Spatial distinction on a scale finer than visual acuity is known as hyperacuity, but known hyperacuity phenomena concern detection of displacements across positions (Westheimer & McKee,
1977), eyes (Schor & Badcock,
1985), and time (Nakayama,
1981), and the underlying mechanisms are totally different from the hyper resolution revealed in this study. It is also known that the images presented in the peripheral visual field, or those presented in motion, look sharper than would be expected from the degraded spatial resolutions under these viewing conditions (Bex, Edgar, & Smith,
1995; Galvin, O'Shea, Squire, & Govan,
1997). This perceptual sharpening is functionally similar to the subresolution fineness perception in that both indicate the visual system's function to overcome spatial resolution limits, although it makes the input image look sharper regardless of whether it is physically sharp or blurred. In another attempt to overcome the spatial resolution limit, the visual system uses the available fine high-contrast luminance edge information that is normally correlated with the color edge information in natural images to extrapolate fine color edge information lost by the low resolution of chromatic processing (Boynton,
1978). Considering the subresolution fineness perception as filling-out of missing high-frequency information from visible low-frequency information, one can find an example of the analogous effect in the opposite direction, i.e., the filling-out of missing low-frequency information from high-frequency information, in the Craik-O'Brien Cornsweet illusion (Cornsweet,
1970). Considering the perception of superfine surface structures from a broader perspective, while the present finding concerns the estimation of the surface meso-structure, the human visual system can estimate even a finer surface microstructure (e.g., polished specular surface, matte Lambertian surface, velvety surface) from the pattern of the surface angular dependence of light reflection (bidirectional reflectance distribution function; Dana, Van Ginneken, Nayar, & Koenderink,
1999). The visual system exploits a variety of strategies to overcome the limitations of spatial processing, and our finding adds a novel effect to the list.