Chapter 1 Human Senses

Transcription

1 Chapter 1 Human Senses GOALS When you have mastered the contents of this chapter, you will be able to achieve the following goals: Definitions Stimuli Define the following terms, which can be used to describe a relationship between you and your environment: system energy state force variable field interaction intensity transducer List the major external stimuli that are detectable by humans. Human Responses Models Describe an elementary threshold measurement experiment, and interpret the data obtained. Use a mental construct, or model, to explain a common human experience. PREREQUISITES You may find it necessary to review your knowledge of the powers of ten notation before you study this chapter. 8

2 Chapter 1 Human Senses OVERVIEW - Without much difficulty you can probably name the five senses of the human body. As man has learned more about his surroundings, he has learned more about himself and about his ability to interact with his environment. In this chapter you will learn about the physical nature of your human senses. SUGGESTED STUDY PROCEDURE - When you begin your study of this chapter, be familiar with each of the four Chapter Goals: Definitions, Stimuli, Human Responses, and Models. (Please note than an expanded discussion of each term listed under Definitions is given on the next page of this.) Next, read Chapter Sections Be sure to attempt some of the more interesting Simple Experiments suggested and consider several of the probing questions posed at the end of most of the sections. (Answers to these questions are given in the second section of this Study Guide.) At the end of the chapter, read the Chapter Summary and complete Summary Exercises 1-4. Now do Algorithmic Problems 1-6 and complete Exercises 1, 2, 3, 4, 7, and 8. Now you should be prepared to attempt the Practice Test on Human Senses found in this Study Guide. This study procedure is outlined below Chapter Goals Suggested Summary Algorithmic Exercises & Text Readings Exercises Problems Problems Definitions Stimuli ,3 3,4,7,8 Human Responses ,3 2,4,5,6 1,2 Models

3 DEFINITIONS SYSTEM A whole entity. In marked contrast to the holistic thinking that characterizes much of human activity, physics uses an analytical technique that seeks to understand complex situations by dividing them into separate parts which we call systems. We try to imagine that a system is a separate part of the universe which we can study without the system being changed either by our study or by whatever is happening in the rest of the universe. For example, if we wish to study the physics of human hearing, we will define the system of study as the human hearing system and include within it all of the parts of the body that are necessary to hear sounds. Of course, such a system is quite unreal since you cannot hear anything if the other parts of your body cease to function. Nevertheless, this mental, somewhat artificial, technique of dividing up the universe into separate systems has allowed us to make great strides in the study of nature. VARIABLE Quantity that is subject to change. Once you have picked a system for study you can analyze the ways you can change or vary the characteristics of the system. For example, you can modify the human hearing system by the use of drugs or the use of ear plugs. The properties of a system that we can change or vary we call variables. One big idea of physics is to find all of the important variables of a system and see how changes in each of the variables affects the rest of the system. You will notice once again the analytical approach, chop a system into parts called variables, and see if we can understand the whole system by finding the ways the variables influence one another. STATE Particular form or condition of a system. It is usual for physicists to define the starting point of their study of a system by attempting to give all of the important variables of the system some initial value thereby specifying the initial state of the system. For example, if you wished to study the influence of various amount of cotton ear plugs on human hearing, you could define your starting condition, or initial state, as a well rested, typical human with no wax or obstructions in the ear canals. TRANSDUCER A sensor or detector that transforms a change in one physical variable to a change in another. In many cases we wish to observe the changes in the properties of a system. Often it is possible to infer a change in a system by measuring a related, but different, property. In such a situation we make use of a transducer, a part of the system that relates the change of one variable of the system to another. For example, the eardrum acts to transform the sounds that fall on your ear into vibrations of the eardrum which are subsequently transformed into the electrical messages that are sent to your brain. The eardrum serves as a transducer. INTERACTION Action or influence exerted between systems. If we wish to study the influence of one system on another we say we will study the interaction between two systems. Then we will proceed to change the values of variables of one system to see if that causes any changes in the values of the variables of 10

4 the second system, e.g., if we change the noise level in the room where our human subject is located that will change the response of a typical person. ENERGY Property of a system which causes changes in its own state or state of its surroundings; measure of ability to do work (physical). One way to specify the state of a system is to compute the energy of the system. Energy is a kind of imaginary property of a system that physicists have invented to help define in a more holistic way the state of a system. We never actually measure energy directly but only calculate it from other variables that we can measure. In a sense, energy is to a system as meaning is to a poem. In general, a group of physicists think that they can objectively agree upon the energy of a system, while a group of poets are not likely to think that they can objectively agree upon the meaning of a poem. Does the fact that ten people can agree upon the same value of an imaginary quantity make it truly objective? FORCE A measure of the strength of an interaction; a push or pull; the effect of a force is to alter the state of motion of a body. A vector quantity with a magnitude measured in Newtons (N). From our earliest experiences as children we know of the interactions between systems by physical contact. From our beginnings as humans we have responded to the direct contact of another person. Throughout our early experiences of collisions with walls and falling down we know of the effects of direct contact interactions. We use the term force to designate the strength of interaction between two systems. We have the idea that a greater force applied to a system is most likely to cause a greater change in the system. FIELD A region of space characterized by a physical property which has a determinable value at every point in the region, e.g., gravitational field, magnetic field, etc. Our experiences with direct contact interactions are so convincing that physicists have invented a concept of a field that can be used to bring into contact systems that may be widely separated from one another. The physicist just imagines a field exists everywhere between the two systems and the field of one system may exert a force on the second system. INTENSITY Energy transported through a unit area in one second. Another idea that is readily associated in our minds with direct contact interactions is the transfer of energy from one system to another, such as the energy of food being transferred to the energy of your body via the life processes. In a similar way we can think of a field as having a source which emanates energy to all objects in its field. We characterize the intensity of a field by the amount of energy its source emanates per unit of area in one second. If we are in the field of a light bulb our eyes interpret the intensity of the bulb in terms of brightness, the more intense the source, the greater is the brightness of the light. 11

5 ANSWERS TO QUESTIONS FOUND IN THE TEXT SECTION 1.2 The Human System 1. A human being is a complex set of interacting systems. To properly describe in a holistic way your present state would require you to define the different states of your basic body systems such as the skeletal-muscular system, digestive system, urinary system, respiratory system, circulatory system, nervous system, and reproductive system. You are usually not very aware of the present state of any of these systems even though your brain must continually monitor the activities that occur in all parts of your body. To determine the present state of your circulatory system you could find your pulse rate, blood pressure, and results of various tests on your blood. Even so, many details of your circulatory system would be left undefined. 2. Your present state is determined by the values of many variables of the body systems listed above. Such variables as pulse rate, blood pressure, etc., can be specified. However, there is evidence that personality features such as self-worth or faith can have an important influence on many of your physiological variables. Historically such variables as faith and self-worth are classified as not being physical observables. SECTION 1.3 The Human Detector 3. At this moment you are interacting with your environment through a wide variety of systems. The force of the chair on your bottom is a mechanical energy interaction. Your eyes are responding to electromagnetic, or light, energy. Your ears are picking up sound energy. Your nose and taste buds sense odors and tastes by chemical energy. Your body is said to be immersed in the gravitational and electromagnetic fields of the earth and sun. The influence of these fields upon you is not well understood. 4. In general, we can think of the odor, sound, gravitational, and light or electromagnetic interactions as being interactions-at-a-distance, while taste of food and the force of the chair may be envisioned as direct contact interactions. SECTION 1.4 Direct-Contact Interactions 5. There are areas of your back, legs, and feet that seem relatively insensitive to touch. Your finger tips, tongue, and forehead is quite touch sensitive. 6. By tasting a variety of known salt concentrations it is believed you could train yourself to be a salt water taster. Just as, after years of practice, persons are able to perfect their taste sense to become professional wine tasters. 7. Both the inside of your arm and your lips are particularly thermal sensitive while your hands and face have fewer nerves to detect heat and cold than other parts of your body. SECTION 1.5 Interaction-at-a-Distance 8. You have surely experienced sunshine, music, noise, voices, smells and food today. Have you climbed some stairs, ridden a bicycle up a hill, or hiked to the top of a mountain? 12

6 9. Sunshine (electromagnetic); music, noise, voices (sound); smells and food (odor); stairs, hill, mountain (gravitational). 10. Your ears are never shut, so the interaction-at-a-distance most common for non-deaf humans is probably sound. SECTION 1.7 Threshold for the Sense of Touch 11. Various whole body variables such as state of restfulness, lack of influence of drugs, normal blood pressure and blood sugar concentrations, etc. 12. One source of error is the inability of a subject to tell exactly when a touch is felt. Doing repeated measurements with each subject in a varying sequence of locations so that several threshold measurements are performed at each location should prove helpful in reducing this uncertainty. 13. Figure 1.3 shows a technique that can be used to determine the distance between distinct contact points. SECTION 1.8 Model Building 14. In each of these cases a powerful group of persons developed an explanation of the behaviors of other groups of humans that defined them as less than human, e.g., savages, enemies of progress, threats to national security. These mental constructs, or models, were used to justify a wide variety of inhumane and unjust treatments. 15. For most scientists, the subject areas of extrasensory perception, of mind-brain research, and of how the human beings develop logical thought are still not scientifically ordered. Two areas of science, molecular biology and astrophysics, have contributed new concepts to our daily language by popularizing the double helix and black holes. PRACTICE TEST 1. You are in a swimming pool several meters away from another person also in the pool. Name below three methods you might use to gain the person's attention. For each case, identify or describe transducer you use and mark the interaction as either a contact (C) or action-at-a-distance (A-D). Method Transducer Interaction (C or A-D) Imagine that you are taking a shower in a bath with "inadequate plumbing" and find the shower temperature difficult to control. As the water temperature changes drastically, please describe the response your body makes to this variable in terms of a. Threshold b. Sensitivity c. Discrimination 13

7 3. The different parts of your body respond with different sensitivity to outside physiological stimuli. Consider the bottom of the feet and their response to four major stimuli as outlined below. Please rank each stimuli from 1- body part most sensitive to stimulus to 4-body part least sensitive to stimulus. Body Part or Area Tested - Bottom of Feet Ranking Stimuli Interaction Heat Contact Visible light Action at a distance Ultraviolet light Action at a distance Low frequency sound Action at a distance 4. What is a "model" in physics? ANSWERS 1. Shouting, Vocal Chords, A-D Making Waves, Hands & Arms, A-D Splashing Water, Hands & Arms, C 2. Threshold - Minimum temperature difference detected by the body Sensitivity - Body's receptors reaction to various incoming energy (heat) levels Discrimination - Detection of temperature differences across the shower spray or ability to tell if the temperature of the water is changing with time. 3. 1, 4, 2, 3 (other answers accepted under other physical conditions). 4. A model is a specification of a unification of ideas which help to visualize a variety of experiences. In physics, these experiences deal primarily with aspects of the physical nature of the world. 14