PSYC 1100 Section 1.7 Sensory Processes

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rolliespring
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PSYC 1100 Section 1.7 Sensory Processes
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2013-10-12 19:02:16
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Sec 1.7
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  1. SENSORY RECEPTOR  CELLS  TRANSDUCE INFORMATION FROM  THE  ENVIRONMENT
  2. Types of Information Transduced
    • -Chemical (taste, smell)
    • -Mechanical (touch, hearing)
    • -Electromagnetic (vision)
    • Information about the physical stimulus is ...
    • a) encoded in the form of neural activity (frequency and action potentials), and...
    • b) relayed to the brain by specific circuits
  3. Psychophysics
    • The field that relates the physical characteristics of stimuli to their psychological characteristics.
    • JND - just noticeable difference. The minimal amount of physical change in a stimulus can be detected
    • Stevens power law -  the relation between physical intensity and psychological intensity is linear on a log-log plot, but different modalities have different slopes
  4. Signal Detection Theory
    • -was designed to handle problems with the measurement of thresholds
    • -subjects report the presence or absence of an event that may or may not have occurred
    • -subjects can be correct or incorrect in different ways
  5. Physical Stimulus for Sound
    • Pressure changes (alternating waves of compressed and rarified medium; could be in air or water)
    • Relation between Physical and Psychological Characteristics of sound:
    • amplitude: measured in decibels (dB), is related to the loudness of a sound
    • frequency: measured in cycles per second (Hz), is related to the pitch of the sound
  6. Frequency of Sound Waves
    • Human frequency range: 20-20000Hz
    • Low frequency → low pitch
    • High frequency → high pitch
    • Humans typically have hearing loss that is strongest in frequency as they age
    • Ultrasound: higher frequencies above the human frequency range
    • Infrasound: lower frequencies below the human frequency range
    • Some animals can perceive ultrasound or infrasound
  7. The Ear
    • Eardrum - vibrates in synchrony with the sound waves
    • Middle ear ossicles - small bones, the hammer, anvil and stirrup (in latin, the malleus, incus and stapes). They convey vibrations from the eardrum
    • Inner ear - the cochlea (means "snail"); sounds are converted into neural signals in the cochlea, and these signals are conveyed to the brain by the auditory nerve, which is a cranial nerve
  8. The Cochlea
    • The organ for detection of sounds (the organ of Corti) is contained within the cochlea. The cochlea contains several membranes and is filled with fluid
    • The basilar membrane vibrates in response to the physical stimulus of sound; it contains hair cells, which are the sensory receptors for hearing
    • Hair cells transduce the physical stimulus into neural signals.
    • Hairs cells are mechanoreceptors. They become excited by the mechanical disturbance of their hairs that occurs when the basilar membrane vibrates
  9. Theories of Pitch Perception
    • Frequency principle (or theory): the frequency of sound is directly related to the frequency of action potentials that are generated
    • Problem: neurons cannot fire fast enough for high frequency sounds...this principle only holds up to 200Hz
    • Place principle (or theory): different places on the basilar membrane respond to different frequencies of sound. The place principle operates at frequencies higher than 200Hz
  10. Vision
    • Physical Stimulus: the visible portion of the electromagnetic spectrum
    • - although it is only a small portion, the visible spectrum represents about 70% of the electromagnetic energy on the surface of earth
    • - wavelength of light is the part of the physical stimulus that is associated with the perception of color 
  11. The Eye
    • Lens - focuses the light onto the retina
    • Retina - contains rods and cones, which are the receptor cells for vision. They contain pigments, and transduce the visible light into neural signals. They also contain other cell types.
    • Blind spot or scotoma - a blind spot is produces because one part of the retina does not contain receptor cells; axons that come to form the optic nerve exit through this spot
    • Optic nerve - contains axons that convey visual information to brain
    • Fovea (also called fovea centralis)- center of retina, in well functioning eye it should also be the projection zone for the center of the visual field
    • Central scotoma - blind spot produced in the center(fovea) when the background light is low
  12. Anatomy of the Retina
    • 3 layers of cells
    • Inner layer: contains receptor cells(rods and cones); they transduce the light stimulus into neural signals; rods and cones have different pigments
    • -  rods: very sensitive to the low levels of light, vary activity along the light/dark continuum; color insensitive
    • - cones: less sensitive to the low levels of light, color sensitive

    Middle layer: 
    bipolar cells convey information from rods and cones to ganglion cells in the outer layer; there also are horizontal and amacrine cells

    Outer layer: 
    ganglion cells receive information from bipolar cells; cell bodies are in the retina, but axons bundle together to form the optic nerve for each eye, leaving the eye through the blind spot
  13. Anatomy of Visual Connections
    • Overall path to primary visual cortex:
    • Retina>Thalumus(LGN)>Visual cortex
    • - optic nerve: axons from ganglion cells, connects eye to brain
    • optic chiasm: axons from the "nasal" or middle half cross to the other side
    • optic tract: axons passing through chiasm to LGN
    • LGN(lateral geniculate nucleus): relay nucleus in thalamus that conveys info to visual cortex; synapse here, neurons go to primary visual cortex in occipital lobe

    Result of optic chiasm crossings: visual image from the left side of the field ends up in the right side of the brain, and vice versa
  14. Dark Adaptation
    • - the increase in sensitivity to light (i.e. decrease in thresholds) that occurs when a subject is shifted from high to low background light
    • There are two components to the dark adaptation processes:
    • 1. a cone-dependent process used under high background light
    • 2. a rod-dependent process used under low background light
    • This is evidence for two visual processes: photopic and scotopic vision
  15. Photopic Vision
    • "day" vision
    • high background light
    • high acuity
    • good color vision
    • low sensitivity
    • cone-dependent
  16. Scotopic Vision
    • "night" vision
    • low background light
    • poor acuity
    • poor color vision
    • high sensitivity to low levels of light
    • small blind spot in center/fovea (central scomata)
    • rod-dependent
  17. Visual Phenomena Change with Different Background Lighting and Location
    • Light sensitivity
    • - better when background light is low
    • - better in periphery of visual field
    • - best with rods in retinal periphery
    • Visual acuity; sharpness of visual image
    • - better with high background ligh
    • - better in center of visual field
    • - more dependent upon cones in the fovea of retina
    • Color vision
    • - better with high background light
    • - better in center of visual field
    • - more dependent upon cones in the fovea
  18. Theories of Color Vision
    • 1. Trichromatic theory - there are three different primary colors
    • 2. Opponent process theory - there are two different processes, and within each process there are antagonistic dimensions or processes
    • - Red vs. Green process
    • - Blue vs. Yellow process
  19. Evidence in Favor of the Different Theories of Color Vision
    • Trichromatic:
    • - there are 3 different types of cones
    • Opponent process:
    • - color blindness
    • - negative after images
    • It appears as though both theories are correct, but at different levels
    • - cones are trichromatic
    • - the rest of the color pathway (e.g. ganglion, thalamic, cortical cells) follows opponent process

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