Perceptual sensitivity maps within globally defined visual shapes.

I Kovács; B Julesz

doi:10.1038/370644a0

Home/Archive/PubMed

PubMed · 8065449

Perceptual sensitivity maps within globally defined visual shapes.

I Kovács·B Julesz

View original source ↗Export metadata ↓

Abstract

An unsolved problem of biology is the processing of global shape in natural vision. The known processes of early vision are spatially restricted (or local) operations, and little is known about their interactions in organizing the visual image into functionally coherent (or global) objects. Here we introduce a human psychophysical method which allows us to measure the effect of perceptual organization on the activity pattern of local visual detectors. We map differential contrast sensitivity for a target across regions enclosed by a boundary. We show that local contrast sensitivity is enhanced within the boundary even for large distances between the boundary and the target. Furthermore, the locations of maximal sensitivity enhancement in the sensitivity maps are determined by global shape properties. Our data support a class of models which describe shapes by the means of a medial axis transformation, implying that the visual system extracts 'skeletons' as an intermediate-level representation of objects. The skeletal representation offers a structurally simplified shape description which can be used for higher-level operations and for coding into memory.

Explore related subjects

Contrast Sensitivity Humans Psychophysics Visual Cortex Visual Perception Journal Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

I Kovács, B Julesz. 1994-08-25. Perceptual sensitivity maps within globally defined visual shapes.. https://doi.org/10.1038/370644a0

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2001

Detection of simple radially symmetric targets: further evidence for the matched filter processing scheme in human pattern detection.

The detection of small radially symmetric targets was studied using a subthreshold summation paradigm. Small disc and disc-like patterns with diameters up to 0.60 were used for superposition on Bessel functions of zero order, subthreshold contrast and various spatial frequencies. Contrast interrelation functions prove linear over the whole range of contrasts used for the Bessel functions while their slopes show systematic variation with spatial frequency. An extrapolation of sensitivity from the slopes reveals that sensitivity can be predicted by a simple model assuming detection to be mediated by a transfer function made up as a cascade of an even bandpass function and the disc pattern spectrum, as has been found previously using one dimensional luminance distributions. Problems concerning the formation of pattern-specific radial symmetric filters are discussed.

Contrast Sensitivity↗

PubMed2001

Interocular interactions reveal the opponent structure of motion mechanisms.

Interactions between motion sensors tuned to the same and to opposite directions were probed by means of measuring summation indexes for sensitivities (d') to contrast increments and/or decrements applied to drifting gratings presented in binocular and in dichoptic vision. The data confirm a phenomenon described by Stromeyer, Kronauer, Madsen & Klein (1984, J. Opt. Soc. Am. A 1, 876-884), whereby opposite polarity contrast changes applied to binocular gratings drifting in opposite directions yield sensitivities significantly higher than same sign changes for which performance complies with probability summation (PS). The effect disappears in dichoptic vision where opposite sign contrast changes yield a performance close to, or below PS, whether they are applied to same or to opposite direction stimuli. Same sign changes in dichoptic drifting stimuli yield a performance higher than PS independently of their relative directions and close to the performances obtained when these same sign changes are applied to dichoptic, static +/- 45 degrees gratings. Opposite sign changes applied to such static gratings yield PS. The data support the view according to which: (i) motion direction is extracted at the monocular site; (ii) motion sensors exhibit mutual inhibition within each eye when tuned to opposite directions; and (iii) binocular summation when tuned to the same direction. The data also suggest that (iv) independently of their directional tuning, all motion sensors converge on a binocular, motion non-specific ('flicker') unit; and that (v) signals carried by ON and OFF pathways are slightly inhibitory to each other.

Contrast Sensitivity↗

PubMed2001

Identification of facial images in peripheral vision.

Contrast sensitivity for face identification was measured as a function of image size to find out whether foveal and peripheral performance would become equivalent by magnification. Size scaling was not sufficient for this task, but when the data was scaled both in size and contrast dimensions, there was no significant eccentricity-dependent variation in the data, i.e. for equivalent performance both the size and contrast needed to increase in the periphery. By utilising spatial noise added to the images we found that in periphery information was utilised less efficiently and peripheral inferiority arose completely from lower efficiency, not from increased internal noise.

Contrast Sensitivity↗