Abstract

We have compared detection and spatial discrimination for motion-defined (MD) and contrast-defined (CD) form in normally-sighted subjects using a hardware stimulus generator of our own design and fabrication.¹ The device displays approximately 1000 dots on a Tektronix 608 display with 100 frames/sec. The dot display is superimposed on a uniform patch of light so that dot contrast can be controlled. A new dot pattern can be generated every frame from a very large menu of patterns. The dot pattern contains a rectangular area whose aspect ratio, orientation, size and location can be controlled on a frame-by-frame basis. The speed and direction of motion of dots inside and outside the rectangle can be controlled independently. When all dots are stationary, the rectangle is perfectly camouflaged. When the velocity of dots inside the rectangle is sufficiently different from the velocity of dots outside the rectangle, the camouflaged rectangle is clearly visible to normally-sighted subjects. In this situation, the rectangle is rendered visible by relative motion. If we switch off all dots outside the rectangle, the rectangle is rendered visible by luminance contrast.

© 1991 Optical Society of America