Biases in judgments of separation and orientation of elements belonging to different clusters

If two demarcated dots are embedded in separate clusters of similar dots in off centre positions, their perceived separation is biased towards the separation between the centres of the clusters (Morgan, Hole, & Glennerster, 1990). We replicated these results and went on to determine whether a similar bias is present for orientation judgments, using a staircase method and a range of cluster orientations and separations. A complex pattern of biases was found including biases for targets at centroids. Orientation attraction towards tangents to the clusters seemed to be involved. We conclude that orientation is subject to different contextual constraints from separation, and that bias towards the edges of clusters needs to be included in models of position coding.