Abstract: A method and apparatus for objectively determining the visual contrast sensitivity function of a human subject involves subjecting the vision of the human subject to a plurality of sine wave gratings differing in spatial frequency and contrast levels. As the subject views the grating patterns on a video monitor, the brain wave activity of the subject is detected and steady state Fourier spectra of the activity are recorded. In each spectrum corresponding to a grating pattern of a particular spatial frequency, a visual evoked potential component may be distinguished from noise by adjusting the contrast level of the grating pattern. A contrast threshold used in deriving the visual contrast sensitivity function is identified for each grating pattern of a particular spatial frequency by pinpointing the contrast level at which the visual evoked potential component becomes indistinguishable from noise in the spectrum.

Abstract: A scene is scanned line-by-line with a video camera transforming the spatial distribution of intensities present in the scene into a time-varying intensity function which is then filtered in real time. The time-varying function is passed through an electrical filter with adjustable passband and center frequency, and the filtered image is written on a storage tube or other suitable fast-memory array. The stored image which has been spatially filtered in the x direction is then scanned and read line-by-line (in the y direction) with the new scan lines perpendicular to the direction in which the image was written on the storage tube (or memory array). This transforms the spatial distribution of intensities on the storage tube (or memory array) into a time-varying function of intensities. This time-varying function is then passed through a second filter with adjustable passband and center frequency.