Chapter 4
Sensation
What Do Sensory
Illusions Demonstrate?
• Streams of information coming
from different senses can interact.
• Experience can change the sensations
we receive.
• “Reality” differs from person to person.
– Our sensory systems create our personal
reality.
Figure 4.1: Elements of
a Sensory System
The Problem of Coding
• How are physical properties coded into
neural activity?
• Doctrine of Specific Nerve Energies
• Types of codes
– Temporal
– Spatial
Linkages: Sensation and
Biological Aspects of Psychology
• Organized sensory information is called a
representation.
• Shared features of representations of
vision, hearing, and skin senses:
– Information from each sense reaches the
cortex via the thalamus.
– Representation of world is contralateral to
the part of the world being sensed.
Linkages: Sensation and Biological
Aspects of Psychology (cont’d)
• Shared features (cont’d.):
– The cortex contains topographical
representations of each sense.
– The density of nerve fibers in a sense organ
determines how well it is represented in the
cortex.
– Each region of primary sensory cortex is
divided into columns of cells that have
similar properties.
– Regions of cortex other than the primary
areas do additional processing of sensory
Sound
• A repeated fluctuation in the pressure of
air, water, or some other substance.
– Produced by vibrations of an object
• Wave: Repeated variation in pressure that
spreads out in three dimensions.
Physical Characteristics of
Sound
• A waveform represents a wave in twodimensions.
• Characteristics of Waveforms
– Amplitude
– Wavelength
– Frequency
Continue
Figure 4.2:
Sound Waves and Waveforms
Return
Psychological Dimensions of
Sound
• Loudness
• Pitch
• Timbre
Figure 4.3: Structures of the Ear
Conduction Deafness
• The three tiny bones of the middle ear
are fused together.
• Prevents accurate reproduction of
vibrations.
• Surgery can break bones apart or replace
them with plastic ones.
• Hearing aids can also help.
Nerve Deafness
• Results when the auditory nerve or the
hair cells are damaged.
• Can be caused by extended exposure to
loud noise.
• Cochlear implants can stimulate the
auditory nerve.
• Hair cell regeneration as a possible
treatment.
Auditory Pathways
• Auditory nerve  brainstem  thalamus
• Various aspects of sound processed in
different regions of auditory system
• Certain parts of auditory cortex process
certain types of sounds
Sensing Pitch
• Different people may experience the
“same” sound as different pitches.
• Pitch-recognition abilities influenced by
genetics.
– Cultural factors are also partly responsible for
the way in which a pitch is sensed.
Locating Sounds
• Determined partly by the very slight
difference when sound arrives at each ear.
• The brain also uses information about the
difference in sound intensity at each ear.
Coding Intensity and Frequency
• The more intense the sound, the more
rapid the firing of a given neuron.
• Frequency appears to be coded in two
ways.
Coding Frequency: Place
Theory
• Sounds produce waves that move down
the basilar membrane.
– Where the wave peaks depends on the
frequency of the sound.
• Hair cells at a particular place on the
membrane respond most to a particular
frequency.
• But how are very low frequencies coded?
Coding Frequency:
Frequency Matching Theory
• Firing rate of an auditory nerve matches a
sound wave’s frequency.
• Sometimes called the volley theory of
frequency coding.
The Ear and Sound Waves: Part
I
The Ear and Sound Waves: Part
2