Scott Janetsky¹, Jordan Dolinar¹, Kuo-Wei Chen¹, Gi-Yeul Bae¹; ¹Arizona State University

Visually guided behaviors are systematically influenced by recent perceptual history. In location estimation tasks, for example, reports are often repelled away from the previous-trial target, even when the previous target is task-irrelevant. Prevailing models attribute this repulsive serial bias to sensory adaptation: the previous target alters the encoding of the current target via bottom-up mechanisms. However, the potential contribution of top-down mechanisms to the bias effect has been under explored. To investigate whether repulsive serial bias could arise when bottom-up sources of bias are minimized, if not completely prevented, we had participants perform a location estimation task with implicit locations: they remembered the center of two reference objects and reported the center location by adjusting the center of two new reference objects. Because there was no explicit stimulus at the center of the two reference objects, participants had to imagine the center location during both encoding and reporting. To avoid the potential adaptation effect from the reference objects, the reference objects for the encoding and reporting were physically deviated from each other across trials. We predicted that, if repulsive serial bias is solely driven by bottom-up sensory adaptation, then the repulsive serial bias in this task would be absent or substantially smaller compared to the repulsive bias for the explicit locations. However, we found that repulsive serial bias for the implicit locations was comparable to the repulsive bias for the explicit locations. This was replicated in follow-up experiments where participants performed a location estimation task either with an implicit target but with an explicit response object or with an explicit target but with an implicit response object. Together, these results demonstrate that repulsive serial bias can occur for higher-level abstract representations and further suggest that bottom-up sensory adaptation is not necessary to explain repulsive serial bias effects.