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Vision Research
Pergamon
Vision Research

Pergamon

0042-6989

Vision Research/Journal Vision ResearchSCIAHCIISTP
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    Threshold vision under full-field stimulation: Revisiting the minimum number of quanta necessary to evoke a visual sensation

    Zele, Andrew J.Feigl, BeatrixAdhikari, PrakashDey, Ashim...
    10页
    查看更多>>摘要:At the absolute threshold of vision, Hecht, Shlaer and Pirenne estimate that 5-14 photons are absorbed within a retinal area containing similar to 500 rods. Other estimates of scotopic threshold vision based on stimuli with different durations and focal areas range up to similar to 100,000 photons. Given that rod density varies with retinal eccentricity and the magnitude of the intrinsic noise increases with increasing stimulus area and duration, here we determine whether the scotopic threshold estimates with focal stimuli can be extended to full-field stimulation and whether summation explains inter-study differences. We show that full-field threshold vision (similar to 1018 mm(2), 10 ms duration) is more sensitive than at absolute threshold, requiring the absorption of similar to 1000 photons across similar to 91.96 million rods. A summation model is presented integrating our and published data and using a nominal exposure duration, criterion frequency of seeing, rod density, and retinal area that largely explains the inter-study differences and allows estimation of rods per photon ratio for any stimulus size and duration. The highest signal to noise ratio is defined by a peak rod convergence estimated at 53:4:1:2 (rods:rod bipolar cells:AII amacrine cells: retinal ganglion cells), in line with macaque anatomical estimates that show All amacrine cells form the bottleneck in the rod pathway to set the scotopic visual limit. Our model estimations that the rods per photon ratio under full-field stimulation is similar to 3000X higher than at absolute threshold are in accordance with visual summation effects and provide an alternative approach for understanding the limits of scotopic vision.

    A unified model for binocular fusion and depth perception

    Ding, JianLevi, Dennis M.
    26页
    查看更多>>摘要:We describe a new unified model to explain both binocular fusion and depth perception, over a broad range of depths. At each location, the model consists of an array of paired spatial frequency filters, with different relative horizontal shifts (position disparity) and interocular phase disparities of 0, 90, +/- 180, or -90 degrees. The paired filters with different spatial profiles (non-zero phase disparity) compute interocular misalignment and provide phase-disparity energy (binocular fusion energy) to drive selection of the appropriate filters along the position disparity space until the misalignment is eliminated and sensory fusion is achieved locally. The paired filters with identical spatial profiles (0 phase disparity) compute the position-disparity energy. After sensory fusion, the combination of position and possible residual phase disparity energies is calculated for binocular depth perception. Binocular fusion occurs at multiple scales following a coarse-to-fine process. At a given location, the apparent depth is the weighted sum of fusion shifts combined with residual phase disparity in all spatial-frequency channels, and the weights depend on stimulus spatial frequency and stimulus contrast. To test the theory, we measured disparity minimum and maximum thresholds (Dmin and Dmax) at three spatial frequencies and with different intraocular contrast levels. The stimuli were Random-Gabor-Patch (RGP) stereograms consisting of Gabor patches with random positions and phases, but with a fixed spatial frequency. The two eyes viewed identical arrays of patches except that one eye's array could be shifted horizontally and could differ in contrast. Our experiments and modeling reveal two contrast normalization mechanisms: (1) Energy Normalization (EN): Binocular energy is normalized with monocular energy after the site of binocular combination. This predicts constant Dmin thresholds when varying stimulus contrast in the two eyes; (2) DSKL model Interocular interactions: Monocular contrasts are normalized before the binocular combination site through interocular contrast gain-control and gain-enhancement mechanisms. This predicts contrast dependent Dmax thresholds. We tested a range of models and found that a model consisting of a second-order pathway with DSKL interocular interactions and a first-order pathway with EN at each spatial-frequency band can account for both the Dmin and Dmax data very well. Simulations show that the model makes reasonable predictions of suprathreshold depth perception.

    Surface slant impairs disparity discontinuity discrimination

    Goutcher, RossWilcox, Laurie M.
    14页
    查看更多>>摘要:Binocular disparity signals are highly informative about the three-dimensional structure of visual scenes, including aiding the detection of depth discontinuities between surfaces. Here, we examine factors affecting sensitivity to such surface discontinuities. Participants were presented with random dot stereograms depicting two planar surfaces slanted in opposite directions and were asked to judge the sign of the depth discontinuity created where those surfaces met. Although the judgement was focussed on the adjacent edges, the precision of depth discontinuity discrimination depended upon the slant of the two surfaces: increasing surface slants to +/- 60 degrees increased discontinuity discrimination thresholds by, on average, a factor of 5. Control experiments examining discontinuity discrimination across surfaces with identical slants showed either biases in discontinuity judgements or reduced threshold elevation. These results suggest that sensitivity to depth discontinuities is affected by processing limitations in both local absolute disparity measurement mechanisms and mechanisms selective for disparity differences. As further evidence in support of this conclusion, we show that our results are well-described by a model of discontinuity discrimination based on the encoding of local differences in relative disparity.

    Degraded visual and auditory input individually impair audiovisual emotion recognition from speech-like stimuli, but no evidence for an exacerbated effect from combined degradation

    de Boer, Minke J.Juergens, TimCornelissen, Frans W.Baskent, Deniz...
    12页
    查看更多>>摘要:Emotion recognition requires optimal integration of the multisensory signals from vision and hearing. A sensory loss in either or both modalities can lead to changes in integration and related perceptual strategies. To investigate potential acute effects of combined impairments due to sensory information loss only, we degraded the visual and auditory information in audiovisual video-recordings, and presented these to a group of healthy young volunteers. These degradations intended to approximate some aspects of vision and hearing impairment in simulation. Other aspects, related to advanced age, potential health issues, but also long-term adaptation and cognitive compensation strategies, were not included in the simulations. Besides accuracy of emotion recognition, eye movements were recorded to capture perceptual strategies. Our data show that emotion recognition performance decreases when degraded visual and auditory information are presented in isolation, but simultaneously degrading both modalities does not exacerbate these isolated effects. Moreover, degrading the visual information strongly impacts recognition performance and on viewing behavior. In contrast, degrading auditory information alongside normal or degraded video had little (additional) effect on performance or gaze. Nevertheless, our results hold promise for visually impaired individuals, because the addition of any audio to any video greatly facilitates performance, even though adding audio does not completely compensate for the negative effects of video degradation. Additionally, observers modified their viewing behavior to degraded video in order to maximize their performance. Therefore, optimizing the hearing of visually impaired individuals and teaching them such optimized viewing behavior could be worthwhile endeavors for improving emotion recognition.

    The vergence horopter

    Harrold, Ashleigh L.Grove, Philip M.
    17页
    查看更多>>摘要:The horopter is defined by the criterion with which it is measured; these include the apparent frontoparallel plane, the region of binocular single vision, and identical visual direction. Another criterion is one that "the positions of the points are such that none provides a stimulus for fusional movement of the eyes". Measuring the horopter using this criterion is the aim of the current paper. Based on previous research investigating corresponding points, we predicted the vergence hompter should trace an arc similar to the empirical horizontal horopter. We further predicted based on the characteristics of vergence eye movements in the periphery, that the range of horizontal disparities that do not elicit a vergence movement would increase with eccentricity. In experiment 1 we conducted the first measurements of the vergence hompter along the horizontal plane of regard and sagittal planes. We found that the vergence horopter consists of a stable range of disparities that do not increase with eccentricity. In experiment 2, we measured Panum's fusional range for the same eccentricities and elevations to determine the placement of the vergence hompter within the fusional ranges. In the horizontal plane, the vergence horopter sits centrally within Panum's fusional range. In the vertical plane, the data are suggestive that the vergence horopter is less slanted than the corresponding fusional range.

    A dark decrement for enhanced dynamic sensitivity of retinal photoreceptors

    Hu, ShenAnastassov, Ivan A.Kreitzer, Matthew A.Slaughter, Malcolm M....
    7页
    查看更多>>摘要:The skate retina provides a native all-rod retina suited for investigating a single type of photoreceptor regarding its properties and signaling to second order cells. Using the aspartate-induced isolated A-wave of the skate eyecup electroretinogram (ERG), it has been shown that adaptation in rods remains Weber-Fechner-like over a 6-log unit increase in background light intensity. Zinc, which can block calcium channels, has been found in the rod synaptic terminal and the synaptic cleft. Histidine is a zinc chelator. Voltage signals from neurons post-synaptic to rods indicate that histidine increases the dark release of glutamate and increases the horizontal cell light response. In histidine, the A-wave response to various light intensities in the dark-adapted retina increased more than fifty percent, corresponding to the effect on horizontal cells. In the presence of background light, although histidine-treated rod light responses remained Weber-Fechner-like, their increment threshold was raised significantly. This indicates that endogenous zinc feedback serves to increase rod sensitivity in a light-adapted retina, despite a corresponding reduction of threshold sensitivity in the dark. We propose that the increase in A-wave amplitude is a result of the increased conductance at the synaptic terminal and that the A-wave can be used to monitor changes in rod transmitter release. Furthermore, endogenous zinc may also provide the benefit of reducing metabolic stress and the risk of glutamate toxicity in the dark.

    Visual adaptation to natural scene statistics and visual preference

    Nguyen, Leena YduyenSpehar, Branka
    9页
    查看更多>>摘要:The amplitude of Fourier spectra for natural scenes falls with spatial frequency (f) and is described by the equation, 1/f(alpha), where exponent alpha corresponds to the slope of the spectral drop-off. For natural scenes a takes on intermediate values similar to 1.25, reflecting their scale invariance. It is also well-established that, on average, images with natural scene statistics are preferred to those that deviate from these properties. Although this average pattern of preference for images with the intermediate values of alpha is robust, there are also marked individual differences in preference for different levels of alpha. This study investigated the effects of adaptation on average and individual visual preferences for synthetic filtered noise images varying in alpha. Participant preferences (N = 58) were measured via a 2AFC task prior to adaptation (baseline) and post-adaptation There were 3 adaptation conditions (alpha = 0.25, 1.25, 2.25) and 5 test levels of alpha (0.25, 0.75, 1.25, 1.75, 2.25). On average, the adaptation elevated preferences for test images with a matching the adaptor conditions, especially in adaptor conditions, alpha = 0.25 and 2.25. We also observed marked individual differences in preference for different levels of alpha. These different preference profiles remained stable throughout the experiment and affected the levels of adaptation observed in different adaptation conditions.