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SINE-WAVE GRATINGS

Sine-wave gratings are used to create and test the contrast sensitivity curve. A sine-wave grating is a repeated number of fuzzy dark and light bars, or cycles. The number of cycles of a grating over a specified visual angle determines its spatial frequency. Below are examples of sine-wave gratings with varying spatial frequencies and contrast levels.

A small number of cycles over a specified visual angle is defined as having a low spatial frequency. A large number of cycles over the same visual angle is defined as having a high spatial frequency. Contrast is the difference between the brightness and darkness of the grating. Mathematically it is defined by c = (Lmax -Lmin)/(Lmax + Lmin). (In references, see: Ginsburg A. Spatial filtering and vision: implications for normal and abnormal vision.)

Vision Is Like Hearing :: Just as the hearing system filters the sounds we hear into independent ranges of sound frequencies, the visual system filters the images we see into independent ranges of sizes, or spatial frequencies. Therefore, we can see that there is a direct analogy between auditory testing and vision testing:

:: In auditory testing, sine-waves of varying sound frequencies and loudness are needed to test the auditory channels involved in functional hearing.

:: In vision testing, sine-waves of varying spatial frequencies (sizes) and contrast are needed to test the visual channels involved in functional vision.

Loudness = Contrast
Sound Frequency = Spatial Frequency
Audiogram = Contrast Sensitivity Function

(In references, see: Ginsburg AP. The evaluation of contact lenses and refractive surgery using contrast sensitivity in contact lenses.)

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