Chapter 4 Section 1

1. Chapter 4 Section 1 Sensation and Perception: The Basics Obj: Distinguish between sensation and perception, and explain how they contribute to an understanding of our environment.

2. Sensation is the stimulation of sensory receptors and the transmission of sensory information to the central nervous system. Sensory receptors are located in sensory organs such as the eyes and ears and elsewhere in the body. The stimulation of the senses is automatic. It results from sources of energy like light and sound or from the presence of chemicals, as in smell and taste.

3. Perception is the psychological process through which we interpret sensory stimulation. Stimulation of the senses and the ways in which people interpret that stimulation are affected by several concepts. These concepts include absolute threshold, difference threshold, signal-detection theory, and sensory adaptation.

4. Absolute Threshold Have you ever had your hearing tested? When you hear the beep, you have just discovered your absolute threshold for hearing that kind of sound. Absolute threshold is the weakest amount of a stimulus that can be sensed. Even before you heard the beep, it was there. The first one you heard was the weakest one you were capable of hearing.

5. Absolute thresholds for humans have long been determined for the senses of vision, hearing, smell, taste, and touch. However, the absolute threshold for a particular stimulus can differ from person to person. Some people are more sensitive to certain sensory stimuli than others are. These differences stem from psychological and biological factors.

6. Difference Threshold For us to function well in the world, we need absolute thresholds low enough to see, hear, smell, taste, and feel what is going on around us – but not so low that our senses are overloaded with information we cannot use. We also need to be able to detect small differences between stimuli - what makes one stimulus different from another stimulus. The minimum amount of difference that can be detected between two stimuli is known as the difference threshold.

7. Signal – Detection Theory As you might imagine, it is easier to hear a friend talking in a quiet room than in a room where other people are laughing loudly. And when your nose is stuffy from a cold, your dinner may seem to have little flavor. In the first case, the setting has made a difference in your sensation and perception. In the second case, your physical condition has made the difference.

8. Signal-detection theory is a method of distinguishing sensory stimuli that takes into account not only their strengths but also such elements as the setting, your physical state, your mood, and your attitudes.

9. Signal-detection theory also considers psychological factors such as motivations, expectations, and learning. For example, even if the place where you are now reading is buzzing with distracting signals such as a breeze against your face, the shadow of passing clouds, or the voices of passersby, you will be able to ignore those influences as long as you are motivated to keep reading. Similarly, people who smell perfumes for a living have learned through years of experience how to detect subtle differences others would not be able to smell.

10. Sensory Adaptation Our sensory stems adapt to a changing environment. Sensory adaptation is the process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli.