Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

The mainstream approach to image quality assessment has centered around accurately modeling the single most relevant strategy employed by the human visual system (HVS) when judging image quality (e.g., detecting visible differences, and extracting image structure/information). In this work, we suggest that a single strategy may not be sufficient; rather, we advocate that the HVS uses multiple strategies to determine image quality. For images containing near-threshold distortions, the image is most apparent, and thus the HVS attempts to look past the image and look for the distortions (a detection-based strategy). For images containing clearly visible distortions, the distortions are most apparent, and thus the HVS attempts to look past the distortion and look for the image's subject matter (an appearance-based strategy). Here, we present a quality assessment method [most apparent distortion (MAD)], which attempts to explicitly model these two separate strategies. Local luminance and contrast masking are used to estimate detection-based perceived distortion in high-quality images, whereas changes in the local statistics of spatial-frequency components are used to estimate appearance-based perceived distortion in low-quality images. We show that a combination of these two measures can perform well in predicting subjective ratings of image quality.

http://vision.okstate.edu/pubs/MAD_JEI.pdf

Most apparent distortion: full-reference image quality assessment and the role of strategy

The Ventriloquist Effect Results from Near-Optimal Bimodal Integration

Horizontal connections, formed primarily by the axon collaterals of pyramidal neurons in layer 2/3 of visual cortex, extend for millimeters parallel to the cortical surface and form patchy terminations. Previous studies have provided evidence that the patches formed by horizontal connections exhibit modular specificity, preferentially linking columns of neurons with similar response characteristics, such as preferred orientation. The issue of how these connections are distributed with respect to the topographic map of visual space, however, has not been resolved. Here we combine optical imaging of intrinsic signals with small extracellular injections of biocytin to assess quantitatively the specificity of horizontal connections with respect to both the map of orientation preference and the map of visual space in tree shrew V1. Our results indicate that horizontal connections outside a radius of 500 microm from the injection site exhibit not only modular specificity, but also specificity for axis of projection. Labeled axons extend for longer distances, and give off more terminal boutons, along an axis in the map of visual space that corresponds to the preferred orientation of the injection site. Inside of 500 microm, the pattern of connections is much less specific, with boutons found along every axis, contacting sites with a wide range of preferred orientations. The system of long-range horizontal connections can be summarized as preferentially linking neurons with co-oriented, co-axially aligned receptive fields. These observations suggest specific ways that horizontal circuits contribute to the response properties of layer 2/3 neurons and to mechanisms of visual perception.

Orientation Selectivity and the Arrangement of Horizontal Connections in Tree Shrew Striate Cortex

This paper presents an efficient metric for quantifying the visual fidelity of natural images based on near-threshold and suprathreshold properties of human vision. The proposed metric, the visual signal-to-noise ratio (VSNR), operates via a two-stage approach. In the first stage, contrast thresholds for detection of distortions in the presence of natural images are computed via wavelet-based models of visual masking and visual summation in order to determine whether the distortions in the distorted image are visible. If the distortions are below the threshold of detection, the distorted image is deemed to be of perfect visual fidelity (VSNR = infin)and no further analysis is required. If the distortions are suprathreshold, a second stage is applied which operates based on the low-level visual property of perceived contrast, and the mid-level visual property of global precedence. These two properties are modeled as Euclidean distances in distortion-contrast space of a multiscale wavelet decomposition, and VSNR is computed based on a simple linear sum of these distances. The proposed VSNR metric is generally competitive with current metrics of visual fidelity; it is efficient both in terms of its low computational complexity and in terms of its low memory requirements; and it operates based on physical luminances and visual angle (rather than on digital pixel values and pixel-based dimensions) to accommodate different viewing conditions.

VSNR: A Wavelet-Based Visual Signal-to-Noise Ratio for Natural Images

Contour integration by the human visual system: evidence for a local "association field".

Our understanding of visual processing in general, and contour integration in particular, has undergone great change over the last 10 years. There is now an accumulation of psychophysical and neurophysiological evidence that the outputs of cells with conjoint orientation preference and spatial position are integrated in the process of explication of rudimentary contours. Recent neuroanatomical and neurophysiological results suggest that this process takes place at the cortical level V1. The code for contour integration may be a temporal one in that it may only manifest itself in the latter part of the spike train as a result of feedback and lateral interactions. Here we review some of the properties of contour integration from a psychophysical perspective and we speculate on their underlying neurophysiological substrate.

Contour integration and cortical processing.

Coherent global motion in the absence of coherent velocity signals

We describe two experiments that investigate the roles of polarity and symmetry in the perceptual grouping of contour fragments. Observers viewed, for one second on each presentation, arrays of oriented, spatial-frequency band-pass, elements, in which a subset of the elements was aligned along a twisting curve. In each of five conditions we measured observers' ability to detect aligned combinations of even- and odd-symmetric elements, of the same and different polarities, against a background of 'noise' elements. As with previous experiments we found that the 'path' could be reliably detected, even when the elements of the path were oriented at angles of up to +/- 60 deg relative to each other. Detection of the path was still possible when the polarity of path elements alternated. However, the probability of detection of the path was raised significantly when the path elements were all of the same polarity. Perceptual grouping of even-symmetric elements was no different to perceptual grouping of odd-symmetric elements. The results provide evidence, that in achieving integration of contour fragments, the visual system uses a process that is to some degree phase selective. We use the results to describe how the visual system may resolve natural contours when they occur against backgrounds that vary over a wide range of intensities. The data presented here have been published in conference-abstract form (Hayes et al., 1993; Field et al., 1997).

/pdf/the-roles-of-polarity-and-symmetry-in-the-perceptual-nrszgzbrbc.pdf

Anthony Hayes

Papers

Contour integration by the human visual system: evidence for a local "association field".

Contour integration and cortical processing.

Coherent global motion in the absence of coherent velocity signals

The roles of polarity and symmetry in the perceptual grouping of contour fragments.

The coding of spatial position by the human visual system: Effects of spatial scale and retinal eccentricity