Pulfrich Pendulum Experiment Essay

The Pulfrich Pendulum; an Experimental Investigation
Abstract This is an investigation into the Pulfrich Pendulum effect and the time that the dim eye lags behind the bright eye. Overall brightness was also investigated to find out whether this had any effect on this phenomenon and whether the time lag changed. A time lag was calculated for participants and recorded, the experiment was then repeated looking at overall brightness and a time lag recorded. The experiment confirmed that a time lag of 7.96ms & 9.04ms occurred during the Pulfrich effect and that overall brightness increased time lag by approx 1ms in comparison to darkness. Introduction The Pulfrich effect is a psycho-optical phenomenon wherein lateral motion of an object in the field of view is interpreted by the brain as having a depth component, due to differences in processing speed between images from the two eyes. The effect is generally induced by placing a dark filter over one eye. The phenomenon is named after a German physicist Carl Pulfrich who first described it in 1922. Two key factors which give rise to this phenomenon is that the brain derives an impression of an object’s distance by comparing the views seen by the two eyes, and the second important factor is that the photoreceptors in the eyes respond more sluggishly when the scene is less bright. Photoreceptors in the retina are the first proper stage of neural processing. There are two types of photoreceptor – rods and cones – which have rather different roles. Rods are very sensitive and function best under scotopic conditions; they are well adapted for night vision. Cones are less sensitive and function best under photopic conditions. In effect they form a separate retinal system for operating in daylight. Rods outnumber cones by 20:1 and are 1000 times more sensitive to light. All photoreceptors do essentially the same thing, they