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B Julesz

Publications and source records attributed to B Julesz.

At least 55 records · Page 3Linked to original sources
PubMed1981

Textons, the elements of texture perception, and their interactions.

Research with texture pairs having identical second-order statistics has revealed that the pre-attentive texture discrimination system cannot globally process third- and higher-order statistics, and that discrimination is the result of a few local conspicuous features, called textons. It seems that only the first-order statistics of these textons have perceptual significance, and the relative phase between textons cannot be perceived without detailed scrutiny by focal attention.

Attention↗
PubMed1981

A theory of preattentive texture discrimination based on first-order statistics of textons.

The many indistinguishable texture pairs having identical second-, but different third- and higher-order statistics, led to the conjecture that globally the preattentive texture discrimination system cannot process statistical parameters of third- or higher-order. Thus in cases when iso-second-order textures yield discrimination this must be based on local conspicuous features called textons (Julesz, 1980). Here it is shown that globally even second-order statistical parameters, such as autocorrelation, cannot be processed by the textural system, and texture discrimination is solely the result of first-order statistics (density) of textons. It is also shown that the perceivable distance of statistical constraints (coherence distance) in densely packed stochastic textures is very short, four dots or less. As of now, only three texton classes were found: color, elongated blobs (line segments) of given width, orientation, and length, and the terminators (end-points) of these elongated blobs. The strength of these textons is demonstrated by several examples.

Form Perception↗
PubMed1981

Binocular stimulation reveals cortical components of the human visual evoked potential.

Dynamic random dot correlograms (RDCs) produced by a rear-projection television system elicited visual evoked potentials (VEPs) in a sample of 10 observers corrected to emmetropia. When the observers viewed the RDCs binocularly through stereo wave length filters, characteristic wave forms were recorded. Four components were reliably recorded at the onset and the offset of the correlated state of the RDCs. These components differ with statistical significance (P less than 0.05) from each other. These RDC VEPs provide a practical technique to evaluate the integrity of binocular and, by inference, cortical processes.

Adult↗
PubMed1980

Cortical binocularity in infants.

The primate visual cortex, including that of man, receives separate input from each eye and these interact in binocular cortical neurones. This organization is known to be vulnerable to disruption in early life. To understand the development of human visual cortex, and to detect and assess disorders of binocular function at the earliest possible age, a robust method is needed for detecting binocular interactions in the infant's visual system. We have done this by recording cortical visual evoked responses (VERs) to the onset and offset of binocular correlation in a large-screen dynamic random dot display. We report here that, in general, the human infant has a functional binocular visual cortex by 3 months of age, with some individuals showing cortical binocularity at an earlier age.

Age Factors↗
PubMed1980

Spatial nonlinearities in the instantaneous perception of textures with identical power spectra.

In 1962, Julesz observed that texture pairs with identical second-order statistics but different third- and higher-order statistics were usually not discriminable without scrutiny. Since second-order (dipole) statistics determine the autocorrelation functions and hence the power spectra, this observation also meant that in preattentive perception of texture the phase (position) spectra were ignored. In the last two decades many new classes of texture pairs with identical power spectra have been invented that were not effortlessly discriminable; however, recently (Caelli & Julesz 1978; Caelli et al. 1978; Julesz et al. 1978) several counterexamples were found. In these texture pairs with identical power spectra some local structures of 'quasi-collinearity', 'corner', 'closure' and 'granularity' yielded strong discrimination. These features can be regarded as the fundamental building blocks of form, that is, the essential nonlinearities of the preattentive perceptual system. Here, it will be shown that these counter-examples are not independent of each other, but can be described by two elementary units; bars (line segments) and their terminators. Furthermore, the preattentive texture perception system can count the number of terminators but ignores their positions.

Form Perception↗
PubMed1980

A disparity gradient limit for binocular fusion.

Ever since Panum, it has been commonly assumed that there is an absolute disparity limit for binocular fusion. It is now found that nearby objects modify this disparity limit. This result sheds new light on several enigmatic phenomena in stereopsis.

Form Perception↗
PubMed1980

On the depth of the cyclopean retina.

The maximum disparity which can elicit depth perception was measured in dynamic random-dot stereograms as a function of stimulus size and duration. Maximum disparity increased with size as a function of the square root of stimulus area, and depth could under optimal conditions be perceived up to several arc degrees of disparity, even for short (48 ms) durations of exposure. These data delineate the limiting disparity/depth characteristics of the cyclopean retina, and provide fresh evidence of the distinction between local and global disparity processing.

Animals↗
PubMed1980

Modifications of the classical notion of Panum's fusional area.

It is generally believed that there is an absolute disparity limit for binocular fusion; objects with disparities within this limit, known as Panum's fusional area, will appear fused and single, while objects with disparities outside the limit appear double. It is demonstrated, however, that the disparity gradient, rather than the disparity magnitude, dictates binocular fusion when several objects occur near one another in the visual field. The disparity gradient is defined as the difference between the disparities of neighboring objects divided by their angular separation. If this ratio exceeds a critical value (approximately 1) then fusion does not occur, even though the absolute disparities of the individual objects may be well within the classical Panum's area. This discovery leads to the reinterpretation of several enigmatic phenomena in stereopsis, including Panum's limiting case.

Humans↗
PubMed1980

Large evoked potentials to dynamic random-dot correlograms and stereograms permit quick determination of stereopsis.

The combination of three technological innovations permits the fast and objective determination of stereopsis in nonverbal subjects: (i) It is shown that dynamic random-dot correlograms (RDC) are as effective as dynamic random-dot stereograms (RDS) in eliciting large evoked potentials (EP), and that the generation of RDC is simpler than that of RDS. (ii) The presentation of RDC in the form of red-green anaglyphs is insensitive to subjects' head tilt, because alternation of correlation (binocular fusion) with uncorrelation (binocular rivalry) does not depend on the direction of binocular disparity, whereas perception of depth in RDS does. (iii) Projection TV techniques, using backprojected large screens viewed from near distances, permit noncooperative subjects (e.g., human infants or monkeys) to be surrounded with the stimulus, so they cannot look away.

Animals↗
PubMed1979

On the limits of Fourier decompostitions in visual texture perception.

Recent discoveries of nonlinear perceptual analyzers in effortless texture discrimination cast serious doubt on the usefulness of Fourier image decompositions to describe suprathreshold visual-texture perception. We now explain the meaning of these results.

Discrimination, Psychological↗
PubMed1979

Symmetry perception and spatial-frequency channels.

It is known that the sum of a random-dot array with vertical bilateral symmetry and one with horizontal bilateral symmetry appears as a random array. Here we show that if the vertically and horizontally symmetrical arrays are spatially filtered, so that their respective spectra are 2 octaves apart, then their superposition does not appear random, but both symmetries can be simultaneously perceived. The low-band array has a stronger perceptual weight than the high-band array. These demonstrations give further evidence that frequency channels are before symmetry perception.

Depth Perception↗
PubMed1979

Psychophysical evidence for global feature processing in visual texture discrimination.

By defining texture as a global feature attained by integration over the image domain, we show that texture discrimination can be predicted for a special class of visual textures (composed of paired dots) as a function of such global features. We derive a psychophysical law based on these global features and show that differences in the variance of orientation, but not of dipole length, result in texture discrimination.

Form Perception↗
PubMed1978

Visual discrimination of textures with identical third-order statistics.

We found a new class of two-dimensional random textures with identical third-order statistics that can be effortlessly discriminated. Discrimination is based on local "granularity" differences between these iso-trigon texture pairs. This is the more surprising since it is commonly assumed that texture granularity (grain) is determined by the power spectrum which, in turn, can be obtained from the second-order statistics. Because textures with identical third-order statistics must have identical second-order statistics (i.e., identical power spectra), visible texture granularity is not controlled by power spectra, and not even by third-order statistics.

Discrimination, Psychological↗