Perception and Reality

Jorge Martins de Oliveira, MD, PhD

Our perception does not identify the outside world as it realy is, but the way we are allowed to recognize it, as a consequence of transformations performed by our senses. Thus, we transform photons into images, vibrations into sounds and noises and chemical reactions into specific smells and tastes. Actually, the universe is colourless, inodorous, insipid and silent.

To modern neuroscience, the real concept of perception started to develop when Weber and Fechner discovered that our sensory system draws out four basic attributes from a stimulus : modality, intensity, duration and location.

We do not accept, nowadays, as it happened in the past, that our perceptive world is just the plain result of an encounter between a ''naive" brain and the physical properties of a stimulus. Actually, perceptions differ, in quality, from those physical characteristics, because the brain extracts an information from the stimulus and interprets it, according to previous similar experiences.

We experiment electromagnetic waves, not as waves, but as images and colours. We experiment vibrating objects, not as vibrations, but as sounds. We experiment chemical compounds dissolved in air or water, not as chemicals, but as specific smells and tastes. Colours, sounds, smells and tastes are products of our minds, built from sensory experiences.

They do not exist, as such, outside our brain. Actually, the universe is colourless, inodorous, insipid and silent. Therefore, we can now answer one of the questions of traditional philosophy : Does a sound exist when a tree falls in a forest, if nobody is present to hear it ? No, the fall of the tree only creates vibrations. The sound occurs if vibrations are perceived by a living being.

Information from the environment or from the body itself, is picked up by the sensory systems and utilized by the brain for perception, regulating corporeal movements and maintaining arousal. A sensory system starts to work when a stimulus, usually from the outside world, is detected by a sensitive neuron, the first sensorial receptor. This receptor converts the physical expression of the stimulus (light, sound, heat, pressure, taste, smell) into action potentials , which transforms it into electric signs.

From there, the signs are conducted to a nearby area of primary processing, where the initial characteristics of the information are elaborated, according to the nature of the original stimulus : colour, shape, distance, shade, etc. Then, the already modified information is transmitted to zones of secondary processing in the thalamus (if originated by olfactory stimuli, it is processed in the olfactory bulbs and then directly conducted to the medial area of the temporal lobe).

In the thalamic zones, older data, originated from both the cortex and the limbic system and containing similar experiences, link to the new information, in order to form a message, which is carried to its specific cortical centre. There, the meaning and importance of the new detected stimulus are determined by a conscious process of identification called perception.

But, what do we perceive ?

We perceive the environment around us, by means of our sensory systems. Each system is nominated according to the type of the information it is related to : vision, hearing, touch, taste, smell and gravity. The last one is associated with the sense of balance. Sensitive receptors capture proprioceptive stimuli which indicate the position of the body as a whole and of its segments, while other fine receptors, called kinesthetic, control our movements, helping us to walk, run and perform other kinetic activities, in a safe and co-ordinated way. Still more refined sensors get special information, like temperature, sexual arousal and blood volume.

Each particular sensory system also distinguishes the qualities of the detected signal. This is why we perceive light in terms of colour and brightness and can tell the tone and highness of a sound. Taste indicates whether a food is suit, bitter or salty. Touch receptors allow us to distinguish how sensations act on our skin : by pressure or by vibration. And, finally, special receptors inform us about the intensity of each stimulus, while others tell us where the stimulus came from, when it started and for how long it will remain.

Although two human beings share the same genetic and biological architecture and function, perhaps what I perceive as a dintinct color and smell is not exatly equal to the the color and smell you perceive. We give the same name to this perception but we cannot know how they relate to the reality of the outside world. Perhaps we never will.

Author: Jorge Martins de Oliveira, MD, PhD. Full Professor and Master of UFRJ (Rio de Janeiro). Associate Professor of UFF. Scientific Coordinator. Coordinador and Director of the Department of Neurosciences of the Institute of Human Being (RJ). Fellow in Research by Saint Vincent Charity Hospital, Cleveland, USA. Full Member of Brazilian Academy of Military Medicine. Member of the Brazilian Academy of Writers Physicians. Graduated by Superior School of War (ESG).


Center for Biomedical Informatics

State University of Campinas, Brazil

Copyright 1997 State University of Campinas