Abstract
Fire is a natural phenomenon of tremendous evolutionary significance, from cooking to tool-making to war and warmth. Might our minds be tuned to the features that characterize this important visual stimulus? Here, we investigated whether and how fire selectively guides visual attention. In a visual search task, adult observers viewed a display containing a variable number of burning fires placed randomly along an imaginary circle, and reported whether a target — one fire burning differently from the others — was present or absent. Stimuli were created from high-resolution video of fires burning (a) normally or (b) in reverse (achieved by playing the video frames backward). Remarkably, subjects were both faster and more accurate to detect a reverse-burning fire among normally-burning fires than a normally-burning fire among reverse-burning fires — a classic “search asymmetry” indicating privileged visual processing of the relevant features. This initial effect was further explored in multiple follow-up experiments. First, this search asymmetry persisted both with in-phase and out-of-phase burning; in other words, subjects were faster to find a reverse-burning fire among normal-burning fires both (a) when the distractor fires all burned in unison, and also (b) when they burned out-of-sync, thus forming a more variable search array. Second, and crucially, we tested the specificity with which the visual properties of fire selectively guide attention, by rotating all of the fires 90°; this simple manipulation completely eliminated the search asymmetry observed earlier, suggesting that these privileged patterns of attention arise only for fire stimuli presented under naturalistic conditions. This experiment also served as a control for the lower-level visual properties of fire, which were equated across conditions. Collectively, these findings raise the intriguing possibility that fire is privileged by visual attention, echoing the evolutionary significance of this vital stimulus.