Orientation formed by a spot's trajectory: a two-dimensional population approach in primary visual cortex.

There exist a large number of visual illusions indicating that perception differs from pure representation of physical input. For example, a spot of light can be characterized by its position, but it does not contribute any information about orientation. However, when moved fast enough, a continuous streak along its trajectory is perceived that helps to determine the orientation of the movement path. The question arises whether the processing of the trajectory and its orientation are simultaneously represented in the primary visual cortex. Here I show that decoding neural population activity within a two-dimensional parameter space represents both (1) physical input given by the actual position of the moving spot and (2) orientation. This latter parameter has no physical counterpart in the stimulus but must be actively formed by spatiotemporal integration of the spot's trajectory.