AVA Annual Meeting 2008 , in conjunction with The University of Manchester ’ s Neuroscience Research Institute VISUAL VARIATION AND BIAS

AVA Annual Meeting 2008 2 We would like to thank the following colleagues for serving as referees: We would like to thank Vicky Catterall (Manchester's Neuroscience Research Institute) for help with organising this meeting. Magnocellular processing in autism Please note that this lecture will be available to watch again on the CRS website. 15.20 Coffee break and posters (Foyer outside lecture theatre 2) 15.40 Session 3 (lecture theatre 2) Chair person: Mark Scase An ERP investigation of changes in facial expression. 16.00 Contrasted pattern of brain activity in negative priming: a MEG study. 17.00 Wine and buffet reception and posters (Foyer outside lecture theatre 2) AVA Annual Meeting 2008 5 Abstracts for oral presentations (in session order) Note: The abstracts in this programme booklet may not correspond to the finally published abstracts in perception Humans are able to see two or more different motions within the same region of the visual field – motion transparency. The separation of transparent motion components offers an opportunity to study the integration of local motion signals. In an attempt to identify constraints for developing a computational model that can solve the problem of separating transparent motion components and that can explain psychophysical observations, we analysed such stimuli and their motion detector responses in space-time (Zanker & Meso, 2007, Perception, 36, 315-16). Here, we extend this work by investigating a range of motion channels tuned to different spatial frequencies and different stimulus patterns, including sinewaves, squarewaves, triangular profiles, and line gratings. These patterns were used to create two kinds of transparency configurations, in which the two components either move in opposite directions at the same speed, or in the same direction at different speeds. Whereas in the opposite-direction configuration local motion signals from pure sinewaves tend to blend into each other and under most conditions disappear, separate components become visible – and discriminable – in high-frequency channels for patterns that contain clear edges such as squarewaves. In the equal-direction configuration local motion components have even less distinct patterns that could reflect the different components, and signals from the transparent components can only be separated by combining the outputs from a set frequency channels to select velocity-related signals that are close to edges. This pattern of results corresponds to psychophysical observations that edges are crucial for the perception of transparency. Background: Subtractive and divisive processes have been used to explain a variety of adaptation effects in …