Sensation and Perception
Thanks to the nose, ears, eyes, tongue, and skin, we can imagine a day at the lake: glimmering blue sky, fresh water, warm sand (if they have it), and honking geese. Our knowledge of the world depends on the senses: vision, hearing, taste, smell, position, movement, balance, and touch. If someone bounces a basketball, our eyes and ears pick up stimuli such as light and sound waves and send neural signals to the brain. This process called sensation occurs when physical energy from objects in the world or in the body stimulates the sense organs.
However, only when the signals come together meaningfully do we actually perceive a bouncing basketball. Perception happens when the brain organizes and interprets sensory information. Sensation and perception occur together, and normally we don’t distinguish between the two separate processes. We use all five of our senses and organize the information we get from them every day of our lives. Sensation is the process by which physical energy from objects in the world or in the body stimulates the sense organs.
The brain interprets and organizes this sensory information in a process called perception. Psychophysics is the study of how the physical properties of stimuli relate to people’s experience of stimuli. Research in psychophysics has revealed much information about the acuity of the senses. Psychologists assess the acuity of the senses in three ways: 1. Measuring the absolute threshold 2. Measuring the difference threshold 3. Applying signal detection theory The absolute threshold is the minimum amount of stimulation required for a person to detect the stimulus 50 percent of the time.
The difference threshold is the smallest difference in stimulation that can be detected 50 percent of the time. The difference threshold is sometimes called the Just Noticeable Difference (JND), and it depends on the strength of the stimulus. If someone were comparing two weak stimuli, such as two very slightly sweet liquids, he’d be able to detect quite a small difference in the amount of sweetness. However, if he were comparing two intense stimuli, such as two extremely sweet liquids, he could detect only a much bigger difference in the amount of sweetness.
Nineteenth-century psychologist Ernst Weber proposed a principle demonstrating the fact that we can’t detect the difference between two stimuli unless they differ by a certain proportion and that this proportion is constant. In other words, the just noticeable difference for a stimulus is in a fixed proportion to the magnitude of a stimulus. Weber’s Law holds true except in the most extreme kinds of stimulation. Researchers use signal detection theory to predict when a weak signal will be detected.
This theory considers the fact that the ability to detect a signal depends not only on the strength of the signal but also on the perceiver’s experience, motivation, expectation, and degree of alertness. Different people respond differently to the same signal, and the same person may detect a particular signal at one time but not another. Furthermore, people can often detect one type of signal in a sensory modality such as hearing or vision but be oblivious to other types of signals in the same sensory modality. When people walk into a restaurant, they probably notice food smells right away.
However, as they sit in the restaurant, the smells gradually become less noticeable. This phenomenon occurs because of sensory adaptation. Sensory adaptation is the decrease in sensitivity to an unchanging stimulus. The smells don’t disappear—the people just become less sensitive to them. Babies have all the basic sensory abilities and many perceptual skills, but these abilities develop and grow more sensitive over time. Babies can recognize the difference between a human voice and other sounds, and they can locate a sound’s origin.
They can recognize the difference between smells and, very early on, can recognize their mother’s particular smell. As for taste, they can differentiate between sweet and salty. Babies also have fairly adept visual abilities. Soon after birth, they can distinguish objects of different colors and sizes. When they are just a few weeks old, they begin to differentiate among contrasts, shadows, and patterns, and they can perceive depth after just a few months. Even innate perceptual skills need the right environment to develop properly.
A lack of certain experiences during sensitive periods of development will impair a person’s ability to perceive the world. People who were born blind but regain their vision in adulthood usually find the visual world confusing. Since these adults were blind in infancy, they missed the sensory experiences necessary for their visual system to develop fully.
Vision, however, would not exist without the presence of light. Light is electromagnetic radiation that travels in the form of waves. Light is emitted from the sun, stars, fire, and light bulbs. Most other objects just reflect light. People experience light as having three features: color, brightness, and saturation. These three types of experiences come from three corresponding characteristics of light waves: * The color or hue of light depends on its wavelength, the distance between the peaks of its waves. * The brightness of light is related to intensity or the amount of light an object emits or reflects.
Brightness depends on light wave amplitude, the height of light waves. Brightness is also somewhat influenced by wavelength. Yellow light tends to look brighter than reds or blues. * Saturation or colorfulness depends on light complexity, the range of wavelengths in light. The color of a single wavelength is pure spectral color. Such lights are called fully saturated. Outside a laboratory, light is rarely pure or of a single wavelength. Light is usually a mixture of several different wavelengths. The greater number of spectral colors in a light, the lower the saturation.