Jack George Thompson

The Effects of Retinal Eccentricity and Orientation on Perceived Length

An experiment was performed to examine the effects of line orientation and retinal locus on the perceived length of a single line. Thirty-five male and female undergraduate volunteers each monocularly judged the length of five test lines presented in two orientations (horizontal and vertical) at five different retinal loci. Displacement of horizontal lines from the fovea on either the horizontal or vertical meridian produced decreases in perceived size. The perceived length of vertical lines, however, decreased only with displacements on the vertical meridian.

Neural Control Systems

Like other multicelled animals, the cells of the human body are organized into highly specialized organs and organ systems that perform specific biological functions (digestion, physical movement, respiration, etc.). The primary function of the nervous system is to coordinate the physiological activity of the different organ systems in response to the demands of the external environment.

The Urinary System

The major by-products of cellular metabolism are heat, carbon dioxide, water, inorganic salts, and nitrogen compounds. In excess quantities, any of these byproducts are toxic, and unless they are excreted from the body, the cells would eventually be destroyed by their own metabolic processes. The skin (Chapter 5) plays a major role in excreting excess heat, and the respiratory system (Chapter 6) plays a major role in excreting carbon dioxide. Except in extremely hot environments, the skin and lungs combined do not excrete sufficient water or salts to balance the quantities produced by cellular metabolism. Moreover, neither system excretes nitrogen compounds such as urea in any quantity. The urinary system performs the complex task of maintaining the chemical balance in the body. Without a functioning urinary system, excess nitrogen compounds accumulate in the blood (uremia), the blood becomes acidic (acidosis), and excess water accumulates in the tissues (edema). Within a few days, the individual lapses into a coma, and death occurs within 2 weeks.

The Cardiovascular System

In order to maintain normal metabolic activity, the cells of the human body must ingest oxygen and nutrients and excrete toxic chemical waste products. The cardiovascular system serves the vital function of circulating oxygen and nutrients throughout the body and removing waste products. As we will discuss later in Chapter 5, the cardiovascular system also plays a major role in maintaining internal body temperatures.

The Respiratory System

The term respiration refers to the exchange of gases. Biologists label the interchange of gases within a cell as true respiration. During aerobic metabolism, oxygen combines with carbon and hydrogen to produce carbon dioxide and water. The exchange of oxygen and carbon dioxide between the blood cells and body cells is called internal respiration. The exchange of gases between the bloodstream and the external environment is labeled external respiration. Thus, technically, the respiratory system consists of every living cell in the body. The term respiratory system, however, is more commonly used to denote the lungs and other organs involved in external respiration.

The Thermoregulatory System

The living cells of the body produce (metabolize) energy from the chemicals absorbed from food during digestion and oxygen absorbed by the lungs in a complex series of relatively inefficient chemical reactions. Only about 20% of the energy produced is used to perform work, and the remaining 80% is converted to heat. Accordingly, metabolism is measured in units of heat called Calories or kilogram calories (1 Calorie = 1,000 calories). A Calorie is the amount of heat needed to raise the temperature of 1 kilogram of water 1°C.

The Skeletal Muscle System II

Like other overlearned behaviors, adults tend to take their own perceptual-motor skills for granted and are often mystified by the obvious difficulty infants and young children display when they attempt to perform “simple” motor movements. Yet, even “simple” physical movements are actually extremely complex acts. Fitts (1964), for example, noted that the motor movements needed to hit a baseball are so complex that the computer program needed to command a robot arm to perform the same act would be as sophisticated as a computer program designed to play chess.

The Female and Male Reproductive Systems

Like all living organisms, humans have finite life spans. Without sexual reproduction, the human species would become extinct.

Mind and Body

Emotions are integral components of human existence. Most people report that their everyday subjective experiences consist of a kaleidoscope of positive and negative feelings. Indeed, we often intentionally behave in specific ways in order to elicit specific emotions. We may consciously choose to read depressing news reports, pick fights, or cheer ourselves up. Intuitively, we realize that emotions are literally the subjective spices of life. Without tears of joy or sorrow, the laughter of amusement or sadism, the pounding heart of love or hate, life would be a barren experience.

The Gastrointestinal System

Both aerobic (with oxygen) and anaerobic (without oxygen) cellular metabolisms require simple hydrocarbons. Although the tissues of both plants and animals are composed of hydrocarbons, these organic compounds are too complex chemically for use in cellular metabolism. The two basic functions of the gastrointestinal (GI) system are to chemically break down the complex hydrocarbons contained in food into simple hydrocarbons and to expel chemical wastes such as fiber that cannot be digested.