The following is my summary of Chapter 8 of Tertium Organum by P D Ouspensky.
How do we perceive the world?
When we look at a solid we see its surface only. The actual perception of solid is a composite sensation of surfaces, weight, mass, density, resistance, etc. We perceive a solid through a combination of senses, which includes the mental sense as well.
We are easily subject to optical illusions when we focus only on the optical sensation and do not integrate that sensation logically with other sensations. Optical illusions thus teach us that, in order to perceive what is there, we need to learn to combine all our senses in a logically consistent manner, and not neglect any one of them.
The ability to perceive correctly requires the ability to combine various senses logically into concepts.
Lower animals possess only sensations. Higher animals possess sensations and representations. Representations are visual sensations of individual objects. Representations have an emotional quality associated with them, which is driven by pleasure and pain. This emotional quality dominates the perception of animals, and expresses itself as instincts. Animals follow these instincts in their actions.
In the absence of concepts animals combine their senses using a logic that is based on emotional quality. This logic, however, relies heavily on the memory of representations. It is thus limited and not helpful in the face of new phenomenon. Animals may not have the visual perception of depth because it takes concepts to perceive the third dimension.
Man possesses sensations, representations and concepts. As perceptions converge into concepts, their emotional quality is replaced by a rational quality. Concepts make it easier to combine the senses logically using a rational basis
Lacking concepts animals see the third dimension as time-phenomena and not something constant. Animals may thus perceive this world in two-dimensions only. Lower animals may even lack the representation with emotional quality that higher animals possess. They may perceive this world only in one dimension.
The perception of the dimensionality of the world may very well depend on the stage of evolution of a life organism.
