Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
107 Cards in this Set
- Front
- Back
Empiricism
|
ALL that we know about the world around us is obtained through our senses
|
|
Goal of the study of the senses
|
to determine how we know what we know about the world (neural basis of sensory experience)
|
|
Psychophysics
|
-behavioral approach to understanding sensation and perception, based on empiricist/materialist philosophies
-examines the quantitative relationship between physical characteristics of a sensory stimulus and sensation/perception (psychological attributes of sensory experience) |
|
Sensation
|
-what we feel when sensory receptors are stimulated
-related to the physical interaction of a stimulus with a sensory receptor |
|
Law of Specific Nerve Energies
|
sensation depends on the TYPE of receptor activated, not the form of activation
|
|
Perception
|
-conscious awareness and interpretation of sensation
-related to which sensory pathway in the nervous system processes information from a receptor -influenced by "top down" processes: cognition, attention, experience -not directly related to the actual stimulus activating the receptor: it is the brain's interpretation of sensation, based on its internal model of reality -hence, similar perceptions may arise from a variety of stimuli sharing a common feature, and may be fooled by illusions |
|
Sensory Receptor
|
modified epithelial or nerve cell specialized to respond to the presence of a stimuli
|
|
Transduction
|
-the conversion of stimulus energy into electrophysiological response
-receptors are morphologically specialized to transduce specific forms of energy |
|
Receptor Potential
|
-the change in membrane potential in a sensory receptor produced by transduction
-transduction current: the membrane current flow that results from sensory transduction |
|
Sensory Transduction Cascade
|
-stimulation: stimulus interacts with primary sensory receptor
-accessory structure: shapes the interaction of the stimulus with the receptor (ex: lens of eye, pacinian corpuscle, outer/middle/inner ear structures) |
|
Transduction Cascade
|
transduction
-the conversion of stimulus energy into electrophysiological response by a receptor -receptors and their accessory structures are morphologically and physiologically specialized to respond optimally to specific forms of energy Transmission- -transduction current: membrane current in a receptor that results from transduction event -receptor (generator) potential: change in membrane potential produced by transduction currents -transmission: directly via generation of action potential, or indirectly via synaptic transmission to sensory afferents |
|
Neuronal Tissue Type
|
-long receptors
-dendritic and axonal processes -transmit information via action potentials -examples: most mechanoreceptors and olfactory receptors |
|
Epithelial Tissue Type
|
-short receptors
-NO axonal process -synaptomimetic: ---functionally and morphologically similar to presynaptic nerve endings ---transduction currents release NT, but may not generate APs -examples: visual, auditory/vestibular, taste receptors |
|
"Classical Senses" - modality receptor classification
|
-smell (olfaction)
-taste (gustation) -touch (somatosensation) -pain (nociception) -proprioception ---joint angle, muscle tension/length ---kinesthesia (movement, body in space) ---balance/orientation -vision -hearing (audition) |
|
"Subliminal Senses" - modality receptor classification
|
-no conscious sensation
-blood pressure -blood chemistry -osmolarity |
|
"Special Senses" - modality receptor classification
|
-electroreception (detection of weak electrical fields)
-magnetoreception (detection of weak electrical fields) |
|
Mechanoreceptors
|
-touch/pressure
-pain -hearing -balance -joint/muscle proprioception |
|
Chemoreceptors
|
-taste
-smell -pain -itch |
|
Electromagnetic Receptors
|
-vision
-electroreception -magnetoreception |
|
Thermoreceptors
|
-warm
-cold |
|
Exteroceptive Site of Stimulation
|
Stimuli external to body, or on body surface
-hearing (audition) -vision -smell (olfaction) -taste (gustation) -touch (somatosensation) |
|
Interoceptive Site of Stimulation
|
Internal Stimuli
-blood chemistry -blood pressure -osmolarity |
|
Proprioceptive Site of Stimulation
|
Joints, muscles, tendons, vestibular apparatus
-balance -position: joint angles -movement (kinesthesia) -force: resistance to movement |
|
Nociceptive Site of Stimulation
|
Pain
-mechano-thermo-receptors -chemoreceptors |
|
Ways to classify receptors
|
-site of stimulation
-stimulus energy -modality -tissue type |
|
Direct Transduction
|
-stimulus interacts directly with ion channels (similar to ionotropic synaptic receptors)
|
|
Indirect Transduction
|
-stimulus interacts with membrane receptors that regulate ion channels (similar to metabotropic synaptic receptors)
|
|
Information Coded by Sensory Systems
|
-modality: what form does the stimulus take
-intensity: how strong is the stimulus? -timing: when did the stimulus occur? -location: where is the stimulus in the world, and what is it's spatial relation to other stimuli? |
|
Determinants of Modality
|
-type of energy in the stimulus
-type of sensory receptor specialized to respond to the stimulus ("labelled line") |
|
Submodality
|
-each modality subdivides sensory "space" to resolve different attributes of a stimulus
-examples: ---audition: auditory receptors are tuned for sound frequency by location and mechanical properties of the sensory epithelium ---vision: rod and cone receptors in the eye are selective for particular wavelengths of light ---taste: taste receptors specialized for sweet, sour, salty, bitter |
|
Intensity Coding
|
-intensity proportional to stimulus energy level (ie amplitude)
-response of the receptor (ie change in receptor potential) is proportional to stimulus amplitude -receptor potential amplitude is encoded by firing rate of peripheral sensory neurons or primary sensory afferents (but code may change centrally) -Adaptation: response may decline under constant stimulation (often interpreted as evidence that change is more important than steady-rate) |
|
Temporal Coding
|
-temporal properties of a stimulus are encoded as changes in the pattern of sensory neuron activity in the periphery
---latency: time from stimulus onset to response ---onset/offset transients ---rate of stimulus change -pattern codes for temporal features may be converted to a "rate/place" code centrally |
|
Temporal Summation
|
-detection threshold is inversely proportional to the stimulus duration when stimulus duration is less than the temporal integration window
|
|
Receptive Field
|
the region of sensory space over which a receptor integrates energy
|
|
Organization of Receptive Fields
|
-receptive fields may be subdivided into regions that respond differentially to stimulation
-examples: ---visual RFs subdivided into a "center" and "surround" that elicit opposing responses to light ---auditory RFs may have excitatory and inhibitory response areas |
|
Explicit Mapping of Space by Receptor Topography
|
-physical space directly (explicitly) "mapped" by spatial pattern (topography) of activated receptors
Vision: -optics of the eye project visual stimuli onto a 2D sensory epithelium retina) -objects in space fall on different regions of the retina Somatosensation: -location is encoded by position of sensory receptors on the body surface |
|
Representation of Space from Neural Computation
|
Hearing
-sensory epithelium represents sound frequency, not space -space perception derived from neural analysis of differences in spatial cues at the two ears generated by head Smell: -sensory epithelium sensitive to chemical odorants -space computed centrally based upon reconstruction of odor "trails" Taste: -receptors for different "tastants" are segregated on the tongue -but does taste have spatial dimensions? |
|
Sensory Discrimination
|
what is the minimal perceptible difference (just-noticeable difference) between two stimuli/;
-Acuity |
|
Acuity
|
a form of "two-point discrimination"
Ernst Weber |
|
Weber "Laws"
|
-jnd is constant fraction of the absolute magnitude of the stimulus...
--when stimulus intensity is weak, jnd is small --when stimulus intensity is strong, jnd is proportionately much greater Weber Fraction: -delta S/S = K -Weber fraction is constant at all values of S |
|
Fechner
|
Weber relationship is logarithmic
-jnd is proportional to the log of the stimulus intensity S=k log R |
|
Tone Frequency Discrimination
|
-jnd for frequency discrimination is constant at low frequencies but grows at higher frequencies
-Weber Fraction (deltaf/f) nearly constant from ~400 Hz - 2000 Hz -above 2kHz, jnd grows steeply with frequency (ie deltaf/f not constant, Weber's Law is violated) |
|
Visual Acuity
|
Acuity is related to:
-size of the receptive field (ie: diameter of the photoreceptor, relative to the projected image on the retina: smaller is better) -spatial density (receptors/mm^2) of receptors in the retina: higher is better Examples: a density of pixels on a tv screen or image sensor of a digital camera |
|
The Chemical Senses
|
-oldest and most common of the senses
-present even in the simplest single-cell organisms -transduction involves same principles and mechanisms used for communication among cells and tissues (chemical transmitters interacting with membrane receptors) -Functions: ~finding food sources, judging value and safety of foods ~avoiding predators and hazardous environments ~social communication ("pheromones"), mating ~monitoring internal physiological state |
|
Taste
|
-sensations relayed by taste receptor cells in the oral cavity
-foods active different, unique combinations of basic tastes |
|
Flavor
|
-depends on both taste (gustation) and small (olfaction) - flavor is a multisensory perceptor
|
|
Somatosensory factors that influence taste:
|
-texture
-temperature -pain |
|
Tastants
|
-taste stimuli
-non-volatile, water-soluble (hydrophilic) molecules -present in relatively high concentrations |
|
Odorants
|
-odor stimuli
-volatile, aromatic (hydrophobic) compounds -present in relatively low concentrations |
|
Tastes
|
-sweet
-sour -salty -bitter -umami (MSG, glutamate) |
|
Nutrients (tastes)
|
salty, sweet
"attractive" |
|
Anti-nutrients (tastes)
|
sour, bitter
"repulsive" |
|
Taste Organs
|
-taste sensation arises from taste receptors located on the tongue and border between hard and soft palate
-NOT clearly localized to specific regions on the tongue or palate |
|
Taste Buds
|
-morphologically specialized "accessory" epithelial structures containing taste receptor cells
-2000-5000 taste buds on human tongue -50-100 receptors (taste cells) per taste bud, along with basal stem cells -located in papillae: ~fungiform ("mushroom like") papillae: upper surface of tongue ~(circum-)vallate ("pimple-like": lined up in a "V" at back ~foliate ("folds", "ridges"): side -taste buds within most paillae respond to only one of the basic tastes at low concentrations, but become less selective at high concentrations |
|
Taste Cells
|
-modified epithelial cells ("short" sensory receptors)
-replaced ("turnover") about every 10 days -differentiate from basal stem cells |
|
Taste Receptors
|
-taste cells (like most receptors) are functionally and anatomically polarized
-apical membrane: microvilli ~protrude through taste pore into mucus of oral cavity ~provide large surface area to maximize contact with dissolved tastants -basolateral membrane ~nucleus and other typical organelles ~synapses onto primary gustatory afferents (first-order taste neurons), which project into the central gustatory pathway |
|
Taste Transduction
|
-mediated by both direct and indirect mechanisms
-some tastants directly carry currents through ion channels (direct transduction) -other tastants bind selectively to specific G protein-coupled membrane receptors (indirect transduction) -individual taste cells often use both types of transduction |
|
Direct Transduction (taste)
|
-salty and sour
-salty: Na+ ions permeate amiloride-sensitive Na+ channels, directly depolarizing membrane -Sour: protons (H+ ions) permeate amiloride-sensitive Na+ channels AND block K+ channels, directly depolarizing membrane -depolarization opens Nav and Cav channels, leading to APs and transmitter release, respectively |
|
Indirect Transduction (taste)
|
-bitter, sweet, and umami
-mediated by G protein-coupled pathways ~binding of tastant to receptor activates G protein/PLC/IP3 cascade ~IP3 elevates internal [Ca2+] ++IP3 causes release of Ca2+ from internal stores ++opens unique Ca2+ activated Na+ channel, depolarizing, membrane, opening Cav channels ~Ca2+ influx raises [Ca2+], activates transmitter release, stimulation of gustatory afferents |
|
G protein-coupled Taste Receptors
|
Bitter receptors
- ~30 different bitter receptors derived from T2R gene family of receptors -all T2R receptors give rise to a common "bitter" taste Sweet and Umami Receptors -T1R gene family ~two tightly-coupled receptor proteins, rather than one ~T1R2 + T1R3: sweet receptor ~T1R1 + T1R3: umami (amino acid) receptor |
|
Early Processing of Tastes
|
-stimulation of taste produces: depolarizing receptor potential; RP sometimes generates APs, Ca2+ influx, transmitter release
-receptor potential magnitude proportional to both type AND concentration of tastant -response selectively for basic tastes varies with receptor cell: 90% respond to two or more tastes -gustatory afferents exhibit taste preferences: receive input from taste receptors with similar tastant selectively |
|
Central Processing of Taste
|
taste cells --> primary gustatory afferents --> gustatory nucleus (brainstem) --> ventral posterior medial (VPM) nucleus of thalamus (forebrain) --> gustatory cortex
|
|
Brainstem Gustatory Pathway
|
-afferents from anterior 2/3 of tongue: facial nerve (cranial nerve VII)
-afferents from posterior tongue: glossopharyngeal nerve (CN IX) -afferents from throat, palate, glottis/epoglottis: vagus nerve (CN X) -taste axons from all three nerves project to the gustatory nucleus in medulla (a subdivision of the solitary nucleus) |
|
Labeled-line coding
|
-Discrete Representation
-taste receptors VERY selective: respond only to one specific taste ("feature detectors") -project to central targets through distinct afferent pathways, leading ultimately to specialized regions of cortex for each tastant |
|
Population Coding
|
-distributed processing
-receptors partially selective: prefer one but respond to a variety of tastants -no segregation of specialized taste regions in cortex -unique taste perceptions arise from differential patterns of activity in the population |
|
Are tastes mapped in brain by labelled lines?
|
Evidence for: taste cells express only one type of taste receptor (sweet receptor, bitter receptor)
Evidence Against: few taste cells, and even fewer taste afferents, respond to only one tastant Why do taste cells expressing only one receptor contribute to more than one taste perception? -taste receptors may have more than one transduction mechanisms (eg- direct and indirect) -primary afferents innervate different types of taste cells located in same and different papillae ("convergence") and therefore are less selective than taste cells |
|
The Sense of Smell
|
-olfaction plays a critical role in the survival of most animal species
-primary functions ~find and evaluating food ~avoiding noxious/toxic aerosols ~predatory-prey interactions ~social behavior and communication ++territoriality ++social aggregation ++mating (pheromones) ++maternal behavior |
|
Odors and Odor Objects
|
-primary task of olfactory system is to identify odor objects of biological significance to the organism
-odor objects are complex and unique mixtures of two or more "odorants" -odorants include: ~small, volatile molecules: alcohols, esters, aromatic compounds, fatty acids ~complex molecules: musks, steroids (often used as pheromones) |
|
Organs of Smell
|
-sniffing actively brings odorants into nasal cavity to contact olfactory epithelium. Important and complex sensory-motor activity that has a significant impact on perception
-olfactory receptor neurons (ORNs) are found in olfactory epithelium of the nasal cavity -olfactory epithelium secretes aqueous mucus within which odorants dissolve. Mucus contains proteins, antibodies, enzymes, salts, and odorant binding proteins that enhance concentration of odorants |
|
Olfactory Epithelium
|
-composed of olfactory receptor neurons (ORNs), basal stem cells, and supporting cells, bilaterally located along nasal passage
-ORNs number in the tens of millions -ORNs replaced every ~28 days by differentiation of basal stem cells (like taste cells, but one of the few places where new nerve cells are created in adulthood) |
|
Olfactory Transduction
|
-apical pole of ORN forms a knob, from which tufted cilia extend into mucus layer
-odorants dissolved in mucus bind to odorant receptors (OR) location on ORN cilia -binding stimulates unqiue G protein transduction cascade resulting in rise of cAMP levels -cAMP directly opens cation channels, creating inward (depolarizing) Na+ and Ca2+ currents -Ca2+ activated Cl- channels open, net outward Cl- flow substantially enhances inward depolarizing current |
|
Transmission of ORN Activity
|
-transduction currents sum to generate APs in ORN
-termination activity: ~odorants diffuse away ~odorants broken down by enzymes ~cAMP activates other pathways ending transduction -desensitization and adaptation: response to repetitive or prolonger stimulation wanes with time |
|
Olfactory Receptor Proteins
|
-OR's are 7 transmembrane domain G protein coupled receptors, similar to B-adrenergic receptors
-mammals share over 1000 different OR genes (biggest gene family known) -many are pseudogens, which do not normally express ORs -only 350 genes in humans actually express ORs -**each ORN typically expresses only one class of OR** -therefore, only ~350 different types of human ORNs relay info for tens of thousands of different odors |
|
Central Projections of Olfactory Nerve Fibers
|
-ORN axons become fibers in the olfactory nerve which projects to the olfactory bulb
-all ORNs expressing a particular OR converge onto one of two mirror locations, termed "glomeruli" in the OB -each OB has ~2000 glomeruli |
|
Odorant Selectivity
|
-each ORN expresses only one OR subtype
-olfactory epithelium contains four distinct spatial zones along A-P axis -expression of given OR subtype is somewhat limited to a single epithelial zone -each OR subtype is activated by many monomolecular odorants, and each odorant can activate many OR subtypes -some OR subtypes are narrowly tuned responding differently to very similar odorants -other OR subtypes broadly tuned, responding several odorant that differ in structure -odorants may either activate or inhibit different ORs |
|
Odorant Selectivity in ORNs
|
-most ORNs are odor "generalists" (they show a spectrum of responses to a variety of odors
-therefore, odor objects activate more than one type of ORN but to a different extent -odorant concentration is also important but dynamic range of response in single ORNs is limited to about one order (factor of 10) of concentration magnitude -conclusion: each ORN cannot uniquely code for either the identity or the strength of odorants -central olfactory system must "disambiguate" identify and strength to discriminate odors (population coding) |
|
Olfactory Glomerulus
|
-glomerulus is an anatomical and functional unit processing input from ORNs expressing the same OR
-glomerulus contains: ~ORN synaptic endings (many thousands) ~dendritic processes of 2nd order olfactory neurons (mitral, tufted, periglmerular) -in each glomerulus, ~25,000 ORNs converge on dendrites of only ~100 second-order glomerulus cells -population of glomeruli forms a topographic map of specific zones (and therefore OR genes) in the olfactory epithelium |
|
Glomerular Circuity
|
-enhances odorant "contract"
-circuity is similar to retina: ~parallel input-output "vertical" pathways via mitral/tufted cells ~each mitral cells gets excitation from single glomerulus ~granule cell interneurons make "horizontal" inhibitory connections between mitral/tufted cells, mediating "lateral" inhibition -lateral inhibition sharpens mitral cell selectively to improve odorant discrimination ("contrast enhancement") |
|
Principles of Odor Map
|
-glomerulus is the basic structural and functional unit for odor mapping and processing in the olfactory bulb
~odorants activate specific spatial patterns of activity in glomerular lay of OB ~identified glomeruli can be correlated with odorant identity -different odorants elicit activity in unique, overlapping populations of glomeruli; patterns may underlie discrimination ~homologous chemical series (alcohols, aldehydes) activate overlapping, but not identical, sets of glomeruli, reflecting similarity of chemical structure -pattern of glomerular activation for an odor is similar across individuals -increasing odor concentration "recruits" activity in additional glomeruli, which may give rise to different subjective perceptions |
|
Olfactory Cortex
|
-piriform cortex
-orbitofrontal cortex: conscious perception of odors and tastes. Receives PC projections via MD nucleus of thalamus -olfactory tubercle: projects to hypothalamus -amygdala (emotion, social interactions, approach/avoidance) -entorhinal cortex: connects to hippocampus, region of temporal lobe important for "working memory", particularly spatial memory |
|
Processing Odors in Piriform Cortex
|
-PC is archicortex, has 3 layers (vs 6 in neocortex)
-topographic representation of odorants seen in olfactory bulb is lost in PC: ~odorants activate PC neurons over a wide area ~activation patterns for different odors are intermingles and overlap extensively with patterns activated by other odors ~the pattern of activation for an odorant is unique and similar across individuals ~PC neurons receive more input from other PC neurons than they do from OB projections |
|
Representation of Odorants in Piriform Cortex
|
-single odorants activate unique pattern of elevated local activity over a wide area in PC
-pattern highly interdigitated with patterns from other odors |
|
Cornea
|
primary refractive element in eye
|
|
Lens
|
secondary refractive element (for near-vision: "accommodation")
|
|
Iris
|
regulates amount of light entering the eye
|
|
Retina
|
epithelial tissue upon which image is projected, containing photoreceptors and associated neuronal circuity
|
|
Extraocular muscles
|
(horizontal, vertical and oblique pairs) control eye movements
-voluntary: saccadic and smooth pursuit -reflexive: image stabilization re head movements |
|
The Retina: a highly modified sensory epithelium
|
-macula: central region with highest density of photoreceptors
-fovea: in-folding of macula (primates only) -optic disk: "blind spot", exit point for optic nerve (axons of retinal ganglion cells) -pigmented epithelium: light absorbing basement membrane providing metabolic support |
|
The Receptor Mosaic
|
-about 125 million photoreceptors in primate retina, packed into hexagonal array
-two classes of receptors: rods and cones -ratio of photoreceptors to ganglion cells is near 1:1 centrally, increases with eccentricity in periphery -central vision processed by fovea is highly over-represented in the output of the retina |
|
Rods
|
-achromatic (best at medium wavelengths)
-low thresholds, function in low-light (scotopic) conditions -extrafoveal- highest density in peripheral retina |
|
Cones
|
-chromatic
-high thresholds, function in bright (photopic) conditions) -three types of cones absorb different wavelengths: ~short (blue-violet): relatively rare ~medium (green): most common ~long (yellow-orange) -clustered densely in the central retina (macula), particularly in the fovea of primates |
|
Primate Fovea
|
-a pit or fold in the center of macula
-in humans, receives light from central 1 degree of visual space -dominated by cones -has the highest density of receptors, bipolar, and ganglion cells -region of maximum visual acuity |
|
Acuity is highest for central vision
|
-RFs in fovea are much smaller and more overlapping than peripheral retina
-ratio of photoreceptors to ganglion cells in fovea is much smaller (often 1:1) than in peripheral retina -therefore, spatial resolution (two-point discrimination) is highest in foveal vision, declines with eccentricity |
|
Photoreceptors
|
-modified epithelial cells (short receptors)
-out segment: transduction ~modified cilium, densely folded ~contains photopigments, transduce light into membrane current ~outer segments replaced daily -inner segment: transmission ~transduction currents lead to transmitter release |
|
Photoreceptor Transduction
|
-in the dark (unstimulated)
~cGMP-gated Na+ channels are open leading to inward (depolarizing) Na+ current (the so-called "dark current") -exposed to light (stimulated) ~photos captured by photopigment rhodopsin ~rhodopsin "photo bleaching": Cis-retinal converts to trans-retinal, which dissociates from opsin -opsin activates photoreceptor G-protein (transducin), which activates enzyme (PDE) that breaks down cGMP -cGMP-gated Na+ channels close, inward current declines, membrane hyperpolarizes |
|
Photoreceptor Sensitivity
|
-dark adapted humans can detect brief flash of only 5-7 photons falling on a small retinal area
-absorption of a single photon elicits a receptor potential change of ~1 mv, which peaks at 1 s, persists several seconds -in dark-adapted rods: ~absorption of only ~30 photons reduces dark current /by half/ ~absorption of 100 photons suppress dark current completely (maximal response) -adaptation to light results in operational (dynamic) range for luminance of ~1000 cd/m^2 |
|
Photoreceptor Receptive Fields
|
-receptive fields in the visual system are defined in terms of degrees of visual space
-photoreceptor RF is spot-like, defined by the cross-sectional area of the outer segment -response is modulated by luminance (more formally, illuminance, expressed in "lux" = lumens/m^2) |
|
Retinal circuits create opponent receptive fields with contrast sensitivity
|
-vertical interactions: luminance response of photoreceptors is transmitted synaptically to bipolar cells, which then synapse on ganglion cells
-horizontal interactions: occur in synaptic "nests" at two levels 1) photoreceptor, bipolar, and horizontal cells 2) bipolar, ganglion, and amacrine cells -result: bipolar and ganglion cells have "opponent", contrast-sensitive receptive fields |
|
On- vs Off- Center Receptive Fields
|
-on-center cells are excited by spot of light confined to circular area in RF center
-off center cells are inhibited by the same stimulus -on-center cells are inhibited by light falling on the "surround" -off-center cells are excited by the same stimulus -note: a population of receptors can generate both on- and off-center RFs, simply by reversing the "sign" of synaptic interactions -"optimal stimulus" maximal contrast between center and surround -"null" stimulus: ~diffuse light event illuminating center and surround elicits ~only slightly higher response than no stimulus at all (darkness) -net result: retina mainly conveys information about local contrast, little about luminance |
|
Color Vision
|
-P cells receive cone input, are color selective virtue of color opponent RFs:
~red-green (most numerous) ~blue-yellow -red-green ganglion cells: ~receive antagonistic inputs from L and M cones ~L-on and M-off excited by red, inhibited by green in center of RF ~L-off and M-on are excited by green, inhibited by red -M cells are achromatic, responding same to either L or M cones in center |
|
Anatomic Substrate of Opponent RFs
|
-bipolar cells receive direct input from one or more receptors ("convergence"), forming the center of the RF
-bipolar cells receive indirect input from ring of receptors surrounding the center (via horizontal cells) forming the surround of the RF |
|
Spatial Frequency Tuning
|
-response of RGCs to sinusoidal gratings depends on both contrast and spatial frequency (SF)
-contrast sensitivity is maximal at a single optimal or "best" SF -best SF is related to the RF size |
|
M Cells
|
-motion and spatial information processing
-in periphery -large somata and RFs -coarse spatial resolution (low) -high contrast sensitivity -respond better to motion -optimized for large-scale moving patterns -rapid conduction velocity -rapid adaptation- sensitive to transients |
|
P Cells
|
-fine features, shape and color processing
-in fovea -small cell bodies and RFs -fine spatial resolution (high) -low contrast sensitivity -respond well to stationary gradients -optimized for fine features -slow conduction velocity -slow adaptation- sensitive to static images |
|
Representation of Visual Space
|
-monocular fields and binocular fields
-optics of eye project upside-down and backwards image of moncular field onto each retina ~nasal views ipsilateral half of monocular field ~temporal views contralateral half of monocular field |
|
Retinogeniculate Pathway
|
-optic nerves exit each eye and project bilaterally to the LGN of the thalamus
~fibers from temporal hemi-retina project to ipsilateral LGN ~fibers from the nasal hemi-retina cross midline ("decussate") in the optic chiasm, project to contralateral LGN -LGN on each side projects ipsilaterally to the primary visual cortex -result: info from each visual hemifield processed in contralateral hemisphere of visual cortex |
|
Organization of Primate LGN
|
-primate LGN is organized into 6 distinct layers
-layers 1 and 2: magnocellular layers (large cell bodies, heavily stained); input from M-RGCs -layers 3-6: parvocellular layers (small cells, lightly stained), input from P-RGHs |