The influence of the number of cycles upon the visual contrast threshold for sptial sine wave patterns

Abstract

Spatial contrast measurements have been carried out with sine wave modulated fields, varying the aperture and the luminance. The modulation threshold turns out to depend upon the number of cycles in the stimulus for numbers of cycles below a critical number of cycles. Beyond this critical number the threshold was constant. This critical number increases with increasing luminance. The maximum in the spatial contrast transfer function around 6–8 c/deg. as it is frequently found by many authors, must be due to an insufficient number of cycles at low frequencies. If corrected for this insufficient number, the spatial transfer function shows no maximum: the threshold is independent of the modulation frequency for frequencies below the cut-off frequency. In the Appendix a description is given of a model that is based upon Fourier analysis.