Sensation

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Chapter 5

• Sensation

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Introduction

• Sensation vs. perception
• Sensation experience of sensory stimuli
• Perception processing sensation
• receive, encode, store and organize sensations
• Sensory analysis begins with bottom-up processing

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Sensation

• Our sensory and perceptual processes work
  together to help us sort out complex processes

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Sensing the World Basic Principles

• Enables organisms to obtain needed info
• Thresholds
• -in order to receive info, must be strong enough
  for us to notice
• Absolute Thresholds
• -measured by recording stimulation needed for
  appearance to be pinpointed 50 of the time

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A. Thresholds

• In order to receive info, must be strong enough
  for us to notice
• Absolute Thresholds
• measured by recording stimulation needed for
  appearance to be pinpointed 50 of the time

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• Signal Detection
• -detecting a weak stimulus depends not only on
  the strength of the signal, but also our
  psychological state
• -as responsiveness is heightened, so are
  false alarms
• -Why do people react differently?
• -Why do reactions vary as circumstances
  change?

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• Subliminal Stimulation
• Can we detect stimuli below the absolute
  threshold?
• Difference Thresholds
• need to detect small differences among stimuli

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Ernest Weber

• Regardless of the magnitude, 2 stimuli must
  differ by a constant proportion for their
  difference to be noticed
• Known as Webers Law
• Exact proportion varies depending on the stimulus
• Our thresholds for detecting differences are a
  roughly constant proportion of the size of the
  original stimulus

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B. Sensory Adaptation

• Diminishing sensitivity to an unchanging stimulus
• after constant exposure, nerve cells fire less
  frequently
• enables us to focus on informative changes in our
  environment w/o being distracted
• perceive our world not exactly as it is, but as
  it is useful for us to perceive it

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Vision

• Eyes transduce energy into neural messages that
  the brain processes into what you see
• Stimulus Input
• We see a small pattern of the whole spectrum of
  electromagnetic radiation
• 2 physical charateristics
• Wavelength (determines hue)
• Intensity determined by waves amplitude
  influences brightness

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The Eye

• Light enters the eye through the cornea
• Passes through the pupil to the lens
• Lens focuses incoming rays through accomodation
  focuses on retina
• Acuity affected by small distortions in the shape
  of the eye

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The Retina

• Receptor cells rods and cones
• Produce chemical changes that operate neural
  signals
• Bipolar and ganglion cells are activated
• Ganglion cells form optic nerve which carries
  info to the brain
• Blind spot created where optic nerve leaves the
  eye

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The Retina cont.

• Cones cluster around fovea provides color vision
• Have own bipolar cells to relay info to cortex
• Preserves cones precise info which allows them
  to better detect fine detail
• Rods enable black and white vision
• As light diminishes, cones are ineffectual
• Rods remain stimulated b/c sensitive to dim light
• Focus energy into one bipolar cell

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Visual Information Processing

• Visual info travels at more abstract levels
• Retina process info before sending to cortex
• Also helps to encode and analyze sensory info
• Most info processing occurs in the brain
• Info sent to the occipital lobe

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Visual Info cont.

• Feature Detection
• Neurons that receive info and responds to scenes
  specific features
• Info passed to temporal and parietal lobes
• Parallel processing
• Brain does several things at once
• Perceptions are constructed by integration of
  different visual teams, working parallel to each
  other

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Color Vision

• Light has 3 primary colors red, green, blue
• Young-Helmholtz Trichromatic Theory
• When combinations of these cones are activated we
  see other colors
• Colorblind people do not have functioning rods
  and cones
• Vision is dichromatic-makes it difficult to
  distinguish red and green

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Color vision cont.

• Ewald Hering
• Some parts of color vision remain a mystery
• Why are color mixtures seen as pure color?
• Afterimages
• Opponent-process Theory
• Explain this theory.

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Color Constancy

• Ability to perceive an object as the same color
  regardless of the environment
• Color experience comes not only from object, but
  everything around it as well
• How do we maintain color constancy if the context
  has changed?
• Comparisons govern our perceptions

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Hearing
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• Also known as audition
• Highly adaptive

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Stimulus Input Sound Waves

• Amplitude of sound waves determine loudness
• Waves also vary in length and therefore frequency
• Frequency determines pitch
• Long waveslow frequencylow pitch
• Short waveshigh frequencyhigh pitch

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Sound waves cont.

• Decibels-measuring unit for sound energy
• Absolute threshold for hearing 0 decibels
• Prolonged exposure to sounds above 85 decibels
  can cause hearing loss

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The Ear

• Sound waves are converted into neural activity
  through mechanical chain reaction
• Outer ear channels waves through auditory canal
  to the eardrum
• Vibrations pass through middle ear to 3 tiny
  bones-What are they called?
• Sent to the cochlea
• vibrations cause the oval window to vibrate the
  fluid in the ear
• Vibrations cause basilier membrane to ripple
  which bends hair cells that line basiler membrane
• Movement of hair cells triggers impulses in
  adjacent nerve fibers, which join to form the
  auditory nerve

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The ear cont.

• Damage to the hair cells accounts for most
  hearing loss
• Loudness detected through intensity of hair cells
  response
• Interpreted by the number of hair cells activated

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1. Perceiving Pitch

• Place theory (Hermann von Helmholtz)
• Hear different pitches b/c different sound waves
  trigger activity at different places along the
  cochleas basilar membrane
• Determined by recognizing place on membrane which
  it receives neural signals
• High frequency at the beginning of the membrane
  low frequency near the end
• Doesnt really explain how we hear low pitched
  sounds

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2. Frequency Theory

• Alternate explanation for determining pitch
• Whole basiliar membrane vibrates w/incoming
  sound, triggering neural impulses to brain at
  same rate as the sound wave
• What is the problem with this?

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3. Locating Sounds

• 2 ears allows for stereophonic hearing
• Sounds usually detected by one ear first
• Lag time usually small
• Brain uses parallel processing
• Not good at locating a sound ahead, behind,
  overhead or beneath us
• Try to receive 2 different messages

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4. Hearing Loss

• Conduction
• Usually caused by punctured eardrum or bones of
  middle ear lose the ability to vibrate
• Sensorineural
• Damage to cochleas hair cell receptors or
  associated nerves
• Can be linked to disease, but most likely age
• More likely to be caused by prolonged exposure to
  loud noises

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Hearing loss cont.

• Once tissue is destroyed, remains dead
• Cells do not rejuvenate
• Nerve deafness can be solved by a cochlear
  implant
• Know what it is and how it works!!

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Other Senses

• Touch (cutaneous)
• 3 types of receptors
• Records pressure
• Records change in temperature
• Injury or poison-remains active
• Pain
• -tells you when something is wrong
• -allows us to change our behavior

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Other senses cont.

• What is pain?
• Senses and brain
• Not located in a specific area
• No one type of stimulus produces pain
• Ronald Melzack and Patrick Wall-gate-control
  theory
• Memories of pain-explain
• Pain control-several different techniques

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Other senses cont.

• Taste-chemical sense
• Need smell to taste sensory interaction
• Major receivers of taste taste buds
• 4 types salt, sour, sweet, bitter
• Reproduce every week or two

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Other senses cont.

• Smell (olfaction)
• Also a chemical sense depends on ability to
  detect chemicals
• Odors are hard to describe and associated
  w/emotion
• Cilia (nose hairs)
• Electrical signals sent to olfactory bulbs which
  sends info to the brain for interpretation

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Other senses cont.

• Body Position and Movement
• Body has own GPS system relies on senses as well
• Vestibular sense monitors the heads position
  and movement
• Equilibrium is found in the inner ear