Chapter 4Sensation

What Do SensoryIllusions 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 ofa 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 andBiological 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 information.

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.

Continue

Physical Characteristics of Sound

• A waveform represents a wave in two-dimensions.

• Characteristics of Waveforms– Amplitude– Wavelength– Frequency

Return

Figure 4.2:Sound Waves and Waveforms

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