Abstract
Objective. Our understanding of surface attitude perception derives largely from studies using synthetic stimuli and gauge figure probes. Here we assess whether these studies generalize to real-world scenes and whether misperception of the gauge figure could lead to bias in these results. Methods: Stimuli were viewed monocularly through a 12° circular aperture. We explored two classes of stimuli and two modes of response. Stimuli: 1) Planar surfaces painted with synthetic textures; 2) Real-world patches from the SYNS dataset (Adams et al., 2016). Response mode: 1) gauge figure; 2) 2D dial with separate slant and tilt indicators. In addition we tested the synthetic textures binocularly with perspective only and with disparity; and compared 2D and 3D gauge figure and dial methods. Results: Slant: Observers made meaningful judgements of slant for both synthetic and real-world surfaces. For synthetic textures, RMS error and sensitivity (JND) were similar for the two methods. While the dial method produced a gain greater than 1, the gauge figure method produced a gain less than 1 and was biased to overestimate slant, possibly due to underestimation of the slant of the gauge figure itself. For real-world surfaces, in contrast, both response modes produced a negative bias: observers underestimated slant. Tilt: For synthetic textures, tilt judgements were precise and accurate for both methods. However, observers were unable to perform the task for real-world surfaces, instead reporting tilts tightly clustered around the cardinal directions. Conclusion: While both gauge and dial methods work well for tilt judgements of synthetic surfaces, for slant judgements both methods generate strong biases, and it remains unclear whether this reflects biased perception of the surfaces, biases in the method, or both. Humans appear to be unable to make reasonable judgements of egocentric tilt for natural surfaces.