Searching near and far: the attentional template incorporates viewing distance

According to theories of visual search, observers generate a visual representation of the search target (the ‘attentional template’) that guides spatial attention towards target-like visual input. In real-world vision, however, objects produce vastly different visual input depending on their location: your car produces a retinal image that is ten times smaller when it’s parked fifty compared to five meters away. Across four experiments, we investigated whether the attentional template incorporates viewing distance when observers search 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. 3) of probe-stimuli when they were presented at the location of size-matching silhouettes. Thus, attentional templates incorporate the predicted size of an object based on the current viewing distance. This was only the case, however, when silhouettes also matched the shape of the search target (Exp 2). We conclude that attentional templates for finding objects in scenes are shaped by a combination of category-specific attributes (shape) and context-dependent expectations about the likely appearance (size) of these objects at the current viewing location.