Academic journal article The American Biology Teacher

Science & the Senses: Perceptions & Deceptions

Academic journal article The American Biology Teacher

Science & the Senses: Perceptions & Deceptions

Article excerpt

Teaching human biology usually begins with two basic subjects--anatomy (structure) and physiology (function). The function of sensation requires two processes: transduction or stimulation (at the level of sensory receptors) and perception or interpretation (in the brain). The nervous system contains structures (sensory receptors) that inform the brain about the external environment in which the body lives (exteroreceptors) as well as enteroreceptors that inform the brain (either with or without involving a conscious response) about the status of the body's internal environment. The human body is commonly said to have five major exteroreceptors: (1) eyes for seeing, (2) ears for hearing (audition) plus balance or motion, (3) nose for smelling (olfaction), (4) tongue for tasting (gustation), and (5) cutaneous exteroreceptors in the skin for the sense of touch or taction (also for pain, pressure, and heat). There are more than five sense receptors if we include enteroreceptors, such as proprioceptors (tension receptors) in muscles, tendons and joint capsules, or chemoreceptors for detecting blood pH, C[O.sub.2], and glucose concentrations, or receptors for heart rate, blood pressure, and other body conditions necessary for homeostasis.

The focus of this article is as follows. Science requires the acquisition and analysis of empirical (sense-derived) data. Given the same physical objects or phenomena, the sense organs of all people do not respond equally to these stimuli, nor do their minds interpret or perceive sensory signals identically. Therefore, along with or subsequent to discussion of basic anatomy and physiology of the human sensory systems, teachers should develop lectures that include consideration of the following general concepts.

* The unimpaired range of human senses to a given phenomenon is often quite limited, especially in comparison to the senses of some other animals.

* Sensory perception between individuals is often highly variable at any given time, as well as within an individual at various times of its life.

* The variability and limitations of human sensory perception have very important implications for conducting scientific investigations, science education, and introspection that are seldom included in biology textbooks.

Human vs. Animal Sensory Limits

When compared to that of other animals, the range of human senses is often severely restricted. For example, human vision is limited to a very tiny part of the electromagnetic spectrum. The senses of some animals far exceed those of human perception (olfactory sense of dogs; ultrasonic echolocation of bats). However, some blind people have been able to develop the ability to echolocate by tapping their canes or clicking their tongues and listening for the echoes.

Some animals have one or more sensory capabilities entirely missing in humans. Sharks and related species, for example, can detect extremely weak electric fields generated by some other animals in their environment. Specialized electroreceptor organs, termed "ampullae of Lorenzini," are located on the snout of these predators, where they function in the detection of prey species. These electroreceptors are also sensitive to variations in water pressure, temperature, and salinity. A line of sensors along the body allows sharks (also fish and amphibians) to detect slight water-displacement movements such as those produced by fish swimming nearby (Fields, 2007). It is commonly said that sharks can "smell" blood in the water. But this would require that the term "olfaction" be defined as the sensing of specific chemicals in the animal's external environment (airborne or aqueous) via chemoreceptors either localized or dispersed over the animal's body surface. Some migratory birds are thought to be able to sense the Earth's magnetic fields and may use them for navigation (Bohannon, 2007).

Humans, however, can overcome some of their sensory limitations by inventing and using scientific instruments and technologies (such as microscopes, x-ray photography, and ultrasound scans) that allow us to detect objects and phenomena far beyond the range of our unaided senses. …

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