Implementation of a Portable Pattern Stimulator and VEP/ERG Recording System Based on an Apple Microcomputer

A portable VEP/ERG recording system was developed by utilizing and adapting a commercially available microcomputer. The system was developed to facilitate the testing of patient and subject populations in whom laboratory recordings prove to be difficult and inconvenient. The system was designed to be compact, self-supporting and easily transportable for use at the bedside of clinical wards, in schools, nursing institutions and the like. Two important considerations were also cost-effectiveness and stimulus and recording versatility. The hardware components include a standard television monitor, a stimulus generator, an Apple II microcomputer and I/O peripherals. During the recording procedure the microcomputer simultaneously executes several tasks; sampling and averaging of up to 14 channels, on-line graphic display of averaged responses and pattern stimulation control. The system stimulus generator, though simple in its design, allows luminance flashes or simultaneous presentation of up to four independent, stable and flicker free checkerboard and bar patterns of different sizes and temporal frequencies. The stimulus patterns can be presented in a reversal or appearance/disappearance mode with adjustable timing and modulation depth. The hardware components and software implementation are described.