This article considers the phenomenon of visual indeterminacy, which occurs when the sensory data gathered from the visual system cannot be integrated with semantic knowledge. A number of examples are given, including from the author's own art work, and some results presented from a scientific study based on them. The implications for the operation of the mind and, in particular, the nature of aesthetic experience are addressed, and the distinction between the perception of visual forms and their cognitive interpretation is discussed. Arguments about the nature of aesthetic experience are then considered from some historical sources and interpreted in light of the distinctions between perception-cognition and form-content. The paper concludes by summarizing the links between aesthetic experience, the operation of visual perception, and visual indeterminacy.