Lecture 9 Flashcards
what are the cells (neurons) of the retina
Photoreceptor cells Bipolar cells Ganglion cells Horizontal cells – Amacrine cells
what are the photoreceptor cells
– neurons responsible for the transduction of light; they project to bipolar cells.
what are the bipolar cells
– neurons that relay information from photoreceptor cells to ganglion cells.
what are the ganglion cells
– the only neurons in the retina that sends axons out of the eye. They receive information from bipolar cells and project to the rest of the brain; their axons give rise to the optic nerve, which leaves the retina through the optic disc (i.e., the blind spot of the retina).
what are the horizontal cells
neurons that interconnect and regulate the excitability of adjacent photoreceptor and bipolar cells. They adjust the sensitivity of these neurons to light in general.
what are the amacrine cells
– neurons that interconnect and regulate the excitability of adjacent bipolar and ganglion cells. There are many different types of amacrine cells and they have many functions.
Receptor proteins that are sensitive to light are known as what
opsins
We use four different types of opsin proteins to detect light, what are they
rhodopsin and the red, green, and blue cone opsins
We use four different types of opsin proteins to detect light: rhodopsin and the red, green, and blue cone opsins. Each of these opsins are what kind of receptors
inhibitory metabotropic receptors.
Each photoreceptor cell in our eye contains only one of these types of opsins, which means we have how many types of photoreceptor cells
four different types of photoreceptor cells: rod cells and the red, green, and blue cone cells.
When light activates the opsin proteins in a photoreceptor cell, they trigger what
a g-protein signalling cascade that closes open sodium ion channels. Thus, the activation of these opsin proteins causes photoreceptor cells to hyperpolarize, which causes them to release less glutamate
It doesn’t matter if it is a rod or cone photoreceptor cell, they all respond to light activation in the same way, by becoming what
less active and releasing less neurotransmitter.
To study neurons involved in visual processing, we record from them (typically with a metal wire) while the animal does what
stares at a computer screen and maintains focus on a particular spot in the center of the screen
We then light up different parts of the screen (using various orientations and colors of light) to see what when testing an animal
where on the screen light can change the activity of the neuron
The area of the computer screen where light is capable of changing the activity of the neuron is that neuron’s what
receptive field. It is that area of visual space
what happens with The first cell in the pathway
When the correct wavelength of light is presented in a photoreceptor cell’s receptive field, the photoreceptor cell hyperpolarizes and becomes less active (releases less glutamate).
what happens with the Second cell in the pathway:
There are two main types of bipolar cells (ON & OFF). When light is presented in the receptive field of ON bipolar cells, they depolarize and release more glutamate. When light is presented in the receptive field of OFF bipolar cells, they hyperpolarize and release less glutamate. They respond differently to the changes in photoreceptor cell activity because they have different kinds of glutamate receptors. ON bipolar cells only have inhibitory glutamate receptors; OFF bipolar cells have excitatory glutamate receptors.
what happens with the Third cell in the pathway:
Retinal ganglion cells generally integrate information from many ON and OFF bipolar cells. Their receptive fields often have a “center-surround” organization and they are called ON or OFF cells, depending on whether they show increased or decreased spiking activity when light is presented in the center of their receptive field.
Retinal ganglion cells that process color information tend to have what types of receptive fields
yellow on, blue off
blue on, yellow off
etc (the ON is in the centre)
Retinal ganglion cells project to where
the thalamus (LGN),
Retinal ganglion cells project to the thalamus (LGN), which in turn projects to where
the cerebral cortex ( V1):
Primary visual cortex
is also known as what
also known as area V1 or striate cortex
Neurons in V1 have larger receptive fields than what
the retinal ganglion cells
Neurons in V1 have larger receptive fields than the retinal ganglion cells. They are most activated when…
a line of light in a particular orientation is detected in the receptive field
Some neurons respond best to what kind of lines
vertical lines, some to horizontal lines, and some to lines oriented somewhere in between.
what are Simple cells
Simple cells in primary visual cortex are sensitive to lines of light, and their receptive fields are typically organized in a center-surround fashion
where are Complex cells found
primary visual Cortex
what are Complex cells
like simple cells but they have larger receptive fields and do not have an inhibitory surround region. Complex cells respond to particular line orientations, but they don’t care if the line reflects the absence or presence of light
Complex cells often respond best to what
moving lines, but only if the line moves in the direction perpendicular to the line orientation
Complex cells often respond best to moving lines, but only if the line moves in the direction perpendicular to the line orientation. Complex cells are mostly in V2. They receive input from what
many simple cells
Every little spot in your visual field is rigorously analyzed. Is there light in that spot and is it oriented this way or that way? The neurons are trying to identify areas where there are sharp transitions between light and dark (or between two colors). The neurons are trying to identify what
borders, edges, corners
The axons of retinal ganglion cells leave the eye and go to the:
Thalamus visual cortex (specifically the lateral geniculate nucleus)
Midbrain
or
Hypothalamus
Thalamus (specifically the lateral geniculate nucleus, which in turn projects where
to the primary visual cortex in the occipital lobe of the cerebrum
Thalamus (specifically the lateral geniculate nucleus, which in turn projects to the primary visual cortex in the occipital lobe of the cerebrum): Visual information is processed in this pathway to determine what
what you are looking at
Thalamus (specifically the lateral geniculate nucleus, which in turn projects to the primary visual cortex in the occipital lobe of the cerebrum): Visual information is processed in this pathway to determine what you are looking at. This pathway creates what
an internal (mental) representation of your entire visual space: the objects in it, their position and relative attentional value.
The axons of retinal ganglion cells leave the eye and go to themidbrain, but specifically where
specifically the superior colliculi
Midbrain (specifically the superior colliculi): Visual information is used here to do what
control fast visually-guided movements. The midbrain doesn’t really know what you are looking at, but it knows where light is moving in visual space.
what happens in the hypothalamus
Visual information is used here to control circadian rhythms (such as sleep-wake cycles). The hypothalamus doesn’t know what you are looking at, but it knows how much light is present in your environment
Visual information is organized in the thalamus before it gets to where
the cerebral cortex
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has how many layers of neurons
six layers of neurons
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons:
The inner two layers (layers 1 and 2) are known as what
the magnocellular layers
what does the the magnocellular layers do
This layer transmits information from rod cells and is necessary for the perception of form, movement, depth, and small differences in brightness.
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons: The outer layers (3-6) are known as what
parvocellular layers
what do the parvocellular layers do
They encode information from red and green cone cells.
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons:
Information from the blue cone cells gets encoded in what
koniocellular sublayers
what are the koniocellular sublayers
interspersed in between each of the other layers
Primary visual cortex (area V1) consists of six layers of neurons (and several sublayers), arranged in bands parallel to surface. These layers show up as what
bands of light or dark in sections of tissue that have been dyed with a cell-body stain.
Like the rest of the brain, the visual cortex is organized in modules which range in size from a few hundred thousand to what
a few million neurons
The modules in V1 overlay the images from the two eyes and do what
determine light orientation and color.
Modules in V2 combine activity from multiple V1 modules. Modules in V3 combine activity from multiple V2 modules. And on and on… This is called what
feedforward processing
Cytochrome oxidase (CO) is an enzyme whose expression levels scale with what
the metabolic rate of the cell
Cytochrome oxidase (CO) is an enzyme whose expression levels scale with the metabolic rate of the cell. essentially More action potentials =
More action potentials = more expression of CO protein
Cells with high expression of CO are found where
in clusters throughout the occipital cortex. These areas are known as the CO blobs
Cells with high expression of CO are found in clusters throughout the occipital cortex. These areas are known as the CO blobs.
These regions process input from the parvocellular/koniocellular cells of the thalamus (LGN) and are responsible for what
color vision
what are the important terms in Depth perception
Monocular vision:
Binocular vision:
Depth perception:
Stereopsis:
what is monocular vision
Some V1 neurons respond to visual input from just one eye.
what is binocular vision
Most V1 neurons respond to visual input from both eyes.
what is depth perception
There are many monocular cues that can be used to estimate depth, such as relative size, amount of detail, relative movement as we move our eyes, etc. These are the cues we use to appreciate depth when looking at a 2 dimensional image (e.g., on a photograph or TV screen).
what is stereopsis
The perception of depth that emerges from the fusion of two slightly different projections of an image on the two retinas. The difference between the images from the two eyes is called retinal disparity. It results from the horizontal separation of the two eyes. It improves the precision of depth perception, which is particularly helpful when trying to plan movements to interact with objects in space.
how much of the cerebral cortex is dedicated to processing visual information
20-25%
Visual association cortex is the part of the occipital lobe that surrounds what
primary visual cortex
Each area of the visual association cortex responds to particular features of the visual environment, such as what
particular shapes, locations, movements, and colors.
Each region forms one or more independent maps of the visual field.
Striate cortex means the same thing as what
primary visual cortex (area V1)
Extrastriate cortex means the same thing as what
visual association cortex (areas V3, V4, V5, etc.)
Vision processing extends into where
the temporal and parietal lobes
what are the ‘What’ and ‘Where’ Visual Streams
dorsal stream
ventral stream
The dorsal stream of visual information processing starts where and ends where
in primary visual cortex and ends in posterior parietal cortex
The dorsal stream of visual information processing starts in primary visual cortex and ends in posterior parietal cortex. It is involved in identifying what
spatial location
The dorsal stream of visual information processing starts in primary visual cortex and ends in posterior parietal cortex. It is involved in identifying spatial location. It encodes what
where objects are, if they are moving, and how you should move to interact with or avoid them.
The ventral stream starts and ends where
starts in primary visual cortex and ends in inferior temporal cortex
The ventral stream starts in primary visual cortex and ends in inferior temporal cortex. It is involved in what
identifying form (shape).
The ventral stream starts in primary visual cortex and ends in inferior temporal cortex. It is involved in identifying form (shape). It encodes what
what the object is and its color (CO blobs).
what is agnosia
An agnosiais a deficit (problem) in the ability to recognize or comprehend certain sensory information, like specific features of objects, persons, sounds, shapes, or smells, although the specific sense is not defective nor is there any significant memory loss.
An agnosia relates to a problem in where
some sensory association cortex (typically in a single sensory modality) - not to problems that relate to the sensory neurons themselves or to the primary sensory areas
For example, being blind or deaf is not considered to be an agnosia…why
Blindness can result from damage anywhere between the eye and primary visual cortex
Visual agnosia relates to damage located where
downstream of primary visual cortex (in visual association cortex, or the dorsal visual stream in the parietal cortex, or the ventral visual stream in the temporal cortex).
what is Akinetopsia
a type of visual agnosia caused by damage in an area of the dorsal visual stream
It is a deficit in the ability to perceive movement
what are the Visual agnosia related to the ventral stream
Cerebral achromatopsia
Prosopagnosia
Extrastriate body area (EBA)
what is Cerebral achromatopsia
Cerebral achromatopsia is a visual agnosia caused by damage to the ventral visual stream. People with it deny having any perception of color. They say everything looks dull or drab, and that it is all just “shades of grey”. (People with regular achromatopsia don’t say those things, because they have no conception of color.)
what is Regular achromatopsia
when all the cone opsins are defective, which results in complete color blindness
what is Prosopagnosia
Failure to recognize particular people by sight of their faces; caused by damage to the fusiform gyrus (fusiform face area)
what is Extrastriate body area (EBA)
involved in perception of human body and body parts other than faces
what is the predictive coding theory of perception
Most of the pathways are bidirectional (axons go both ways). To some extent, descending neural activity from the top areas reflect predictions about what the input is most likely be in the next moment (based on previous experience). This descending information cancels out the correctly predicted ascending information, so the only information that actually ascends are errors in visual predictions.
Each level of the network (except the lowest level, which represents the image) attempts to predict the responses at the next lower level via feedback connections. What propagates up is the prediction error signal, which is used to improve future predictions. This is the predictive coding theory of perception.
MOVING ON TO HEARING NOW
AUDITORY SECTION CHAPTER 7
what is The Stimulus of heading
Sounds
what are Sounds
Sounds are vibrations of air molecules. They are produced by objects that vibrate and set molecules of air into motion
When an object vibrates, its movements cause the molecules of air surrounding it to alternately condense and rarefy (pull apart), which produces what
sound waves that travel away from the object at the speed of sound (approximately 700 miles per hour in air)
what range can our ears hear
If the air is vibrating any where between 30 and 20,000 times per second, these waves will stimulate receptor cells in our ears and will be perceived as sound
Sound has how many physical dimensions
3
what are the 3 physical dimensions of sound
loudness
putch
timbre
what is loudness
corresponds to the amplitude or intensity of the molecular vibrations
what is pitch
(tone) corresponds to the frequency of the molecular vibrations. It is measured in hertz (Hz) or cycles per second.
what is timbre
corresponds to the complexity of the sound. We use timbre to help identify the source of the sound wave (through learning processes).
what are he 3 main parts of the ear
pinna
tympanic membrane
ossicles
what is the pinna
Sound is funneled through the pinna (the external ear)
what is the tympanic membrane
Sounds coming down the ear canal cause the tympanic membrane (the eardrum) to vibrate. These vibrations are transferred to the middle ear
what are ossicles
The middle ear is comprised of three ossicles (small bones)
what are he 3 ossicles
the malleus, incus and stapes
Vibrations of the ossicles are transferred to where
the membrane behind the oval window
Vibrations of the ossicles are transferred to the membrane behind the oval window. These vibrations are transmitted to what
the fluid-filled cochlea (the inner ear),
what is the fluid-filled cochlea (the inner ear),
long coiled tube-like structure that contains sensory neurons.
what is the basilar membrane
The basilar membrane encodes high notes on the end closest to the oval window. Like a xylophone, the low notes correspond to the longest (widest) section.
The cochlea is divided how
into three longtudinal divisions
The cochlea is divided into three longtudinal divisions:
scala vestibuli, scala media and scala tympani.
The receptive organ is the what
organ of Corti
The receptive organ is the organ of Corti. It consists of what
the basilar membrane, the tectorial membrane and the auditory hair cells
The hair cells are what
the auditory receptors
Fine cilia extensions of the outer hair cells attach to what
the fairly rigid tectorial membrane
what produces receptor potentials.
Sound waves cause the basilar membrane to move relative to the tectorial membrane, which directly bends the cilia of the outer hair cells and indirectly (by moving water) bends the cilia of the inner hair cells. This bending of the cilia produces receptor potentials.
The cilia of hair cells are the connected to each other by what
tip links
what are tip links
elastic filaments that attach the tip of one cilium to the side of adjacent cilium.
The point of attachment of a tip link to a cilium is called what
a insertional plaque
Each insertional plaque has a single ion channel in it that does what
opens and closes according to the amount of stretch exerted by the tip link.
what can break hair cell tip link connections
Loud noises
Loud noises easily break hair cell tip link connections… what happens then
hair cells cannot transmit auditory information without tip links
do tip links grow back
usually grow back within a few hours
Tip link breakage generally corresponds to what
temporary hearing loss (such as after a loud bang or loud concert).
Tip link breakage is probably a protective measure, because why
too much glutamate release onto the cochlear nerve causes permanent cell death (excitotoxicity).
what % of 20 year olds seem to have some noise-induced hearing loss.
20%
The major principle of auditory coding is what
that different frequencies of sound produce maximal stimulation of hair cells at different points on the basilar membrane
The major principle of auditory coding is that different frequencies of sound produce maximal stimulation of hair cells at different points on the basilar membrane.
This approach to encoding sensory information is known as what
place coding
The position of the most active hair cell in the cochlea indicates what
the fundamental frequency (the pitch) of the sound wave.
Moderate to high frequencies are entirely encoded by what
place coding
Very low frequencies are largely encoded by what
rate coding
explain Place Coding
because of mechanical construction of cochlea and basilar membrane, acoustic stimuli of different frequencies cause different amounts of movement along the the membranes. Higher frequencies produce more movement at the end closest to the stapes causing more activity in the hair cells located there
explain rate coding
system by which information about different frequencies of sound waves is coded by the firing rate of neurons in auditory system
are there more outer or inner hair cells
outer
Although there are 3 to 4 times more outer hair cells than inner hair cells, what transmits auditory info to the brain
inner hair cells
what do Outer hair cells do
act like muscles to change the sensitivity of the tectorial membrane to vibrations. By manipulating the flexibility of the tectorial membrane, outer hair cell regulate the sensitivity and frequency selectivity of inner hair cells.
People without functional inner hair cells are what
completely deaf.
People without functional outer hair cells can or cannot hear?
can hear, but not very well.
give a summary of Pitch Perception
Moderate to high frequencies are encoded by place coding. Low frequencies are partly encoded by rate coding
give a summary of Loudness
Loudness corresponds to the total number of hair cells that are active and their overall activity levels
give a summary of timber
Timbre is perceived by assessing the precise mixture of hair cells that are active throughout the entire cochlea. (More on next couple slides.)
what are the parts to timbre
Fundamental frequency
overtone
what is Fundamental frequency
The lowest and most intense frequency of a complex sound. This frequency is what is most often perceived as sound’s basic pitch.
what is overtone
Sound wave frequencies that occurs at integer multiples of the fundamental frequency
The timbre of sound refers to what
the specific mixture of frequencies (fundamental frequency plus overtones) that different instruments emit when the same note is played. It is the complexity of the sound wave.
We analyze the timbre of a sound and how the timbre changes over time to identify what
which instrument made the sound
Overtones why are they integer multiples?
The fundamental frequency of a sound wave is the lowest frequency in the wave. Natural sounds are comprised of a fundamental frequency and a collection of overtones, which are generally integer multiples of the fundamental frequency
Because strings (and membranes) are clamped on each end, oscillations tend to only occur at integer multiples of the fundamental frequency
