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Flashcards in 3 - Sensation and Perception Deck (29):

Sensation-Perception relationship

- sensory signal is converted to an electrical signal via transduction in sensory receptors
- signal is sent via the spinal cord to the brain
- a percept is formed in the brain
- the perception is interpreted in light of past experience and attention to form a Perceptual Understanding
- off of which a behavioural response is based


Sound waves

- longitudinal waves in the air caused by vibration
- frequency indicated pitch
- intensity (amplitude) indicates loudness


Protection in the middle and outer ear

- in the middle ear, skin cells migrate outwards to prevent dead cell debris
- middle ear is slightly acidic to prevent bacterial growth
- ear wax has anti-fungal and antibacterial properties as well as being waterproof
- shape and depth of the middle and outer ear prevent damage to the Tympanic Membrane (ear drum)
- outward pointing hairs prevent objects getting in


Amplification by the outer ear

- the outer ear acts like a closed tube resonator, causing amplification of sounds with a frequency of 2-5 kHz (due to its length)
- 2-5 kHz is the standard human speech frequency
- length of a closed tube resonator is equal to 1/4 of the wavelength of the sounds it amplifies

- this works because the nodes (no total difference in amplitude) concentrate at the Tympanic Membrane


Protection by the middle ear

- reflex reaction to a loud sound causes Stepedius muscle and Tendor Tympani muscle to contract, locking the Ossicles, so sound isn't transmitted through the middle ear


Acoustic Impedence in the middle ear

- Middle ear starts at the Tympanic Membrane and ends at the footplate
- footplate has 17x less area so pressure increases 17x
- this helps the sound travel through the fluid-filled inner ear


Function of the Inner Ear

- three chambers
- inner chamber contains organs of corti which are mechanoreceptors, which detect movement of surrounding fluids or membranes (sound)


Organ of corti

- many hair cells on it with cilia on the exterior, decreasing in size, the largest of each cell is the Kinocilium

- these hair cells can not produce action potentials, but synapse onto neurons that can
- extracellular fluid in the ear has a high [K]+ concentration (opposite to other cells), so [K]+ diffuses in at resting

- the ion channels in the stereocilia are mechanically gated so open due to sound wave vibration in the fluid of the inner ear



receptor potential to action potential
- sound wave bends stereocilia towards the kinocilium
- mechanically-gated ion channels open and allow Potassium to flood into the cell, down its concentration causing a receptor potential
- depolarising receptor potential spreads to the rest of the cell, opening voltage-gated [Ca]2+ channels
- Calcium floods in causing Glutamate release into the synapse
- Glutamate binds to AMPA receptors on the post-synaptic neuron and may cause an action potential in the auditory nerve to the brain


Hearing Pathway

- Spiral ganglion (in the cochlea)
- to the Cochlear Nuclear Complex (via Cochlear nerve)
- to the Superior Olivary Complex (via Trapezoid Body)
- to the Inferior Colliculus (via Lateral Lemniscus)
- to the Medial Geniculate Nucleus
- to the Auditory Cortex


Frequency coding of sound information

Place Coding:
- in the Cochlea, different hair cells activate different afferent neurons, and are activated by different frequency sounds
> highest frequency at the beginning (widest) part of the cochlea, and lowest frequency at the end (smallest) part
- Place Coding is poor for low frequencies but is good for frequencies above 1000Hz, and is the only coding method for frequencies about 300Hz

Temporal Coding:
- determining the frequency of the sound by matching that with the frequency of nerve impulses fired in the afferent neuron
- the theoretical limit for frequency of neuron firing is 1000Hz but in reality, sustained activation can only fire as fast as 300Hz
- useful with lower frequencies


Intensity coding of sound

By firing rate:
- the faster a neuron is firing, the louder the sound

By number of neurons:
- a neuron firing at high frequency will recruit nearby neurons to amplify the message


Beyond the Auditory Cortex

From the auditory cortex via:
- Posterodorsal Stream
> to the Posterior Parietal Cortex (PPC) to process 'where' information

- Anteroventral Stream
> to the Superior Temporal Region (ST) in the temporal lobe, processing 'what' information

- Both of these converge on the prefrontal cortex


Superior Olivary Complex

- is involved in location coding
- the first structure to receive biaural input


Hearing Loss

Two types according to the area of damage:
- Conductive Hearing Loss
> damage to the middle or outer ear
+ impact on hearing threshold but nor normally discrimination (can hear okay, but not quiet sounds)

- Sensorineural Hearing Loss (2)
> Cochlear hearing loss (if effecting the inner ear)
> Retrocochlear hearing loss (if effecting the auditory nerves)
+ impact on discrimination but not necessarily threshold (all sounds become muddy)


Severity of hearing loss

Defined by the threshold for hearing

Mild (20-40 dB)
- difficult to follow speech
Moderate (40-70 dB)
- difficult following speech without a hearing aid
Severe (70-90 dB)
- normally need to sign or lip read
Profound (90-120 dB)
- hearing aid has no effect


Glue Ear

- the number one cause of conductive hearing loss in the UK
- common in children
- Tympanic Membrane gets covered with a gluey substance
- Impact on hearing threshold but not discrimination

Risk Factors:
- genetic
- immune suppression drugs
- attending day-care (infection)
- allergies
- overcrowded housing (infection)
- passive smoking
- use of dummy beyond 11 months

- can insert a Grommet (tube) into the Tympanic Membrane to drain fluid and equalise pressure
- this can lead to scarring


Cochlear Hearing Loss (NIHL)

Noise Induced Hearing Loss (NIHL)
- effects 5% of people
- normally due to industrial noise / military / music
- normally bilateral and symmetrical
- can impact threshold and discrimination
- 2nd most reported occupational injury

- due to damage of the stereocilia (hair cells)
- no treatment so prevention is key


The eye

- Dioptric Apparatus
> involved in the refraction of light
> lens stiffens with age


The Retina

- site of transduction in the eye
- more rods than cones
- in the Fovea (focal point of the retina) there are more cones than rods



- have a rod structure at the outer segment
- tend to connect to multiple cells

- have a cone structure at the outer segment
- connect with only one cell

- the outer structures contain photopigment which is comprised of a protein (opsin) and lipid (retinal)
> there are different types of opsin (e.g. rods have rhodopsin)


Transduction in Vision

- visual pigment in the photoreceptor absorbs a photon of light from an incoming stimulus, activating the protein (rhodopsin)
- activated rhodopsin binds to Transducin, causing Transducin to dissociate from GDP and bind to GTP (G-protein)
- the Alpha part of the Transducin molecule (is still attached to GTP) dissociates from the Beta and Gamma subunits
- the activated Transducin (Alpha unit + GTP) activates Phosphodiesterase (PDE) causing a drop in cGMP (cyclic GMP)
- this causes closure of cation channels and a Hyperpolarising Receptor Potential, meaning less NT is released into the synapse with the Bipolar Cells

- Unlike other sensory systems, a stimulus in vision causes a decrease in NT, thus current flows in the dark not the light
> this is called Dark Current


Receptive Fields

- activation of the centre of the receptive field causes the opposite effect to activation of the surrounding area
- useful because it detects change in light


Visual Pathways

- Retina
- Optic Nerve
- to the Lateral Geniculate Nucleus
- OR sub-cortically to the Superior Colliculus
- from Lateral Geniculate Nucleus to the Visual Cortex


Geniculostriate Pathway

- retina is divided into 2 halves: Temporal and Nasal
- Information from both halves goes via the Optic Nerve to the Optic Chiasm
- At the Optic Chiasm:
> the nerve from the Temporal Retina remains on the same side
> the nerve from the Nasal Retina crosses over to the opposite side of the brain
- once leaving the optic chiasm, the optic nerves become the Optic Tract
- these nerves then synapse onto Optic Radiations in the Lateral Geniculate Body
- and finally synapse in the Primary Visual Cortex

- Different Layers of the Lateral Geniculate Nucleus interact with different areas of the Striate Cortex
> thus allowing to infer differences


Colour Coding from Photoreceptors

- Red cones, Green cones, Blue cones and Rods all overlap in the colour they detect, but it's the ratio of activation of these cells that determines colour coding

Opponent Processing Theory:
Excitatory impulse from Red Cone + Inhibitory from Green Cone
= Red-Green interpretation

Excitation from Red Cone and Green Cone
= Luminance

Excitation from Red, Green and Blue Cones
= Blue-Yellow interpretation


Visual Information Processing

- information from different sub-modalities is computed and compared in terms of reliability


Laws of Pragnanz

Law of Proximity:
- objects near eachother tend to be grouped together
Law of Continuity:
- lines are seen as following the smoothest path


Which photorececptors are better in dim light?

Also, in dim light, light isn't causing Rhodopsin activation and thus isn't causing Sodium Channel CLOSING