11/5/2012 1:09:00 PM
Frequency coded place stimulated on tympanic membrane
Intensity codded by frequency of firing
Place Theory (Support)
Neuronal population throughout the auditory relay system (brainstem >
thalamus > auditory cortex) do respond to very specific frequencies)
Damage to basilar membrane will result in hearing loss to predictable
Particularly the case for high frequencies
Ageing occurs lower hearing
Place Theory (Problems)
Low frequencies generate a general movement of the basilar membrane. We
should therefore hear mixed frequencies, but we do not.
Low frequency hearing loss is extremely rare.
Frequency theory cannot explain how higher frequencies are coded but place
Place theory cannot explain how low frequencies are encoded, but frequency
What about mid-frequencies (1000-5000Hz)?
Localization of Sound
Time difference between arrival of the sound
Intensity difference between ears.
Cochlear Implants (Bionic ear)
If the cochlea is destroyed, hearing is not possible.
Consists of a microphone, a processor, a transmitter and receiver/stimulator,
An electrode array (perhaps 20-50), collects the impulses from the
Sends them to different regions of the auditory nerve.
The sound the listener hears is not completely natural.
Only a small number of electrodes not thousands. Problem of encoding in the auditory system.
The sound processor send out a signal (pulse)
If a stimulus intensity remains constant, our sensory receptors adapt to it.
The receptor is capable of firing. This is due to neuronal fatigue
Physics of light
Electromagnetic signal whose wavelength varies from 400 to 700
nanometers (tis is called “light”).
Short wavelengths (400-500nm = violet-blue)
Cones and rods
Outgrowth from the brain
Bad sensor because it consists of a series of cells
At the back of the 3 layers are light sensors (cones and rods)
Optic nerve sensor is infront of light sensors and where it begins is where it
blocks rods and cones making the eyes have a blind spot
The rods and cones have a chemical reaction to light.
If the reaction is strong enough, the bipolar cells will be activated
Bipolar cells activate the ganglion cells
The axons of the ganglion cells converge at the “blind spot” to form the optic
This system is a filter system to only allow relevant information in
The Cones Cones - packed in the centre of the retina, near the fovea (where vision is
most acute – “acuity”)
Colour vision: three types of cones
For red, green, blue
A single cone may project to a single (or