Sensation And Perception Flashcards
Four Receptors and Senses
Photoreceptors sense Light
Chemoreceptors sense Chemicals/Molecules
Mechanoreceptors sense Mechanical Forces
Thermoreceptors sense Temperature
Empiricism
Knowledge comes from outside the mind.
The environment shapes the brain and our experience of the world.
“Black Slate”/Nurture
Rationalism
Certain fundamental principles drive/shape knowledge.
Our brain’s architecture shapes and constrains experience.
“Innate Tendencies”/Nature
Sensation to Perception - 3 Steps
- Sample physical information
- Integrate and encode it in the brain
- Interpret and use it
Wavelength
Visible light is electromagnetic radiation of 380-760 nanometres.
Wavelengths in order of shortest to longest:
- Gamma Rays
- X-rays
- UV
- Visible Light
- Infrared
- Microwaves
- Radio waves
Photoreceptors
How they work:
When light hits a photopigment molecule, it splits. The split activates the photoreceptor cell and this is the moment of transduction from light wave to neural impulse.
Photoreceptors are at the back of the eye so photopigments can be readily replenished.
Types of Photoreceptors: Rods and Cones
Rods. Cones
Response. Slow. Fast
Recovery. Slow. Fast
Acuity. Low. High
Sensitivity High. Low
Location Peripheral Central Retina
Retina.
Types. One Three (L, M, S)
How many. 120 million. 6 million
Function. Peripheral Detailed, central,
and chromatic vision
low-light
achromatic
vision.
Three Types of Cones
Short (blue) peak at 440 nanometres.
Medium (green) peak at 540 nanometres.
Long (red) peak at 570 nanometres.
Colourblindness
Most commonly lose Large/Medium differentiation (red/green colourblind).
Common in Caucasian males.
X-linked genetic trait.
Less commonly lose Small cones, albinism (no cones) or brain injury.
Two Retinal Mechanisms.
Two Retinal Mechanisms for Edge Enhancement:
- Lateral Inhibition.
- Centre-surround retinal ganglion cells.
Two Types of Retinal Ganglion Cells
Midget Cells
Receive input from cones
Receive input from smaller number of cells.
Project to the parvocellular pathway - high acuity colour pathway to the brain (central vision).
Parasol Cells
Receive input from rods
Project to the magnocellular pathway - low acuity but highly sensitive pathway to the brain (low light, peripheral vision, motion and contrast).
Hair Cells in the Inner Ear
Three Functions:
- Sound Perception (cochlea)
- Head Motion Perception (semicircular canals)
- Gravity Perception (inner ear)
Sounds
High Amplitude - loud sound
Low Amplitude - soft sound
Low Frequency - low-pitched sound
High Frequency - high pitched sound
Cochlear Implants
How they Work:
- Sounds are picked up by the microphone
- The signal is coded and turned into electrical pulses
- The pulses are sent to the coil and transmitted across the skin to the implant
- The implant sends a pattern of electrical pulses to the electrodes in the cochlea
- The auditory nerve picks up the electrical pulses and sends them to the brain.
Mechanoreceptors in the Cochlea
They provide:
- Loudness - amplitude of sound wave increases firing rate.
- Pitch - which part of the cochlea is activated.
- Timbre - composite frequencies - simultaneous activation of multiple locations on the cochlea.
- NOT location - this comes from time and volume differences between the two ears.
Mechanoreceptors in the Skin
Multiple systems: light touch, firm pressure, vibration, pain and skin stretch.
All types respond to physical deformation.
Receptors shapes are specialised for different types of pressure.
Distribution of Touch Receptors
Two Point Discrimination Threshold
- Touch the skin with one or two points.
- Gradually move the points closer together. At some point two will feel like one.
- This distance is the two point discrimination threshold.
- If two points stimulate two receptors, you will feel two points. If two points stimulate one receptor, you will feel only one.
- Density of receptors in the skin is highest on the hands and face, lowest on the upper arm, calf etc.
Haptic Touch
Exploring objects with your subcutaneous mechanoreceptors:
Vibrations = roughness/texture
Position of fingers around object = shape
Skin Stretch, Tendon Stretch = weight
Chemoreceptors
Function like a lock and key. Specific classes of receptors are sensitive to specific molecule types.
Found in:
Tongue (gustation)
Nasal Epithelium (olfaction)
Other locations e.g. lungs, stomach
The Tongue (gustation)
Each of the papillae on the tongue contains multiple taste buds.
Each taste bud contains multiple chemoreceptors.
Five known receptor types: Salty Sweet Bitter Sour Savoury (umami)
Taste Receptors and Tastants
Receptor. Signals
Salty = NaCL (electrolytes) Sour = Acid (spoiled/unripe food) Bitter = Toxins, inedible substances Sweet = Sucrose (calorie-dense foods) Umami = Glutamate (protein-rich food)
Taste Preferences
Innate preferences
Exposure to amniotic fluid and breast milk
Exposure to flavours over lifespan
Genetic variability in taste bud numbers
Aguesia
Inability to taste.
Temporary loss of taste is common.
Permanent aguesia is rare, usually caused by nerve damage or deformity.
Nasal Epithelium
Inhaling brings odorants to the nasal epithelium.
Odorants bind to proteins in the cilia of the receptor cells and activate the cell.
Each cell has only a single receptor type.
Axel and Buck - 2004 Nobel Prize
Roughly 100 different odorant receptors, each one coded by a different gene.
Genetic codes for olfaction receptors alone comprise 3% of our genes.
Can We Localise Smells
Orthonasal vs Retronasal - clear differences in perception/recognition.
Left vs Right nostril arrival times.
Might be mediated by pain pathways.
Scent tracking - better with two nostrils than one.
Pheromones
Odorants to communicate and control conspecific behaviour.
Anosmia
Loss of sense of smell.
Temporary loss due to inflammation/blockage is routine.
Permanent loss due to range of causes (congenital, head trauma, disease, ageing). Roughly 1-2% in young, >12% in elderly.
Chemoreceptors in the Body
The aortic and carotid arteries contain CO2 and O2 sensitive chemoreceptors that sample blood leaving the heart and communicate with brain areas that control breathing rate.
Chemoreceptors in the gastric system cause stomach pain, nausea and vomiting.