Microcomputer display timing: Problems and solutions

The 525-line composite video display standard is described and discussed from the viewpoint of its usefulness in psychology experiments. While a frame is displayed every 33.3 msec, it consists of two interlaced 262.5-line subframes displayed in 16.7 msec each. Thus, a display consisting of 16 or fewer video lines may be presented in 1 msec or less. The hardware of some microcomputers may be modified to make the video vertical synchronization timing signal available to latency timing software. This modification permits response signal and latency timing with 1-msec or better precision. A modification that permits display blanking under software control is also noted, and a detailed description of both modifications is given for the popular APPLE II microcomputer. Other problems discussed include moving display materials into display buffer areas in time for single-scan precision timing, software speed problems, and the tradeoffs between video and light-emitting diode displays.