ABSTRACT
The perception of spatial magnitudes has several features that reflect the magnitudes as they really are. Spatial magnitudes are unit-free in perception. A criterion of differentiation of characters more closely tied to recognition is this: characters that are differentiated must be perceptible and recognizable again on the basis of a certain kind of intentional content in which the characters are given in normal human perception. The intentional content of the perception of the characters must be one that engages recognition. The recognizability condition for characters in a successful, reliable, and knowably reliable notational system can fail even when instances of the characters in the notation are discriminably different in perception. Recognizability is dependent on the psychological capacities of perception and memory, this characterization can be applied only relative to some background set of perceptual and memory capacities.
