Integration regions for visual hyperacuity

doi:10.1016/0042-6989(77)90206-1

Vision Research

Volume 17, Issue 1, 1977, Pages 89-93

https://doi.org/10.1016/0042-6989(77)90206-1 Get rights and content

Abstract

The robustness of vernier acuity to retinal image motion is not due to target feature detection while the pattern is swept past one or more “templates” that match the target offset. Stimuli which by themselves are subthreshold. devoid of contours or even of contrary information content, can be pooled and used for a visual hyperacuity response, i.e. differential spatial localization precise to a few seconds of arc in the human fovea. These integration processes take place in regions extending over several min arc in the direction along which differential localization takes place, and not only, as suggested by Hering, along the length of vernier lines.

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U¨ber die Grenzen der Sehscha¨rfe
Ber. math.-phys. Cl. d. Ko¨nigl. Sa¨chs. Gesell. Wiss. Leipzig, Naturwiss. Teil
(1899)
WestheimerG. et al.
Temporal and spatial interference with vernier acuity
Vision Res.
(1975)

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The angular subtense of each pixel was 1 arcmin at the test distance. Horizontal offsets of the monocular Gabor targets of less than a single pixel width were accomplished by sub-pixel resolution (Westheimer & McKee, 1977). The binocular target comprised two 4.2 × 3.2 deg rectangular random dot stereograms (RDS) presented with a depth edge corresponding to 10 arcmin of horizontal relative disparity.
When monocular Vernier targets are presented with binocular disparate elements, an increase in vertical separation elevates alignment thresholds and also shifts its perceived visual direction towards the visual direction of the binocular disparate surround. This observation has been termed binocular capture. There is increasing evidence that this shift in the visual direction of the monocular target may be related to the type of position encoding mechanism involved in processing the relative position signal. This study investigated the interaction between capture magnitude and vertical separation for stimulus conditions that favored the recruitment of linear or non-linear position encoding mechanisms. Relative alignment thresholds and bias were measured for a pair of vertically separated (8′, 30′, 60′, 120′) monocular Gabor gratings (1, 2, 4 and 8 cpd). Grating stimuli were constructed to constrain relative alignment judgments to the carrier grating (CO) or to the envelope (EO). Relative alignment thresholds and bias were also measured for a pair of vertically separated monocular Gabor gratings comprising a 1 cpd vertical square wave grating (SQ) or a 1 cpd missing fundamental grating (MF). Capture magnitudes were significantly larger across vertical separation and varied proportionally with relative alignment threshold for the EO and MF conditions. This was not evident with the CO and SQ conditions. The stark difference in capture magnitudes between the stimuli conditions suggest that the increase in capture magnitude observed with increasing vertical separation is intimately related to the transition from a “capture-immune” first-order spatial filter mechanism to a “capture-vulnerable” non-linear/feature-based position encoding mechanism.
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What will be examined instead is whether help may be derived from some of the theoretical concepts that were found useful in geometrical superresolution techniques enabling enhanced retrieval of information contained in an optical image that has been passed through a receptor layer with defined geometrical limitations, for example operations such as filtering, masking, or superimposed movement. The result of a single experiment, which addresses the role of factors in the realms of time, space and motion, helps to highlight the operation of the apparatus by which the location of a feature element is identified by the human visual system (Westheimer and McKee, 1977). A pair of vernier lines, detectably offset in one direction, is briefly exposed for 5 ms sequentially in four spatially displaced locations.
Classically, diffraction theory sets a boundary for the resolving capacity of optical instruments. Yet some visual thresholds have values much better than the traditional resolution limit. Recent developments in superresolution, an area of optical physics and engineering with claims of transcending the stated resolution limits of optical instruments, are reviewed and their possible relevance to visual spatial processing and to the exploration of the eye's structure are assessed. In optical or diffractive superresolution the transmitted spatial-frequency band is not so much extended as either multiplexed with or displaced into regions that are usually beyond reach, with no overall gain in information transfer because prior knowledge is used to make inferences of possible object structure from the image. The Uncertainty Principle for photon position and momentum is never disobeyed. The study of the neural substrate of visual hyperacuity does, however, overlap that of “geometrical superresolution,” in which techniques are used for transcending limits imposed by the receptor lattice in analyzing fine image structure.
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The influence of binocular disparate targets on the perceived visual direction of adjacent monocular targets has been termed “binocular capture”. The magnitude of capture increases significantly with increasing vertical separation between monocular targets. This study sets out to elucidate the interaction between spatial frequency content, contrast polarity and vertical separation between monocular targets to establish the roles of the monocular target’s positional uncertainty and the underlying position-encoding mechanism in the production of binocular capture. Relative alignment thresholds and bias were measured separately for a pair of vertically separated monocular Vernier spatial frequency ribbons and a pair of monocular Gaussian bars presented across a random dot stereogram. Ribbon pairs comprised carrier frequencies that were either matched (8 cpd or 1 cpd) or mismatched (top ribbon 1 cpd, bottom ribbon 8 cpd, and vice versa). The Gaussian bars were presented with either matched contrast (bright/bright) or opposite polarity (bright/dark) contrast. Capture magnitudes increased significantly with vertical separation for all ribbon conditions and for both contrast polarity conditions. In these conditions, capture magnitude co-varied with relative alignment threshold. The matched 1 cpd ribbons showed a significant effect of separation and relative alignment threshold on capture magnitude for low contrast stimuli but not for high contrast stimuli. The results are consistent with the hypothesis that perceived visual direction of a monocular target becomes increasingly dependent on the surround visual direction when its relative position signals are poor. Furthermore, its vulnerability to capture by the surround visual direction seems to be dependent on the underlying position encoding mechanism employed to compute relative position information of the monocular target.
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2009, Journal of Experimental Psychology: Human Perception and Performance

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: This work was supported by the National Eye Institute, U.S. Public Health Service, under Grant EY-00220, and carried out during GW's tenure as an Adolph C. and Mary Sprague Miller Research Professor.

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Integration regions for visual hyperacuity

Abstract

U¨ber die Grenzen der Sehscha¨rfe

Ber. math.-phys. Cl. d. Ko¨nigl. Sa¨chs. Gesell. Wiss. Leipzig, Naturwiss. Teil

Temporal and spatial interference with vernier acuity

Vision Res.