We are frequently faced with the necessity of looking for the picture required for the visualization of an object, not in the perception of this particular object, but in a different perceptual image.... we can assert the discrepancy between the perceived picture and the objective state. This discrepancy... proves absolutely nothing against the fact that all visualizations are merely sense qualities of the perceptual space.... If the parallelism is... to be visualized, we must supplement our assertion by the description of certain qualities with which we are familiar from perceptual space.

The Philosophy of Space and Time (1928, tr. 1957)