Week 9: Sensation & Perception Flashcards
What is sensation?
The manner in which our sense organs receive information from the environment
Detecting a stimulus
What is perception?
The manner by which people select, organise, and interpret sensations
The summation of all sensory inputs mixed with goals, ideas, expectations
Understanding a stimulus
What is transduction?
The manner by which physical energy is converted into sensory neural processes
What is the former model of the organisation within the sensory system?
Receptors - transduced here, then goes along nerves into the THALAMUS, into the PRIMARY SENSORY CORTEX - SECONDARY SENSORY CORTEX - ASSOCIATION CORTEX
However it is much more complicated than this
What is the neocortex?
A thin sheet of cells that cover the rest of the brain
How are the cells in the neocortex organised?
Into 6 stereotypical layers
They are all arranged in the same way (types, arrangements, connections)
What are layers 1-3 of the neocortex for?
Cortex-cortex transmission
What is layer 4 of the neocortex for?
From the thalamus to the cortex (inbox)
Cells mostly get input from the thalamus
What are layers 5-6 of the neocortex for?
5 - send to all the way down to toes (muscles)
6 - to thalamus etc
(outbox)
What is the sensory organ and receptors for vision?
What do they do?
The eye
Rods and cones
Transduce neural signals up the optic nerve
What is the primary visual pathway?
Retina, optic nerve, optic chiasm, thalamus, occipital lobe
Are there any senses that do not go through the thalamus?
Olfaction does not
Multisensory integration?
Information is assimilated from various individual sensory systems and coordinated
What external energy is involved in hearing?
Occurs via sound waves which result from rapid changes in air pressure caused by vibrating objects
What is pitch?
The frequency of vibration
How many times does it go up and down in a period of time
What is loudness?
Sound wave intensity (increased amplitude)
What is timbre?
Provides information about the nature or complexity of the sound
Where are primary auditory receptors located and what are they?
Located in the inner ear (cochlea)
- Tiny hair cells that convert sound energy into neural impulses (sent along to primary auditory cortex)
What is the external ear called? and the role?
The pinna
Includes the lobe and canal they funnel sound waves into the eardrum
What is the name of the eardrum?
Tympanic membrane
What is the middle ear?
A hollow region between the eardrum and cochlea that contains the ossicles
What are ossicles?
Middle ear bones
- Malleus
- Incus
- Stapes
These vibrate at the frequency of soundwaves and transmits that to the inner ear
What is the process of energy moving through the ear?
Sound waves come in along the ear canal, making the eardrum vibrate.
This vibrations mess with the 3 middle ear bones.
The stapes vibrates the membrane called the oval window
Vibrations transferred into the fluid of the cochlea to reach the internal structure, the organ of corti
What is the cochlea?
The cochlea is a snail shaped structure of the inner ear containing the sensory organ for the auditory system - the organ of corti
What are the different parts of the organ of corti?
The basilar membrane - the hair cells reside on this
Hair cells - hair cells move, each of them is for a different frequency depending on where located on basilar membrane (varies with distance from the sound typically)
Tectorial membrane on top - resting on hair cells
What does the stimulation of hair cells trigger?
Action potentials in the auditory nerve
How is the primary auditory cortex organised?
In a similar way to the hair cells in the organ of corti - for differing frequencies. But it is more complicated
Each of the cells responds preferentially to different frequencies
What is the superior temporal gyrus?
The secondary auditory cortex
What are odorants?
Molecules that give off a smell - they bind to receptors in olfactory cilia (in the nose)
What are glomeruli?
Clusters of convergent olfactory sensory neurons (clusters of receptors - send up to the cortex)
Where are the receptor cells in the nose?
In the upper part - embedded in a layer of mucous covered tissue
What is the process of olfaction?
Odorants come in through the nose
There is a porus portion of skull near olfactory bulb -the olfactory receptors come through this region chemicals bind here and send of action potentials that move to olfactory bulb
From here there are diffuse projections to the limbic system and then back to orbitofrontal cortex through the thalamus but in an indirect way
What does the porus part of the skull where olfactory receptors reside mean?
Easy to damage - kills axons
A lot of head injuries can damage this area
Why are smells so emotional and can trigger memories?
Because the limbic system is involved in the olfaction process
What is taste referred to as?
Gustation
Where are the taste receptors? What are they called?
They are in the tongue and oral cavities
These are in clusters of about 50 (located around papillae)
What are the 4 primary tastes?
Sweet
Salty
Sour
Bitter
Each have sensory receptors of their own except for salty and sour - these act on ion channels
What is the 5th taste?
Umami - meat or savoury
Explain the structure of a taste bud?
There is a bulb or pore at the tip - for things to get in
Signals get sent down taste cells towards the gustatory afferent axons
What is the process of gustation?
Taste receptors on tongue - signals going out to solitary tract
Projecting to thalamus to cortex
Is the somatosensory system a singular system?
No there is actually 3 seperate and interacting systems
What are the 3 main systems that interact to form the somatosensory system?
Exteroceptive: external stimuli (touch pressure and pain)
Proprioceptive: body position
Interoceptive: internal body conditions (temperature and blood pressure)
Topographic organisation of the somatosensory cortex?
Each neuron in a particular column has a receptive field in some part of the brain
The more important/sensitive the part of the body is, the more area dedicated to it
What does the iris do
Controls how much light enters the eye
What does the pupil do
It is a circular hole where the light enters the eye
What is the cornea
It is a curved transparent layer covering the iris and the pupil
The curvature is responsible for bending incoming light to focus it on the back of the eye
What is the lens
It does the same as the cornea but can change its curvature to accommodate as it is made up of cells
What does the retina do
It is a thin membrane that is at the back of the eye it is technically part of the brain
Receives light that the lens has focussed and convert it into neural signals for the brain
What is the optic nerve
It contains the axons of ganglion cells and travels from the retina to the brain
What is the fovea
It is the central part of the eye responsible for acuity (sharpness of vision) this is why we move our eyes
Retina is spread aside for the optic nerve to run through
What is the blindspot of the eye
Is a region of the retina that contains no rods or cones - nothing to detect vision
Where are our sensory receptors in the eye?
At the back of the eye - moves along the cells to the front of the eye to optic nerve
What are cones?
Photopic (daytime) vision
High acuity colour information but need good lighting
Only found at the fovea - we move our eye so that we can have high acuity on what we want to focus on
What are rods?
Scotopic (night time) vision
High sensitivity, allowing for low-acuity vision in dim light but no colour information
How many ganglion cells for each cone?
1:1
Whereas there are many rods for each ganglion cell
Contralateral representation in the visual field?
Right visual field is represented in the left part of the brain and vice versa
optic chiasm - cross over structure
How does vision reach the primary visual cortex?
Up optic nerve until reaches the optic chiasm and crosses over, then to lateral geniculate nucleus which is the thalamus - to the primary visual cortex
There is also a path taking information straight from the retina to the superior colliculus
What is the organisation of the primary visual cortex (V1)?
Neurons are organised into vertical columns
Each neuron responds to stimuli from the same part of the retina
Related columns are clustered with half receiving input from the left eye and the other half from the right eye
What is the flow of visual information after it reaches the thalamus?
Primary visual cortex (striate) - secondary visual cortex (prestriate) - visual association cortex (posterior parietal cortex & inferotemporal cortex)
What happens as visual information flows through the hierarchy (eg. V1, V2 and so on)?
The receptive fields become larger and respond to more complex and specific stimuli
What does the primary visual system receive information from?
Most input from lateral geniculate nucleus
What kind of cells do receptive fields have? and what are their characteristics?
- Simple cortical cells: receptive fields are divided by straight lines, responding best to bars or edged, monocular
- Complex cortical cells : respond to straight lines of particular orientation - position of the stimulus in the field doesn’t matter, binocular
Which part of the brain gets sensory input from all systems?
The superior colliculus
What is synesthesia?
Messed up multi-sensory input
Synesthesia is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway
What is found in the brain of those with synesthesia?
Stronger white matter connectivity - more axons between sensory areas
Explain the cells in the lateral geniculate nucleus (see slide 47)
If the ‘on’ bit of the cell is stimulated then you are fully activating the nucleus and it is firing at maximal activation - when a light stimulus is applied, fires rapidly
If the light only reaches the ‘off’ section then the light is going to inhibit it and it wont fire at all. when light isn’t applied they fire at a baseline slow rate
If the light is 50/50 on/off then we get no change, they just cancel each other out
Total deafness in humans?
Rare but if occurs, in one of two forms
- Conductive deafness (damage to ossicles)
- Nerve deafness (damage to cochlea)
What does partial cochlea damage result in?
Loss of hearing at particular frequencies
Lesions to the auditory cortex in monkeys and humans?
Hindered sound localisation and pitch discrimination
What is anosmia and how does it occur?
The inability to smell
- most commonly occurs after a blow to the head that damages the olfactory nerves
What is ageusia and how common is it and why?
The inability to taste
- Not very common at all due to many pathways carrying taste - lots of backups to get information into perception
Asomatognosia?
The failure to recognise ones own body parts (eg. the case of the man who threw his own leg out of bed)
What is a loss of colour vision called and how does it typically occur?
Achromatopsia
Typically occurs due to bilateral damage to the occipital lobe in V4 that processes colour
What is a scotoma?
Discrete regions of blindness
What is neglect syndrome?
Involuntary failure to attend to sensory stimuli presented to the side of space opposite to the site of brain injury
E.g. only shaving one side of your face
What does the McGurk effect show?
Shows how our vision can alter what we believe we are hearing
Trilone paradox?
Tones can contain both a higher and lower frequency in them but our brains have a preference to what to listen to
How does V1 size relate to the size illusion success?
Strongly correlated to the size of the V1 - Smaller V1 = stronger illusion
Why?
Larger V1 = stronger resolution because each neuron integrates across a smaller part of the visual field
