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 PhysiologyPhysiological PsychologyPsychophysics

Sensory experiencePhysical stimulus

Domain of Sensory physiology

Domain of sensory psychophysics

Domain of sensoryphysiological psychology

Physiological response

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

Greatest compressionof molecules

Least compressionof molecules

One cycleAmplitude

Higheramplitude(Louder)

Loweramplitude(Softer)

Higher frequency(Higher pitch)

Lower frequency(Lower pitch)

(a)

(b)

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

ExampleP (in sound-pressure units) 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.)

1

10

100

1000

10,000

100,000

1,000,000

10,000,000

100,000,000

1,000,000,000

0

1

2

3

4

5

6

7

8

9

0

20

40

60

80

100

120

140

160

180

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

Pinna

Soundwaves

AuditoryCanal-

Stirrup

Cochlea

Auditorynerve

Semicircularcanals

Roundwindow

Oval windowWhere stirrupattaches

Eardrum(tympanicMembrane)

Bone

Hammer

Anvil

13

Anatomy of the Ear

Outer ear Middle ear Inner ear

A sound causesthe basilarmembrane to waveup and down.

Basilarmembrane

Hair cells

Tectorialmembrane

Round window

Eardrum

Oval window

Cochlea,partiallyuncoiled

Stirrup

AnvilHammer

Soundwaves

Auditorycanal

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

Basilarmembrane

Distalend

Proximalend

Oval window

Direction of traveling 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

Piccolo, soft

Bassoon, loud

Piccolo, loud

Bassoon, soft

Distance along basilar membrane

(a)

Distance along basilar membrane

(b)

Effect of bassoon on basilar membrane

Vibration amplitude of basilar

membrane

Vibration amplitude of basilar

membrane

Effect of piccolo on 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

Piccolo, soft

Bassoon, loud

Piccolo, loud

Bassoon, soft

Distance along basilar membrane

(a)

Distance along basilar membrane

(b)

Effect of bassoon on basilar membrane

Vibration amplitude of basilar

membrane

Vibration amplitude of basilar

membrane

Effect of piccolo on basilar membrane