Mechanism underlying the perception of shape and material properties of light transmitting objects

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In the project we aim to investigate several aspects of material and shape perception of light transmitting objects. The first two of four sub-projects focus on the perceived transmittance properties of thin planar transparent layers. In this work we refer to the filter model of perceived transparency proposed by Faul and Ekroll (2002, 2011). The goal of the first sub-project is to improve, extend and validate a parameter space for this model that we have recently developed. The dimensions of this space are approximately perceptually independent and perceptually uniform. These properties makes it well suited to intuitively manipulate, describe and predict the perceived properties of transparent layers. In the second sub-project we study constancy of the perceived layer transmittance under changes in the color of the illuminant. As potential influences on the degree of constancy we consider the structure of the background, color adaptation, the recognizability of an illumination change, and the subjects' task. The focus of the other two sub-projects is on the perception of realistic three-dimensional transparent objects. Specular reflections and background distortions that are clearly visible in such objects provide additional sources of information that may be used to infer the objects' properties. In the third sub-project we investigate, whether this information can be used to infer the refractive index of the objects' material. In theory, this seems possible because both the strength of specular reflections and the degree of background distortion increase with the refractive index. Our previous experiments with static distortion patterns led to negative results. In this sub-project we will test, whether changes in the distortion pattern caused by object motion relative to the scene and/or the observer can be used to estimate the refractive index. In addition we also consider the strength of specular reflection and the pattern of total reflections as potential cues for the refractive index. In a fourth sub-project we study 3D-shape perception in the special case of light-transmitting objects. The results that we obtained so far indicate that in this case shape perception relies on different cues and is often less accurate than in the case of opaque objects. A goal of this sub-project is to quantify how the accuracy and precision of shape recognition depends on the properties of the scene and the target object. Furthermore, we will try to identify regularities in the retinal image that are used by the visual system to recognize the shape of light transmitting objects.