RESUMO
Methods for automated stimulus display and accurate response time measurement with IBM-compatible PCs are of great importance in cognitive research designs. Accurate measurements of reaction times are required to interpolate other measures, such as speed of mental processing. We present a description of hardware and software that displays stimulus images and performs reaction timing that is not dependent on PC performance characteristics. This is accomplished by electronically bypassing timing errors normally inherent to the operation of the computer. A high-precision external timer measures the time between stimulus onset and a subject's push-button response while a video blanking circuit controls the video presented to the monitor screen. Two options for accurately detecting stimulus onset are presented: (1) A photodetector can be used to sense the actual onset of the stimulus on a secondary video monitor screen; (2) the video blanking circuit can provide a signal coincident with the initiation of video to the monitor. Both methods result in a system timing accuracy of 100 microseconds.
