The application of Fourier analysis to the visibility of gratings explores how the human visual system detects grating patterns of different waveforms. Contrast thresholds for sine, square, rectangular, and saw-tooth wave gratings were measured across a wide range of spatial frequencies. Fourier theory shows that the contrast threshold for a grating is primarily determined by the amplitude of its fundamental Fourier component. Gratings with complex waveforms cannot be distinguished from sine-wave gratings until their higher harmonic components reach their independent threshold. These findings suggest that the visual system contains linearly operating, independent mechanisms selectively sensitive to limited ranges of spatial frequencies. The study used a cathode-ray tube to generate grating patterns with different waveforms, and contrast thresholds were determined by subjects adjusting the contrast until the pattern was barely detectable. Results showed that contrast sensitivity varies with spatial frequency, and that the sensitivity of square-wave gratings is generally higher than that of sine-wave gratings. The ratio of contrast sensitivities for square and sine-wave gratings was found to be approximately 4/π, consistent with Fourier analysis. Rectangular-wave gratings showed that their contrast sensitivity depends on the duty cycle, with the sensitivity ratio reaching a maximum when the duty cycle is 0.5 (square-wave). Saw-tooth gratings had a higher contrast sensitivity ratio compared to sine-wave gratings. The perception of suprathreshold gratings showed that square-wave gratings can be distinguished from sine-wave gratings when their third harmonic reaches its own threshold. The study suggests that the visual system contains multiple independent channels, each with a narrowband filter tuned to a specific frequency range. This model explains the observed contrast thresholds and the independence of higher harmonic components. Neurophysiological evidence supports the existence of frequency-selective channels in the visual system, with retinal ganglion cells showing band-pass contrast-sensitivity characteristics. The findings indicate that the visual system operates linearly under constant illumination conditions, with separate mechanisms responding maximally at specific spatial frequencies.The application of Fourier analysis to the visibility of gratings explores how the human visual system detects grating patterns of different waveforms. Contrast thresholds for sine, square, rectangular, and saw-tooth wave gratings were measured across a wide range of spatial frequencies. Fourier theory shows that the contrast threshold for a grating is primarily determined by the amplitude of its fundamental Fourier component. Gratings with complex waveforms cannot be distinguished from sine-wave gratings until their higher harmonic components reach their independent threshold. These findings suggest that the visual system contains linearly operating, independent mechanisms selectively sensitive to limited ranges of spatial frequencies. The study used a cathode-ray tube to generate grating patterns with different waveforms, and contrast thresholds were determined by subjects adjusting the contrast until the pattern was barely detectable. Results showed that contrast sensitivity varies with spatial frequency, and that the sensitivity of square-wave gratings is generally higher than that of sine-wave gratings. The ratio of contrast sensitivities for square and sine-wave gratings was found to be approximately 4/π, consistent with Fourier analysis. Rectangular-wave gratings showed that their contrast sensitivity depends on the duty cycle, with the sensitivity ratio reaching a maximum when the duty cycle is 0.5 (square-wave). Saw-tooth gratings had a higher contrast sensitivity ratio compared to sine-wave gratings. The perception of suprathreshold gratings showed that square-wave gratings can be distinguished from sine-wave gratings when their third harmonic reaches its own threshold. The study suggests that the visual system contains multiple independent channels, each with a narrowband filter tuned to a specific frequency range. This model explains the observed contrast thresholds and the independence of higher harmonic components. Neurophysiological evidence supports the existence of frequency-selective channels in the visual system, with retinal ganglion cells showing band-pass contrast-sensitivity characteristics. The findings indicate that the visual system operates linearly under constant illumination conditions, with separate mechanisms responding maximally at specific spatial frequencies.