Sensation and Perception
What are dBs and how are they calculated?
Decibels dB = 20 x log(p / po) dB = decibels p = sound pressure of stimulus po = a standard sound pressure
Understand place theory, including how and why sounds are processed at different locations in cochlea
Different frequencies of sound are processed at different places in cochlea Thus, perceived pitch is related to the place along the cochlea that is sending the strongest signals to the brain High frequencies are found at the base because: The base is thinner than the apex (3-4 times) The base is more taut than the apex (i.e. stiff; 100 times)
Experience
Past experience of sounds can affect our perception of them If you are more familiar with a melody, you can pick it out of a lot of surrounding sound easier. Similar to knowing a second language—you can pick out the words from distractors or other sounds
The path that sound takes to get to the brain
SONIC MG (superior olivary nucleus, inferior colliculus, medial geniculate nucleus)
Why can other animals smell more chemicals at lower concentrations than we can?
Sensitivity is a largely a function of the number of ORNs present A human ORN can be stimulated by a single odorant molecule, the same as other animals. But humans do not have as many ORNs as other animals.
What do the receptors for different cutaneous senses look like?
Skin receptors that don't end in a capsule are called free nerve endings. They provide information about most of the additional somatosensory modalities (temperature, pain, itch, pleasure)
How important is smell for humans vs. other animals?
Smell is not as important for humans as for other animals. In humans, smell is said to be microsmatic - not as salient in our perceptual experience, and not crucial for survival or reproduction. If macrosmatic animals do not have a sense of smell, they will not reproduce
Monaural cue for elevation
Some frequencies are enhanced (amplified) by the pinna more than others, depending on the elevation that the sound comes from.
Which animal is best at sound localization and why?
The only animal that is better than humans at sound localization is elephants--they have a large head which helps with ILDs. You would need to turn around and foveate on the object that makes the noise. Humans have a true fovea.
How is texture perceived?
The texture of coarse, bumpy surfaces is detected with Merkel receptors. Bumps press on these receptors, and the brain looks at the pattern of activated receptors. Can detect roughness based on some Merkel discs being activated and others not being activated.
What happens when signals reach the cortex? Tonotopic map?
The tonotopic map is preserved in the brain. Front processes low frequency sounds and the back of the brain processes high frequency sounds.
Is there any evidence that smell might be important for us in ways that we don't realize?
There is evidence that humans react to pheromones. Men who smell a shirt worn by a woman who is ovulating will rate it as more pleasant smelling than a shirt worn by a woman who is not ovulating. This can tell us that pheromones may affect reproduction in humans.
What are the different senses of "touch" and why is each important?
Thermoreception: feeling temperature Nociception: feeling pain Pruritoception: sense of itch Pleasure reception: feeling of pleasure Proprioception - sensing the position of the body in space Kinesthesis - sensing the movement of the body in space
How does thermal perception work?
Thermoreceptors activate and depolarize neurons when skin temperature reaches certain range The receptors for innocuous and noxious temperatures are called transient receptor potential (Trp) channels <63 degrees—start to feel pain from the cold >109 degrees—start to feel pain from the heat Each receptor is specific to a certain degree range
What do Ruffini cylinders respond to?
continuous pressure or stretch connects to SA 2 Channel (slowly adapting 2 channel)
What are dB SPL?
dB SPL = 20 log (p/20) Scientists usually use 20 micropascals (unit of pressure) as the reference value (po), because it is near the threshold of hearing at 1,000 Hz When this reference value is used, the amplitude is described as dB SPL, which means decibels in reference to this standard sound pressure level (SPL)
What is complicated about hearing inside rooms?
direct sounds hit your ear before indirect sounds If there is a long lag time, your brain will not stream those sounds and you will hear an echo.
What taste receptors do we have? Where are they located?
filiform papillae--cover the entire surface of the tongue; do not contain taste buds fungiform papillae--shaped like mushrooms; at the tip and the sides foliate papillae--a series of folds along the back of the tongue on the sides circumvilliate papillae--shaped like flat mounds surrounded by a trench; at the back of the tongue Single papilla can have up to ~10 taste buds Single taste bud can have up to 50 taste cells
Function of Merkel receptors
help you determine how much pressure to use; also help to feel details different textures They are closest to the surface of the skin
Sound travels at _________ in air
340 m/s
How many basic tastes do we have and what are they?
5 basic tastes salty sweet sour bitter umami
Cortical plasticity
A pair of sounds can be perceived as different or can cause different physiological responses at an early age, but if the child doesn't have experience discriminating between the two sounds, then the child loses the ability to tell the difference between them, and physiological responses to the sounds become the same. The brain is shaped by experience to respond to sounds that are used in the particular language the child is learning. Occurs between 6 months and 12 months.
Odor identification and discrimination
Absolute threshold: can tell that there is some chemical in the air Humans can discriminate over 100,000 different odors Recognition threshold: can tell what category that smell falls into We are very poor at identifying odors
Pitch coding in the brain
Although pitch perception was originally thought to be determined primarily by place coding, a large amount of evidence points to temporal coding (the timing of nerve impulses in auditory nerve fibers) as the most important determinant of pitch perception, especially below 5,000 Hz. Pitch is related to frequency and periodicity. High frequency and periodicity = high pitch. Holds for frequencies below 5,000 Hz.
What is conditioned taste aversion?
Associating a food with sickness or something else bad (will cause a person to avoid it) Build up an aversion: experimenters inject rats with lithium chloride after they eat fruit loops (which causes them to be sick)—they will then avoid fruit loops for their entire lifetime
Why is sound localization more complicated than visual localization?
Because in visual localization, the object seen creates an image on the retina that directly corresponds to where it is in space. In sound localization, the sound stimulates the cochlea based on its frequencies, not on where the tones are coming from. Two tones with the same frequency that originate in different locations will activate the same hair cells sand nerve fibers in the cochlea.
What cues work for different locations, and for what types of sounds do they work?
Binaural—cues that require both ears Interaural level difference Interaural time difference Monaural—cues that require one ear Spectral cue Distance cues
Auditory canal
Canal increases the pressure changes in the frequency range 1,000-5,000 Hz. It also protects tympanic membrane
Why does capsaicin produce a burning sensation in mammals?
Capsaicin is a chemical that activates Trpv1 receptors in mammals Birds do have Trpv1 receptors, so they can feel heat (as in the temperature of the air), but capsaicin does not activate it
What do they transduce?
Chemical particulates in the air
What are the different types of hearing loss?
Conductive hearing loss—problem with external/outer ear or middle ear; problem getting sound from the air outside to the inner ear; hearing of all the frequencies of sound is reduced Sensorineural hearing loss—damage to structures in the inner ear, the auditory nerve, or the brain; more difficult to treat; selectively lose the ability to hear high frequencies of sound.
How do you prevent hearing loss?
Do not expose ears to high dBs of sound; at loud events, with headphones, and with power tools
How does echolocation work?
Echolocation is locating objects by sending out high-frequency pulses and sensing the echo created when these pulses are reflected from objects in the environment used by bats and dolphins
Interaural Time Difference (ITD)
Effective for low frequency sounds Also effective for sudden onset sounds For high frequencies, there is not as much of an offset, and this makes it difficult to use ITD for sound localization.
What's the difference between First vs. Second pain?
First pain, sharp (Aδ) Second pain, achy or burning (C) The thicker the axon, the faster the action potential will travel. Also, the more myelin you have, the faster the action potential will travel. C fibers are much slower than the rest.
Does taste go beyond what we perceive with our mouths?
Flavor = Basic tastes + Smell + Texture + Temperature + Level of Hunger + Vision You can satiate yourself to a single taste, but other tastes will still stimulate those neurons Taste is also related to culture and to political identification
How can we treat hearing loss?
Hearing aids Cochlear implants Receiver is implanted underneath the skin on the skull. Electrodes depolarize auditory nerve fibers that are below the hair cells. Uses the place theory to transmit different frequencies of sound.
Range of hearing vs. other animals?
Humans can hear between 20-20,000 Hz: our ears are most sensitive to sounds that are between 1,000 and 5,000 Hz Dogs can hear between 40-60,000 Hz (higher than humans) Elephants are the one of the only animals that hear below 20 Hz
How many inner hair cells and outer hair cells are there?
Humans have 3,500 inner hair cells per ear and 12,000 outer hair cells per ear
How are physical and emotional pain related and how are they processed in the brain?
In one condition, they had women receive shocks and then in the next condition, they had women watch their partner receive shocks. There is activity in the ACC but not in the S1. Social rejection activates parts of pain matrix (ex. ACC) However, for people who took Tylenol, their activity was significantly less than people who took a placebo
Understand ways to increase and decrease pain
Increase: Wind-up-- response to a continuing or repeated noxious stimulus builds up over time; it occurs in the dorsal horn cell The purpose of wind-up is that it's a way for the nervous system to keep you feeling pain, so that the injury can heal. Inflammation--When you damage your skin through sunburn, the skin produces chemicals that will increase sensitivity to pain. (Hyperalgesia and allodynia) Decrease: Adaptation-- response to a continuing or repeated noxious stimulus decreases over time; Adaptation occurs in the primary afferent; each time the primary afferent intensity goes down, it sends a reduced signal to the dorsal horn cell, the dorsal horn cell then sends a reduced signal to the brain for pain intensity Opioid drugs Top-down processing (e.g. Placebo)
Be able to describe the process of sound transduction
Inner hair ciglia are bent and tip links are elongated Potassium enters the hair cell, which creates a change in polarization Gated ion channels open and calcium enters the hair cell This triggers the release of a neurotransmitter from the inner hair cell to the afferent nerve fibers These afferent nerve fibers then send an electrical signal to the brain
List each type of mechanoreceptor
Merkel receptors Meissner corpuscle Ruffini cylinder Pacinian corpuscle
Distributed or labeled-lines coding?
Labeled-lines (specificity) coding Tastes are hardwired in the brain to elicit certain responses Taste receptors are specialized: 1) by their chemoreceptors to be sensitive to particular chemicals and 2) by their central connections to cause particular sensations and behaviors when they are stimulated Although, there may be several neurons that respond to the sweet taste.
What fiber types transmit the signals for proprioception, touch, temp, and pain?
Large diameter Aα (A alpha) fibers---Convey proprioceptive information Aβ (A beta) fibers---Convey touch information Small diameter Aδ (A delta) fibers---Temperature, pain and itch C fibers---Temperature, pain and itch
What physiological codes could be operating to process location?
Narrowly tuned neurons and/or Broadly tuned neurons Humans have broadly tuned neurons that will respond to different ITDs Each neuron is still sensitive to a specific offset (they will respond when they receive stimuli at the same time--Jeffress Neural Coincidence Model) Narrowly tuned: birds...............Broadly tuned: mammals
What is the transduction apparatus, where is it located, and how does it work?
Organ of Corti (in the cochlear partition) The inner hair cells is where the transduction occurs. As the fluid flows through, the hairs are bent back and forth, and they open channels when in one direction and close the channels in the other direction. The basilar membrane goes up and down as a wave of fluid comes through. This causes the hairs to brush back and forth on the tectorial membrane.
Understand how sounds differ from one another (ex. timbre, chroma, periodic, etc.)
Periodic--repeat the process over and over again Pitch - attribute of sensation in terms of ordering periodic sounds in a musical scale Tone height - perceptual experience of increasing pitch with increasing fundamental frequency Tone chroma - middle C has same tone chroma as high C; Repeats with octaves Timbre--Related to harmonic structure of tone; also related to attack and decay of sound
What are receptive fields like at different levels of nervous system?
Peripheral afferent: very small; where on the skin, if you touch it, can you get the nerve fiber to fire? Thalamic neuron: excitatory center and an inhibitory surrounding. There are simple cells and complex cells for touch. Different orientations and different movements that are processed by specific neurons.
Describe physical properties of sound and relate to psychological properties of sound
Physical properties of sound: Pressure changes in the air or another medium Psychological sound: The experience we have when we hear As the changes in air pressure get bigger, the sound gets louder—the speakers are pressing out and condensing the air molecules more Pitch is perceptual; Frequency is physical Loudness is perceptual; Amplitude is physical
What are the important anatomical structures that relay sounds to the transduction apparatus?
Pinnae--helps with sound localization Auditory canal Eardrum Ossicles (malleus, incus, stapes)--transmit vibrations
Who suffers from hearing loss?
Presbycusis Does not affect all frequencies of sound equally; It is sensorineural Affects males more than females Caused by factors in addition to the normal aging process Noise-Induced Hearing Loss Exposure to loud noises can break tip links and cause degeneration of hair cells; Dead hair cells will not regenerate
How can differences in taste be explained?
Some of us can taste chemicals that others can't Ex. PTC & PROP Higher densities of papillae But difference in ability to taste still exists when this is controlled for 25 types of bitter receptors, or more Supertasters (25% of population) Our taste cells undergo continuous renewal--could develop new taste buds that react better to a certain food than past taste buds have
Location of sounds
Sound coming from a single source is usually in one particular place, or continuously changing location
Similarity of pitch and timbre
Sounds of a particular timbre and pitch range usually produced by same sound source
Proximity in time
Sounds that have different onset (attack) and offset (decay) times tend to be produced by different sources Sounds that occur in rapid progression tend to be produced by the same sound source
Auditory continuity
Sounds that stay constant or that change smoothly are usually produced by the same source If some sounds change and others stay constant, the groups of sounds are perceptually segregated
Give some examples of two sounds that would be streamed and two that would be segregated
Streamed two people playing on the same xylophone (when played together, the individual melodies are lost) when two sounds appear to be coming from the same location in front of you (as opposed to either side)---the galloping Segregated When a song is played in two different octaves, the sounds are segregated When two sounds come from different locations, they are segregated
Understand tactile acuity, including receptors and cortical mechanisms that produce it
The ability to detect details on the skin Fingers have best acuity—even at 3-4 mm between the two probes, someone can tell that there are two points. Merkel receptors are best suited to provide tactile acuity The spacing between each merkel receptor is larger and larger as you go away from the fingertips. Receptive field sizes of cortical neurons become larger as you go away from the fingertips--More convergence of Merkel discs.
How are signals processed at different levels?
The chemotopic map reflects a pattern of activation in the olfactory system. Odorant->chemotopic map activated ->scattered activation (piriform cortex) ->pattern for odor object
Eardrum
The eardrum vibrates in synchrony to the frequency hitting it. The eardrum vibrates back and forth, causing the 3 smallest bones in the body (malleus, incus, and stapes) to vibrate back and forth.
Duplex theory of texture perception
The idea that texture perception is determined by both spatial and temporal cues that are detected by two types of receptors.
What factors determine whether sounds are perceptually segregated or streamed?
The principles of auditory grouping--heuristics similarity of pitch and timbre proximity in time auditory continuity location of sounds experience
How are the signals transmitted to the CNS?
The receptors are connected to the central nervous system by nerves The spinal cord sends the signals to the brain
What is the importance of chemical senses?
They are very important in terms of survival and evolution. Bad smells and bitter tastes cause us to reject foods that are toxic for our bodies. Smell and taste are the gatekeepers of the body Identify substances that the body needs for survival Identify substances that may be harmful to the body
How are the fiber types different?
They differ in terms of the size of the myelin sheath.
What do Merkel receptors respond to?
They respond to continuous pressure and connect to the SA 1 Channel (slowly adapting 1 channel)
What psychophysical experiments increased our understanding of the duplex nature of this ability?
Until recently, research on texture perception focused on spatial cues and coarse surfaces What happens when bumps are too close to cause differential activation of Merkel discs? Mark Hollins and colleagues conducted psychophysical experiments to determine the role of temporal cues in texture perception Used much finer textures than those used previously. Two fine surfaces felt essentially the same roughness in stationary condition When allowed to move finger, difference in roughness revealed Coarse surfaces were rated equally rough in moving and stationary conditions There may be some temporal cues in texture perception
What other theories of pitch perception are there, and what types of sounds do they work for?
Volley Principle: When you have multiple neurons participating in the coding of one sound stimulus.You have a population of nerve fibers that fire to the condensation of a sound wave. There is a signal sent every time, but not every fiber fires every time. Works up to about 5,000 Hz
What sorts of measurements did Von Bekesy make?
Von Bekesy found that most of the membrane vibrates to a frequency of sound, but some parts more than others. Envelope is max displacement that the wave causes at each point. Maximum displacement is closest to the stapes (base) for highest pitch. Maximum displacement is closest to the apex for lowest pitch.
Understand olfactory transduction and transmission to the brain
We have 350 different olfactory receptor (OR) types embedded in the olfactory mucosa. Only 2% of the molecules that enter your nose are picked up by the receptors. Each ORN expresses only one type of receptor Across fiber (distributed) pattern of responses One receptor type will respond with varying degrees of different chemicals. Similar to the visual system and the FFA.—the neurons respond to many different faces to varying degrees There are about 350 centers in the Glomeruli—one for each type of receptor Piriform cortex: primary olfactory area Orbitofrontal cortex: secondary olfactory area When you get to the Piriform cortex there does not seem to be an orderly way that the neurons are represented.
Phase locking
periodicities causing higher firing rates
Auditory streams
When a song is played rapidly, the low notes sound as though they are a melody played by one instrument and the high notes sound like a different melody played by another instrument. This is called auditory stream segregation.
What is the precedence effect?
When sound is presented first in one speaker and then in the other, with enough time between them, they are heard separately, one after the other. If there is only a short delay between the two sounds, then the sound is perceived to come from the lead speaker only--this is the precedence effect
Interaural Level Difference (ILD)
Works for high frequency sounds but does not work for low frequency sounds. There will be an acoustic shadow on the opposite side of the sound. (if the sound is louder in one ear than the other, this is a good cue that the sound came from the direction that the louder sound was heard from.) Low frequency sounds can go around the head and does not create a shadow.
Is top-down processing important for smell?
Yes, top-down processing is important for smell. Over time (through learning), the neurons fire together and there is not so much scattered activation—neurons that fire together, wire together Both attention and expectation play roles in processing the odors and flavors of foods Top-down processing can make it faster to identify smells and flavors
What other chemicals stimulate thermoreceptors?
cinnamon, mint, horseradish, chili, lemon, etc
Function of Pacinian corpuscles
largest and deepest receptor; fine textures such as silk or desk
Allodynia
normally innocuous stimulus causes pain
Hyperalgesia
noxious stimulus causes more pain than normal
Function of Meissner corpuscles
rapidly adapting; helps with handgrip control They are on ridges on fingerprints
Function of Ruffini cylinders
responds to the stretching of skin; have a lot of them at the joints By just stimulating one ruffini cylinder, a person does not feel anything.
What do Meissner corpuscles respond to?
slight difference in touch (Ex: a glass slipping out of your hand) connect to the RA 1 Channel (rapidly adapting 1 channel) fires "on" and "off"
What factors contribute to food flavor?
smell and taste
The imaginary horizontal line that goes 360 degrees around the head is called:
the azimuth
What is the purpose of outer hair cells?
they are cochlear amplifiers Depolarization of outer hair cells activates a protein that physically elongates cell The elongation amplifies the movement of the basilar membrane, thus amplifying the signal sent through the inner hair cells.
Hair cells are connected to one another by...
tip links Tip link—strand of proteins Tip links control the gates for ion transmission into hair cells, and control the signals they send to the brain
What evidence suggests place theory is correct?
tonotopic map There are certain cells that are sensitive to different frequencies. --found through tuning curves of different cells Become less sensitive as you go away from their preferred frequencies
What do Pacinian corpuscles respond to?
vibration and fine textures by moving fingers connects to RA 2 Channel (rapidly adapting 2 channel)
What is missing from place theory explanation?
von Békésy's measurements couldn't really explain our ability to distinguish frequencies that are really close to one another. We can distinguish between a 200 Hz tone and a 201 Hz tone, and the envelope graphs don't demonstrate that. Also, von Békésy was working with cochleas from dead bodies, whose outer hair cells were not working as they would in live bodies.
