Sensation and perception. Traditionally, any analysis of the levels and structure of knowledge begins with sensuous knowledge, which is divided into three levels: sensation, perception and representation. The point of departure of all intellectual life lies in sensuousness and not in thought, which both historically and ontogenetically is derived from the senses. In sense perception we experience the direct effect of the objective world, its resistance to us. In the act of contemplating an object, a person relates directly to it, he senses it and feels the authenticity, the reliability of its existence. For example, in an orange we sense the orange colour, the firmness, the specific smell, the taste, the shape and the size. Sensations arise under the influence of processes coming from the external and internal environment and acting upon our sense organs. External irritants may be sound or light waves, mechanical pressure, chemical effect, and so on.
Sensation is the reflection of certain properties of objects during their immediate action on a sense organ, the conversion of excitation into a fact of consciousness.
The sense organs are, as it were, channels or windows open to the external and intra-organic world, through which enormous streams of impulses are constantly flowing into the brain. The sense organs carry on their cognitive function by means of a certain system of motive acts depending on the object that they reflect. For instance, a feeling hand reproduces the shape of an object by actively touching it, while the eye, like a feeling hand, passes over an object at a distance in various directions, and observes it.
The modal division of sensations is based on the specific features of the influence they reflect: touch, vision, hearing, vibration, temperature, smell, taste, and so on. Visual sensations are crucial in human sensuous cognition. They provide us with thirty times more information than we obtain through hearing. The visual is also more reliable. Visual sensations originated from the sensations of touch. Not for nothing is it said that the seeing eye is the pupil of the feeling hand. And when we doubt the reliability of the "pupil's" evidence, we resort to the assistance of the teacher: we feel the object with our hands. Spatial, tangible sensibility is the chief means of getting to know the world geometrically, as an assembly of material bodies. Hearing also plays an important role in sensuous reflection. Its development is mainly connected with the sound structure of language as the basic means of communication and also with the sound structure of music.
Sensations are the most reliable bond between knowledge and the universe and we should know nothing about the sensuous properties of things without them.
What is perception? No matter what object we take, it possesses many diverse aspects and properties. Take a lump of sugar for example. It is hard, white, sweet, has a certain shape, mass and weight. All these properties are combined and we perceive and comprehend them not separately but as a whole, a unity—a lump of sugar. Consequently, the objective basis of perception, as perception of a whole image, is the unity and, at the same time, the diversity of the various properties of the object in question. A perception is an integral image directly reflecting the object or objects influencing the sense organs, their properties and relations. It is a stage of knowledge higher than, and substantially different from, sensation. Perception implies a comprehension of the object, its properties and relations, based on the reception of a recently received impression into the system of knowledge already available, whereas sensations may simply "flash past" on the periphery of consciousness and remain out of the focus of concentrated thought. Perception, on the other hand, is thinking, living contemplation; we looked at things with our external eyes and see them with our internal vision. The depth of this comprehension depends on a person's intellectual level, his total experience.
Representation. Representations come about through the perception of external stimuli and their preservation in time by the memory. A perception refers only to what is actually happening at a given moment. A representation is an image of an object that at some time influenced the sense organs and is later revived from the traces left in the brain while the object is absent; it may also be an image created by an effort of the imagination. As imaginal knowledge a representation is the highest form of sensuous reflection. Objects that are not present before us or not accessible to our sense organs are present in our consciousness and are grasped by the mind in the form of representations, which synthesise many comparable sense impressions. A representation differs from a perception in that it rises above the immediate givenness of an object and links it with a concept by means of some general principle and in itself becomes a focal point of thought.
In epistemology a representation means something more than the act of direct contemplation in the form of an image of an absent object. It is a summing-up of historically accumulated empirical material registered in books, tables, the recordings of various apparatuses, minutes, and so on. It is a synthetic intellectual form, richer in content that its previous stage. It comprises everything that people know about the object in question. It is a cache of social memory, whose contents have not yet been theoretically processed by thought.
The mental process which creates representations and mental situations not directly received as entities is imagination, which creates images of the desirable or possible future, and also images of things that are not to be found in personal experience but can be put together out of the elements that are there. These images may simply reproduce something that exists or has existed, or may anticipate the future and guide practical actions to its actual, real creation. The more real the reflection in the imagination, the more productive is its regulative and stimulative activity, which possesses a great power of imaginative generalisation.