The document summarizes the parallel visual pathways from the retina to the cortex. It discusses:
1) 90% of retinal ganglion cell axons project to the dorsal lateral geniculate nucleus (dLGN) in the thalamus, which relays signals to the primary visual cortex.
2) The remaining 10% project to other midbrain structures like the superior colliculus for visual reflexes and the pulvinar for attention.
3) The dLGN is laminated and retinotopically organized. It contains magnocellular and parvocellular layers that provide parallel processing of visual information to the cortex.
The document provides an overview of visual processing in the brain. It describes the two major visual pathways - the dorsal pathway which processes motion and travels to the parietal cortex, and the ventral pathway which processes colour and form and travels to the temporal cortex. It outlines the key stages of visual processing from the retina through the lateral geniculate nucleus and into the primary and higher-level visual cortices.
Signal detection theory provides an approach for understanding how humans make decisions about detecting stimuli when there is uncertainty. It assumes the brain must differentiate between neural activity caused by background noise alone versus neural activity caused by a stimulus superimposed on the noise. The theory accounts for factors like sensitivity to the stimulus and cognitive biases. A key concept is that the brain establishes a criterion for determining whether the neural activity reflects a stimulus, which can be adjusted to prioritize hits or avoid false alarms. The sensitivity and specificity achieved for different criteria are represented using tools like receiver operating characteristic curves.
Rods and cones are the two types of photoreceptors in the retina. Rods contain the photopigment rhodopsin, which absorbs blue-green light. Cones contain one of three photopigments that absorb either long, middle, or short wavelengths of light. Rods are more numerous in the periphery of the retina while cones are concentrated at the fovea. The visual system undergoes light and dark adaptation to function across varying illumination levels. Light adaptation occurs quickly as photopigments bleach and recover. Dark adaptation is slower as rods take 30 minutes to fully recover sensitivity.
Objective, subjective and cyclopegic refractionGauriSShrestha
This document discusses objective, subjective, and cycloplegic refraction. Objective refraction uses optical principles to obtain a measurement without accommodation. Subjective refraction finds the lenses that place the far point at infinity for best visual acuity. Cycloplegic refraction determines the total refractive error during paralysis of the ciliary muscles by cycloplegic drugs. Cycloplegic refraction is indicated for children, accommodative esotropia, and suspected hyperopia or pseudomyopia. Cyclopentolate is commonly used but the appropriate drug and dosage varies by age. Spectacle prescription from cycloplegic findings is an art considering emmetropization in children.
In computer vision and image processing the concept of feature detection refers to methods that aim at computing abstractions of image information and making local decisions at every image point whether there is an image feature of a given type at that point or not. The resulting features will be subsets of the image domain, often in the form of isolated points, continuous curves or connected regions. This lecture teaches you the basics of feature detection.
https://www.udemy.com/learn-computer-vision-machine-vision-and-image-processing-in-labview/?couponCode=SlideShare
This document provides an overview of artificial neural networks and their application as a model of the human brain. It discusses the biological neuron, different types of neural networks including feedforward, feedback, time delay, and recurrent networks. It also covers topics like learning in perceptrons, training algorithms, applications of neural networks, and references key concepts like connectionism, associative memory, and massive parallelism in the brain.
This document discusses eye strain caused by computer use and methods to reduce it. Prolonged viewing of screens can cause eye dryness, fatigue, and vision issues due to focusing close up. Proper monitor settings like refresh rate and resolution help, as do taking breaks and eye exercises. Computer glasses with special lenses, coatings and designs address these problems better than traditional glasses by providing clear intermediate vision. Choosing the right type based on a computer vision exam maximizes visual comfort for computer tasks.
The document provides an overview of visual processing in the brain. It describes the two major visual pathways - the dorsal pathway which processes motion and travels to the parietal cortex, and the ventral pathway which processes colour and form and travels to the temporal cortex. It outlines the key stages of visual processing from the retina through the lateral geniculate nucleus and into the primary and higher-level visual cortices.
Signal detection theory provides an approach for understanding how humans make decisions about detecting stimuli when there is uncertainty. It assumes the brain must differentiate between neural activity caused by background noise alone versus neural activity caused by a stimulus superimposed on the noise. The theory accounts for factors like sensitivity to the stimulus and cognitive biases. A key concept is that the brain establishes a criterion for determining whether the neural activity reflects a stimulus, which can be adjusted to prioritize hits or avoid false alarms. The sensitivity and specificity achieved for different criteria are represented using tools like receiver operating characteristic curves.
Rods and cones are the two types of photoreceptors in the retina. Rods contain the photopigment rhodopsin, which absorbs blue-green light. Cones contain one of three photopigments that absorb either long, middle, or short wavelengths of light. Rods are more numerous in the periphery of the retina while cones are concentrated at the fovea. The visual system undergoes light and dark adaptation to function across varying illumination levels. Light adaptation occurs quickly as photopigments bleach and recover. Dark adaptation is slower as rods take 30 minutes to fully recover sensitivity.
Objective, subjective and cyclopegic refractionGauriSShrestha
This document discusses objective, subjective, and cycloplegic refraction. Objective refraction uses optical principles to obtain a measurement without accommodation. Subjective refraction finds the lenses that place the far point at infinity for best visual acuity. Cycloplegic refraction determines the total refractive error during paralysis of the ciliary muscles by cycloplegic drugs. Cycloplegic refraction is indicated for children, accommodative esotropia, and suspected hyperopia or pseudomyopia. Cyclopentolate is commonly used but the appropriate drug and dosage varies by age. Spectacle prescription from cycloplegic findings is an art considering emmetropization in children.
In computer vision and image processing the concept of feature detection refers to methods that aim at computing abstractions of image information and making local decisions at every image point whether there is an image feature of a given type at that point or not. The resulting features will be subsets of the image domain, often in the form of isolated points, continuous curves or connected regions. This lecture teaches you the basics of feature detection.
https://www.udemy.com/learn-computer-vision-machine-vision-and-image-processing-in-labview/?couponCode=SlideShare
This document provides an overview of artificial neural networks and their application as a model of the human brain. It discusses the biological neuron, different types of neural networks including feedforward, feedback, time delay, and recurrent networks. It also covers topics like learning in perceptrons, training algorithms, applications of neural networks, and references key concepts like connectionism, associative memory, and massive parallelism in the brain.
This document discusses eye strain caused by computer use and methods to reduce it. Prolonged viewing of screens can cause eye dryness, fatigue, and vision issues due to focusing close up. Proper monitor settings like refresh rate and resolution help, as do taking breaks and eye exercises. Computer glasses with special lenses, coatings and designs address these problems better than traditional glasses by providing clear intermediate vision. Choosing the right type based on a computer vision exam maximizes visual comfort for computer tasks.
The document discusses the anatomy and physiology of the visual system, including:
- The retina contains rod and cone photoreceptors which detect light and have receptive fields.
- Ganglion cells in the retina receive input from photoreceptors and have center-surround receptive fields.
- Signals from the retina project to the lateral geniculate nucleus and then primary visual cortex.
- Cells in visual cortex have orientation selectivity and respond best to edges or movement in preferred directions.
Vision occurs through a process called phototransduction where light is converted to nerve impulses in the retina. In photoreceptors like rods and cones, light causes changes in the visual pigment rhodopsin which initiates a biochemical cascade leading to hyperpolarization and decreased neurotransmitter release. Ganglion cell signals are transmitted to the brain where visual perception involves the integration of light sense, form sense, contrast sense and color sense provided by trichromatic and opponent process theories of color vision.
The visual pathway conveys visual signals from the retina to the visual cortex. Light is detected by photoreceptors (rods and cones) and converted to electrical signals. These signals pass through bipolar and ganglion cells in the retina and then through the optic nerve, optic chiasm, optic tracts and lateral geniculate body to the visual cortex via the optic radiations. Lesions along this pathway can cause different visual field defects including hemianopia and quadrantic defects depending on the location of the lesion. Common causes of lesions include tumors, vascular abnormalities and infections.
This document discusses low vision in childhood, including various pathologies that can cause low vision such as Leber's amaurosis, optic atrophy, and retinitis pigmentosa. It outlines the visual prognosis and visual field defects associated with each condition. The document also discusses the use of low vision aids in children, noting that children are more accepting of aids and that aids should be introduced early. Various types of aids are described, from magnifiers to closed-circuit television. The document concludes with references.
This document discusses lens reflections and antireflective coatings. It notes that reflections from lenses can be troublesome as they produce ghost images, falsify image positions, and cause haze and loss of contrast. Antireflective coatings (ARCs) work on the principle of interference to reduce reflections by using thin film layers that create constructive and destructive interference. ARCs are produced by depositing materials like magnesium fluoride or sodium oxide onto lenses through vacuum evaporation to create layers less than 1/300 the thickness of a human hair. ARCs provide advantages like better vision through increased light transmission and reduced glare.
lecture 16 from a college level introduction to psychology course taught Fall 2011 by Brian J. Piper, Ph.D. (psy391@gmail.com) at Willamette University, includes anatomy of eye/brain, dorsal pathway, ventral pathway, figure/ground, many illusions, synesthesia
Parallel computing is a type of computation in which many calculations or the execution of processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different forms of parallel computing: bit-level, instruction-level, data, and task parallelism. Parallelism has been employed for many years, mainly in high-performance computing, but interest in it has grown lately due to the physical constraints preventing frequency scaling. As power consumption (and consequently heat generation) by computers has become a concern in recent years, parallel computing has become the dominant paradigm in computer architecture, mainly in the form of multi-core processors.
The document discusses several topics related to visual perception, including how the brain processes visual information, how perception can be influenced by experience, and how different animals perceive the world visually in various ways. It also covers Gestalt theory, which proposes that the brain organizes visual elements into unified whole forms or patterns. Some key Gestalt principles include figure-ground, similarity, proximity, and closure.
The document summarizes four major theories of information processing:
1) The stage theory proposes information is processed and stored in three stages: sensory memory, short-term memory, and long-term memory.
2) The levels-of-processing theory states retrieval depends on the depth of elaboration during encoding, from superficial to deep semantic analysis.
3) Parallel distributed processing theory posits information is processed simultaneously across networks rather than sequentially as in stage theory.
4) Connectionist theory emphasizes information storage in networks of brain connections that become stronger through elaboration.
1) The document discusses visual motion perception, including when and how humans perceive motion. It describes real motion versus apparent motion and discusses factors like luminance, color, and contrast that can affect motion perception.
2) A key area of the brain for motion perception is area MT (also known as V5), where neurons are selectively tuned to respond to different directions of motion. Damage to area MT can impair a person's ability to perceive motion.
3) The document also discusses eye movements and how the visual system accounts for them to distinguish between self-motion and object motion.
This document summarizes a collaboration project on the anatomy, physiology, genetics, and evolution of the eye. It discusses the anatomy of the iris and pupil. It describes the physiology of vision including refraction, accommodation, and visual processing in the brain. It covers genetics of eye development including the role of the Pax6 gene. Finally, it discusses the evolution of light-sensitive proteins, development of simple eyes, and adaptations involving the lens, color vision, and eye movement.
This document discusses various applications of parallel processing. It describes how parallel processing is used in numeric weather prediction to forecast weather by processing large amounts of observational data. It is also used in oceanography and astrophysics to study oceans and conduct particle simulations. Other applications mentioned include socioeconomic modeling, finite element analysis, artificial intelligence, seismic exploration, genetic engineering, weapon research, medical imaging, remote sensing, energy exploration, and more. The document also discusses loosely coupled and tightly coupled multiprocessors and the differences between the two approaches.
This document discusses strategic planning concepts for an organization including vision, mission, business definition, objectives, and goals. It defines each concept and provides examples. The vision is a description of the future environment an organization wants to create. The mission defines the organization's role in society by addressing a specific societal need. Objectives are quantifiable end results to be achieved by a certain time. Goals are intermediate results that contribute to achieving objectives. The business definition clarifies what business the organization is in or should be in. Setting objectives and goals helps coordinate decisions, formulate strategies, and assess performance.
Colour vision allows for the discrimination of different colours that are excited by different wavelengths of light. Colour vision is mediated by cone cells and functions best in bright light, while in dim light all colours appear grey. There are three properties that specify colour - hue determined by wavelength, saturation describing colour intensity, and brightness indicating light intensity. The distribution of colour vision in the retina ranges from blue-blind in the very centre to monochromatic vision in the far periphery. Two main theories describe the mechanisms of colour vision - the trichromatic theory involving three cone types sensitive to red, green and blue, and the opponent colour theory where red-green and blue-yellow opponent cells code colour contrasts. Both theories are useful, with tr
The document discusses color vision and color blindness. It begins by describing the structure of the retina and how rods and cones detect light and enable vision. It then discusses theories of color vision from Aristotle to modern trichromatic and opponent-process theories. The document also covers tests for color vision deficiency and different types of color blindness caused by genetic mutations. It notes some challenges faced by those with color vision deficiencies and potential implications in medicine. It concludes by outlining an experimental device called the eyeborg that aims to help treat color blindness by converting color wavelengths into sounds.
This document discusses parallel processing and parallel organizations. It describes four types of parallel organizations: single instruction single data (SISD), single instruction multiple data (SIMD), multiple instruction single data (MISD), and multiple instruction multiple data (MIMD). MIMD systems are further broken down into shared memory and distributed memory architectures. Cache coherence protocols like MESI are discussed for maintaining consistency across caches in shared memory multiprocessors.
This document discusses the neurophysiology of vision, including the visual pathway and visual processing in the brain. It describes how visual impulses travel from the retina through the optic nerve, optic chiasm, optic tracts, lateral geniculate bodies, and optic radiations to the visual cortex. It explains the retinotopic organization and processing of visual information in primary and extrastriate visual areas. Furthermore, it covers concepts of parallel magnocellular and parvocellular pathways, and serial processing of visual features in the visual cortex.
Keratometers measure the radius of curvature of the central cornea using the principle of reflected light and angular size measurements. They utilize a doubling principle to measure the size of the reflected corneal image. Modern automated keratometers focus the corneal image electronically without the need for doubling. Keratometry is used to determine refractive power and monitor corneal shape changes.
This document defines and explains the properties of prisms, including their apical angle, deviation angle, minimum and maximum deviation, index of refraction determination using thick prisms, prism base directions in relation to a patient, and prism diopter units. It provides equations and examples to demonstrate how to calculate deviation angles, minimum and maximum deviations, index of refraction, and prism power in degrees and diopters.
The eye is a spheroid structure around the size of a ping pong ball that functions to distinguish light, dark, shape, color, brightness and distance. It includes structures like the eyelids, conjunctiva, cornea, iris, pupil, lens, vitreous humor, retina, blood vessels and optic nerve. The retina contains light-sensitive photoreceptor cells called rods and cones that convert light into electrical signals to the brain where they are interpreted as vision.
The retina contains photoreceptor cells that convert light into neural signals. These signals are processed in the retina and transmitted to the lateral geniculate nucleus and primary visual cortex via two main pathways - the parvocellular and magnocellular pathways. The parvocellular pathway is involved in processing color and spatial detail, while the magnocellular pathway processes motion. In the primary visual cortex, neurons respond selectively to visual features like orientation, direction of motion, and binocular disparity. Higher visual areas become specialized for functions like color perception in V4 and motion processing in V5.
The retina contains light-sensitive photoreceptor cells that absorb light and convert it into neural signals. Rods function better in low light and mediate peripheral and night vision, while cones require brighter light and help with color vision and central vision. Photoreceptors transmit signals through a series of inner retinal neurons to the optic nerve. The retina has different cell distributions and functions in different areas, with the high-acuity fovea containing only cones. Electroretinography tests evaluate the retina's response to light stimuli and help diagnose retinal diseases and conditions.
The document discusses the anatomy and physiology of the visual system, including:
- The retina contains rod and cone photoreceptors which detect light and have receptive fields.
- Ganglion cells in the retina receive input from photoreceptors and have center-surround receptive fields.
- Signals from the retina project to the lateral geniculate nucleus and then primary visual cortex.
- Cells in visual cortex have orientation selectivity and respond best to edges or movement in preferred directions.
Vision occurs through a process called phototransduction where light is converted to nerve impulses in the retina. In photoreceptors like rods and cones, light causes changes in the visual pigment rhodopsin which initiates a biochemical cascade leading to hyperpolarization and decreased neurotransmitter release. Ganglion cell signals are transmitted to the brain where visual perception involves the integration of light sense, form sense, contrast sense and color sense provided by trichromatic and opponent process theories of color vision.
The visual pathway conveys visual signals from the retina to the visual cortex. Light is detected by photoreceptors (rods and cones) and converted to electrical signals. These signals pass through bipolar and ganglion cells in the retina and then through the optic nerve, optic chiasm, optic tracts and lateral geniculate body to the visual cortex via the optic radiations. Lesions along this pathway can cause different visual field defects including hemianopia and quadrantic defects depending on the location of the lesion. Common causes of lesions include tumors, vascular abnormalities and infections.
This document discusses low vision in childhood, including various pathologies that can cause low vision such as Leber's amaurosis, optic atrophy, and retinitis pigmentosa. It outlines the visual prognosis and visual field defects associated with each condition. The document also discusses the use of low vision aids in children, noting that children are more accepting of aids and that aids should be introduced early. Various types of aids are described, from magnifiers to closed-circuit television. The document concludes with references.
This document discusses lens reflections and antireflective coatings. It notes that reflections from lenses can be troublesome as they produce ghost images, falsify image positions, and cause haze and loss of contrast. Antireflective coatings (ARCs) work on the principle of interference to reduce reflections by using thin film layers that create constructive and destructive interference. ARCs are produced by depositing materials like magnesium fluoride or sodium oxide onto lenses through vacuum evaporation to create layers less than 1/300 the thickness of a human hair. ARCs provide advantages like better vision through increased light transmission and reduced glare.
lecture 16 from a college level introduction to psychology course taught Fall 2011 by Brian J. Piper, Ph.D. (psy391@gmail.com) at Willamette University, includes anatomy of eye/brain, dorsal pathway, ventral pathway, figure/ground, many illusions, synesthesia
Parallel computing is a type of computation in which many calculations or the execution of processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different forms of parallel computing: bit-level, instruction-level, data, and task parallelism. Parallelism has been employed for many years, mainly in high-performance computing, but interest in it has grown lately due to the physical constraints preventing frequency scaling. As power consumption (and consequently heat generation) by computers has become a concern in recent years, parallel computing has become the dominant paradigm in computer architecture, mainly in the form of multi-core processors.
The document discusses several topics related to visual perception, including how the brain processes visual information, how perception can be influenced by experience, and how different animals perceive the world visually in various ways. It also covers Gestalt theory, which proposes that the brain organizes visual elements into unified whole forms or patterns. Some key Gestalt principles include figure-ground, similarity, proximity, and closure.
The document summarizes four major theories of information processing:
1) The stage theory proposes information is processed and stored in three stages: sensory memory, short-term memory, and long-term memory.
2) The levels-of-processing theory states retrieval depends on the depth of elaboration during encoding, from superficial to deep semantic analysis.
3) Parallel distributed processing theory posits information is processed simultaneously across networks rather than sequentially as in stage theory.
4) Connectionist theory emphasizes information storage in networks of brain connections that become stronger through elaboration.
1) The document discusses visual motion perception, including when and how humans perceive motion. It describes real motion versus apparent motion and discusses factors like luminance, color, and contrast that can affect motion perception.
2) A key area of the brain for motion perception is area MT (also known as V5), where neurons are selectively tuned to respond to different directions of motion. Damage to area MT can impair a person's ability to perceive motion.
3) The document also discusses eye movements and how the visual system accounts for them to distinguish between self-motion and object motion.
This document summarizes a collaboration project on the anatomy, physiology, genetics, and evolution of the eye. It discusses the anatomy of the iris and pupil. It describes the physiology of vision including refraction, accommodation, and visual processing in the brain. It covers genetics of eye development including the role of the Pax6 gene. Finally, it discusses the evolution of light-sensitive proteins, development of simple eyes, and adaptations involving the lens, color vision, and eye movement.
This document discusses various applications of parallel processing. It describes how parallel processing is used in numeric weather prediction to forecast weather by processing large amounts of observational data. It is also used in oceanography and astrophysics to study oceans and conduct particle simulations. Other applications mentioned include socioeconomic modeling, finite element analysis, artificial intelligence, seismic exploration, genetic engineering, weapon research, medical imaging, remote sensing, energy exploration, and more. The document also discusses loosely coupled and tightly coupled multiprocessors and the differences between the two approaches.
This document discusses strategic planning concepts for an organization including vision, mission, business definition, objectives, and goals. It defines each concept and provides examples. The vision is a description of the future environment an organization wants to create. The mission defines the organization's role in society by addressing a specific societal need. Objectives are quantifiable end results to be achieved by a certain time. Goals are intermediate results that contribute to achieving objectives. The business definition clarifies what business the organization is in or should be in. Setting objectives and goals helps coordinate decisions, formulate strategies, and assess performance.
Colour vision allows for the discrimination of different colours that are excited by different wavelengths of light. Colour vision is mediated by cone cells and functions best in bright light, while in dim light all colours appear grey. There are three properties that specify colour - hue determined by wavelength, saturation describing colour intensity, and brightness indicating light intensity. The distribution of colour vision in the retina ranges from blue-blind in the very centre to monochromatic vision in the far periphery. Two main theories describe the mechanisms of colour vision - the trichromatic theory involving three cone types sensitive to red, green and blue, and the opponent colour theory where red-green and blue-yellow opponent cells code colour contrasts. Both theories are useful, with tr
The document discusses color vision and color blindness. It begins by describing the structure of the retina and how rods and cones detect light and enable vision. It then discusses theories of color vision from Aristotle to modern trichromatic and opponent-process theories. The document also covers tests for color vision deficiency and different types of color blindness caused by genetic mutations. It notes some challenges faced by those with color vision deficiencies and potential implications in medicine. It concludes by outlining an experimental device called the eyeborg that aims to help treat color blindness by converting color wavelengths into sounds.
This document discusses parallel processing and parallel organizations. It describes four types of parallel organizations: single instruction single data (SISD), single instruction multiple data (SIMD), multiple instruction single data (MISD), and multiple instruction multiple data (MIMD). MIMD systems are further broken down into shared memory and distributed memory architectures. Cache coherence protocols like MESI are discussed for maintaining consistency across caches in shared memory multiprocessors.
This document discusses the neurophysiology of vision, including the visual pathway and visual processing in the brain. It describes how visual impulses travel from the retina through the optic nerve, optic chiasm, optic tracts, lateral geniculate bodies, and optic radiations to the visual cortex. It explains the retinotopic organization and processing of visual information in primary and extrastriate visual areas. Furthermore, it covers concepts of parallel magnocellular and parvocellular pathways, and serial processing of visual features in the visual cortex.
Keratometers measure the radius of curvature of the central cornea using the principle of reflected light and angular size measurements. They utilize a doubling principle to measure the size of the reflected corneal image. Modern automated keratometers focus the corneal image electronically without the need for doubling. Keratometry is used to determine refractive power and monitor corneal shape changes.
This document defines and explains the properties of prisms, including their apical angle, deviation angle, minimum and maximum deviation, index of refraction determination using thick prisms, prism base directions in relation to a patient, and prism diopter units. It provides equations and examples to demonstrate how to calculate deviation angles, minimum and maximum deviations, index of refraction, and prism power in degrees and diopters.
The eye is a spheroid structure around the size of a ping pong ball that functions to distinguish light, dark, shape, color, brightness and distance. It includes structures like the eyelids, conjunctiva, cornea, iris, pupil, lens, vitreous humor, retina, blood vessels and optic nerve. The retina contains light-sensitive photoreceptor cells called rods and cones that convert light into electrical signals to the brain where they are interpreted as vision.
The retina contains photoreceptor cells that convert light into neural signals. These signals are processed in the retina and transmitted to the lateral geniculate nucleus and primary visual cortex via two main pathways - the parvocellular and magnocellular pathways. The parvocellular pathway is involved in processing color and spatial detail, while the magnocellular pathway processes motion. In the primary visual cortex, neurons respond selectively to visual features like orientation, direction of motion, and binocular disparity. Higher visual areas become specialized for functions like color perception in V4 and motion processing in V5.
The retina contains light-sensitive photoreceptor cells that absorb light and convert it into neural signals. Rods function better in low light and mediate peripheral and night vision, while cones require brighter light and help with color vision and central vision. Photoreceptors transmit signals through a series of inner retinal neurons to the optic nerve. The retina has different cell distributions and functions in different areas, with the high-acuity fovea containing only cones. Electroretinography tests evaluate the retina's response to light stimuli and help diagnose retinal diseases and conditions.
1. Visual Evoked Potentials (VEPs) provide an objective assessment of visual function, especially of the retina and optic nerve.
2. VEPs measure the electrical response of the visual cortex to visual stimuli, such as flashing lights or patterns.
3. The major components of the VEP response are the N75, P100, and N145 waves. Abnormalities in the latency and amplitude of these waves can help localize lesions along the visual pathway.
Visual evoked potentials (VEPs) record electrical signals from the scalp in response to visual stimuli. VEPs are useful for objectively assessing visual function, especially of the retina and optic nerve. The VEP involves presenting a visual stimulus such as a flashing light or alternating checkerboard pattern. Electrodes placed on the scalp record the P100 waveform generated in the striate and peristriate cortex in response to the stimulus. Analysis of the P100 latency, amplitude, and interocular latency difference can help detect and localize abnormalities in the retina, optic nerve, optic tract, and visual cortex.
- Visual signals are processed through multiple stages in the retina, visual pathway and visual cortex before visual perception.
- In the retina, photoreceptors transmit signals to bipolar and ganglion cells which transmit to the lateral geniculate nucleus.
- The LGN relays signals to the primary visual cortex which contains columns for processing features like orientation, ocular dominance and color.
- Extrastriate visual areas further analyze signals for motion, depth and color perception before perception in the visual cortex.
This document summarizes the physiology of vision. It discusses:
1) How visual impulses are processed and transmitted from photoreceptors in the retina through the visual pathway to the visual cortex.
2) The types of cells involved in retinal processing and their functions, including rods, cones, horizontal cells, bipolar cells, amacrine cells and ganglion cells.
3) How visual signals are transmitted from the retina through the optic nerve, lateral geniculate body, and optic radiations to the primary visual cortex.
4) The layers and connections of the primary visual cortex and properties of simple, complex and hypercomplex cells in the visual cortex.
The document summarizes key aspects of retinal anatomy and physiology:
- The retina is the innermost layer of the eyeball and is divided into the posterior pole and peripheral retina. It contains photoreceptor cells (rods and cones), bipolar cells, ganglion cells, and other supporting cells.
- The macula and fovea are specialized regions for high acuity central vision. The fovea contains a high concentration of cones and allows for the sharpest vision.
- Photoreceptor cells contain light-sensitive visual pigments and undergo a process of phototransduction to convert light signals to electrical signals. These signals are then transmitted through the retinal layers and optic nerve to the
Magnocellular and Parvocellular pathways1.pptxLaithLutfi1
The document summarizes the magnocellular and parvocellular pathways in the visual system. The magnocellular pathway begins in the retina with parasol ganglion cells that project to the magnocellular cells in the lateral geniculate nucleus. It provides information about motion, depth, and low spatial frequency to the visual cortex. The parvocellular pathway begins with midget ganglion cells that project to the parvocellular cells in the LGN. It provides information about color and high spatial frequency details to the visual cortex. The two pathways differ in cell size and function, with the magnocellular pathway specialized for motion and the parvocellular pathway for color and fine detail.
Anatomy of the Human Eye ( PDFDrive ).pdfRockyIslam5
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Physiology of the visual pathway & cerebral integrationHenok Samuel
The document summarizes the physiology of the visual pathway and cerebral integration. It discusses how light is converted to electrochemical signals in the retina which are then relayed by retinal ganglion cells whose axons form the optic nerve. It describes the retinotopic organization and different types of ganglion cells that project to various areas in the lateral geniculate nucleus and superior colliculus. It also discusses how information is transmitted from the LGN via the optic radiations to the primary visual cortex and then onto dorsal and ventral visual processing streams in the brain.
The document discusses the physiology of vision. It describes the main mechanisms of vision including light incidence, transduction, transmission of visual sensations, and visual perceptions. It then discusses the anatomy of the eye, including the cornea, lens, retina, and aberrations like spherical aberration. It also covers topics like accommodation, visual processing in the retina, visual pathway to the brain, and analysis in the primary and secondary visual cortices.
The physiology of vision involves three main mechanisms:
1) Initiation of vision through phototransduction in photoreceptors
2) Processing and transmission of visual signals from photoreceptors to retinal neurons and ganglion cells
3) Visual perception involving light sense, form sense, contrast sense, and color sense in the visual cortex
1. The retina contains light-sensitive rods and cones that detect light and transmit signals through neurons to the brain.
2. Light exposure causes the photopigment rhodopsin in rods to decompose, hyperpolarizing the rods and decreasing the "dark current" of sodium ions flowing into them.
3. The fovea contains only cones, maximizing visual acuity, while the peripheral retina contains more rods for low-light vision.
The document summarizes key aspects of physiology in the inner retina:
1. Rods and cones synapse with bipolar cells in the retina, which in turn synapse with ganglion cells that converge and leave the eye as the optic nerve. Horizontal and amacrine cells connect receptor and ganglion cells.
2. The retina contains layers and a visual cycle involving vitamin A and photoreceptors that increases light sensitivity in dark adaptation.
3. Ganglion cells receive signals from rods and cones and transmit information about light intensity, movement, and visual details to the lateral geniculate body.
The retina is the internal layer of the eyeball , which is a thin membrane having a purplish red color in living subject. This is a presentation by Dr. Shah-Noor Hassan regarding ANATOMY OF RETINA
This document provides an overview of the visual pathway from the eye to the primary visual cortex. It describes the key structures and cell types involved including the retina, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, optic radiations, and striate cortex. The retina contains rods and cones that convert light signals to neural signals relayed by the optic nerve. The optic chiasm allows for decussation of fibers so that the left visual field is processed in the right hemisphere and vice versa. The lateral geniculate nucleus acts as a relay station and contains magnocellular, parvocellular, and koniocellular cells before projections reach the primary visual cortex via the optic radiations
Visual System - the visual pathway basicRituYadav112
It consists of a brief description of the visual system. The different types of cells present in the retina and their connections among each other. Signal transmission in the retina. Some basic description about the visual field , receptive field and some basic terminologies. The brief description about the visual pathway. The visual cortex and the primary and extrastriate Visual Cortex.
The retina is the innermost layer of the eye that converts light into neural signals. It contains several layers of tissue and cell types that carry out this visual transduction process. The outermost layer contains pigmented cells, followed by photoreceptor cells (rods and cones), bipolar and ganglion cells that transmit signals to the brain. Within the retina, the macula provides high-acuity central vision and the optic disc is where retinal ganglion cell axons exit as the optic nerve. The retina receives its blood supply from the central retinal artery and precise vascular architecture is important for normal visual function.
Functional retinal physiology - Archana.pptxMMC, IOM
1. The retina contains different layers and cell types that work together to convert light stimuli into neural signals. Photoreceptors detect light and hyperpolarize, bipolar cells exhibit spatial antagonism, and ganglion cells generate action potentials that are transmitted to the brain.
2. Within the retina, there are two main types of bipolar cells (on-center and off-center) and two main types of ganglion cells (midget and parasol) that differ in their receptive field properties and transmission of sustained vs. transient responses.
3. The different retinal cell types form pathways through the lateral geniculate nucleus to the visual cortex that allow for the processing of visual information like spatial resolution, color
Similar to Dorso-Lateral Geniculate Nucleus and Parallel Processing (20)
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NSAIDs are analgesic, antipyretic and anti-inflammatory drugs.
Non-narcotic, non-opioid, aspirin-like drugs
Primarily, acts on peripheral pain mechanism and do not depress the central nervous system
Some protective role against cancer and cardiovascular diseases (e.g., aspirin, antithrombotic effects)
Accounts for 5% of all drugs prescribe globally
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1) Optometrists in Nepal, who are graduates with a Bachelor of Optometry degree and provide eye care services including refraction, low vision rehabilitation, and eye disease management and referral.
2) The scope of optometry in Nepal, which involves primary, secondary, and tertiary eye care services across settings like community vision centers and hospitals.
3) The development of optometry education in Nepal, which began in 1998 and now has 66 graduated optometrists, many of whom work in eye care facilities or have private practices.
Convergence is the simultaneous inward rotation of the eyes to maintain single binocular vision at near distances. Convergence insufficiency is a common cause of eye strain and headaches in people who do intensive near work. It involves reduced ability to converge the eyes voluntarily. Symptoms include blurred vision, eye fatigue, and headaches. Assessment involves measuring near point of convergence, fusional vergence ranges, and near-distance exophoria. Treatment focuses on exercises to improve convergence ability, base-in prism reading glasses, and in severe cases surgery may be considered.
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Pediatric refraction is one of the challenging areas of optometry practice. I am so glad to share some of the important aspect of pediatric refraction.
1) Binocular vision requires the separate visual fields and points of fixation of the two eyes to overlap, with neural signals from each eye reaching the same area of the brain to allow for perceptual coordination.
2) Abnormal binocular vision can involve suppression, anomalous retinal correspondence, eccentric fixation, diplopia or confusion. Tests like Worth four-dot, Bagolini, and synoptophore help identify sensory anomalies.
3) Stereopsis, the highest grade of binocular vision, involves fusing slightly disparate retinal images to perceive depth. Tests like Titmus, TNO, and Lang stereotests measure depth perception through stereopsis.
This document provides an overview of motor evaluation techniques for strabismus. It discusses the detection of phoria and tropia through observation of eye and head position. Both objective measurement methods like prism and cover testing as well as subjective methods using tools like Maddox rods, red glass, and synaptophores are outlined. The document also describes the use of tests to determine deviation direction, size, and type. Key examination factors like comitancy, refractive correction, and test distance are defined. Neurological causes of strabismus are explored through demonstrations of Hess screen and diplopia charting.
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2. Introduction
• The most significance
– Number of optic nerve fibres project to the
Lateral Geniculate Nucleus (LGN) in the
Thalamus
• Relay to the form vision
– From LGN, the visual pathway proceeds to
the primary visual cortex, V1
• Complex processing of visual signals
– Visual processing and object recognition is
enhanced by more than 30 extrastriate
cortical areas
3. Targets of the retinal projection
Retinal ganglion cell axons
Major Minor
•Several small
hypothalamic nuclei
•Suprachiasmatic , supra
optic, paraventricular
nuclei
•Accessory optic system
•Nucleus of optic tract
•Dorsal, medial and
terminal nuclei
4. dLGN
90% retinal ganglion cells project to
dLGN
Is Laminated and shows Retinotopic
Organization
Each layer receives input from a specific
eye and class of ganglion cell
5. Superior Colliculus
A midbrain structure conjunction with cortical frontal
eye fields and the brain stem reticular formation
Is laminated and retinotopically organized nucleus.
Visually guided saccadic eye movements
Retinal projection segregates with alternating
columns of left and right eye terminals.
10% of all retinal ganglion cells project to the SC
Are small caliber originate from ganglion cells with
small dendritic fields and do not project to other
retinal targets
6. The Pretectum
A group of small midbrain nuceui is just rostral to the
SC
Receives signals from a group of small diamter
retinal ganglion cells with large receptive fields
Involve with the control of the pupillary light
reflex by means of a projection to the Edinger-
Westphal nucleus of oculomotor complex.
Show consensual response
7. The Pulvinar nucleus
Largest nucleus mass
Receive projections from the small caliber fibres
from the optic nerve and the SC
It projects to several visual cortical area
including V1 and extrastriate, parietal areas
Represents second pathway that can bypass
the LGN to get the visual V1 and may plays a
role in processing from vision
Code importance of visual stimuli-silence or
attention
◦ Eg, the eye hand co-ordination
8. Hypothalamic nucleus
Receives direct sparse retinal
projection that leave the dosal surface
of the optic chiasma and has been
implicated in the synchronization of
circadian rhythms
9. The paraventricular and supraoptic
nuclei
Involve with the regulation of the light
dark cycle for neuroendrocrine
functions
10. The Accessory optic systems
The lateral terminal nucleus
The medial terminal nucleus,
the dorsal terminal nucleus
NOT in the mid brain
Important role in optokinetic
nystagmus in viewing with prolong
large field motion
11. Overview of dLGN
Key gateway to visual signals
entering the cortex
Less agreement in role of vision
◦ Receptive field properties of dLGN cells=
retinal ganglion cell input
Regulate the flow and strength of
visual signals sent to cortex
12. Structural organization
Layers 2,3,5 receives input from Ipsilateral eye
Ipsi
Layers 1,4,6 receives input from Contralateral eye
Contra
Dorsal four layers-small neurons-P
layers
cells=Parvocellular layer (midget cells)
Ventral two layers-Large neurons M
cells=magnocellylar layers (parasol cells)
Between P and M cells=very small bistratified cells-
konio cells
Combination of all these layers=Parallel Processing
13. K6
K5
K4
Konio cells
K3
K2
K1
Coronal section of dorsolateral nucleus of the monkey
14. Structural Organizations
Superior hemifield in retina=Lateral zone
Inferior hemifield= medial zone
Central (foveal)= posterior zone
Peripheral-anterior zone
Each layer receives monocular input
contalateral input is received from contralateral eye only
(nasal fibres)
Ipsilateral input receives input from ipsilateral eye only
(temporal fiblres)
15. Difference in M,P,K cells
Morphology of dendrites
Calcium binding protein content
Physiologic properties
Axonal projection within visual cortex
16. Difference in cell structures
P cells orients • M cells complex • K cells orients
perpendicular to radially branching parallel to the
the cell layers dendrites dLGN layers
Maintain compact • Sample more • A few long
profile widely within M dendrites
Small receptive layers • Larger receptive
field centres • Large receptive field
Calcium binding field • Calcium binding
protein- • Calcium binding protein- calbindin
parvalbumin protein- D 28K
parvalbumin
17. Cell Classes
Two principal cell classes
• Relay cells: send axon
cells • Interneurons whose
to visual cortex axons remais with in
• Glutamic acid -neuro the dLGN
trasmitter • γ-aminobutyric acid-
• 4:1 neurotransmitter
• 1:4
18. X cells and y cells
First evidence of parallel processing
in the mammalian retina (Enroth-
Cugell and Robson, 1966)-cat
ganglion cells to spatial stimuli
specifically sine wave gratings
19.
20. X- and Y-cells
X- cells linear cells
◦ For an X-cell a spatial gratings can be
positioned within the cell’s receptive field such
that no response is elicited.
◦ Excitation and inhibition are linearly summed
and cancel each other. The excitation is equal to
the inhibition.
Y-cells nonlinear cells
◦ Y- cells doesn’t sum spatial information in a
linear fashion.
21. Afferent axons
80% input from midget ganglion cells
7-9% input from parasol ganglion cells
Retinal input for K cells?
22. Efferent axons
In primates- efferent out put from LGN terminates
within the primary visual cortex and the visual
sector of the thalamic reticular nucleus
A minor efferent projection from LGN terminate in
several extrastriate ares-originates from K LGN
cells
◦ Implicates as residual vision in Blind Sight (loss of
primary visual cortex)
Inconclusion, most K cells and all P and M cells
send axons to primary visual cortex
23.
24. Efferent Axons
P cells send efferent axons to 4Cß of
Primary Visual Cortex
M cells send efferent axons to 4Cά
more sparesly to layer 6
K cels send their axons to cortical layer
3B where they terminate in patches of
cells and some k cells also send axons
to cortical layer to 1
25. Receptive field properties
On and OFF centre with opposing
surrounds
K relay cells appear to have
nonstandard visual receptive field
28. Response Time
Parvo
◦ Sustained response when presented with a long duration
stimulus
◦ Sustained neurons respond to a stimuli for a
longer period of time they are better suited to
code Low Temporal Frequency Stimuli
Magno
◦ Transient response to the same stimulus with only
Brief burst at stimulus onset and offset (transient
amacrine cells)
◦ Transient respond to rapid illumination changes
give M-neurons the capability to resolve high
temporal frequency stimuli
29. Receptive Fields
Parvo
◦ Smaller Receptive Fields
◦ Higher Spatial Frequency Resolution
◦ Parvo cells make up the great majority of
retinal ganglion cells, both foveal and
nonfoveal.
Magno
◦ Larger Receptive Fields
31. Retinal Concentration
Parvo
◦ Represents 90% of Foveal Ganglion Cells
Magno
◦ Concentration is constant outside the
fovea
◦ Represents 10% of non-Foveal Ganglion
Cells
32. Functions of the Pathways
Magno System
◦ “Where” System
◦ Alerts us that a visual event has occurred
◦ Detects movement with rapid transmission
◦ Dorsal cortical processing stream
Parvo System
◦ “What” System
◦ Details of the event are analyzed
◦ Ventral cortical processing stream
33. Characteristics of Parvo and Magno neurons
Characteristics P Cell M Cell K cell
Some size Medium large small
Receptive field Centre Centre variable
organization surround surround
Dendrite field size Small Medium large
Contrast sensitivity Low/ weak High but Intermediat
saturated e
Cortical projection 4Cß 4Cά 3b and 1
Color coding Color Non color Some blue
opponent opponent on
Speed of transmission Slow Fast
34. Characteristics of Parvo and Magno neurons
Characteristics P Cell M Cell K cell
TMTFs low high variable
Preferred spatial High Low Low
frequency
Speed of transmission medium (4 Fast (2msec) Low (5msec)
msec)
Spatial linearity Linear Linear or -
nonlinear
Color vision and contrast Poor at high Poor low
sensitivity spatial frequency
frequency contrast
Temporal Sustained Transient Both type
responsiveness
A striking features of the dlGN is its division into three distinct sections, each constituted of a different types of neuron. The two most ventral layers in Fig 13.1 consist of large neurons referred to as magno cells, and the dorsal four layers consist of smaller neurons referred to as parvo cells. In between these principal layers , in interlaminar regions are collections of yet smaller cells called konio cells.
Retinotopic map= each point in visual space represented along a line perpendicular to the layers is precise with the each point in the retina
Single receptive field centre of midget ganglion cells constituted single cone contributing highly developed visual acuity
Color opponency- wave length based discrimination is good
Color opponency- wave length based discrimination is good