Instrumentation designed to simulate the effects of prisms used in studies of visual rearrangement

Abstract

A system is described which simulates some of the visual rearrangements and changes in sensorimotor relations that occur when experimental subjects move their eyes while looking through a contact lens with a prism attached. The simulated system is more convenient than a system based on the use of a contact lens. and it is based on measures of eye movement that are important in research on the perceptual effects of visual rearrangement. The effects that occur are reviewed in this paper. We also show in detail how the artificial system, which has an eye-movement monitor interfaced with a computer and display. simulates the former effects. The data show that experimental subjects who experience visual rearrangement by simulated means manifest the same kind of perceptual adaptation produced in studies in which visual rearrangement is generated by means of a prism mounted on a contact lens. The system. which simulates the effects produced by prisms. consists of an eye monitor. a PDP-9 computer. and a cathode ray tube (CRT). In order to describe system operation. it is necessary to review the effects produced by prisms as well as the experimental uses of prisms reported in the literature. USE OF PRISMS IN PAST RESEARCH IN PERCEPTION Optic devices like prisms have been employed typically when an investigator wants to study perceptual adaptation to visual rearrangement. and thus wants to displace the apparent location of objects relative to an observer or to alter the shape of contours by making. for example. straight lines look curved or curved lines look straight. For a recent review of much of the literature. see Gyr (1972). Visual rearrangements such as the latter-when produced by a contact lens with a prism mounted on it-lead to unusual visual effects when subjects start to scan the rearranged contours by moving their eyes. For example. suppose subjects scan an apparently straight but physically curved contour in the usual way. i.e .. bv means of a straight movement of the eye parallel to the contour; they expect to see a line which retains its orientation and is easily kept in focus. What the subjects see instead is a line that changes orientation as~function of their eve movements. and which therefore cannot be ti~ated by a straight eye movement. In fact. fixation can be maintained only by moving the eye in a parth similar to the true. curved. rather than the apparent. straight. shape of the object. Some perceptual adaptation theorists would say that subjects subjected to such experimental Requests for reprints should be sent to

Changes in the perception of spatial location: A test of potentiation vs. recalibration theory

“…However, as noted previously, this latter contention seems at odds with a previous experiment by , the authors (Gourlay, Gyr, Walters, & Willey, 1975). It has also been challenged recently by Craske and Crawshaw (1975) and by Wallach and Halperin (1977).…”

“…A previous experiment by the authors (Gourlay, Gyr, Walters, & Willey, 1975) had shown adaptation to curvature using a similar CRT-simulation methodology and under conditions in which it is unlikely that potentiation could have played a part. Two possibilities for the failure were considered.…”

Impact of oculomotor retraining on the visual perception of curvature.

“…Gourlay, Gyr, Walters, and Willey (1975) report a method for accomplishing this which is somewhat similar to the method we employ.…”

“…Instead of using an optical device, it is preferable to produce the desired rearrangement of the visual world by a computercontrolled visual display, the position of which is continuously contingent upon the eye position of the observer. Gourlay, Gyr, Walters, and Willey (1975) report a method for accomplishing this which is somewhat similar to the method we employ.…”

Motor-sensory feedback and geometry of visual space: an attempted replication

“…H & R accordingly reasoned that shape adaptation, like adaptation to displacement, ought to be inducible by having S experience spatial rearrangement associated with voluntary movement, but that this need not involve direct exposure to actually-rearranged curved or straight lines. It is on this point that the H & R study diverged from the rest of the literature on visual shape adaptation (e.g., Festinger, Burnham, Ono, & Bamber, 1967;Gourlay, Gyr, Walters, & Willey, 1975;Gyr & Willey, 1970;Sirigatti, 1974;Slotnick, 1969;and Victor, 1968). By not training S with actual curved contours, H & R did not need to control for other variables that have plagued the interpretation of many other studies, such as the so-called Gibson effect (Gibson, 1933), which concerns the induction of shifts in the perception of straightness after brief fixation of a curved line.…”