 Perceptual representations represent magnitudes by means of magnitudes. In the case of vision, for example, they represent magnitudes like illumination, contours, color and they do so by means of magnitudes in the early sensory cortices. The early visual cortices are retinotopic (Grill-Spector and Malach 2004 for a summary and Talavage et al. 2004 on equivalent claims regarding the non-visual sense modalities). If you are looking at a triangle, there is a roughly triangle-pattern activation of direction-sensitive neurons in your primary visual cortex. This is iconic format par excellence. And if you visualize a triangle, there is also a roughly triangle-pattern activation of direction-sensitive neurons in your primary visual cortex (Kosslyn et al. 2006). Again, iconic format par excellence, at least according to the ‘representation of magnitudes, by magnitudes’ criteria.