment than normal trichromats, though they remained less sensitive than normal trichromats. Although the effectiveness of chromatic pedestals in impairing color discrimination was less for anomalous than for normal trichromats, the chromatic pedestals were more effective for anomalous observers than would be expected if the anomalous post-receptoral visual system were the same as in normal trichromacy; the hypothesis of zero compensation can be rejected. This might suggest that the effective contrast of the pedestal is post-receptorally amplified. But on closer analysis, the results do not support candidate simple models involving post-receptoral compensation either.
查看更多>>摘要：Under ecological conditions, the luminance impinging on the retina varies within a dynamic range of 220 dB. Stimulus contrast can also vary drastically within a scene and eye movements leave little time for sampling luminance. Given these fundamental problems, the human brain allocates a significant amount of resources and deploys both structural and functional solutions that work in tandem to compress this range. Here we propose a new dynamic neural model built upon well-established canonical neural mechanisms. The model consists of two feed-forward stages. The first stage encodes the stimulus spatially and normalizes its activity by extracting contrast and discounting the background luminance. These normalized activities allow a second stage to implement a contrast-dependent spatial-integration strategy. We show how the properties of this model can account for adaptive properties of motion discrimination, integration, and segregation.
查看更多>>摘要：Under ecological conditions, the luminance impinging on the retina varies within a dynamic range of 220 dB. Stimulus contrast can also vary drastically within a scene and eye movements leave little time for sampling luminance. Given these fundamental problems, the human brain allocates a significant amount of resources and deploys both structural and functional solutions that work in tandem to compress this range. Here we propose a new dynamic neural model built upon well-established canonical neural mechanisms. The model consists of two feed-forward stages. The first stage encodes the stimulus spatially and normalizes its activity by extracting contrast and discounting the background luminance. These normalized activities allow a second stage to implement a contrast-dependent spatial-integration strategy. We show how the properties of this model can account for adaptive properties of motion discrimination, integration, and segregation.
NSTL
Elsevier