4PAHPBIO Psychology and the Brain Week 3
Psychology BSc Year 1 Signals and Perception
SIGNALS AND PERCEPTION
3.1 THE DISTINCTION BETWEEN SENSATION AND PERCEPTION
AND THE RELATIONSHIP BETWEEN THEM.
Sensation
• The detection of stimuli from the environment
• Involves the cells of the nervous system that are specialised to detect stimuli
• The stimuli occur in energy form, which is transformed into action potentials and sent through the
nervous system
Perception
• The conscious experience and interpretation of information from the
senses
• Involves neurons in the central nervous system
• When perceiving information, it is important to know the key features,
such as the source
Sensation and Perception
• Bottom-up sensory signals are combined in the brain with top-down
previous experience and attention (such as memories and awareness of specific contexts
• This helps us to help us to create a perceptual understanding of a situation and determine an
appropriate behavioural response
3.2 THE PROCESS OF TRANSDUCTION FOR AUDITORY
INFORMATION AND HOW THE STRUCTURE OF THE SENSE ORGAN
SUPPORTS THE ENCODING OF THE SENSORY SIGNAL. 3.3 HOW
AND WHERE KEY INFORMATION IS CODED FOR WITHIN THE
AUDITORY SYSTEMS.
AUDITION (OR HEARING)
• Hearing has 3 primary functions: to detect sounds, determine the location and recognise the identity
of these sources – and thus, their meaning and relevance to us (Heffner & Heffner, 1990)
The Stimulus
• Sounds are produced by objects that vibrate, causing molecules of air to alternate between
compressing and expanding
o The waves travel away from the object at around
1200kph
• If the vibration ranges between around 30-20,000 times
per second, the waves will stimulate receptor cells in
human ears
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,4PAHPBIO Psychology and the Brain Week 3
Psychology BSc Year 1 Signals and Perception
Sound waves
Physical Perceptual
Sound Wave Human Perception Range
Dimension Dimension
Frequency Pitch 20 Hz – 20 KHz
Amplitude Loudness 0-140 dB
Complexity Timbre Varies by auditory sensitivity and
context
THE EAR
Structures
Functions
Outer Ear
• Sound is funnelled via the pinna/auricle (external ear) and through the external auditory canal
• It amplifies certain sounds by forming a closed tube resonator—the length of the tube determines
which frequencies are amplified, which in humans are the frequencies of human speech
• It also helps with sound localisation (only in the vertical plane for humans)
• The pinna has protective functions
o Wax is antibacterial and antifungal and creates an acidic environment to be hostile to
bacteria and other creatures
o Hairs that line the outer eat prevent the entry of small particles and insects
• The tympanic membrane (eardrum) separates the outer ear from the middle ear and vibrates with
the sound
Middle Ear
• The small hollow region behind the tympanic membrane contains three small bones (ossicles)
which move because of eardrum vibrations
o The malleus (hammer) connects with the membrane, transmitting the vibrations via the
incus (anxil) and stapes (stirrup) to the cochlea
• Protects the ear by the middle ear reflex, which can lock the position of the ossicles, preventing
transmission of sound to the cochlea (important in loud environments)
• It can reflect sound waves off fluid surfaces to amplify sound waves to prevent the loss of signal as
it enters the fluid-filled cochlea (such as when in a swimming pool)—acoustic impedance matching
• The bottom of the stapes presses against the membrane behind the oval window (the opening of
the cochlea)
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, 4PAHPBIO Psychology and the Brain Week 3
Psychology BSc Year 1 Signals and Perception
Inner Ear
• The cochlea is filled with fluid, so sounds transmitted through the air must be transferred to its liquid
medium
o The round window (a flexible membrane-covered opening) allows the fluid inside the
cochlea to move back and forth
o Pressure changes in the fluid underneath the basilar membrane are transmitted to the
membrane of the round window
• The base of the stapes vibrates against the membrane behind the oval window and introduces
sound waves of high or low frequency into the cochlea
o When the base of the stapes pushes in, the membrane behind the round window bulges out
o The vibrations cause part of the basilar membrane to flex back and forth
• The cochlea is divided longitudinally into three sections: the scala vestibuli, the scala media, and
the scala tympani
o The organ of Corti, within the scala
media, sits on top of the basilar
membrane and extends towards the
tectorial membrane overhead
• There are both inner and outer cilia—auditory
hair cells (about 3,500 inner and 12,000 outer
hair cells)
o The bases of the inner hair cells are
anchored to the basilar membrane by
Deiters’ cells, and the tips of the outer
hair cells are attached to the tectorial
membrane
• The inner hair cells transduce sound waves into electrical signals
AUDITORY HAIR CELLS AND TRANSDUCTION
Cilia (Stereocilia)
• Hair cells contain cilia (stereocilia), which form synapses with dendrites of neurons which bring
auditory information to the brain via their axons
o Cilia are rigid due to a core of actin filaments surrounded by myosin filaments (Flock, 1977)
o Adjacent cilia are linked to each other by tip elastic filaments (tip links)
o The tallest cilium is called the kinocilium
• Each stereocilia has mechanically gated potassium channels, voltage-gated sodium channels,
glutamate vesicles and synapses with a post-synaptic neuron containing AMPA receptors
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