Chapter 5 Introduction

Sensation and Perception 5

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CHAPTER OUTLINE

  • Perceptual Systems

  • From Physical Stimulus to Psychological Experience

    Transduction

    Receptor Cells

  • The Visual System

    Visual Perception

    • CULTURAL OPPORTUNITIES: Perceiving Absolute and Relative Size

      From Eye to Brain: Biological Bases of Visual Perception

    • RESEARCH TOOLKIT: Eye Tracking

  • The Auditory System

    Auditory Perception

    From Ear to Brain: Biological Bases of Auditory Perception

  • The Olfactory System

    Perceiving Odors

    From Nose to Brain: Biological Bases of Olfaction

  • The Gustatory System

    Gustatory Perception

    From Mouth to Brain: Biological Bases of Gustation

    • THIS JUST IN: Taste Maps in the Brain

  • The Haptic System

    Haptic Perception

    From Skin to Brain: Biological Bases of Haptic Perception

    The Kinesthetic System

  • Sensation and Perception in a Social World

    The Experience of Pain

    The Perception of Faces

    Motivated Perception

  • Attention

    Auditory Selective Attention

    Visual Selective Attention

  • Looking Back and Looking Ahead

HUBERT DOLEZAL, A 29-YEAR-OLD AMERICAN, kept a diary while visiting St. John’s of Kissos, a small seaside village on the rocky coastline of Greece. Here are some of his entries:

  • Day 1 (early in day): The first few steps I took … tremendously shaky. These steps were awkward, difficult. Any task requiring … precise performatory coordination is horrendously strenuous.

  • Day 1 (later in the day): I notice a substantial improvement in my ability to walk a straight line after walking only 40 feet.

  • Day 2: For the first time, I was able to walk down 6–8 steps without help. The most serious difficulty now is [on] such relatively trivial tasks as operating my portable tape recorder.

  • Day 3: This is the first time I’ve been able to walk upstairs alternating steps (i.e., one footstep per step).

  • Day 5: I’ve abandoned the use of my walking stick.

  • Day 6: I’m more sure-footed than ever before. For the first time, I’ve successfully alternated feet going down the last 6 of the 50 stairs. This was unthinkable even yesterday; yet this morning I did it fairly naturally and briskly.

  • Day 9: For the first time, it’s relatively easy to change batteries in the portable tape recorder.

  • Day 11: Carrying heavy suitcases up and down wet and slippery mule trails poses no problem.

What a rapid recovery! But from what? On Day 1, it sounded as if our visitor to Greece had sustained major injuries to his legs. Yet on Day 2, he was walking down stairs. On Day 2, he couldn’t operate a simple electronic device. Maybe his hands were injured? A few days later, though, he operated the device easily.

Here’s what actually happened. What Hubert Dolezal “recovered” from was not an injury, but a dramatic alteration in perception. As part of an experiment, on Day 1 he donned upside-down glasses, that is, glasses with special prisms that turned his entire field of vision upside down.

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He had been seeing right side up for a lifetime. Yet within days, Dolezal adapted to seeing upside down. How could the visual system—a primary topic in this chapter on sensation and perception—have adapted so quickly to images of a world turned upside down?

Before we delve into the chapter, here’s a quick fact about vision. Due to the curvature of the front of your eye, images of the world reverse—left to right, and up to down—before reaching the back of your eye. This raises another question: How did you adapt to images of a world turned upside down?

IMAGINE YOU ARE an organism—any creature, great or small—crawling around in the world. What is your most fundamental challenge? Finding food? Avoiding predators? Or maybe it is staying warm or getting rest if you’re injured.

Each of these is important. Yet they all rely on something even more fundamental: accurate sensation and perception. To find food, you’ve got to be able to see or smell it. To avoid predators, you have to see, smell, or hear them. Avoiding cold and recovering from injury require that you sense the inner environment of your body, to know that you’re cold or injured. Survival requires sensation and perception, our focus in this chapter.