Sensation and Perception Overview
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Questions and Answers

What is the significance of eccentricity in the context of vision?

  • It indicates the distance from the periphery to the fovea.
  • It affects the concentration of rods and cones in the retina.
  • It describes how visual acuity varies across different zones of the retina. (correct)
  • It determines the wavelength ranges humans can perceive.

    • What happens to rhodopsin when light hits the photoreceptors?

  • It enhances the production of cGMP.
  • It remains intact and continues to absorb light.
  • It breaks down into retinal and opsin units. (correct)
  • It transforms directly into opsin, releasing cGMP.

    • Which statement best describes the function of cones in human vision?

  • They are involved in the transduction process only in low light conditions.
  • They primarily detect colors and function best in bright light. (correct)
  • They are responsible for night vision and peripheral awareness.
  • They are concentrated in the periphery for enhanced motion detection.

    • What is the impact of higher levels of cGMP in the photoreceptors?

    <p>It maintains a depolarized state of the cell.</p> Signup and view all the answers

    What role does vitamin A play in the function of photoreceptors?

    <p>It is necessary for the regeneration of retinal.</p> Signup and view all the answers

    What is the primary difference between the pigments in rods and cones?

    <p>Rods contain only one type of opsin, whereas cones can contain multiple types.</p> Signup and view all the answers

    Which phenomenon describes the over-representation of the central visual field in the visual cortex?

    <p>Topographic mapping</p> Signup and view all the answers

    When light reaches the photoreceptors, what biochemical change occurs that affects cGMP levels?

    <p>cGMP is broken down due to the activation of opsin.</p> Signup and view all the answers

    What does sensation primarily refer to in the context of visual processing?

    <p>The physical responses to environmental stimuli by sensory organs.</p> Signup and view all the answers

    Which statement accurately describes the difference between bottom-up and top-down processing?

    <p>Bottom-up processing is based on sensory input, while top-down processing is influenced by knowledge and experiences.</p> Signup and view all the answers

    What role does the cornea play in vision?

    <p>It primarily filters out UV light and assists in bending light.</p> Signup and view all the answers

    How does the size of the pupil affect vision?

    <p>A larger pupil can reduce acuity due to increased edge effects.</p> Signup and view all the answers

    What is the role of the retina in the visual process?

    <p>It contains photoreceptors that interact with the world and send signals to the brain.</p> Signup and view all the answers

    What phenomenon explains the brain's reconstruction of visual images?

    <p>The blind spot.</p> Signup and view all the answers

    Why is the arrangement of photoreceptors different in humans compared to octopuses?

    <p>Octopuses have photoreceptors facing the lens, while humans have them facing away.</p> Signup and view all the answers

    What happens to visual acuity at large pupil sizes?

    <p>A large pupil size can reduce acuity due to edge effects.</p> Signup and view all the answers

    What effect do horizontal cells have on photoreceptors?

    <p>They enhance the contrast by inhibiting photoreceptors.</p> Signup and view all the answers

    Which type of bipolar cell is excited by light surrounded by darkness?

    <p>On-center bipolar cells</p> Signup and view all the answers

    How do bipolar cells contribute to the detection of visual signals?

    <p>They combine inputs from multiple receptor cells to lower the detection threshold.</p> Signup and view all the answers

    What is the primary role of horizontal cells in the retina?

    <p>To enhance contrast through inhibitory feedback.</p> Signup and view all the answers

    What neurotransmitter plays a key role in the signaling process of bipolar cells?

    <p>Glutamate</p> Signup and view all the answers

    What determines whether a bipolar cell is hyperpolarized or excited?

    <p>The type of neurotransmitter present.</p> Signup and view all the answers

    What is the primary function of horizontal cells in the retina?

    <p>To enhance contrast through lateral inhibition.</p> Signup and view all the answers

    What is the effect of stimulation from dark areas on horizontal cells?

    <p>They send a lot of inhibitory output, especially for the center.</p> Signup and view all the answers

    What does the term 'receptive field' refer to in the context of photoreceptors?

    <p>The specific area where light can trigger a response in a photoreceptor.</p> Signup and view all the answers

    What defines a non-inverting bipolar cell?

    <p>It responds to darkness and is excited by glutamate.</p> Signup and view all the answers

    How does convergence in the visual system affect the information processed?

    <p>It simplifies the information by reducing the output from many inputs.</p> Signup and view all the answers

    What optical phenomenon results from the lateral inhibition process in the retina?

    <p>Mach bands.</p> Signup and view all the answers

    What is the effect of GABA release by horizontal cells in the dark?

    <p>It hyperpolarizes photoreceptors, reducing their activity.</p> Signup and view all the answers

    What main purpose does the reduction of information serve in the visual system?

    <p>To eliminate unnecessary details, focusing on changes.</p> Signup and view all the answers

    What happens to the activity of photoreceptors when light hits them?

    <p>They are stimulated and begin to depolarize.</p> Signup and view all the answers

    Which term describes the effect of neighboring photoreceptors on each other's activity?

    <p>Lateral interactions.</p> Signup and view all the answers

    What is the main characteristic of high convergence in retinal ganglion cells?

    <p>Minimal input required to trigger a response.</p> Signup and view all the answers

    What is the function of the center-surround receptive field in ganglion cells?

    <p>To respond to contrast between light and dark in its input.</p> Signup and view all the answers

    How does the on-center/off-surround receptive field respond when light is presented in the surround?

    <p>It sends a strong inhibitory signal.</p> Signup and view all the answers

    What happens at the edges of a receptive field in relation to Mach bands?

    <p>The contrast between center and surround is maximized.</p> Signup and view all the answers

    In the off-center/on-surround configuration, what leads to a darker appearance at the edge?

    <p>Increased activity in the surround.</p> Signup and view all the answers

    What traditional explanation accounts for the optical illusions seen in a Hermann grid?

    <p>Inconsistent receptive field fitting at intersections.</p> Signup and view all the answers

    Which part of the ganglion cell's receptive field leads to a weak output when stimulation is uniform?

    <p>Both center and surround are equally stimulated.</p> Signup and view all the answers

    How does low convergence in ganglion cells affect the detection of light?

    <p>It enhances sensitivity to localized light sources.</p> Signup and view all the answers

    Study Notes

    Sensation and Perception

    • Sensation is the physical response of sensory organs and neural systems to the environment.
    • Perception is how sensory information is organized, interpreted, and consciously experienced. It is influenced by knowledge, experiences, and thoughts.
    • Sensation and perception are not the same thing. Perception is not a perfect representation of the outside world.

    On The Eye Level

    • Light scatters from a point and needs to be brought back to a point on the retina.
    • The cornea bends most of the light, filters out UV light, and affects vision.
    • The iris controls the size of the pupil, which determines the amount of light entering the eye.
    • A large pupil can lead to lower acuity vision.
    • The lens and cornea bend light to invert the scatter for clear vision.
    • The retina contains the photoreceptors that interact with light.
    • The optic nerve carries signals from the retina to the brain.
    • The blind spot is located where the optic nerve leaves the retina.
    • Humans have a blind spot because the photoreceptors face away from the lens, and nerve fibers pass through the photoreceptor layer.
    • Octopuses have better vision because their photoreceptors face the lens.
    • Eccentricity is the distance from the fovea (highest density of photoreceptors) on the retina, with 0 being the fovea.
    • The center of the visual field has a higher density of neurons than the periphery, creating a distorted representation of the world around us.
    • This neural representation still maintains spatial relationships.

    Photoreceptors

    • The human eye is sensitive to light in the 400-750 nanometer range.
    • The main difference between rods and cones is the wavelengths they are receptive to.
    • Cones detect colors and are concentrated in the fovea. Women have 4 types and men 3.
    • Rods are for night vision and are bleached during the day.
    • Photoreceptors convert light into neural activity.

    Phototransduction Cascade

    • Photoreceptors are normally depolarized, even when not stimulated by light.
    • This is due to high levels of cyclic guanosine monophosphate (cGMP), which opens sodium channels.
    • Rhodopsin, the pigment in rods, breaks down when exposed to light.
    • This causes a decrease in cGMP, hyperpolarizing the cell.

    Receptive Fields

    • A receptive field is the region of space that can activate a cell.
    • Photoreceptors are only the first step in visual processing.

    Convergence

    • Information is reduced in the retina through convergence—many photoreceptors converge onto fewer retinal ganglion cells.
    • This reduces the amount of information that needs to be transmitted to the brain.
    • It also increases the complexity of the information by detecting changes and disregarding constants, similar to how compression techniques work in digital data.

    Lateral Interactions

    • Horizontal cells connect photoreceptors, affecting their activity.
    • They can either increase or decrease activity.
    • This is due to the release of GABA, an inhibitory neurotransmitter.

    Mach Bands

    • Lateral inhibition enhances contrast at edges.
    • This makes darker areas appear darker and lighter areas appear lighter at the edges of objects.
    • This enhances edge detection.

    Bipolar Cells

    • Connect to multiple photoreceptors.
    • Receive input from horizontal cells and photoreceptors.
    • Respond to glutamate differently depending on the glutamate receptor:
      • Inverting: Respond to light by using mGluR6 receptor, where glutamate is inhibitory.
      • Non-inverting: Respond to darkness using AMPA receptors, where glutamate is excitatory.

    Retinal Ganglion Cells

    • Receive input from bipolar cells.
    • Show center-surround receptive fields.
    • The center and surround respond to different inputs.
    • The ganglion cell’s response depends on the local change in the visual field.

    Center-Surround Receptive Fields of Ganglion Cells

    • Respond to contrast:
      • On-center: Respond to light in the center—responds best to light surrounded by dark.
      • Off-center: Respond to dark centers—responds best to dark surrounded by light.

    Mach Bands at the Retinal Ganglion Cell Level

    • The center-surround receptive fields of ganglion cells are responsible for the perception of Mach bands.
    • The receptive fields fit best at the edges of objects, as there is a difference between the center and surround input.
    • The receptive fields fit poorly at the centers of objects.

    Hermann Grid

    • The traditional explanation for the illusion is that the receptive fields of ganglion cells do not fit well at the intersections of the grid.
    • The surround is more active, reducing activity in the center and making the intersections appear darker than the rest of the grid.

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    Early Visual Processing PDF

    Description

    This quiz explores the fundamental concepts of sensation and perception, highlighting their differences and the role of sensory organs. It covers the functioning of the eye, including the cornea, iris, lens, and retina, and their contribution to vision. Understand how light interacts with these structures for clearer perception.

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