A low-cost computer-controlled function generator suitable for generating visual grating displays

Abstract

This paper reports a simple low-cost computer peripheral for generation of gratings. Its advantages are minimal CPU operations, reliability, and variety of programmable output functions. The luminance gratings used in the study of human spatial and temporal vision can be generated in several ways. These include optical techniques (Antis & Comerford, 1975) and electronic waveform generators for the Y-axis and Z-axis (e.g., Fischer, 1976; Hughes & Snow, 1973; Shapley & Rossetto, 1976; Stamps & Bourne, 1972), coupled to a TV raster or cathode-ray oscilloscope (CRO) with a time base for the X-axis. Either analog (Rogers, 1976) or digital (Brown, 1977) techniques can be used to provide moving gratings. All the latter methods are related to the original technique described by Campbell and Green (1965). In addition, a microprocessor could be used as a scheduling device for switching peripheral generators (Keemink, van der Wildt, & Van Deursen, 1979). An alternative is to calculate the appropriate waveform for the Z-modulation profiles. Further, stimulus parameters can be preprogrammed. A microcomputerbased system reported by Fritsch and Keck (1978) uses the sequential digital-to-analog (0/A) output of a pre