Psych3 The Biological Basis of Psychology Lecture 10

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Psych3 The Biological Basis of
PsychologyLecture 10 Sensation Perception I
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Lecture 10 Objectives

• Describe basic principles of NS function
• Describe flow of information in NS
• Define sensation and perception
• Describe principles of sensory pathways
• Describe the pathway of light through the eye to
  the retina
• Define acuity, sensitivity, accommodation,
  convergence and binocular disparity
• Describe the function of binocular disparity
• Describe the anatomy of the retina
• Describe the differences in structure, function
  and location of rods and cones
• Draw the pathway from the retina to the visual
  cortex and explain how information in the right
  visual field reaches the left primary visual
  cortex and vice versa
• Explain how the visual cortex contains a
  retinotopic map
• Explain the arrangements of the cells in the
  visual cortex
• Explain how on/off cells and dual-opponent color
  cells may
• account for seeing differences in color.
• Describe the effect of damaging primary visual
  cortex, secondary
• visual cortex and the dorsal versus ventral
  stream
• of the associational visual processing pathways

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Overview

• Functional approach to nervous system
• Sensory (input) system
• Visual pathway
• Visual cortex

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Anatomical vs. Functional Approaches to NS

• Anatomcial approach (last day) defines and
  classifies based on where neurons are.
• Functional approach defines and classifies
  based on what neurons do.

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Basic Functions of NS

• Function of brain generate behavior (including
  the planning that should precede behavior).
• Major purpose is to increase chances of organism
  to survive (biological perspective)
• Evolution has favored conservation of highly
  complex types of behavior in some species (e.g.
  humans) that serve to facilitate survival and
  reproduction.
• To generate behavior there are three primary
  (sub) functions
• Creating a sensory reality
• Integrating information
• Producing motor response

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Basic Principles of NS Function

• Principle 1 The sequence of brain processing is
  
• In -gt Integrate -gt Out
• Senory processes
• Integration processes
• Motor processes
• Principle 2 Sensory and Motor Divisions Exist
  throughout the nervous system.
• In PNS spinal nerves are segregated into sensory
  (incoming) and motor (outgoing) in the dorsal
  root and ventral root nerves.
• In CNS spinal cord is segregated into sensory
  (incoming) and motor (outgoing) nuclei in the
  dorsal horn and ventral horn.
• Brain systems have specific connections with
  sensory and motor pathways, toorest of course
  will describe these.

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Basic Principles of NS Function

• Principle 3 Many of the brains circuits are
  crossed.
• Left side of brain receives sensory info from
  right side of body/world
• Left side of brain controls motor responses on
  right side of the body.
• Principle 4 The brain hemispheres are both
  symmetrical and asymmetrical.
• Most brain function is duplicated in each
  hemisphere
• Some brain functions (e.g. aspects of language)
  are localized to one side (e.g. left side).

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Basic Principles of NS Function

• Principle 5 The nervous system works through
  excitation and inhibition.
• We have learned that at a cellular level inputs
  lead to EPSP or IPSP (either fast or slow).
• System level processes work the same way (i.e.
  summation of all neuron level inputs). e.g.
  Motor neurons in spinal cord are normally under
  inhibition, behavior is removal of inhibition to
  allow excitation.
• Principle 6 The NS functions on
• multiple levels.
• NS functions organized hierarchically.
• e.g. motor control signal from brain
• controls spinal cord which controls muscle.

Primary
Secondary
Tertiary
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Basic Principles of NS Function

• Principle 7 Brain systems are
• organized both hierarchially and
• in parallel.
• Cross-talk between pathways at
• many levels. e.g. spinal cord reflex
• sensory neuron cross-talks to motor neuron.
• Principle 8 Functions of the brain are both
  localized and distributed.
• Specific brain nuclei carry out a specific aspect
  of integration.
• Brain function involves integration performed by
  many brain nuclei in different parts of the brain
  (sometimes far apart) which constitute systems.

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Overview

• Functional approach to nervous system
• Sensory (input) systems
• Visual pathway
• Visual cortex

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Principles of Sensory Systems

• Receptor (Transduction) Mechanism detection
  of environmental info and convert to neuronal
  info (i.e. change in frequency of action
  potentials).
• Relay Centers series of projection neurons
  between specific brain nuclei.
• Cross Midline it just does
• Hierarchical organization convergence of
  parallel pathways into cortical nuceli (areas)
  (e.g. primary sensory cortex, secondary sensory
  cortex, etc).

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Topographical mapping in visual paths
Spatial organization of relay centers Carries
information on where in world stimulation was
derived. Information is mapped within the
nuclei. Anatomy information
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Comments on sensory processing perception

• Visual perception, as all sensory perception,
  requires higher order processingcortical
  processing
• Sensory information is processed in parallel
  through 2 streams
• Conscious stream we are aware of what we are
  sensing Perception
• Unconscious stream we are not aware of what we
  are sensing
• i.e. we sense much more than we perceive brain
  has filtration systems!
• Sensory processing is hierarchical, functionally
  segregated, paralleland integrated.

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Overview

• Functional approach to nervous system
• Sensory (input) system
• Visual pathway
• Visual cortex

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The Eye Gateway to Vision

• Light enters the eye through the pupil (hole in
  the iris)
• The size of the pupil is regulated by the iris
  (contractile tissue that gives your eyes their
  color)
• Parameters of vision
• Sensitivity ability to detect objects in dim
  lighting
• Acuity ability to see details (high when pupils
  constricted)

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Anatomy of the Eye

• The lens is behind the pupil and focuses light on
  the retina
• Accommodation adjusting the shape of the lenses
  to bring images into focus
• Retina contains the receptor (phototransduction)
  mechanism for detecting light is the first
  structure in the visual system.

Note images is 2-D because it maps on a surface.
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But we really have two eyes

• Some perceptual processes in vision result from
  having two independent sites of visual input
• Convergence turning inward to see objects up
  close
• Binocular disparity difference in the position
  of the same image on 2 retinas?enables you to
  construct a depth perception (i.e. see 3-D) from
  two 2-D images on your retinas

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Anatomy of the Retina

• Retina is 5 layers of cells that line the back of
  the eye
• Photoreceptor layer contains the receptors for
  light (transduction)
• Retinal ganglion cell layer sends axons to the
  brain
• Inside-out configuration the receptors are on
  the 5th layer, (furthest away from the lens)
  when activated, the neurochemical signal then
  travels back through the other 4 layers to the
  brain
• First neurons (fire action potentials) are
  ganglion cells which have axons that go to brain
  and create a blind spot.

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Anatomy of the Retina

• Two types of receptors Cones and Rods
• Cones photopic vision good-lighting, high
  acuity, low sensitivity, color dense in fovea
  not activated in dim light low convergence from
  retina
• Rods scotopic vision dim-lighting, low acuity,
  high sensitivity, no color activated in dim
  light high convergence from retina

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Visual pathway Retina-geniculate-striate pathway

• Retina--gt
• Both retinas detect light from both the right and
  the left visual fields (follow the colors in the
  figure)
• Ultimately, information from the right visual
  field?left visual cortex
• Ultimately, information from the left visual
  field?right visual cortex
• Information from the left visual field hits the
  right side of each retina vice versa
• Information travels along the optic nerves (one
  of the cranial nerves) which exit the eye
• 2 sets of optic nerves
• One set travels ipsilaterally carrying
  information from the lateral (outside) part of
  the retina
• One set travels contralaterally, crosses over at
  the optic chiasm and carries information from the
  medial (inside) part of the retina

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Visual pathway Retina-geniculate-striate pathway

• Retina--gtlateral geniculate nucleus (LGN) of the
  thalamus?visual cortex
• Right optic nerve carries information about the
  left visual field from both retinas
• Left optic nerve carries information about the
  right visual field from both retinas
• Optic nerves terminate in the lateral geniculate
  nuclei (LGN) of the thalamus retinal ganglion
  cells synapses with LGN neurons.
• LGN send neurons to the primary visual cortex

LGN
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Retina-geniculate portion of the pathway

• Information from the right visual field goes to
  the left LGN and vice versa
• Like the cortex, the LGN is divided into layers
• Parvocellular layers small cell bodies
• Responsive to color
• High Acuity (low convergence)
• Stationary and slowly moving objects
• Info from cones
• Magnocellular layers large cell bodies
• Movement
• Info from rods
• High convergence
• The more light information, e.g. from cones (low
  convergence), the more visual cortex devoted to
  that part of the retina in the visual cortex
  (i.e., the fovea has the largest
  representation/number of cortical cells in the
  visual cortex).

Path goes to the striate cortex Thus,
retina-geniculate-striate pathway
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Retinotopic mapping of spatial info
Each level of the system is organized like a map
of the retina i.e. Retinotopic For vision,
spatial information is mapped within the nuclei
and tracts. Anatomy information
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Overview

• Functional approach to nervous system
• Sensory (input) systems
• Visual pathway
• Visual cortex

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A word about cortex layers in general

• The cortex consists of 6 layers of cells
• Each layer consists of different cell types
• Some layers receive information and process it
• Other layers send information following
  processing i.e. cortex contains multiple-layer
  circuits.
• In most cortex, the cells responding to a certain
  type of information are arranged in columns
  comprises a functional unit

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Columns of the primary visual cortex orientation

• Cells involved in processing similar information
  are grouped into columns in the visual cortex
• i.e., cells receiving information from the same
  area of the visual field are aligned in columns
• ocular dominance columns the columns for each
  eye alternate so each column contains clusters of
  cells dealing with information from each eye
• Gives appearance of parallel line striated
  appearance based on activation patterns produced
  by each eye.
• Columns for contrast, columns for orientation,
  columns for velocity etc. etc.

Activation (glucose use) during visual processing.
Inject dye into one retina, it travels back to
cortex
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Column organization in Primary Visual Cortex.
Cells at different layers of cortex within a
column respond to same type of input e.g.
maximal firing with line of specific orientation.
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Column organization in Primary Visual Cortex.
Cells at same layers of cortex within different
columns respond to different types of input e.g.
maximal firing with line of specific orientation.
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Basic processing in the primary visual cortex
contrast

• Involves on-center and off-center cells in Layer
  IV of cortex (where information from the LGN
  enters cortex)
• cells have a circular receptive field to which
  they respond (corresponding to an area on the
  retina)
• On-center cells fire when light hits the center
  of their receptive field
• Off-center cells fire when light hits the
  periphery of their receptive field
• The cells are arranged in columns
• Cells are responding to brightness contrast
  between two areas of their receptive field

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Color columns of the visual cortex

• The perception of color also depends upon the
  analysis of contrast between adjacent areas
• Visual cortex contains dual-opponent color cells
• Circular receptive fields with a center and a
  periphery (just like on or off center cells)
• Difference cells are turned on or off when the
  center of their receptive fields is activated by
  a hue or a particular wavelength of light and the
  periphery is activated by a different wavelength

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Cortical Arrangement of Color vision

• Dual-opponent cells are arranged in columns
  penetrating all the layers of the cortex, located
  in the middle of ocular dominance columns
  Blobs

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Higher cortical processing of vision

• Visual information from the LGN enters into
  Primary (Striate) Visual Cortex (in occipital
  lobe)?edges and lines (i.e., on-center and
  off-center cells etc)
• Damage results in blindness (scotoma)
• Information is then passed on to secondary visual
  cortex (prestriate)? specialized for detection of
  color, movement, and complex recognition
• Damage results in agnosias
• Information is then passed on to visual
  association cortex?integration with other senses
  and generation of movement

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Damage to higher visual cortical processing areas

• Dorsal versus Ventral stream of visual processing

Difficulty reaching for objects they can
describe Control of behavior
ventral
Can reach for objects they cannot
describe Conscious perception of what is there
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Higher cortical processing of vision

• Information is then passed on to visual
  association cortex?integration with other senses
  and generation of movement
• As you move up the visual hierarchy, the
  receptive fields become larger and the
  information processing is more specialized and
  complex e.g. Grandmother cells
• Information then passed on to subcortical
  structures?emotion, memory etc

Neurons in the occipital lobe form columns that
respond to basic shapes. e.g. line orientation
Neurons in the temporal lobe form columns that
respond to categories of shapes.