Expansion and compression of space within and beyond the boundaries of an object

Objects illusorily distort our perception of space, as indexed by perceived distances between two reference points placed within an object compared with the perceived distances between two dots placed in a ground region. This paper examines several novel aspects of such distortions across three experiments that employed a staircase procedure to determine the point of subjective equivalence between dot distances for one pair of dots within or near an object, compared to dots that were placed on a ground region. We replicate and expand upon prior findings that showed that dots within an object’s boundaries are perceived as further apart than they are – an expansion effect. We also verify and quantify a subjective experience that was previously unreported – dots positioned within the object but near or on the boundaries, as well as dots positioned beyond the extent of an object’s boundaries, are perceived as closer together (compressed) versus ground-region dots. We additionally demonstrate that expansion and compression extend into space laterally adjacent to an object. These findings demonstrate novel properties of the impact of objects on the perception of spatial relationships, and place important constraints on potential mechanisms that could explain object-based warping.