Integration Mechanisms for Heading Perception

Previous studies of heading perception suggest that human observers employ spatiotemporal pooling to accommodate noise in optic flow stimuli. Here, we investigated how spatial and temporal integration mechanisms are used for judgments of heading through a psychophysical experiment involving three different types of noise. Furthermore, we developed two ideal observer models to study the components of the spatial information used by observers when performing the heading task. In the psychophysical experiment, we applied three types of direction noise to optic flow stimuli to differentiate the involvement of spatial and temporal integration mechanisms. The results indicate that temporal integration mechanisms play a role in heading perception, though their contribution is weaker than that of the spatial integration mechanisms. To elucidate how observers process spatial information to extract heading from a noisy optic flow field, we compared psychophysical performance in response to random-walk direction noise with that of two ideal observer models (IOMs). One model relied on 2D screen-projected flow information (2D-IOM), while the other used environmental, i.e., 3D, flow information (3D-IOM). The results suggest that human observers compensate for the loss of information during the 2D retinal projection of the visual scene for modest amounts of noise. This suggests the likelihood of a 3D reconstruction during heading perception, which breaks down under extreme levels of noise

Embedding a block-based intra mode in frame-based pixel domain wyner-ziv video coding

Distributed source coding principles have been recently applied to video coding in order to achieve a flexible distribution of the complexity burden between the encoder and the decoder. In this paper we elaborate on a pixel based Wyner-Ziv video codec that shifts all the complexity of the motion estimation phase to the decoder, thus achieving light encoding. We observe that the correlation noise statistics describing the relationship between the frame to be encoded and the side information available at the decoder is not spatially stationary. For this reason we introduce a mode decision scheme either at the encoder or at the decoder in such a way that when the estimated correlation is weak we opt for intra coding on a block-by-block basis. Moreover we discuss the effect of using a side information computed either from lossless or from quantized frames.