Lecture 3 - The sixth sense - and the rest
We all know about just five of the senses: we know about them because the messages from them produce conscious perceptions. Those five senses rule our lives: they tell us everything that we need to know about the world around us, with a richness of description that has inspired famous painters to entertain our eyes, composers to excite our ears and great chefs and wine-makers to stimulate our noses and our palates! Yet our five senses, which give us all the wonderful variety of our sensory experiences, depend on just four types of detector cells - sensitive to chemical substances, to light, to temperature change and to mechanical distortion.
Our sensory systems, using these four types of receptor cells, provide information about only a tiny fraction of all the forms of energy and chemical events around us. Other animals enjoy sensory experiences that we can glimpse only through physical instrumen ts of detection and measurement. For instance, our eyes are sensitive to only a narrow range within the whole spectrum of electromagnetic radiation; but many species can detect and make use of ultraviolet light; rattlesnakes have infrared detector organs to sense the position of their warm prey; and many insects can sense the plane of polarisation of light. Similarly, our hearing is limited to a band of about ten octaves, but many animals can detect very high-frequency sound and bats use ultrasound echo-location for guiding their flight. We now know that certain birds and fish can sense extremely low frequencies of sound vibration and again may use the information in navigation. Even more amazing are the senses that are completely different from ours - the electric field organs of many fishes and the magnetic sense of bacteria and birds. Animals have the senses that they need to have; each species lives in a sensory world of its own.
About the 1982 CHRISTMAS LECTURES
Our sense organs are windows on the world. But just like windows, as well as giving us a view of the physical world, the senses also restrict our outlook on the things around us. Philosophers have worried for centuries about the reliability of the human senses and about the relationship between the real world and the world as we see, hear and feel it. Is the world only a creation of our minds?
I am no philosopher, so I am happy to accept that there is a real world out there and that our sense organs simply describe it to our brains. But this means that the world we know through our perceptions is created by processes in our brains and the validity of this imagined world depends crucially on the way that our sense organs and our brains work together to perform the magic of perception. My aim in these lectures is to describe the way that the sense organs act as biological instruments of detection, measurement and analysis. I shall try not to be a 'human chauvinist' but will show that our senses, perfect though they are for our needs, are only a small part of the repertoire of biological instruments of detection and measurement that evolution has invented.
It is hard to accept that our perception of things around us is incomplete, but the fact is that we are blind and deaf to much that is happening in the world. We sense what we need to sense. Every animal lives in its own perceptual world, a world of its own creation. Let us be proud of the incredible performance of our own sense organs and brains but let us not forget that other creatures have marvellous sense organs that we do not. They live in other worlds, in perceptual worlds created by their own particular sense organs, worlds that we can never experience directly but can only dream about.Join me in these lectures on a journey to the edges of your own perceptual world and into the sensory worlds of other animals. I shall give the members of the audience plenty of opportunities to test their own senses and to discover how they work, and we shall be joined, from time to time, by animals who will show us all how very clever their sense organs are!
About Colin Blakemore
Sir Colin Blakemore (1 June 1944 – 27 June 2022) was a British neurobiologist, specialising in vision and the development of the brain. His own research work was mainly concerned with the mechanisms in the brain for the interpretation of signals from the eyes, and especially in the early development of vision during the first few days and weeks of an animal's life. He was well known for his work in communicating science to the public and published many popular books.