Wyniki wyszukiwania - Biblioteka Nauki

1

The effects of spatial and temporal cueing on metacontrast masking

100%

Bruchmann M. , Hintze P. , Mota S.

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tom 7

132-141

EN

We studied the effects of selective attention on metacontrast masking with 3 different cueing experiments. Experiments 1 and 2 compared central symbolic and peripheral spatial cues. For symbolic cues, we observed small attentional costs, that is, reduced visibility when the target appeared at an unexpected location, and attentional costs as well as benefits for peripheral cues. All these effects occurred exclusively at the late, ascending branch of theU-shaped metacontrast masking function, although the possibility exists that cueing effects at the early branch were obscured by a ceiling effect due to almost perfect visibility at short stimulus onset asynchronies (SOAs). In Experiment 3, we presented temporal cues that indicated when the target was likely to appear, not where. Here, we also observed cueing effects in the form of higher visibility when the target appeared at the expected point in time compared to when it appeared too early. However, these effects were not restricted to the late branch of the masking function, but enhanced visibility over the complete range of the masking function. Given these results we discuss a common effect for different types of spatial selective attention on metacontrast masking involving neural subsystems that are different from those involved in temporal attention.

2

A theory of moving form perception: Synergy between masking, perceptual grouping, and motion computation in retinotopic and non-retinotopic representations

88%

Öğmen H.

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tom 3

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nr 1-2

67-84

EN

Because object and self-motion are ubiquitous in natural viewing conditions, understanding how the human visual system achieves a relatively clear perception for moving objects is a fundamental problem in visual perception. Several studies have shown that the visible persistence of a briefly presented stationary stimulus is approximately 120 ms under normal viewing conditions. Based on this duration of visible persistence, we would expect moving objects to appear highly blurred. However, in human vision, objects in motion typically appear relatively sharp and clear. We suggest that clarity of form in dynamic viewing is achieved by a synergy between masking, perceptual grouping, and motion computation across retinotopic and non-retinotopic representations. We also argue that dissociations observed in masking are essential to create and maintain this synergy.

3

A Curvature-Tensor-Based Perceptual Quality Metric for 3D Triangular Meshes

75%

Torkhani F. , Wang K. , Chassery J. M.

Machine Graphics and Vision

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2014

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tom Vol. 23, No. 1/2

59--82

EN

Perceptual quality assessment of 3D triangular meshes is crucial for a variety of applications. In this paper, we present a new objective metric for assessing the visual difference between a reference triangular mesh and its distorted version produced by lossy operations, such as noise addition, simplification, compression and watermarking. The proposed metric is based on the measurement of the distance between curvature tensors of the two meshes under comparison. Our algorithm uses not only tensor eigenvalues (i.e., curvature amplitudes) but also tensor eigenvectors (i.e., principal curvature directions) to derive a perceptually-oriented tensor distance. The proposed metric also accounts for the visual masking effect of the human visual system, through a roughness-based weighting of the local tensor distance. A final score that reflects the visual difference between two meshes is obtained via a Minkowski pooling of the weighted local tensor distances over the mesh surface. We validate the performance of our algorithm on four subjectively-rated visual mesh quality databases, and compare the proposed method with state-of-the-art objective metrics. Experimental results show that our approach achieves high correlation between objective scores and subjective assessments.

4

Spatio-temporal low-level neural networks account for visual masking

75%

Polat U. , Sterkin A. , Yehezkel O.

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tom 3

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nr 1-2

153-165

EN

Temporal masking is a paradigm that is widely used to study visual information processing. When a mask is presented, typically within less than 100 msec before or after the target, the response to the target is reduced. The results of our psychophysical and visual evoked potential (VEP) experiments show that the masking effect critically depends on a combination of several factors: (1) the processing time of the target, (2) the order of presentation of the target and the mask, and (3) the spatial arrangement of the target and the mask. Thus, the masking effect depends on the spatial-temporal combination of these factors. Suppression was observed when the mask was positioned within a spatial range that was found to evoke inhibition, and when the temporal separation between the target and the mask was short. In contrast, lateral facilitation was observed when the mask was presented at a spatial separation that did not evoke inhibition from the target's vicinity and with a temporal sequence that preceded the target, or when it was presented simultaneously with it, but not when the target preceded the mask. We propose that masking effects, either suppression or facilitation, reflect integration into the spatial and the temporal domains of the feedforward response to the target and the lateral inputs evoked by the mask (excitatory and/or inhibitory). Because the excitation evoked by the mask develops and propagates slowly from the mask's location to the target's location, it lags behind the response to the target. On the other hand, inhibition that is produced in the vicinity of the target evolves more rapidly and follows the onset and offset of the stimulus more closely. Thus, lateral excitation that overcomes the inhibition may facilitate the grouping of local elements into a global percept by increasing the survivability of the object and its accessibility for perceptual awareness.