Download Sensation & Perception and more Slides Psychology in PDF only on Docsity! Sensation and Perception Syed Aftab Shah Lecture 3 Sensory, Perception Sensation is the process by which we receive information from the environment. • A. What kind of information? A stimulus is a detectable input from the • environment: • 1. Light—vision • 2. Sound—hearing • 3. Chemicals—taste and smell • 4. Pressure, temperature, pain—sense of touch • 5. Orientation, balance—kinesthetic senses • B. Environmental information (stimuli) exists in many forms: • 1. A physical stimulus must first be introduced. For example: air • vibrations, gases, chemicals, tactile pressures • 2. Sound - Properties of sound • i. Intensity (influences mainly loudness) • ii. Frequency (influences mainly pitch) • iii. Wave form (influences mainly timbre) • iv. As noted above, there is not a one-to-one relationship between physical properties and perceptual experience. For example, intensity can also influence perception of pitch. Perception is the process of selecting and identifying information from the environment. Perception is the interpretation of information from the environment so that we can identify its meaning. Sensation usually involves sensing the existence of a stimulus, whereas perceptual systems involve the determination of what a stimulus is. Expectations and perception: Our knowledge about the world allows us to make fairly accurate predictions about what should be there—so we don’t need a lot of information from the stimulus itself. 1. Bottom-up processes are processes that are involved in identifying a stimulus by analyzing the information available in the external stimulus. This also refers to information processing that begins at the receptor level and continues to higher brain centers. 2. Top-down processes are processes that are involved in identifying a stimulus by using the knowledge we already possess about the situation. This knowledge is based on past experiences and allows us to form expectations about what we ought to perceive. a. This also refers to information processing that begins in higher brain centers and proceeds to receptors. b. Top-down processes allow for perceptual judgments and bias to start influencing how we process incoming stimuli and information. Early incoming information is already being processed in terms of top-down influences and previous experience. Visual Optical Illusions • Koffka’s Ring • White’s illusion • Simultaneous Contrast Effect • Table Optical illusion • Criss-Cross illusion • Stepping Feet illusion • Checker-Shadow illusion • Shading Depth and Faces What is PSYCHOPHYSICS? Psychophysics is the study of the mathematical or functional relationship between physical energy and psychological experience. For example, how much more intense must a stimulus be in order for us to perceive a change in intensity? • Psychophysics tells us that the amount of change needed depends on the initial intensity. Classroom lights can provide a simple demonstration of this; if the main lights are already on and you add an additional light, perception of brightness changes little. But if you start with the room mostly dark and add the same additional light, there is a large change in perception of brightness. Absolute Threshold Example Imagine putting your hand on a stove, and turning it on. At first, you wont feel much heat because it takes time for the burner to heat up. After a point, you will detect heat on the palm of your hand - it will be hot enough for you to notice it. This isn’t the point at which your hand burns from the heat. But it is just at the point at which it is hot enough for you to notice. Difference Threshold Example • Lets say that I asked you put your hand out, I place in it pile of sand. • I start pouring sand in your hand until you notice any change in the overall weight of the hand. • As soon as you can detect any change in the weight, that difference between the weight of the sand before I added that last bit of sand and the weight of the sand after I added it, is the difference threshold. Attention • Attention: a process in which consciousness is focused on particular stimuli • 1. Selective attention: ability to focus on one stimulus while excluding other stimuli that are present. “Invisible Gorilla Experiment” • 2. Divided attention: ability to respond to more than one stimulus
