An investigation of the ability of the human visual system to encode spatial phase relationships

Evidence is presented that the human visual system contains broad-band mechanisms capable of encoding the spatial phase relationship between a fundamental spatial frequency and higher frequencies up to its third harmonic. Compounds of a fundamental and its harmonics above the third become progressively more difficult to discriminate by means of phase information alone. Measurements were also made of the amount of spatial summation found in various detection and phase discrimination tasks using simple or compound gratings composed of a fundamental frequency (F) and its third harmonic (3F). A task requiring the discrimination of the phase relationship between a low contrast (F) and a high contrast (3F) shows less spatial summation than does a task requiring the detection of the (F) component by itself. A simple model is advanced to account for these results qualitatively. The model is based upon the hypothesis that the human visual system analyses the retinal image in patches of a range of sizes and that phase relationships may be discerned only between components that are detected by different elements of the same patch mechanism.