The Pulfrich phenomenon in a large population of young healthy subjects.

Background: To determine whether the Pulfrich phenomenon, an optical illusion occurring in many ophthalmological diseases, is perceived equally in both eyes in a large group of healthy medical students.

Subjects And Methods: A pendulum bob swinging perpendicular to the direction of observation was observed with either the right or the left eye covered with neutral density filters (50, 80 or 90 % absorption) and the apparent elliptical pendulum movement measured in depth. Interocular time delay was calculated from depth.

A bedside test to determine motion stereopsis using the Pulfrich phenomenon.

Objective: Many diseases induce asymmetric delays in the visual pathway, resulting in a spontaneous Pulfrich phenomenon (PP). The PP is a visual stereoillusion that may cause difficulties in persons when traveling in cars, crossing the road, or playing ball games. The authors developed and tested a simple new bedside procedure to detect PP.

Picrotoxin potentiates contraction while inhibiting Ca current but increasing birefringence signal in frog skeletal muscle fibers.

In single frog skeletal muscle fibers, picrotoxin (5 mM) potentiated the voltage-dependent component of contractions in response to 2-s depolarizing pulses while greatly inhibiting the simultaneously recorded tubular Ca current in a normal-Ca, Na- and CI-deficient solution, provided the contractions were generated at long time intervals (2 min). In normal Ringer's solution, picrotoxin reversibly increased the amplitude of the early large birefringence signal and the amplitude and duration of the simultaneously recorded twitch tension, suggesting that the drug may increase, directly or indirectly, the release of Ca from the SR.

Psychophysical determination of visual processing time by comparing depth seen in Pulfrich and Mach-Dvorak illusions.

A practical course for preclinical medical students was developed to illustrate aspects of binocular vision and mechanisms of primary visual transduction. It is based on a graphic analysis of two optical illusions, the Pulfrich and the Mach-Dvorak phenomena. A pendulum swinging in a plane perpendicular to the direction of observation appears to follow an elliptical path when viewed binocularly with a filter in front of one eye (Pulfrich illusion) or with alternating occlusion of the right and left eye above a critical frequency (Mach-Dvorak illusion).