patternreversal

Pattern reversal refers to a type of visual stimulus commonly used in vision research and clinical electrophysiology. In a pattern reversal paradigm, a high-contrast visual pattern, typically a black-and-white checkerboard, periodically reverses its luminance arrangement so that white squares become black and black squares become white. This reversal is repeated at a controlled rate, producing reliable, time-locked responses in the visual cortex.

Stimulus parameters vary, but standard implementations use a checkerboard with equal black and white areas, a defined spatial frequency (cycles per degree), and a reversal rate often in the range of about 1 to 2 Hz. The stimulus is usually presented on a mid-gray background with the observer fixating the center. Pattern reversal is compatible with monocular or binocular viewing and can be delivered with different check sizes to probe different visual pathways.

Neural responses to pattern reversal are typically recorded with electroencephalography (EEG) or magnetoencephalography (MEG). The pattern evokes a robust cortical response, most prominently a P100 component occurring approximately 100 milliseconds after each reversal, along with earlier components. The amplitude and latency of these responses provide information about the integrity and timing of the early visual pathway, and changes can indicate conditions affecting the optic nerve or visual cortex.

Applications include clinical assessment of visual pathway function, such as detecting optic neuritis and monitoring diseases like multiple sclerosis, as well as basic research into visual processing and cortical pathways. Pattern reversal remains a standard stimulus in visual evoked potential protocols due to its reliability and ease of administration.