Sensation Flashcards
what do our senses do?
our senses gather information about the outside world and translate it from physical energy into something the brain can use to produce an internal state called sensation in the form of brightness or loudness
what is sensation and perception?
sensation is the beginning stages
sensations are translated into perception
perception is the later, interpretation stages
conscious experiences about the world and yourself, prior knowledge, memory, current emotional state influence how sensations are translated into our knowledge of reality
stages of conversion from physical energy to neural energy
- accessory structures modify physical stimulus e.g. lens of the eye, outer ear modifies sound
- transduction is when physical energy is picked up by receptors and converted into neural energy e.g. cells in the retina respond to light energy (physical energy) and stimulates nerve (neural energy) - receptors respond best to changes in energy levels, otherwise adaptation occurs e.g. acclimatising after entering a cold pool
- sensory nerves send transduced neural energy to the brain - nerve signals first go to the thalamus (relay station) then onto different parts of the cortex for further processing e.g. visual or auditory cortex e.g. retina -> optic nerve -> thalamus -> visual cortex
- sensation is produced once message reaches brain - information is then interpretated in the context of the situation
how are senses and thresholds measured?
noise: random excitation or inhibition of neurons that either increases or decreases the sensed intensity of a physical stimulus
difficult to measure thresholds for individuals for light and sound
nervous system interprets information differently
nerve cells are active even when there is no stimulation coming from the outside world
that activity of nerve cells is called neural noise which can be excitatory or inhibitory
what does excitatory and inhibitory mean?
excitatory: cells ready to fire or fire - more active cell
inhibitory: cells don’t fire
excitatory and inhibitory stimuli change how intense the outside source is - same amount of energy - not directly linked to what is going on in your environment but is what is going on in your nervous system
implications of noise
- repeated presentations of the same physical level of intensity do not always produce the same internal sensation
- if a physical signal (e.g. sound units) is doubled that does not always produce a doubling of sensation (may not appear twice as loud)
- absolute threshold (lowest level of intensity at which a person detects stimulus) - defined as the physical intensity at which a person can detect the stimulus 50% of the time
threshold helps to determine if people have hearing loss or if senses are working or in music industry
explain Weber’s law
difference threshold is the smallest amount of change in the intensity of a stimulus before a change is detected
requires 2 stimuli to detect a difference
what is the smallest amount of change before a difference is detected? look at how much of the standard can change before you detect a difference
Weber fraction
difference threshold increases in proportion to the standard (stimulus with original intensity)
produces fraction:
change in intensity of stimulus / intensity of standard = C
∆I/I = C
what energy is involved in hearing?
physical energy –> sound waves
what is pitch?
frequency of the sound waves
measured in Hertz (Hz)
humans range from 20Hz to 20000Hz
dogs range up to 80000Hz
frequently = high pitch
infrequently = low pitch
what is volume?
amplitude of the sound waves
measured in decibels (dB)
higher wave = louder sound
lower wave = quieter sound
what is timbre?
‘nature’ of the sound e.g. instruments
‘simple’ wave - similar to sine graph
‘complex’ wave - similar to sine graph but zig-zag
how does sound work?
- Sound travels through pinna and ear canal into middle ear.
- Ear drum vibrates in response to sound waves.
- Small bones connected to the ear-drum (hammer, anvil, stirrup) vibrate in response to ear drum vibrates. Vibrates one after each other
- Stirrup vibrates against oval window and causes oval window to vibrate which causes waves within the fluid filled cochlea.
- Fluid in cochlea begins to move with the cilia.
- Fluid causes basal membrane to vibrate which stimulates hair cells or nerve cells to cause a sensation .
what is place theory?
different places on the basilar membrane vibrate more depending on pitch
low frequencies at apex, high frequencies at the base near oval window
research supports that artificially stimulate particular areas of the membrane, produces sensations of hearing different pitches
elderly and hearing
- Elderly who cannot hear certain high pitches show evidence that there is damage to the base of basilar membrane.
- Pitches are determined by where the hair cells on the basal membrane are being stimulated: if there is a high frequency then the base is stimulated, if there is a low frequency then the apex is stimulated
- may need cochlea implants
problems for place theory
Below 1000 Hz, no specific place on the membrane vibrates more than any other.
However, we can distinguish between tones that are below that frequency.
alternative to place theory
Frequency (temporal) Theory
Basilar membrane is like a guitar string. The higher the frequency of the sound, the faster it vibrates.
It is the rate that the hair cells are stimulated that matters, not which hair cells (place theory).
problem for frequency theory
Above 1000 Hz, cell cannot fire any faster (refractory period).
However, we can distinguish between tones that are above that frequency.
frequency and volley theory
There is alternation in the firing of hair cells (volleying).
Groups of hair cells fire in alternation, sending a higher frequency of signal to the brain.
problem for frequency and volley theory
Very high frequencies (e.g., 10,000 Hz) would need very complex teamwork
what energy is involved in vision?
physical energy –> light energy
how is light measured?
light is wavelike
measured in nanometers
1nm = 1 billionth of a meter
electromagnetic spectrum
x-rays (10-1 nm)
ultraviolet (101 nm) - visible light is in between
infrared (103 nm) - visible light is in between
radar (105 nm)
FM radio (109 nm)
TV (1011 nm)
am radio (1012 nm)
colours and wavelengths of light
- violet 400 nm
- blue 500 nm
- green 570 nm
- yellow 600 nm
- orange 650 nm
- red 700 nm
how does the eye work?
- The cornea is the first thing the light reaches.
- Iris is the opaque tissue that controls the size of the pupil and the colour of the eye – controlled by sphincter muscles.
- Pupil is the opening that lets light into the eye.
- Lens focuses the object you’re looking out – projected onto the back of the eye – changes thickness depending on what you are looking at (close or far) – controlled by ciliary muscles – lens loses malleability and get weaker as you get older.
- Vitreous humour is the jelly-like fluid that fills the eye – floaters reside here.
- Retina is the tissue at the back of the eye – retina contain photoreceptors (receives light) which contain substance called photopigment.
- When light is projected onto photoreceptors, the photopigment contained within it chemically breaks down, which initiates transmission of information to the brain
- When photopigment breaks down in response to light, it is said to have been bleached (it literally becomes lighter in colour)
- This sends nerve signals to the optic nerve thalamus visual cortex in brain
what are the two types of photoreceptors?
rods and cones
what are rods?
vision in dim light
no colour information
few are located on the fovea
contain the photopigment rhodopsin
what are cones?
vision in bright light
colour information
fine details
contain the photopigment iodopsin
3 different types of iodopsin –> 3 different types of cones which are sensitive to different wavelengths of light: short, medium and long
the trichromatic theory: colours of the spectrum
colours that can be made of either a unique wavelength of light or a combination of unique wavelengths
what are primary colours?
colours that can produce any colour on the spectrum when combined in the right amounts
what are primary pigments
red blue and yellow
subtractive mixture
what are primary lights
red blue and green
additive mixture
cones sensitive to short wavelengths produce sensation of…
blue
cones sensitive to medium wavelengths produce sensation of…
green
cones sensitive to long wavelengths produce sensation of…
red
what happens when colour mixes?
colour mixtures will cause more than one type of iodopsin to be bleached
combination of iodopsin breakdown produce sensation of other colours on the spectrum
support for trichromatic theory
Dichromatic colour-blindness - some people have only two types of iodopsin: either blue and green or blue and red.
Need both red and green iodopsin to distinguish red from green in the world; dichromats can’t make this distinction
Monochromatic colour-blindness - only have one type of iodopsin. They see only shades of monochrome - need more than one type of iodopsin to see colour variation.
problems for trichromatic theory
Dichromats can see yellow. Yellow is (supposedly) the sensation when both red and green iodopsin is bleached. How can both be bleached if dichromats don’t have either green or red iodopsin?
Other theories (e.g., opponent process theory) have been proposed to work in conjunction with trichromatic theory.
what are the opponent pairs that visual receptors are organised into?
blue/yellow
red/green
black/white
can cause colour afterimage if you overwork the receptors
how do we see? photoreceptor –> sensation
Information from rods and cones is conveyed to ganglion cells (via bipolar cells) which send info up the optic nerve to the brain.
(Ganglion cells found in retina are particularly important for feature analysis)
The place where optic nerve leaves the eye is known as the optic disk (blind spot). Optic nerve connected to retina by optic disk.
All information from the eye meets at the optic chiasm which re-routes it to the thalamus, and then to the visual cortex (in the occipital lobe).
Information from left visual field goes to right cerebral hemisphere; information from right visual field to the left cerebral hemisphere.
what are the three different receptors involved with touch?
temperature
pressure
pain
temperature and touch
- It’s relative so adapt easily. At 32 degrees Celsius (physiological zero) neither warmth nor cold is felt. Above that temperature, we feel warmth, below that temperature, we feel cold.
- However, if skin temperature is raised or lowered, what is sensed as hot or cold changes…(buckets of water example)
pressure and touch
- It’s relative so adapt easily. Changes in pressure are felt; large adaptation; don’t feel our wristwatch pressing on our skin except for only a short while.
pain and touch
Specific neural pathways – pain receptors in skin
pain pathways with neurotransmitters: Substance P produces pain; Endorphins decrease it.
stimulating parts of brain with electrodes can release endorphins to reduce pain.
endorphins are released in anticipation of pain as well (classical conditioning)
acupuncture may work by stimulating endorphins.
smell and pheromones
- chemicals secreted in the body which produce a physiological response usually in others
- Dogs, monkeys, rodents all respond to pheromones
- Females secrete pheromones when ovulating, males will detect this.
- Do humans?
- women are asked to dance more often if ovulating
- Some evidence that women on the same dormitory floor “sync up” menstrual cycles (menstrual synchrony)
- mechanism may be pheromones (?)
- how linked is ovulation with the desire to have sex?
- Behavioural or pheromones?
smell and olfaction
- Over time, ability to detect odour drops to about 30%.
- 8% of people lose sense of smell: lose interest in sex (tightly linked)
- Olfaction tightly linked to taste (inability to smell during a bad cold reduces taste sensation)
how does smell work?
Nasal passages with olfactory mucosa which contain olfactory receptor cell. Transduction occurs, connected to nerve, going to brain to the olfactory bulb which produces sense of smell.
what do taste buds sense?
bitter
salty
sour
sweet
umami
how many taste receptors are there?
four maybe five
what other factors effect taste?
olfaction
mood
texture
add flavour to food
