Sensation and Perception

1
Sensation and Perception

• In this part of the course we will try to answer
  such questions as
• How do we see and hear?
• Why does a TV only need three phosphors (Red,
  Green and Blue) to allow us to see all colors?
• Why are some sounds easier to hear than others?

2
Sensation

• Sensation - the registration of physical stimuli
• Hearing - anatomy and function of the ear
• Vision - anatomy and function of the eye
• Psychophysics - the measurement of sensory
  experiences

3
Sensation

• What is the purpose of sensory processing?
• To transform physical stimuli in the environment
  into neural signals in the brain
• Example (Hearing) Sound waves are transformed
  into vibrations in the ear, and the strength of
  those vibrations are coded by sensory neurons

4
Three Domains of Sensory Research

• Sensory Physiology
• Physiological Psychology
• Psychophysics

5
Hearing Sound Waves

• Auditory perception occurs when sound waves
  interact with the structures of the ear.
• Sound Wave - changes over time in the pressure of
  an elastic medium (for example, air or water).
• Without air (or another elastic medium) there can
  be no sound waves, and thus no sound

6
Characteristics of Sound

• Frequency of a sound wave is related the pitch of
  a sound
• Amplitude of a sound wave is related to loudness
  of a sound

7
Frequency of Sound Waves

• The frequency of a sound wave is measured as the
  number of cycles per second (Hertz)
• 20,000 Hz Highest Frequency we can hear
• 4,186 Hz Highest note on a piano
• 1,000 Hz Highest pitch of human voice
• 100 Hz Lowest pitch of human voice
• 27 Hz Lowest note on a piano

8
Intensity of Various Sounds
P (in sound- pressure units)
Example
Log P
Decibels
Softest detectable sound Soft whisper Quiet
neighborhood Average conversation Loud music from
a radio Heavy automobile traffic Very loud
thunder Jet airplane taking off Loudest rock band
on record Spacecraft launch 9from 150 ft.)
0 1 2 3 4 5 6 7 8 9
0 20 40 60 80 100 120 140 160 180
1 10 100 1000 10,000 100,000 1,000,000 10,000,000
100,000,000 1,000,000,000
9
Intensity of Sound Waves

• The physical intensity of sound waves is measured
  on the decibel (dB) scale
• Intensity (in dB) 20 log (P/P0)
• P intensity of sound being measured
• P0 the lowest intensity 1,000 Hz tone we
  can hear

10
Anatomy of Ear

• Purpose of the structures in the ear
• Measure the frequency (pitch) of sound waves
• Measure the amplitude (loudness) of sound waves

11
Major Structures of the Ear

• Outer Ear - acts as a funnel to direct sound
  waves towards inner structures
• Middle Ear - consists of three small bones (or
  ossicles) that amplify the sound
• Inner Ear - contains the structures that actually
  transduce sound into neural response

12
Anatomy of the Ear
13
Anatomy of the Ear
14
Transduction of Sounds

• The structures of the ear transform changes in
  air pressure (sound waves) into vibrations of the
  Basilar Membrane.
• As the Basilar Membrane vibrates it causes the
  hairs in the Hair Cells to bend.
• The bending of the hairs leads to a change in the
  electrical potential within the cell

15
Coding of Sounds
The pattern of vibration along the Basilar
Membrane depends on the Frequency of the sound
wave
16
Coding Sounds

• Low frequency sounds cause more vibration near
  distal of Basilar Membrane
• High frequency sounds cause more vibration near
  proximal end of Basilar Membrane

17
Coding and Auditory Masking

• The way in which waves travel down the Basilar
  Membrane causes some sounds to interfere with (or
  mask) our ability to hear other sounds
• Low frequency sounds provide better masking than
  high frequency sounds.

18
Auditory Masking

• Low frequency sounds effectively mask high
  frequency sounds
• High frequency sounds can not effectively mask
  low frequency sounds