Can Shadows Create a Sense of Depth to Mid-air Image?

Shadows are an important factor in the perception of object position and shape. In this study, we investigated the effect of shadows on the perception of the shape of a mid-air image by projecting shadows of different shapes onto a mid-air image that is displayed in real space. Specifically, participants viewed one oval cylinder with a shadow and one oval cylinder without a shadow individually and were forced to choose which had the greater thickness in the depth direction. As a result, we found that shadow shapes possibly changed the perception of the thickness of the mid-air image.