Dipole analysis of the influence of linear arrays of points on visually perceived eye level (VPEL).

Previous research has shown that a visual field consisting of as little as one peripherally located luminous line that is pitched from vertical in a dark field induces large changes in an observer's visually perceived eye level (VPEL). The effects of this severely reduced inducing stimulus are surprisingly close to the effects of a highly structured pitched visual field. In the present report we describe two experiments with inducing stimuli that were still further reduced to one or two linear arrays of points of light.

Short-lived effects of a visual inducer during egocentric space perception and manual behavior.

A pitched visual inducer has a strong effect on the visually perceived elevation of a target in extrapersonal space, and also on the elevation of the arm when a subject points with an unseen arm to the target's elevation. The manual effect is a systematic function of hand-to-body distance (Li and Matin Vision Research 45:533-550, 2005): When the arm is fully extended, manual responses to perceptually mislocalized luminous targets are veridical; when the arm is close to the body, gross matching errors occur. In the present experiments, we measured this hand-to-body distance effect during the presence of a pitched visual inducer and after inducer offset, using three values of hand-to-body distance (0, 40, and 70 cm) and two open-loop tasks (pointing to the perceived elevation of a target at true eye level and setting the height of the arm to match the elevation).

A tilted frame deceives the eye and the hand.

A roll-tilted visual frame induced a vertical line to appear roll-tilted in the opposite direction (rod-and-frame illusion). This visual illusion was measured by finding the physical roll-tilt of the line that appeared vertical-visually perceived vertical (VPV). In separate measurements, the roll-tilted visual frame was also found to induce an illusion in the felt orientation of the hand.

Perception time measured with the slope-transition paradigm (STP): category, set size, and task manipulations.

A perception time measure was obtained with the 'slope-transition paradigm' (STP), which is described in detail. In two experiments with the paradigm, participants viewed two sequential data frames, each presented for a wide range of durations. They made a binary response based on combined information from the two frames.

Separating perception time from response time: the slope transition paradigm.

This paper describes the slope transition paradigm (STP), a variant of rapid serial visual presentation (RSVP) that separates early (perceptual) processing time from total response time. The paradigm is based on a very simple idea: provide varying amounts of time for perceptual processing and find the moment when the subject begins to waste time waiting for more data. That moment is a measure of how much time was actually needed.