Spatial location and hyperacuity: flank position within the centre and surround zones

Abstract

Sensitivity to a horizontal displacement of a vertical line was measured in order to ascertain the influence of the location of parallel flanking lines on the apparent position of features in visual space. The first experiment confirmed that the introduction of the flank added a component to the apparent shift which was towards the flank for small separations (less than 3-4') and away from the flank with larger separations. The second experiment investigated the notion that apparent location is derived by collecting information only from zones adjacent to the target and limited in the vertical extent by the target's height i.e. information orthogonal to the target's main axis. This was done by placing a vertical flank at a horizontal distance from the target that would be clearly within one zone or the other and measuring the effect of a vertical separation between the two flank halves. In the surround zone the amount of repulsion obtained was not influenced by vertical separation of the flank halves, even when they were several minutes higher (or lower) than the target line. In the central zone attraction was only obtained when the vertical separation was small enough to provide some overlap of the lines in the horizontal direction. With larger separations substantial repulsion was obtained. We conclude that while the central 'attraction' zone may only use information distributed in the direction of the line's displacement, it does so only within a 3-4' range on either side of the target line. The surround zone is not similarly limited in the region over which it collects information to influence the apparent location of features.

Cortical dynamics of three-dimensional form, color, and brightness perception: I. Monocular theory

“…Such hyperacuity is, of course, well known to exist (Bad-cock & Westheimer, 1985a& Westheimer, , 1985bBeck & Schwartz, 1979;Ludvigh, 1953;Watt & Campbell, 1985;Westheimer, 1981;Westheimer & McKee, 1977). In Section 30, I show that the type of hyperacuity that we have modeled to compensate for positional uncertainty at line ends and comers has also predicted properties of recent data about hyperacuity that possess no other explanation at the present time.…”

The warped geometry of visual space near a line assessed using a hyperacuity displacement task

“…The threshold for the most experienced observer (HR) is at the lower range of the values reported by Badcock & Westheimer (1985a). The other observer (DJ) has a threshold which is higher than those of experienced observers.…”

“…To map out the size and shape of the inhibitory zone (only) discussed by Badcock & Westheimer (1985a), a single flanking line is used (see Figure 6). Badcock & Westheimer found that reversing the contrast of the flanking line did not change the induced shift in the inhibitory zone.…”

The influence of contrast and spatial factors in the perceived shape of boundaries

“…Similar effects were registered by Hock and Eastman (1995) with inducing and test lines in close succession. Within this short range, Badcock and Westheimer (1985a) registered repulsion effects between a test line and an induction pattern made up of two collinear segments separated for a length equal to the test line extension. 1 With separations greater than 3-4 arcmin, only repulsion was observed, independently of the test and inducing lines contrast polarity.…”

“…One possible explanation follows from previous psychophysical research documenting the misperception of distances separating segments or edges (Badcock & Westheimer, 1985a, 1985bGreene & Brown, 1995;Rentschler, Hilz, & Grimm, 1975). Both attraction and repulsion effects have been described-that is, a test line appeared that was located, with respect to the flank line, at a distance shorter than the true value and farther away, respectively.…”