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B.C. Hansen, J.K. DeFord, E.A. Essock; When Do Humans Show a Horizontal Effect Instead of an Oblique Effect?: An Analysis Across Breadth of Orientation and Spatial Frequency Content . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4091.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have recently shown (VSS 2002, ARVO 2001 & 2002) that with stimuli of broadband spatial frequency content (either visual noise or natural scenes), performance for detecting oriented content is worst at horizontal, best at obliques, and intermediate at vertical orientations -- an anisotropy quite different from the well-known oblique effect obtained with simple line or grating stimuli. Here we assess at which point (in terms of orientation and spatial frequency band-size) the anisotropy produced 'switches' from the traditional oblique effect obtained at narrowest spatial and orientation bandwidths to the horizontal effect demonstrated previously with a 45o orientation band and 1-octave spatial frequency band. Methods: Stimuli were generated by making broadband isotropic visual noise patterns (1/f slope) and filtering the amplitude spectra to contain a test increment of amplitude within a restricted range of orientation and spatial frequency. The extent of the test increment's orientation and frequency bandwidth was systematically varied. A standard matching paradigm was used to assess the perceived strength of the added oriented structure in a test pattern by having the observers adjust the amplitude of the oriented structure in a comparison pattern to make a match. Results: The traditional oblique effect was produced only when a fairly small range on content (orientations and high spatial frequencies) was present and the horizontal effect was observed for broadband content of about 20o. and 1-octave in frequency. A blend of the two anisotropies was observed at intermediate breadths of band content. Conclusions: Human vision is certainly anisotropic, but although the oblique effect is observed in simplified test conditions typical of the laboratory or eye clinic, anisotropic performance really follows a "horizontal effect" pattern in conditions typical of every-day viewing when isolated single sinewaves are rarely encountered.
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