Internal representation of visual texture as the basis for the judgment of similarity

The relationship between Fourier spectra of visual textures (represented both by the actual frequency components and by the response of four hypothetical channels selectively sensitive to spatial frequency) and the perceptual appearance of the textures was investigated. Thirty textures were synthesized by combining seven spatial frequencies whose amplitudes were randomly chosen and then scaled to give an overall contrast of .9. Similarity judgments were collected using both the method of triadic comparison (two subjects, 4,060 trials each) and the method of paired comparison (six subjects, 435 trials each). The similarity judgments were subjected to MDSCAL and INDSCAL dimensions were found to be optimally oriented in terms of spatial frequency information without rotation. The seven spatial frequency components accounted for 90.6% of the variance in the 3-D INDSCAL space, while the four channels accounted for 91.8% of the variance in the first two dimensions. The data further suggest that the four channels may interact in an opponent process manner. The results support the idea that the visual internal representation of stimuli is based on spatial frequency analysis rather than feature extraction.