PSEUDORANDOM BINARY SEQUENCE STIMULATION APPLIED TO THE VISUAL-EVOKEDRESPONSE - NORMATIVE DATA AND A COMPARATIVE-STUDY WITH PATTERN AND FLASH STIMULATION

The investigation of patients who are unable to fixate the pattern vis ual stimulus generally requires the use of diffuse flash stimulation t o elicit the visual evoked response. However, by comparison with patte rn, flash stimulation has proved relatively insensitive in identifying lesions of the visual pathway. We investigated a more complex method of flash stimulation. A pseudorandom binary sequence has been used to generate the diffuse visual evoked response stimulus. The pseudorandom binary sequence, rather than producing a single flash, switches in a pseudorandom fashion between two levels of illumination. The result is a diffuse visual stimulus approximating band-limited white noise. The series is periodic, enabling signal averaging to be performed. By app lying the methods of random signal analysis, the impulse or transient response of the visual pathway can be determined. Our normal pseudoran dom binary sequence visual evoked response impulse function, derived f rom 29 normal subjects, had the morphologic characteristics of the con ventional flash visual evoked response and a major positive component (P100), whose latency mean and standard deviation closely matched that of our normative pattern visual evoked response. However, the P100 am plitude standard deviation was significantly greater than that produce d by conventional pattern and flash stimulation. We investigated 140 p atients by means of pattern, flash and pseudorandom binary sequence st imulation. The pseudorandom binary sequence visual evoked response pro ved to be almost 12 times more effective than flash visual evoked resp onse in detecting lesions of the visual system.