Sensation

SENSATION

• Senses gather info from outside world -> sensations (brightness, loudness)

• Translate physical energy -> something brain can use

• Sensation vs Perception

  • Perception: knowledge, conscious experience of the world, involvement to turn sensations into perceptions

Stages of conversion in sensation

• From physical energy into neural energy

1. All senses have some form of accessory structure - modifies physical stimulus - biological parts of the body (lens of eye changing shape looking at different distances)

2. Transduction: physical energy -> receptors -> neural energy

   • Cells in retina that respond to light energy (physical) -> certain wavelength of light -> respond -> stimulates nerves

   • Not a purely objective process - respond to change in energy levels, adaptation

     • Getting used to smells - adapting, getting used to cold water over time

3. Sensory nerves send transduced neural energy to brain -> thalamus

   • Thalamus: middle man, relay station -> cortex (visual, auditory, etc.)

   • Not a single process - different levels of processing as you go deeper into nervous system

4. Sensation produced once message reaches the brain

Measuring senses and thresholds - psychometrics

• Thresholds need to be measured

• Subjective elements, way nervous system is able to determine information

• Neural noise: nerve cells active, even when no stimulation coming from outside world

  • Excitatory: cell is ready to fire, already firing then gets stimulated from outside world

  • Inhibited: not firing, having a rest - changes how intense outside stimulus is

  • Not dependent on outside stimulus, dependent on what is happening in your nervous system

  • Changes all the time, nervous system in constant state of flux

• Repeated presentations of same physical level of intensity don’t always produce same internal sensation

• If physical signal is doubled -> not always producing doubling of sensation

• Absolute threshold: lowest level of intensity, physical, in which a person detects a stimulus 50% of the time

• Understand graphically what is going on and how it relates to excitation and inhibition that is going on in the nervous system

• Absolute threshold no noise -> straightforward, can't see it and then they can

• Absolute threshold noise -> more realistic, real world reaction

  • Trying to back track and figure out what could they have seen if there was no noise (50%)

• Thresholds important -> determining how the senses are working (hearing loss etc) -> digital music, getting rid of music that is below the threshold - streaming, able to create smaller files that can be streamed

• Scientific: relationship between outside world and internal world

Weber's Law

• Psychophysicist

• Focus on difference thresholds: smallest amount of change in intensity of stimulus before change is detected

  • Need 2 stimuli - what is smallest amount of change before person can tell there is a difference

  • First object: standard - how much change from standard before you can detect change

  • Difference threshold increases in proportion to the standard - if standard is very low, only need tiny amount of change to detect difference

  • As standard got more intense, units went up -> needed a bigger change before you need to detect a difference -> followed nice simple pattern

  • Weber fraction/Weber's Law: difference threshold increases in proportion to the standard (stimulus with original intensity)

    • Change in intensity of stimulus/intensity standard

• Doesn’t always apply to every type of sense - doesn’t tend to work with vision very well

Hearing

• Units of sound waves

• Frequency of waves gives wave its pitch -> if wave is occurring frequently -> higher pitch (opposite applies)

• Measured in Hertz (Hz)

• Humans can hear from 20Hz - 20,000 Hz

  • Anything outside of this is outside of our audible range

  • Dog hears up to 80,000 Hz (dog whistle)

• Amplitude of wave gives volumes - decibels (dB) - worried about sounds over 100 dB

• Complexity (timbre) - nature of the sound (instruments in music - they all sound different but have the same pitch)

  • Complexity = physical dimensions

• Eardrum vibrates from soundwaves - small bones in ear vibrate in response to ear drum vibrating - hammer, anvil -> stirrup connected to oval window and vibrates against it - oval window part of cochlea - cochlea attached to auditory nerve, fluid in cochlea begins to move - stimulates hair/nerve cells inside cochlea - travels to auditory nerve and then signals get sent to brain

• Round window, every time something hits against oval window, it has a bit of give and allows vibration to occur

• Hearing pitch - place theory

  • Argues that different parts of basilar membrane vibrate more depending on pitch

  • Low frequencies at apex, high frequencies at the base (near oval window) - stimulating hair cells on cilia at one part of the membrane -> which cilia on the basilar membrane determines whether we are listening to high pitch or low pitch

• E.g. cochlear implants that can stimulate parts of the membrane -> can hear frequencies depending on where the implant is allowing vibrations

  • Speech made up of high frequencies - elderly people cannot hear certain high pitches - shows that there is damage to base of basilar membrane

• Doesn’t explain everything

• Issues:

  • Below 1000 Hz, no place on basilar membrane that vibrates more than another - can hear difference between 200 Hz and 800 Hz tone with no difficulty - can distinguish between tones that are below that frequency

• Frequency (temporal) theory

  • Basilar membrane -> guitar string. Higher frequency of sound -> faster it vibrates

  • It is the rate that the hair cells are stimulated that matters, not which hair cells (place theory)

  • Issues:

    • Above 1000 Hz cell cannot fire any faster (refractory period) - can distinguish between tones that are above that frequency

• Frequency and Volley theory

  • Idea is that hair cells not just acting in unison, doing teamwork - one group fires as fast as they can, another does the same, then they work together which sends a higher frequency to the brain

    • Not doing the exact same thing at the same time - each doing as much as they can and work together

  • Issues:

    • Very high frequencies (e.g. 10,000 Hz) would need very complex teamwork

Vision

• Sense that has been studied the most in psychology

• Rich part of our experience

• Physical energy: light

  • Whether light is described or a particle/wave is a debate

  • Assuming it is wavelike

  • Highly frequent: nanometres (1nm = 1 billionth of a meter)

• Light part of electromagnetic spectrum - different wavelengths

  • E.g. x-rays 10 to the 1 nm; TV 10 to the 11 nm

• Visible light - above ultraviolet light (cant see it) - cant see infrared radiation -> between these two extremes is where we get visible light

  • Only see a small bit of the spectrum

  • Colours of the rainbow: white light being refracted, spread apart, see different colours of the rainbow

  • Violet - 400nm -> all the way to red 700nm (violet, blue, green, yellow, orange, red)

  • Ultraviolet and infrared out of view for us but still part of spectrum

• Eye

  • Light comes in through pupil -> ends up on back of eye which becomes a screen, retina, image being projected onto

  • Transparent surface (cornea) first thing light will reach - aqueous humour behind that, like a goo - pupil, opening that allows light into eye, changes sizes - iris is opaque tissue that controls size of the pupil, colour of eyes, controlled by different sphincter muscles that allows to change the size of the pupil - lens is critical for vision because it focuses on the object that it is looking at so image is focused on back of the eye, changes shape to allow focus onto retina, stretches out on distant objects and thickens on closer things, controlled by ciliary muscles (reading glasses when you get older - lens loses mailability as you age, weakens over time and loses flexibility) - vitreous humour behind lens, fluid that fills centre of eyeball, light that goes through fluid before it reaches retina, floaters are little crystals that sit around vitreous humour - retina, where action happens, lens has focused an image being looked at and projected it, have literal image on back of eye

  • Retina: photoreceptors PR (light, receiving)

    • Receive light

    • Photopigment PP: critical for all aspects of vision

    • When light projected on PR, the PP chemically breaks down - initiates transmission of info into the brain by photoreceptors by the optic nerve -> thalamus -> visual cortex

      • Called bleaching - process, chemical reaction that occurs, literally gets lighter as light is shown on it

    • PR important for vision, 2 types on retina named from shape

      • Rod: responsible for vision in dim light, do not give any info about colour, very few located on focal point of visual field (fovea), rods operating in periphery of vision - PP called rhodopsin, bleached mostly with light near middle of spectrum

      • Cones: vision in bright light, colour info, fine details, need lots of light to work - 3 different type of PP (iodopsin), 3 different types of cones sensitive to different waves of light (short, medium, long) which allows us to see colour

• Colour vision: Trichromatic (Young/Helmholtz) Theory

  • All different colours of spectrum can be seen when wavelengths of light broken down

  • Colours can be made of either a unique wavelength of light or a combination of unique wavelengths

  • Primary colours: colours that can produce any colour on the spectrum when combined in right amounts

    • Light is additive mixture, liquid is subtractive mixture

      • White light made up of all wavelengths of light

      • Pigments: what has been taken away from white light and has been allowed to reflect, white light hits paper if nothing is on it, if you put pigment on it that looks red, all pigments extracted except red

      • Blue, red, green -> white (light)

      • Blue, yellow, red -> dark grey (pigment)

      • Pigments: colour you see is what is allowed to be reflected

    • Primary colours of light: red, blue, green

      • Different from pigments: light is additive mixture, pigments subtractive mixture

      • If you combine all 3 colours you get white light - white light made up of all these different wavelengths of light

    • Pigments: what is being taken away from white light and is being allowed to reflect - all wavelengths have been subtracted except for that colour

      • Mixing red, yellow, blue -> dark grey

    • Pigments and light work in completely different ways - keep them separate

  • Have 3 different types of cones that are sensitive to different wavelengths

    • Short wavelengths: blue (sensation)

    • Medium wavelengths: green (sensation)

    • Long wavelengths: red (sensation)

      • These 3 are primary colours of white - can get combinations

      • Don’t have cones that respond to yellow, but have cones that allow combinations of colours that produce yellow

      • Colour mixtures will cause more than one type of iodopsin to be bleached

      • From just 3 cones you can see different colours of the rainbow

• Support

  • Colour blindness - tend to be male

  • Dichromatic colour blindness: only have 2 types of iodopsin (either blue/green, or blue/red)

  • Monochromatic colour blindness: only have one type of iodopsin - only see shades of monochrome - need more than one type of iodopsin to see colour variation

• Problems

  • Dichromats can see yellow - sensation of yellow is supposed to occur when red and green iodopsins are bleached - how can they see yellow? Problem

  • Opponent process theory (not covering this)

  • Visual receptor types are organised in opponent pairs:

    • Blue/yellow

    • Red/green

    • Black/white

    • Can cause colour afterimages

  • Colour after effects: if you focus too much on one colour, another colour can show up based on colour pairings mentioned above

Photoreceptor to sensation (seeing)

• Info comes from rods and cones in respect to colour

  • Ganglion cells: cells in retina -> bipolar cell layer -> send info up optic nerve to the brain

  • Feature analysis

  • Optic nerve -> retina (optic disc)

    • Where optic nerve is connected, there are no photoreceptor cells

    • Have a blind spot - can find it

    • All info from eye meet

      

      s at optic chiasm which re-routes it to the thalamus -> visual cortex (in occipital lobe)

    • Info in occipital lobe is split into visual fields - left and right

      • Info from left field -> right hemisphere

      • Info from right field -> left hemisphere

    • Occipital lobe: highest level of processing

    • Think of vision, not only due to rods and cones, but there is more and more processing as you get to the occipital lobes

Touch

Receptors

• Temperature

  • Receptors in sensation are relative - adapt quite easily to different situations

  • 32 degrees c -> physiological zero -> neither warm nor cold

  • If skin temp is raised or lowered, what is sensed as hot/cold changes

• Pressure

  • Relative as well - changes

• Pain

  • Neural pathways: go from one part of nervous system to another

  • Pain receptors in skin; particular substance known as neurotransmitter -> allows nerves to communicate with each other

  • Body makes own endogenous opioids -> endorphins -> body's own painkiller

    • People who run long distance describe a runner's high -> body is releasing endorphins to combat pain experienced from the run

  • Can stimulate certain parts of brain with electrodes to ease pain

  • Endorphins released in anticipation of pain (classical conditioning) to combat pain

  • Acupuncture may work by stimulating endorphins

  • Interesting - prefer to not have it, but if you see people who have nerve damage it can cause complications, pain is useful for survival and protection

Smell

• Olfactory sense

• Pheromones - chemicals secreted in body that gives physiological response (androsterone)

  • E.g. dogs respond to pheromones - when female is ovulating she releases pheromones and this is smelled by the male

• Evolutionary psychologists interested in ovulation, pheromones etc.

• Humans different from other mammals - not clear high/low receptive periods like other mammals - this could be evolving out of this type of cycle

  • How linked is menstrual cycle in desire?

  • Not as clear as with other mammals - but there are hints - may give off different kinds of signals

    • Watch how women dance in nightclubs and how interested men are whilst women are ovulating

• Menstrual synchrony: has been criticised

  • Human females that spend a lot of time together/close proximity -> cycles sync up

  • May be pheromones, reason for this is not clear

• Pheromones not clear cut

• Pheromones work with animals

  • Farmers use pheromones to try and get animals to mate with each other

• High adaptation

  • Over time ability to detect odours drops by 30% -> get used to smell

  • 8% people lose sense of smell -> associated with lost of interest in sex -> might be linked to pheromones?

• Olfaction linked to taste

• Physiology

  • Nasal passages with olfactory mucosa -> olfactory receptor cells -> turn into neural signal through transduction -> cilia pick up odour -> connected to nerve which goes to brain, covered in myelin sheath for protection-> place in brain where it is processed -> olfactory bulb

Taste

• Main senses: tastebuds located on the tongue

  • Bitter, salty, sour, sweet, umami? (MSG - monosodium glutamate) 

• Operates a bit like colour sensation

  • Trichromatic theory: different combinations change flavours

• Olfaction - smell of food (aged cheese on a cracker may be delicious, cheese on its own may smell terrible)

• Sensors located on the tongue

  • Bumps on tongue - papillae

  • Between papillae (they're not the tastebuds) - taste buds and taste cells -> nerves go to brain and give us our sense of taste

  • Some people can lose sense of taste if they smoke a lot -> trenches get filled up with gunk that comes from tar

    

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