Abstract
There is a current debate concerning whether people's physiological or behavioral potential alters their perception of slanted surfaces. One way to directly test this is to physiologically change people's potential by lowering their blood sugar and comparing their estimates of slant to those with normal blood sugar. In the first investigation of this (Schnall, Zadra, & Proffitt, 2010), it was shown that people with low blood sugar gave higher estimates of slanted surfaces than people with normal blood sugar. The question that arises is whether these higher estimates are due to lower blood sugar, per se, or experimental demand created by other aspects of the experiment. Here evidence was collected from 120 observers showing that directly manipulating physiological potential, while controlling for experimental demand effects, does not alter the perception of slant. Indeed, when experimental demand went against behavioral potential, it produced judgmental biases opposite to those predicted by behavioral potential in the low blood sugar condition. It is suggested that low blood sugar only affects slant judgments by making participants more susceptible to judgmental biases.
Highlights
Does our perceptual experience of space reflect our behavioral potential (Proffitt, 2006; Proffitt, Bhalla, Gossweiler, & Midgett, 1995)? Several studies regarding the perception of geographical slant have shown that this may be the case (Proffitt et al, 1995; Bhalla & Proffitt, 1999)
If the cognitive task were removed and the backpack were either left out of the experiment or provided with a plausible explanation, might we find that participants who believed the drink was a sugared drink that was intended to lower their estimates provide lower estimates even in the case when the drink was a sugar-free placebo? If compliance with even this alternative experimental demand were mediated by blood sugar levels, this situation would make a prediction opposite to that of the effort hypothesis: Participants with lowered blood sugar should give lower estimates in compliance with their beliefs about the intended purpose of the drink
If we found that slant estimates were elevated by low blood sugar in an experiment controlling for backpack demand, this could provide strong evidence in favor of perception being influenced by physiological or behavioral potential
Summary
Does our perceptual experience of space reflect our behavioral potential (Proffitt, 2006; Proffitt, Bhalla, Gossweiler, & Midgett, 1995)? Several studies regarding the perception of geographical slant (i.e., surface pitch relative to horizontal; Sedgwick, 1986; see Stevens, 1983) have shown that this may be the case (Proffitt et al, 1995; Bhalla & Proffitt, 1999). Durgin and Li observed that many angular variables thought to be quite central to perception, such as the perceived declination of gaze, and optical slant (surface orientation relative to the direction of gaze) seemed to be exaggerated in perceptual experience whether judged explicitly (by verbal estimation or vertical/horizontal bisection) or implicitly, as when judging surface slant along different lines of sight They argued that many perceptual biases, including distance underestimation and slant overestimation, could be understood in terms of efficient coding of angular variables that could more precisely guide both cognition and action (see Li & Durgin, 2012). Such stable-coding theories argue against there being an advantage to slant being transiently affected by such things as backpacks or fatigue (Durgin, Hajnal, Li, Tonge, & Stigliani, 2010)
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