Illusory position shift induced by plaid motion

AbstractIn the motion-induced position shift (MIPS), the position of a moving pattern tapered by a stationary envelope is perceived to shift in the direction of the motion. It was found that plaid motion also elicited a MIPS in the direction of global motion and this global MIPS could not be predicted by the average of the local MIPSs due to component motions. We also used a pseudo plaid pattern and again observed a global MIPS that could not be predicted by the local MIPSs due to the components of the pseudo plaid pattern. We suggest the possibility that the receptive-field positions of global motion detectors shift in the direction opposite to global motion, resulting in a positional displacement in activation via population coding

An adaptable metric shapes perceptual space

How do we derive a sense of the separation of points in the world within a space-variant visual system? Visual directions are thought to be coded directly by a process referred to as local sign, in which a neuron acts as a labeled line for the perceived direction associated with its activation. The separations of visual directions are however not given. Nor are they directly related to the separations of signals on the receptive surface or in the brain which are modified by retinal and cortical magnification, respectively. To represent the separation of directions veridically the corresponding neural signals need to be scaled in some way. We considered this scaling process may be influenced by adaptation. Here we describe a novel adaptation paradigm, which can alter both apparent spatial separation and size. We measured the perceived separation of two dots and the size of geometric figures after adaptation to random dot patterns. We show that adapting to high density texture not only increases the apparent sparseness (average element separation) of a lower density pattern, as expected, but paradoxically, it reduces the apparent separation of dot pairs and induces apparent shrinkage of geometric form. This demonstrates for the first time a contrary linkage between perceived density and perceived extent. Separation and size appear to be expressed relative to a variable spatial metric whose properties, while not directly observable, are revealed by reductions in both apparent size and texture density