COGNITIVE NEURO EXAM 2
Neurons in the primary visual cortex respond selectively to oriented edges, i.e., tuning to specific features.
(A) An anesthetized animal is fitted with contact lenses to focus the eyes on a screen, where images can be projected; an extracellular electrode records the neuronal responses. (B) Neurons in the primary visual cortex typically respond vigorously to a bar of light oriented at a particular angle and less strongly—or not at all—to other orientations. (C) Orientation tuning curve for a neuron in primary visual cortex. In this example, the highest rate of action potential discharge occurs for vertical edges—the neuron's "preferred" orientation.
Path of light entering eye
cornea, pupil, lens, retina
why do we have so many cones in the fovea?
coz it gives us more detailed and precise info about stimuli unlike rods
What is rhodopsin?
A light-sensitive protein critical for low light contrasts and found in the rods.
Perceptual Reorganization experiment
Temporarily gluing two figures (digits 2 & 3) also led to changed overlap between cortical representations of affected and unaffected fingers. (each finger has cortical representation) -moved away from 3 and closer to 5 for glued condition
What is monocular vision?
The ability to see separate objects with each eye at the same time
what is the occipital pole?
The occipital pole is an anatomical landmark that corresponds to the posterior portion of the occipital lobe. It is formed by the convergence of the superior and inferior occipital gyri in the majority of individuals; the middle occipital gyrus also contributes when it is present 1
which region is more closely related to our subjective perception?
VO
Which brain regions support color perception?
When two isoluminant colors alternate at frequencies >= 25 Hz, observers perceive only one fused color. But which brain regions can distinguish between the fused chromatic flicker and its matched non-flickering control? This may tell us which brain regions support perception (conscious experience), not the stimulus features per se. Experiment: (a) The left and right stimuli alternated at different rates or contrast. (b) BOLD response to the flickering stimuli in three visual areas: V1, V4, and VO (ventral occipital)-- u can see the colors separately. The activation profile in VO matched the participants' perceptual experience because the color changes in the stimulus were invisible at the high 30-Hz rate or when the contrast was below threshold. In contrast, the activation profiles in V1 and V4 were correlated with the actual stimulus when the contrast was above threshold.
simple cells respond to
dark or light bar in receptive field (vertical bar)
what can high field fMRI help us do?
decode ocular dominant column and orientation
What is sensation?
detecting the presence of a stimulus
MT region also support processing of
dynamic auditory information, sound of footsteps, passing cars, etc.
if a light bar hits all three neurons from previous question in their surround (off region), what will happen?
action potential will not be fired and primary neuron in LGN will not be activated/it will be inhibited instead
what are horizontal cells important for?
form circuitry needed in the retina
What are ocular dominance columns?
functional columns of cells extending from pia to white matter that all share the same eye dominance (left and right eye)
what are the three layers of the retina?
ganglion cells, bipolar cells and horizontal cells (middle layer), rods and cones (deepest layer)
if someone loses hearing what can we do?
implant a cochlear implant to bring back hearing (make it similar to the original cochlea so input is the same and the way its transduced is the same
epiretinal implant (retinal implant)
implant electrical device in the retina which receives light. this light info will activate ganglion cells (allows people to gain the feeling of light)
what is vision?
light entering the eye
what is the signal pathway in the retina?
light will enter the retina and will be transduced by the rods and cones in the retina and then go to bipolar cells and then go to ganglion cells which will transmit singla to the brain
red cones respond best to
longer wavelengths of light (500nm)
What is achromatopsia?
loss of color vision (see in black and white)
upper visual field goes to
lower bank
activated areas in the brain during color stimulation are more..
medial
green cones respond best to
medium wavelengths of light (530nm)
Studies have shown that our _______________ sensory regions provide a representation that is closely linked to the physical stimulus, and our perceptual experience depends more on activity in the ___________________ and association sensory regions.
primary; secondary
what is perception?
process of interpreting the stimulus;
do rods share a a bipolar cell?
yes (30 can connect with one but for cones usually one cone can connect to one bipolar cell)
does cone density decrease further away from fovea?
yes (more rods in periphery and less in central. more cones in central vision)
does part of v2 respond to central space?
yes (so a close area in v3 will also respond to central space while areas in v1 and v3 that are near each other will respond to peripheral space)
do we perceive movement when we look at the enigma pattern? why does this happen?
yes, we perceive movement but its not there. this happens coz the pattern activates the MT region
In 1970s, the work done or inspired by Hubel & Wiesel showed that after a kitten was born, if one of its eyes was sutured, the visual system cannot develop very well.
• E.g., the ocular dominance columns failed to develop; • The cortex sites for the sutured eye was taken over by the intact eye. • The damage was permanent.
How to study synesthesia effect?
• For colored-grapheme synesthesia, researchers have used modified Stroop test in which the letters/numbers are printed in colors that either congruent or incongruent to the individual's synesthetic color: (see how fast they reply)
Neural plasticity study using experimental design:
• In a study by Merabet et al (2008), one group of participants were deprived of visual information (blindfolded) for 1 week, the other group not. Then they received intensive braille training for 5 days. • At the end of the training, they found blindfolded participants performed better on reading braille (and other tactile tasks). • These participants showed a BOLD response in visual cortex during tactile stimulation. • They also showed disruptions in Braille reading when rTMS was applied over the visual cortex. • On day 6, after blindfolds were removed, the activation in the visual cortex disappeared, indicating the changes in cortical activation is temporary.
Mapping visual fields with functional magnetic resonance imaging (fMRI).
(a) The participant views a rotating circular wedge while fMRI scans are obtained. The wedge passes from one visual quadrant to the next, and the BOLD response in visual cortex is measured continuously to map out how the regions of activation change in a corresponding manner. (b) Retinotopic maps in the human brain identified with fMRI, showing representations in the right hemisphere of the angular position of a stimulus; the color wheel indicates stimulus position. The data are shown on a 3-D MRI reconstruction (left), inflated brain (center), and flat map (right). Five hemifield maps are seen along the medial bank of the intraparietal sulcus (IPS). (c) The same data are plotted on a flat map with colors indicating stimulus position from fovea to periphery. The boundaries between visual cortical areas in (b) and (c) are defined by the reversals in the retinotopic maps
horizontal cells can if activated can inhibit a cell and reduce the signal that reaches the ganglion cell
,..
Multisensory integration requires the different stimuli be coincident in both space and time. What does this mean?
- A flash of light can be perceived as two flashed if synchronized spatially and temporally with two beeps. - This won't happen if the auditory and visual stimuli are not from the sample location or temporally synchronized. (beep and flash must happen at same time)
Some of the studies have used "visual illusions" to investigate perception. Why?
- This is because in visual illusions there is a discrepancy between the real stimuli and our perception of them. Then, we can see which brain regions can differentiate perceptions and which can differentiate the true stimuli.
are multisensory signal treated by the brain as more reliable signal that a single sensory channel?
yes
Functional reorganization in congenitally blind individuals. (study by sadato et al (1998)
-A study by Sadato et al (1998) found the sighted participants had a significant drop in activation in the primary visual cortex during a tactile discrimination task. If the participants performed a visual task, activation in the auditory and somatosensory cortex decreased. -However, in blind participants, activation in the primary visual cortex increased during discrimination tasks when they were actively using the tactile information, including reading Braille. -This suggests that blind people recruit visual neural resources for tactile processing, or auditory processing (next slide). -In secondary visual areas—lateral occipital (a) and medial occipital (b)—the BOLD responses to an English-language story, a foreign language story, and music were higher in blind individuals compared to blindfolded sighted individuals, although the effect was modest for music. This difference was not seen in the more ventral fusiform gyrus (c). Asterisks indicate when a particular condition is significantly different from the rest.
Direction and speed tuning of a neuron from area MT
-The cell was active only when the stimulus fell within its receptive field. Second, the cell's response was greatest when the stimulus moved in a certain direction. Third, the cell's activity was modulated by the speed of motion; - (a) A rectangle was moved through the receptive field of this cell in various directions. The red traces beside the stimulus cartoons indicate the responses of the cell to these stimuli. In the polar graph, the firing rates are plotted; the angular direction of each point indicates the stimulus direction, and the distance from the center indicates the firing rate as a percentage of the maximum firing rate. The polygon formed when the points are connected indicates that the cell was maximally responsive to stimuli that moved down and to the left; the cell responded minimally when the stimulus moved in the opposite direction. (b) This graph shows speed tuning for an MT cell. In all conditions, the motion was in the optimal direction. This cell responded most vigorously when the stimulus moved at a speed of 64° per second.
what are the two types of photopigments in photoreceptors?
-Photopsin (for cones) • Rhodopsin (for rods)
Synesthesia
-Synesthesia my be due to unusual cross - activation of one cortical area by another. • Studies found within the domains where individual experience synesthesia (color, touch, etc.), these people have enhanced sensory abilities (e.g., better at discriminating colors). • Studies also found the brain regions respond to true color and synesthetic color can be different. • Evidence shows modified white matter track connection may play a role.
Hubel & Wiesel's work in 1970s:
-single cell recording method center-on surround-off LGN cell vs. orientation cells in V1
are the photoreceptors at the deepest layer of the retina?
yes
can we recognize cats even if they vary in perspective?
yes
what is the Primary Projection Pathways?
-the right visual field stimuli goes to the left eye (temporal side of left eye) and nasal side of right eye). -the left visual field stimuli goes to the right eye (temporal side of right eye) and nasal side of left eye. -then the signal will go from the photoreceptors in the retina to the bipolar cells and then to the ganglion cells -axon of ganglion cells forms optical tract -the nasal side will cross over at the optic chiasm -the temporal side of axons will go ipsilaterally -left visual field info will be processed in right hemisphere and right visual field info will be process in left hemisphere -the first stop of the visual stimuli in the brain is at the lateral geniculate nucleus LGN which is found in the thalamus -ganglion cells form a synapse with LGN neurons and then the LGN sends info to the primary visual field (v1) cochlear (?) sulcus -info may also go to superior colliculus if not to the LGN which is important for eye movement and visual attention -may also go to the pulvinar nucleus (important for visual processing and multi sensory info) -may go to superior chiasmatic nucleus in the hypothalamus which controls rhythm
anterior region responds to peripheral stimuli
..
red colored region responds to foveal/central stimuli
..
• To study brain regions that support multisensory, researchers will examine brain activities in different regions when participants process stimuli from different modalities that presented simultaneously, then compare them with those when the stimuli are presented separately. • Multisensory regions are usually supported by association regions. • Superior temporal sulcus (posterior part) is close to auditory cortex, visual cortex, and somatosensory cortex. This region supports visual, auditory, and somatosensory integration! Proximity rule is roughly correct. • However, even unimodal regions can be affected by signals from other sensory models.
..
what is photopsin?
: A light-sensitive protein critical for color vision and found in the cones
what is an example of a subcortical area in the brain?
A subcortical example is the superior colliculus - one of the brain's eye movement control center • It integrates both visual and auditory (and tactile) information to make eye movement
What is a retinotopic map?
As with the somatosensory and auditory systems, the receptive fields of visual cells within neural regions such as the LGN and V1 form an orderly mapping between an external dimension (e.g., spatial location) and the neural representation of that dimension
do different neurons prefer different orientation of light bars?
yes
Neural plasticity: Perceptual Reorganization
Cortical reorganization may be general phenomenon after something happens to one modality. • When a sensory system is absent, inputs from a different sensory system may expand in terms of their cortical recruitment (called cross-modal plasticity). • The recruitment appears to be multimodal: in the congenitally blind, "visual areas' are circuited during tactile and auditory tasks; in the deaf, "auditory areas" are recruited during tactile and visual tasks. • This may explain why deaf individuals have enhanced visual perception. • However, it should be noted that most of these studies (that compared deaf/blind participants with normal controls) used a cross-sectional design, i.e., they compared different groups of people. • These studies cannot draw firm conclusion because unrelated individual experience differences may play a role. Cross sectional design cannot exclude this possibility.
_____ stimulates V5 and can produce transit deficits in motion perception
TMS
Critical time period for visual development was also found in humans.
Late cataract removal in children (after critical period) can cause permanent visual deficits. Similar situation can happen for infants born with strabismus. (cross eye) • This won't happen in human adults. • Spoken language development also has a critical time period. (you get an accent if u learn a language during or after teen years)
Motion Detection
Monkeys were trained to watch a screen with moving dots and then move their eyes to indicate the perceived direction of a patch of dots. To make the task challenging, only a small percentage of the dots moved in a common direction; others moved in random directions. The researchers then found neurons in the MT that are tuned to specific directions, and electrically stimulated these neurons while monkeys were doing the task. The stimulation increased the probability the monkeys would report that the stimulus was moving in the cell's preferred direction.
Stimuli used in a ______ experiment to identify regions involved in color and motion perception
PET
_____________ in retina transduce light into neural signals.
photoreceptors
What is synesthesia?
Stimulation of one sense cause illusory perceptual experience in another sensory modality, e.g., people may hear words/music as color, see achromatic letters as colored (colored-grapheme synesthesia). -seeing colors when u listen to music
lesion in v4 study.
a patient with unilateral lesion of right V4 has achromatopsia and is unable to perceive color -Color perception thresholds in each visual quadrant (UL = upper left; LL = lower left; UR = upper right; LR = lower right). The patient was severely impaired on the huematching task when the test color was presented to the upper-left visual field. The y-axis indicates the color required to detect a difference between a patch shown in each visual quadrant and the target color shown at the fovea. The target color was red for the results shown on the left and green for the results shown on the right. Hue angle refers to the color wheel and is the number of degrees between the actual color and the first color recognized as a different hue -Stimuli used to assess form perception in the patient with damage to area V4. On basic tests of luminance (a), orientation (b), and motion (c), the patient's perceptual threshold was similar in all four quadrants. Thresholds for illusory contours (d) and complex shapes (e) were elevated in the upper-left quadrant. This means, the patient showed impairment on tests of higher-order shape perception. -cant see complex shapes (hierarchal organization)
What is the McGurk effect?
a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. -what we see changes what we hear (if we see "fa" we hear "fa" even tho "ba" is being said)
activated areas in the brain during movement stimulation are more..
more lateral (MT area)
What is akinetopsia? what is it caused by?
motion blindness. -usually caused by the bilateral lesions to the posterior and alter portions of the middle temporal gyrus (V5)
can v4 differentiate color created by flickering colors?
no
is our visual processing only bottom up?
no theres top down processing -you may recognize what ur looking at first, and then that lead to object recognition and you noticing all the simple visual features (you see something slightly and u notice what it is and then u begin to see simple features)
260 million receptions but only 2 million ganglion cells!
ok chile- i never asked
the fiber of ganglion cells in the retina form..
optic nerve fibers
What is remote sensing/exteroceptive perception?
perceiving information at a distance (vision and audition)
• The physiological mechanisms driving plasticity at the cellular level have been studied primarily in nonhuman animal models. • The results suggests a cascade of effects operating across different time scales. • Immediate effect are likely to be the results of a sudden reduction in inhibition that normally suppresses inputs from neighboring regions. • Inhibition from neighboring regions are a general scheme (circuit) in the brain (e.g., retina-geniculated center-on surround-off, basal ganglia central-excitatory surround-inhibitory circuit, motor area finger representations, etc.) • Inhibitory neurotransmitter GABA may play a role: When GABA levels are high, activity in individual cortical neurons is relative stable! (e.g., Some animals tend to bend all fingers together. The inhibitory circuit may be evolutionary new and modify the existing all-bend control.) -Changes in cortical mapping over a period of days probably involve changes in the efficacy of existing circuitry, e.g., after loss of normal somatosensory input (e.g., through amputations), cortical neurons previously responded to that input might undergo denervation hypersensitivity, become more responsible to other existing weak input. • The growth of intracortical axonal connections and even sprouting of new axons might contribute to very slow changes in cortical plasticity. • Cortical tissues may be capable of assuming a wide arrange of cognitive functions, which become specialized during development due to intrinsic connectivity and experience. But when normal input is absent, the sensory areas may become part of a broader network for more general cognitive functions. However, more research on neural plasticity at different levels is needed to draw more certain conclusions.
perceptual reorganization
how do u measure the neural activity on certain neurons in the brain when viewing an object? how can you learn more about the brain areas functions in vision?
put an electrode in that area and for area MT for example which detects moving stimuli, u would present moving stimuli and then look at the neuron activity in area MT. TO learn about functions, place electrodes in that area and present moving object at different orientation and see how the neurons in that area respond and if they respond best to certain movement or orientation
what is the visual search task?
putting one vertical bar among many horizontal bars, you will be asked to find the vertical/different bar and ur reaction time will be recorded
what is the receptive field like for LGN neurons?
receptive field is small and has center on surrounding off pattern (if light hits the center it activates but if it hits the surround then the surround will activate. this is connected to horizontal cells which will then activate and inhibit ganglion cells and lead to lateral inhibition which will reduce firing rate co LGN will not receive the signal)
what does area MT respond to?
respond to moving objects in visual field
what is the hierarchical arrangement in vision?
retina, LGN, V1, V2, V3, V4, MT (when u go to deeper area in the brain the brain analyzes more complex info whereas the retina only analyzes very basic stimuli like a point of light -all lower level info get combined more and more the deeper u go in the visual stream of info
on the retina we have two photoreceptors. what are they?
rods and cones
Blue cones respond BEST to (all cones can still respond to other wavelengths they just respond best to some wavelengths than others)
shorter wavelengths of light (430nm)
What is lateral inhibition?
signals from neurons at the center of the receptive field inhibit neurons on the periphery
Multisensory integration can occur at different regions in the brain, both _____________________
subcortically and cortically
does fMRI allow u to look at the distribution of neuron activity in vision in many different neurons at once?
yes
does multimodal/multisensory perception occur at the cerebral cortex?
yes
is single cell recording invasive?
yes
What is a receptive field?
the area of external space within which a stimulus must be present in order to activate a neuron.
what is the disadvantage of cones being connected to one bipolar cell at a time?
the brain will know it got a signal but not the precise locations
What is the fovea?
the central focal point in the retina, around which the eye's cones cluster (many cones on fovea)
What is parallel processing?
the processing of many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions -first it looks at simple visual features -then object recognition -and then knowledge (understanding what it is that we are seeing)
if you line up three LGN neurons together they will converge to one primary visual cortex neuron. if a light bar hits all three neurons in the middle (on region), what will happen?
these three will fire action potentials (firing rate will increase)
what are the advantages of rods at night?
they can detect very low intensities of light
what is the advantage of cones being connected to one bipolar cell at a time?
u can detect precise locations of stimuli
lower visual field goes to
upper bank
what brain area was found to be responsible for color info?
v4
Patient M.P. reported by Zihl et al. (1983)
viewed the world as a series of snapshots. Rather than seeing things move continuously in space, she saw moving objects appear in one position and then another. (like things are jumping and not moving)
are there any diffs between vision and audition?
vision is purely remote sensing but audition can detect loud sounds and detect danger.
What is binocular vision?
vision using two eyes with overlapping fields of view, allowing good perception of depth.
does stimulation of the visual cortex respond to both color and movement?
yeah it will literally respond no matter what
Response time to an auditory stimulus is faster when the visual cortex is disrupted.
• Participants responded as quickly as possible to a visual or auditory stimulus. A single TMS pulse was applied over the occipital lobe at varying delays after stimulus onset (x-axis). • The y-axis shows the change in response time for the different conditions. Responses to the visual stimulus were slower (positive numbers) in the shaded area, presumably because the TMS pulse made it harder to perceive the stimulus. Interestingly, responses to auditory stimuli were faster (negative numbers) during this same period. • There seems a short early time window that the two modalities can influence each other. (Romei et al., 2007) -response to auditory stimulus is faster when visual cortex is disrupted
what kinds of wavelengths do cones respond to?
• Short • Medium • Long
what are the benefits of remote sensing?
▪ Benefits include not needing physical contact to explore an object or environment. ▪ Some objects or environments may be inaccessible or dangerous. Remote sensing through audition, vision, or olfaction allows an individual to detect important information
