The influence of object location on identity: a "spatial congruency bias".

Objects can be characterized by a number of properties (e.g., shape, color, size, and location). How do our visual systems combine this information, and what allows us to recognize when 2 objects are the same? Previous work has pointed to a special role for location in the binding process, suggesting that location may be automatically encoded even when irrelevant to the task. Here we show that location is not only automatically attended but fundamentally bound to identity representations, influencing object perception in a far more profound way than simply speeding reaction times. Subjects viewed 2 sequentially presented novel objects and performed a same/different identity comparison. Object location was irrelevant to the identity task, but when the 2 objects shared the same location, subjects were more likely to judge them as the same identity. This "congruency bias" reflected an increase in both hits and false alarms when the objects shared the same location, indicating that subjects were unable to suppress the influence of object location--even when maladaptive to the task. Importantly, this bias was driven exclusively by location: Object location robustly and reliably biased identity judgments across 6 experimental scenarios, but the reverse was not true: Object identity did not exert any bias on location judgments. Furthermore, while location biased both shape and color judgments, neither shape nor color biased each other when irrelevant. The results suggest that location provides a unique, automatic, and insuppressible cue for object sameness.