On-line control of moving masks and windows on a complex background using the ATVista videographics adapter

In reading research, the moving mask and moving window paradigms have proved to be invaluable in determining the chronometric and spatial characteristics of processing written text. The success of these methods has lead to a demand for their application in research on real-world scene perception. However, we will argue that the technical implementation of eye-contingent mask (window) movement across a stable text cannot be applied to scene research. A new technique is proposed that allows graphical masks or windows of arbitrary form, size, and content to be moved quickly over a complex graphical stimulus. Thismoving overlay technique makes use of the ATVista graphics adapter, a board with the ability to mix an internally stored and an externally generated image into one composite image. A high-performance moving mask or window is created by programming the internal image to be movable and partly transparent. The technique is implemented on a standard personal computer interfaced with an eyetracker, thus bringing mask (window) movement under online eye-movement control. We discuss general principles of the technique and illustrate them with performance data from a concrete experimental setup.