Searching near and far: The attentional template incorporates viewing distance

Abstract

Humans are remarkably proficient at finding objects in cluttered environments. A widespread explanation for this, is that observers generate a representation of the search target (or ‘attentional template’), which guides spatial attention towards target-like visual input. Any object, however, can produce vastly different visual input depending on its exact location; your car will produce a retinal image that is ten times smaller when it’s parked fifty compared to five meters away. Across four behavioral experiments, we investigated whether observers take viewing distance into account when searching for familiar object categories. On each trial, participants were pre-cued to search for a car or person in the near or far plane of an outdoor scene. In ‘search trials’, the scene reappeared and participants had to indicate whether the search target was present or absent. In intermixed ‘catch-trials’, two silhouettes were briefly presented on either side of fixation (matching the shape and/or predicted size of the search target), one of which was followed by a probe-stimulus. We found that participants were more accurate at reporting the location (Exp. 1&2) and orientation (Exp. 4) of probe-stimuli when they were presented at the location of size-matching silhouettes. Thus, attentional templates incorporate contextual predictions about object appearance (e.g., size as inferred from viewing distance). This was only the case, however, when silhouettes also matched the shape of the search target (Exp 1&3). We conclude that canonical attributes of an object (shape) are necessary for contextual attributes (size) to guide the allocation of attention.