CHECKERBOARD STIMULATOR

Typical Number in Hospital:

Cost Bands: 4

References: 2

This provides an image in the form of a checkerboard on a screen using one or two slide projectors which alternate the black and white areas of the checkerboard, or the same effect is produced on a television image. It is used to provide the optical stimulus in the measurement of the visual evoked potential (VEP), sometimes called the visual evoked response (VER), which is a test of the detection and transmission of a light stimulus through the various stages of the eye, optic nerve, and visual cortex, as picked up from electrodes placed over the visual cortex. The VEP is measured to identify disorders of the visual system and neural disorders which may also affect the visual system.

The VEP signals are very small and it is normally necessary to employ signal averaging techniques to remove noise and artefacts. The checkerboard stimulator is triggered to change pattern at the start of the measurement cycle so that responses are synchronized in time with the stimulus, or conversely the checkerboard stimulator triggers the measurement process.

The VEP may also be measured using a flash stimulus but the reason for using a checkerboard is that there is no change in the average light level as the pattern reverses.