Psychology Sensation and Perception Introduction The Senses & Hearing
To view other note of Psychology Click Here.
Introduction
Thanks to the nose, ears, eyes, tongue, and skin, we can imagine a day at the beach: glimmering blue sky, salty water, warm sand, and crying seagulls. 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.
The Senses
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.
Measuring the Senses
Psychologists assess the acuity of the senses in three ways:
- Measuring the absolute threshold
- Measuring the difference threshold
- 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.
Example: 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.
Weber’s Law
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.
Sensory Adaptation
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.
Development of the Senses
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.
Sensitive Periods
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.
Example: 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.
Hearing
Hearing, or audition, depends on the presence of sound waves, which travel much more slowly than light waves. Sound waves are changes in pressure generated by vibrating molecules. The physical characteristics of sound waves influence the three psychological features of sound: loudness, pitch, and timbre.
- Loudness depends on the amplitude,or height, of sound waves. The greater the amplitude, the louder the sound perceived. Amplitude is measured in decibels. The absolute threshold of human hearing is defined as 0 decibels. Loudness doubles with every 10-decibel increase in amplitude.
A Whisper to a Scream
The loudness of normal human conversation is about sixty decibels. A whisper is about twenty decibels. A shout right into someone’s ear is about 115 decibels. Being exposed to sounds that are over 120 decibels, even for brief periods, can damage the auditory system.
- Pitch, though influenced by amplitude, depends most on the frequency of sound waves. Frequency is the number of times per second a sound wave cycles from the highest to the lowest point.The higher the frequency, the higher the pitch. Frequency is measured in hertz, or cycles per second. Frequency also affects loudness, with higher-pitched sounds being perceived as louder. Amplitude and frequency of sound waves interact to produce the experiences of loudness and pitch.
What’s Audible?
Humans can hear sounds that are between 20 and 20,000 hertz.
- Timbre, or the particular quality of a sound, depends on the complexity of a sound wave. A pure tone has sound waves of only one frequency. Most sound waves are a mixture of different frequencies.
The Structure of the Ear
Knowing the basic structure of the ear is essential to understanding how hearing works. The ear has three basic parts: the outer ear, the middle ear, and the inner ear.
The visible part of the ear is the pinna, which collects sound waves and passes them along the auditory canal to a membrane called the eardrum. When sound waves hit the eardrum, it vibrates. The eardrum transmits the vibration to three bones, or ossicles, in the middle ear, which are called the hammer, the anvil, and the stirrup. The diagram of the ear shows how they got these names: they actually look like a hammer, an anvil, and a stirrup. In response to the vibration, these ossicles move one after another. Their function is to amplify the sound vibrations.
From the ossicles, vibrations move through a membrane called the oval window to the cochlea of the inner ear. The cochlea is a coiled, fluid-filled tunnel.
Inside the cochlea are receptors called cilia or hair cells that are embedded in the basilar membrane. The basilar membrane runs along the whole length of the coiled cochlea. Vibrations that reach the inner ear cause the fluid in the cochlea to move in waves. These waves in turn make the hair cells move.
The movement triggers impulses in neurons that connect with the hair cells. The axons of these neurons come together to form the auditory nerve, which sends impulses from the ear to the brain. In the brain, the thalamus and the auditory cortex, which is in the temporal lobe of the cerebrum, receive auditory information.
Pitch Perception
Two theories explain how people distinguish the pitch of different sounds: place theory and frequency theory.
Place theory explains how people discriminate high-pitched sounds that have a frequency greater than 5000 Hz. Place theory states that sound waves of different frequencies trigger receptors at different places on the basilar membrane. The brain figures out the pitch of the sound by detecting the position of the hair cells that sent the neural signal.
