There is reason to believe that large variations in viewing distance affect the perception of optical slant because farther portions of uphill slants appear steeper (Bridgeman & Hoover,
2008) whereas downhill slants appear shallower when viewed from a far distance (Ross,
2006). The present study used parametric manipulation to model the effects of viewing distance on perceived optical slant using both traditional verbal estimation (Proffitt et al.,
1995) and an aspect-ratio task that has been used to study exocentric distance perception (Loomis, Da Silva, Fujita, & Fukusima,
1992; Loomis & Philbeck,
1999; Philbeck,
2000). Whereas a variety of methods have been used to study perceived slant, some of these, such as haptic matching tasks (palm boards), have been shown to be biased measures (Durgin, Hajnal, Li, Tonge, & Stigliani,
2010). In contrast, verbal measures appear not to be intrinsically biased (Durgin, Li et al.,
2010). For this reason, in the first experiment of the present study, verbal estimates of slant, an explicit measure of perceived slant, were used to develop a model of optical slant perception as a function of viewing distance. The model was then tested in
Experiment 2, using an aspect-ratio task to implicitly measure perceived slant.