sensation and perception 2 Flashcards
passive perceiver vs active perceiver
passive:
- process of perceiving does not distort nature of external information
- current state of knowledge does not affect perception
active:
- we actively use information in the environment to adjust our perceptions
- current state of knowledge does not affect perception
what are the problems with the passive perceiver
distal stimulus is not the same as the proximal stimulus
what is the proximal stimulus and distal stimulus
proximal:
- stimulus as it appears to the sensory receptors
distal:
- actual 3D object out in the world
active perceiver - what is perceptual constancy and unconscious inference
ability to maintain the same dimensions of an object, even when viewing the object from a different angle or from further away
our perception of size is related to the amount of space that an object occupies in the retina - a closer object occupies more space than a far away object
- this process is known as unconscious inference
how do we achieve constancy
we use supplemental information in the image on our sensory systems
for size: we may estimate distance using linear perspective or binocular vision, or vergence of the eyes
for lightness: we may estimate the location of shadows or estimate the overall brightness of the scene and take that as an estimate of illumination
unconscious inference
the outer ear comprises:
the pinna
auditory canal
eardrum
the middle ear comprises
the ossicles:
the malleus (attached to the eardrum)
the incus (bound by ligaments to the malleus and stapes)
the stapes (bound to and strikes the oval window like a bass drum pedal)
functions of the middle ear: overload protection
granted by the acoustic reflex, which stiffens the ear drum and restricts the ossicles’ movement
prevents shooting your ears out
functions of the middle ear: impedance (resistance) matching
fluid filled inner ear is more resistant (greater impedance) than the air filled middle ear (sound would be lost if it were not amplified by the middle ear)
amplification is achieved by the ossicles , and by forcing the vibrations from the large eardrum onto the much smaller oval window
inner ear: cochlea - organ of Corti and Basilar membrane
organ of Corti sits on top of the basilar membrane
more specifically, the portion of the organ of the Corti that makes contact is called the tectorial membrane
the tectorial and basilar membranes slide back and forth, bending the hair cells (receptors)
bending triggers electrical changes in the hair cells, which generates the release of neurotransmitters
the bending occurs in the cilia, not the whole cell
hair cell receptors
come in two varieties: inner and outer hair cells
both types contain bristle like structures on their tops t
we have much more outer hair cells than inner, but the inner are “most favoured” - 95% of auditory nerve fibres “take their orders” from the inner hair cells
theories about how inner ear activity could code frequency - temporal theory
originally posited that the higher the frequency, the greater the number of action potentials in the cochlea, but was later modified to the volley theory
what is a limitation of the temporal theory, and how can we circumvent this (volley theory)
each neuron has a refractory period of about 1ms, which would mean that we couldn’t hear frequencies greater than 1000Hz
therefore, modified to the volley theory, which posits that a group of neurons could have inter leaved responses that could achieve rates greater than 1000Hz
what is a problem with volley theory
might depend on one neuron that supervises the other interleaved responses, and this “supervisor” would have its own refractory period of 1ms
so temporal and volley theory could be true, but most likely at low frequencies only
to code higher frequencies, place theory was proposed
theories about how inner ear activity could code frequency - place frequency
holds that a travelling wave of excitation is maximal at different places on the basilar membrane
auditory pathways
auditory nerves make their way to the medial geniculate nucleus of the thalamus
neurons in the MGN project to primary auditory cortex, A1
in A1, some neurons receive input from both ears
these are called binaural neurons
what do binaural neurons do
they help us to localise sounds
A1 is tonotopic - what does this mean
positions of various frequencies represented in A1 correspond to positions back in the basilar membrane
olfactory system
mucus layer: layer of snot that traps chemicals that are the smell particles
olfactory hairs: extensions of the receptor cells can receive the chemicals
olfactory filaments: like a telephone wire, sends message to olfactory bulb
olfactory bulb: large, collects signals and relays them to the tract
olfactory tract: gathers the signals and tells the brain there is a stink in the air
limbic system: emotional visceral portion of the brain interprets the information
stimulus
olfactory receptors pick up chemicals
signal relayed through cribriform plate by the olfactory filaments
signal gathered by olfactory bulb
signal sent down cranial nerve 1 (olfactory tract)
brain translates this using limbic system
gustatory system
tongue: home of taste buds
taste buds: number around 10,000 and cover 2/3 of the tongue
papilla: 2 kinds - fungiform and circumvallate
gustatory hairs: stimulation of these long microvilli send a signal to larger cells
gustatory cells: signal from hairs send wave of depolarisation to sensory nerves
sensory nerves: cranial nerves 7, 9 and 10 are stimulated
something is eaten
saliva breaks down material
sent to tastebuds
gustatory cells stimulated by Gus. Hairs
signal gathered by sensory nerves
signal sent down cranial nerves 7, 9 and 10
brain translates this
what are the 5 kinds of taste
sweet - triggered by shapes of sugar, saccharine and amino acids
sour - triggered by H+ groups
salty - triggered by salts
bitter - triggered by OH groups
umami - triggered by aminos
