On the tunnel effect

The experiments described in this paper consist of presenting observers with two similar objects in successive movement in the same plane but of which the end of the first and the beginning of the second are hidden by a screen (tunnel). Under proper experimental conditions the impression received is one of continuous and uniform movement by a single object passing behind the screen.

The hidden phase of this movement assumes all of the characteristics of true, visible movement for its entire extent, and any lengthening of the duration of the invisible phase gives the impression of a momentary halt behind the screen at a definite point. A modification of the position or of the relative orientation of the visible portions of the trajectory influences the apparent form of its invisible portion. This form can be made to assume the aspects of complicated curves which are sketched and described by different observers with remarkable consistency.

All these phenomena are dependent upon the objctive conditions: the speed of the objects while they are visible, the length of the tunnel, the duration of the invisible phase, the relative position of the visible portions of the trajectory; and they vary systematically with these conditions. As one or other of these conditions is varied, the impression of continuity may give way to one of a simple succession of independent movements.

It is thought that the absence of sensory qualities justifies the use of the term “amodal data” to describe the way in which the hidden movement phase makes itself known to the observer. These “amodal data” form the bridge between the modal phases and become an integral part of the total sensory experience. These properties are determined by the nature of the complex system of excitations in the same way as those of the modal phases and one can thus consider this amodal aspect of the combined experience as a truly perceptual phenomenon.