Unit 4: Sensation and Perception

AP students in psychology should be able to do the following:

• Discuss basic principles of sensory transduction, including absolute threshold, difference threshold, signal detection, and sensory adaptation
• Describe sensory processes (e.g., hearing, vision, touch, taste, smell, vestibular, kinesthesis, pain), including the specific nature of energy transduction, relevant anatomical structures, and specialized pathways in the brain for each of the senses
• Explain common sensory disorders (e.g., visual and hearing impairments)
• Describe general principles of organizing and integrating sensation to promote stable awareness of the external world (e.g., Gestalt principles, depth perception)
• Discuss how experience and culture can influence perceptual processes (e.g., perceptual set, context effects)
• Explain the role of top-down processing in producing vulnerability to illusion
• Discuss the role of attention in behavior
• Challenge common beliefs in parapsychological phenomena
• Identify the major historical figures in sensation and perception (e.g., Gustav Fechner, David Hubel, Ernst Weber, Torsten Wiesel)

Introduction

"I have perfect vision," explains my colleague, Heather Sellers, an acclaimed writer and teacher. Her vision may be fine, but there is a problem with her perception. She cannot recognize faces.

In her memoir, You Don't Look Like Anyone I Know, Sellers (2010) tells of awkward moments resulting from her lifelong prosopagnosia - face blindness.

In college, on a date at the Spaghetti Station, I returned from the bathroom and plunked myself down in the wrong booth, facing the wrong man. I remained unaware he was not my date even as my date (a stranger to me) accosted Wrong Booth Guy, and then stormed out of the Station. I can't distinguish actors in movies and on television. I do not recognize myself in photos or videos. I can't recognize my stepsons in the soccer pick - up line; I failed to determine which husband was mine at a party, in the mall, at the market.

Her inability to recognize faces means that people sometimes perceive her as snobby or aloof. "Why did you walk past me?" a neighbor might later ask. Similar to those of us with hearing loss who fake hearing during trite social conversation, Sellers sometimes fakes recognition. She often smiles at people she passes, in case she knows them. Or she pretends to know the person with whom she is talking. (To avoid the stress associated with such perception failures, people with serious hearing loss or with prosopagnosia often shy away from busy social situations.) But there is an upside: When encountering someone who previously irritated her, she typically won't feel ill will, because she doesn't recognize the person.

Unlike Sellers, most of us have (as Module 18 explains) a functioning area on the underside of our brain's right hemisphere that helps us recognize a familiar human face as soon as we detect it - in only one - seventh of a second Gacques & Rossion, 2006). This ability illustrates a broader principle. Nature's sensory gifts enable each animal to obtain essential information. Some examples:

• Frogs, which feed on flying insects, have cells in their eyes that fire only in response to small, dark, moving objects. A frog could starve to death knee-deep in motionless flies. But let one zoom by and the frog's "bug detector" cells snap awake.
• Male silkworm moths' odor receptors can detect one - billionth of an ounce of sex attractant per second released by a female one mile away. That is why silkworms continue to be.
• Human ears are most sensitive to sound frequencies that include human voices, especially a baby's cry.

In this unit, we'll look more closely at what psychologists have learned about how we sense and perceive the world around us.