Ethical Issues in Psychological Research by 3t42uIp5

VIEWS: 6 PAGES: 25

									The Major Senses
 There are 6 major senses
  vision
  hearing
  touch
  taste
  pain
  smell
 The list can be extended with balance, joint
  senses and others
 Vision has been studied most extensively


                                         1
Vision

Purpose of the visual system
 transform light energy into an
  electro-chemical neural response
 represent characteristics of objects
  in our environment such as size,
  color, shape, and location




                                 2
Light - The Visual Stimulus

                             White
                             light
                                                               Prism




                                             Visible light
                            400          500            600           700




    Gamma                    Ultra-     Infrared                     Broadcast           AC
                  X-rays     violet                   Radar
    rays                     rays       rays                         bands               circuits

  10 -5   10 -3     10 -1     10 1    10 3     10 5   10 7    10 9     10 11     10 13   10 15      10 17
                                                                                     3
                   Wavelength in nanometers (billionths of a meter)
Light - The Visual Stimulus

Light can be described as both a
 particle and a wave
Wavelength of a light is the distance
 of one complete cycle of the wave
Visible light has wavelengths from
 about 400nm to 700nm
Wavelength of light is related to its
 perceived color


                                  4
Structure of the Eye
                                                       Retina
                                                Lens
                                                                    Fovea (point
                                       Iris                         of central focus)




                                   Cornea
                   Light rays           Pupil
                                                                         Optic
                                                                         nerve
                                                       Blind spot


 The eye works like a camera, using a lens to focus light onto a photo-
 sensitive surface at the back of a sealed structure.
                                                                     5
Organization of Retina
    5 cell types
     Photoreceptors
       rods and cones
     Horizontal Cell
     Bipolar Cell
     Amacrine Cell
     Ganglion Cell

                         6
  Organization of Retina
        Cross section of retina                                               Back of
        shown vastly magnified               Photochemical is located here    the eye
        in the diagram to the right

Light




                 Light




                            To
                           optic Ganglion Amacrine Bipolar Horizontal Cone
                                                                        7    Rod
                           nerve   cell     cell     cell     cell
Function of Photoreceptors
The photoreceptors transduce the
 energy in light into a neural response
This occurs when light entering the
 eye is absorbed by photopigment
 molecules inside the photoreceptors
When light interacts with the
 photopigment, it results in the
 photoreceptor becoming more
 negatively charged (hyperpolarization)

                                  8
Distribution of
Rods and Cones
Cones - concentrated in center of
 eye (fovea)
  approx. 6 million
Rods - concentrated in periphery
  approx. 120 million
Blind spot - region with no rods or
 cones


                               9
                        Distribution of
                        Rods and Cones


                                                        Blind spot
                                    Fovea                                                                    Rods           Cones
                   180                                                                        180
                                            Blind spot                                                                      Fovea


                                                                          Thousands of cones per
                                              Fovea
Thousands of rods per




                   140                                                                        140


                                                                             square millimeter
  square millimeter




                   100                                                                        100

                        60                                                                         60
                                                                                                                                 Blind spot
                        20                                                                         20

                        0                                                                          0
                                60    40     20     0    20    40    60                                    60     40     20    0     20    40     60
                                                                                                                                 10
                             Distance on retina from fovea (degrees)                                    Distance on retina from fovea (degrees)
Differences Between
Rods and Cones
Cones
  allow us to see in bright light
  allow us to see fine spatial detail
  allow us to see different colors
Rods
  allow us to see in dim light
  can not see fine spatial detail
  can not see different colors

                                     11
Receptive Fields and Rod
vs. Cone Visual Acuity
                              Light



             Spots of light                  Spots of light

                               Receptive
                                 fields
                               Ganglion                       Light
                                 cells
                                Bipolar
 (a) Fovea                       cells                         (b) Periphery of retina

                              Photo-
                              receptors
                              (cones)

                                 Photo-
                                 receptors
                                 (rods)
                              Pigmented
                              epithelium                               12
Receptive Fields and Rod
vs. Cone Visual Acuity
Cones - in the fovea, one cone often
 synapse onto only a single ganglion
 cell
Rods - the axons of many rods synapse
 onto one ganglion cell
This allows rods to be more sensitive
 in dim light, but it also reduces visual
 acuity


                                   13
Color Vision
Our visual system interprets
 differences in the wavelength of light
 as color
Rods are color blind, but with the
 cones we can see different colors
This difference occurs because we
 have only one type of rod but three
 types of cones


                                   14
Color Mixing

Two basic types of color mixing
 subtractive color mixture
   example:       combining different color
    paints
 additive color mixture
   example: combining different color lights




                                      15
Additive Color Mixture
By combining lights
 of different
 wavelengths we can
 create the perception
 of new colors
Examples:
  red + green = yellow
  red + blue = purple
  green + blue = cyan


                          16
Trichromatic Theroy
of Color Vision
Researchers found that by mixing only
 three primary lights (usually red, green
 and blue), they could create the
 perceptual experience of all possible
 colors
This lead Young and Helmholtz to
 propose that we have three different
 types of photoreceptors, each most
 sensitive to a different range of
 wavelengths
                                    17
Sensitivity Curves for the
Three Types of Cones
 Physiological studies
  revealed that Young
  and Helmholtz were                                1.50




                          Relative responsiveness
  correct                                                  “Blue”
                                                           cones
                                                                    “Green” “Red”
                                                                    cones cones
 We have three types
                                                    1.00




                                  of cones
  of cones
                                                    0.50
 Light of different
  wavelengths will
  stimulate these cone
                                                    0.00
                                                           400 450 500 550 600 650 70
  types by different                                        Wavelength in nanometers
  amounts                                                     (billionths of a meter)


                                                                           18
Trichromacy and TV
All color televisions are based on the fact
 that normal human color vision is
 trichromatic
Although we perceive the whole range of
 colors from a TV screen, it only has three
 colored phosphors (red, green, and blue)
By varying the relative intensity of the
 three phosphors, we can fool the visual
 system into thinking it is seeing many
 different colors
                                     19
Opponent Process Theory
of Color Vision
Some aspects of our color
 perception are difficult to explain
 by the trichromatic theory alone
Example: afterimages
  if we view colored stimuli for an
   extended period of time, we will see
   an afterimage in a complementary
   color

                                  20
Complementary
Afterimages




                21
Opponent-Process Theory

To account for phenomena like
 complementary afterimages, Herring
 proposed that we have two types of
 color opponent cells
  red-green opponent cells
  blue-yellow opponent cells
Our current view of color vision is that
 it is based on both the trichromatic and
 opponent process theory

                                  22
Visual Pathway
           Visual area
           of the thalamus
                         Optic
                        nerve

                   Optic
                   chiasm
                                 Optic   Retina
                                 tract



  Visual
  cortex



                                          23
Visual Pathway
Axons of the ganglion cells come
 together to form the optic nerve
Half of optic nerve fibers cross
 into opposite hemisphere and
 synapse onto LGN (lateral
 geniculate nucleus)
LGN neurons synapse onto
 primary visual cortex
                             24
Overview of Visual System

 The eye is like a camera, but instead of using
  film to catch the light we have rods and cones
 Cones allow us to see fine spatial detail and
  color, but can not function well in dim light
 Rods enable us to see in dim light, but at the
  loss of color and fine spatial detail
 Our color vision is based on the presence of 3
  types of cones, each maximally sensitive to a
  different range of wavelengths



                                         25

								
To top