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  • 1
    Electronic Resource
    Electronic Resource
    Perceived visual speed constrained by image segmentation (1996)
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 161-163 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We previously measured the human ability to combine speed information from multiple moving stimuli and showed that whereas increasing the number of stimuli improved speed discrimination, increasing the area of a single stimulus by the same factor did not6 (Fig. 1). These data do not show the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/381161a0
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    Paper (German National Licenses)
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  • 2
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    The unique criterion constraint: a false alarm? (2002)
    Springer Nature
    Details
    Publication Date: 2002-08-01
    Print ISSN: 1097-6256
    Electronic ISSN: 1546-1726
    Topics: Biology , Medicine
    Published by Springer Nature
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    PAPER CURRENT
  • 3
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    Visual Search and Attention (2001)
    Cell Press
    Details
    Publication Date: 2001-08-01
    Print ISSN: 0896-6273
    Electronic ISSN: 1097-4199
    Topics: Biology , Medicine
    Published by Cell Press
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  • 4
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    Perceived visual speed constrained by image segmentation (1996)
    Springer Nature
    Details
    Publication Date: 1996-05-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 5
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    Integration of speed signals in the direction of motion (2002)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Speed discrimination tasks were used to examine the spatial and temporal characteristics of the integration mechanism involved when signals are extended in the direction of motion. We varied the aspect ratio of a signal patch whose speed differed from the background, while holding the area of the signal patch constant, so that the signal patch could be either extended in the direction of motion or extended orthogonal to the direction of motion. Speed discrimination thresholds decreased dramatically as the signal patch was extended in the direction of motion. The spatial and temporal integration regions were larger than would be expected if the integration mechanism were a low-level motion detector. The mechanism was tuned for direction of motion. The data are discussed with reference to two alternative integration mechanisms: a low-level detector that is elongated in the direction of motion and a higher level integration mechanism characterized by cooperative or facilitatory interactions between low-level detectors tuned to the same direction of motion. Our data are consistent with a second-level, direction-specific process that integrates the responses of low-level motion detectors.
    Keywords: Life Sciences (General)
    Type: Perception & psychophysics (ISSN 0031-5117); Volume 64; 6; 996-1007
    Format: text
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  • 6
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    Constraints on Neural Mechanisms Underlying the Spatial Integration of Speed Information (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We measured human ability to integrate speed information presented simultaneously at multiple locations in the visual field. Observers did a two-interval forced-choice speed discrimination task with n grating patches in each interval at 4' eccentricity from fixation. In the first (integration) paradigm, all gratings in each interval moved at the same speed and observers were asked to pick the interval containing the faster gratings. Speed discrimination improved as the number of gratings in each interval increased. The observed decrease in threshold is not due simply to an increase in the effective area because performance with a single grating two, four, or six times the area of the original grating showed no such improvement. Furthermore, the improvement with n was still observed even when the speeds of the individual gratings in each interval were independent samples from a Gaussian distribution and the grating directions were balanced (i.e. equal numbers of gratings moved to the left and right). These results indicate that the neural mechanisms responsible for the integration of speed information act as if each patch provides an independent sample of speed, independent of grating direction. The results are not consistent with simple summation across space by a directionally selective mechanism with a large receptive field. In the second (search) paradigm, only one of the gratings in an interval moved faster and observers were asked to pick this interval. In this case, thresholds increased with the number of distractor gratings. The decrease in performance with increased n is common in search tasks and is often attributed to a bottleneck in the information that observers can process simultaneously. However, the results in the integration paradigm show that subjects indeed have access to and can use additional information with increasing n, at least up to 4 patches. Finally, simple detection models predict the trends in both the search and integration paradigms without invoking an input bottleneck.
    Keywords: Behavioral Sciences
    Type: Society for Neuroscience; Nov 13, 1994 - Nov 18, 1994; Miami Beach, FL; United States
    Format: text
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  • 7
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    Stereo transparency and the disparity gradient limit (2002)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient 〉1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.
    Keywords: Life Sciences (General)
    Type: Vision research (ISSN 0042-6989); 42; 16; 1963-77
    Format: text
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  • 8
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    Speed Discrimination: Multiple Stimuli Appear Better Than One (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: We reported that for a 21FC task with multiple moving grating patches (Gabors) in each interval, thresholds for speed discrimination decreased with the number of patches, while increasing the area of a single grating produced no such effect. Furthermore, this decrease occurred regardless of the spacing of the patches about a circle of eccentricity 4 degrees, i.e., whether they were maximally separated or almost touching. These results suggest that it is the multiple, discrete grating patches that cause thresholds to decrease, rather than the spatial arrangement. To test this hypothesis, we measured the effect of dividing a large grating into four quadrants, by superimposing a mean-luminance cross on it. The mean speed discrimination thresholds (Weber Fractions) for four observers were 19, 15, and 11 plus or minus 2%, for the single large grating, the grating with cross, and the 4 maximally-separated, small gratings, respectively. Thus, breaking up a single large grating into multiple parts caused thresholds to improve, despite the fact that less of the original patch was visible. To investigate the possible contribution of total bounding contour length, we measured the effect of coalescing three small grating patches into a single banana-shaped patch, while keeping the total contour length constant. These two conditions were compared to a single, circular Gabor patch of equivalent area that had (necessarily) a smaller contour length. Preliminary data from 3 of 4 observers were similar for the small-grating and banana configurations, but increased for the single, large grating, suggesting that contour length might play a role. We are also investigating the role of low-level factors pertinent to the large grating, such as the pooling of signals from motion units at different eccentricities, and the stimulation of extended inhibitory motion surrounds, as well as the possible contribution of topdown influences that segment the stimulus into distinct objects.
    Keywords: Behavioral Sciences
    Type: 25th Annual Meeting of Society for Neuroscience; Nov 11, 1995 - Nov 16, 1995; San Diego, CA; United States
    Format: text
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  • 9
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    Constraints on Neural Mechanisms Underlying the Spatial Integration of Speed Information (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: We measured human ability to integrate speed information presented simultaneously at multiple locations in the visual field. Observers did a two-interval forced-choice speed discrimination task with n grating patches in each interval at 4deg eccentricity from fixation. In the first (integration) paradigm, all gratings in each interval moved at the same speed and observers were asked to pick the interval containing the faster gratings. Speed discrimination improved as the number of gratings in each interval increased. The observed decrease in threshold is not due simply to an increase in the effective area because performance with a single grating two, four, or six times the area of the original grating showed no such improvement. Furthermore, the improvement with n was still observed even when the speeds of the individual gratings in each interval were independent samples from a Gaussian distribution and the grating directions were balanced (i.e. equal numbers of gratings moved to the left and right). These results indicate that the neural mechanisms responsible for the integration of speed information act as if each patch provides an independent sample of speed, independent of grating direction. The results are not consistent with simple summation across space by a directionally selective mechanism with a large receptive field. in the second (search) paradigm, only one of the gratings in an interval moved faster and observers were asked to pick this interval. In this case, thresholds increased with the number of distractor gratings. The decrease in performance with increased n is common in search tasks and is often attributed to a bottleneck in the information that observers can process simultaneously. However, the results in the integration paradigm show that subjects indeed have access to and can use additional information with increasing n, at least up to 4 patches. Finally, simple detection models predict the trends in both the search and integration paradigms without invoking an input bottleneck.
    Keywords: Behavioral Sciences
    Type: 24th Annual Meeting of the Society of Neuroscience; Nov 13, 1994 - Nov 18, 1994; Miami Beach, FL; United States
    Format: text
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  • 10
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    Contour completion through depth interferes with stereoacuity (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Local disparity signals must interact in visual cortex to represent boundaries and surfaces of three-dimensional (3D) objects. We investigated how disparity signals interact in 3D contours and in 3D surfaces generated from the contours. We compared flat (single disparity) stimuli with curved (multi-disparity) stimuli. We found no consistent differences in sensitivity to contours vs. surfaces; for equivalent amounts of disparity, however, observers were more sensitive to flat stimuli than curved stimuli. Poor depth sensitivity for curved stimuli cannot be explained by the larger range of disparities present in the curved surface, nor by disparity averaging, nor by poor sensitivity to the largest disparity in the stimulus. Surprisingly, sensitivity to surfaces curved in depth was improved by removing portions of the surface and thus removing disparity information. Stimulus configuration had a profound effect on stereo thresholds that cannot be accounted for by disparity-energy models of V1 processing. We suggest that higher-level 3D contour or 3D shape mechanisms are involved.
    Keywords: Life Sciences (General)
    Type: Vision research (ISSN 0042-6989); 42; 18; 2153-162
    Format: text
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