Recently in the astronomy education research literature, the competency to be able to extrapolate three-dimensionality in ones’ mind from 1D and 2D representations has been identified as an important factor for success in learning astronomy and understanding the Universe. However, only little research has been done in investigating this competency (Eriksson et al. 2014; Heyer et al. 2013), while at the same time there is a growing interest for what and how 3D representations can contribute to learning astronomy (Cole et al. 2018). This paper discusses the competency to extrapolate threedimensionality in one’s mind and reports on the preliminary findings from an investigation concerning students’ and professors’ perception of threedimensionality when looking at 2D representations (images and simulations) of a sample of nebulae.