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Titolo:
INHOMOGENEITY AND ANISOTROPIES FOR MOTION DETECTION IN THE MONOCULAR VISUAL-FIELD OF HUMAN OBSERVERS
Autore:
VANDEGRIND WA; KOENDERINK JJ; VANDOORN AJ; MILDERS MV; VOERMAN H;
Indirizzi:
UTRECHT BIOPHYS RES INST UTRECHT NETHERLANDS UNIV UTRECHT,DEPT MED & PHYSIOL PHYS,BUYS BALLOT LAB 3584 CC UTRECHT NETHERLANDS UNIV UTRECHT,DEPT COMPARAT PHYSIOL 3584 CH UTRECHT NETHERLANDS
Titolo Testata:
Vision research
fascicolo: 8, volume: 33, anno: 1993,
pagine: 1089 - 1107
SICI:
0042-6989(1993)33:8<1089:IAAFMD>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
CORTICAL MAGNIFICATION FACTOR; SPATIAL WHITE NOISE; RANDOM-DOT PATTERNS; OLD-WORLD MONKEYS; DIRECTIONAL ANISOTROPY; INDIVIDUAL VARIABILITY; COHERENT MOTION; PRIMATE RETINA; PERCEPTION; DISPLACEMENT;
Keywords:
MOTION DETECTION; MOTION ANISOTROPIES; INHOMOGENEITIES OF THE VISUAL FIELD; MOTION PERIMETRY;
Tipo documento:
Article
Natura:
Periodico
Citazioni:
48
Recensione:
Indirizzi per estratti:
Citazione:
W.A. Vandegrind et al., "INHOMOGENEITY AND ANISOTROPIES FOR MOTION DETECTION IN THE MONOCULAR VISUAL-FIELD OF HUMAN OBSERVERS", Vision research, 33(8), 1993, pp. 1089-1107

Abstract

Signal-to-noise-ratio (SNR) thresholds were measured for the detection of coherent motion in moving random pixel arrays of constant root-mean-square contrast (35%) and constant average luminance (48 cd/m2) for8 or 16 directions of motion at 25 positions in the visual field of the right eye. Five observers took part in this perimetric study of motion detection. The 24 eccentric positions were chosen on 8 equally spaced radial lines at the eccentricities 6, 24, and 48, the 25th position was centred on the fovea. At these positions we analysed the threshold SNR-value as a function of motion direction alpha. A significant modulation of the threshold with alpha is called an anisotropy. Anisotropies were found for low to medium velocities at positions on and near the vertical meridian, where the thresholds proved to be highest for vertical motion directions (up or down). On the horizontal meridian no significant anisotropies were found. Also on the oblique radials anisotropies were found, especially at 225-degrees (lower nasal quadrant ofthe visual field, upper temporal quadrant of the retina), but these were milder than those on the vertical meridian. The diameter of the stimulus is an important parameter and its influence was explored, albeit incompletely. Also inhomogeneities were found. This is defined as a consistent modulation of the threshold SNR-value with position A, the position along an equi-eccentricity circle (A-inhomogeneity), or with eccentricity E (E-inhomogeneity) or both. A simple acuity-scaling optimized for the nasal retina takes care of most of the E-inhomogeneity, but an A-inhomogeneity stays rather prominent. It too is characterizedby higher thresholds near the vertical meridian than near the horizontal meridian. The findings suggest that iso-threshold curves are elliptical or egg-shaped with their long axis on the horizontal meridian and shifted somewhat out of naso-temporal symmetry towards the nasal half of the retinal field. As with the anisotropies the inhomogeneity grows in amplitude for decreasing velocity below medium velocity values of 1-2 pixels/frame, but in contradistinction to the anisotropies it ispresent and even increases in amplitude for increasing velocities above these medium values of 1-2 pixels/frame as well. The results are discussed in the light of other perimetric studies of motion detection and acuity, in the light of a model postulating the cooperation of groups of velocity-tuned bilocal motion detectors, and in the light of recent ideas on structure and function of primate cortical areas and processing streams.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 28/10/20 alle ore 18:54:54