Transcript 2320Lecture6

Reading Assignment!
We’ll discuss the chapter by Gregory
in your book on Thursday of next
week
Extra Credit
Participate in a perception experiment
and get an extra 1% added on your
final mark!
Extra Credit
•128-Sensor EEG Experiment
•Virtual Reality Auditory Environment
•takes about 2 hours
•make appointment with me after class or by email
Extra Credit
Sensory Systems:
• Auditory (hearing)
Visual (sight)
Gustatory (taste)
Olfactory (smell)
Somatosensory (touch/temperature/pain)
Vestibular (balance)
Some Themes
• Sensory systems extract information about the
environment by transducing energy
• Perceptual mechanisms interpret that
information and fill in the missing parts
Some Themes
• Sensory systems in the brain are organized in a
way that reflects the nature of the sensory
surface
– somatotopy, retinotopy = spatiotopy
– cochleotopy = tonotopy
• Sensory information is often handled by
contralateral hemisphere
Are you getting it?
• We’ve gone through a lot of material
• REMEMBER: The goal wasn’t to memorize
a bunch of facts
• I want you to think critically about how
these systems work and what that means for
perception
Are you getting it?
• Here’s an example of the kind of question I
might ask you:
When a sound source is moving toward you, the
spacing between the regions of compression
and rarefaction is smaller than when it is moving
away from you, what effect does this have on
the percept of the sound ?
• Notice it requires both fact regurgitation and
some reasoning.
How to practice getting it:
• Make up your own questions!
• tell your friends, get them to ask you
questions
• Notice and think about the world around
you
What if you’re not getting it?
Try these (in this order):
• Revisit the lecture slides online
• Use Sensation and Perception text as a
resource!
• Talk to me after class or by appointment
Hearing
•
•
•
•
•
Detection
Loudness
Localization
Music
Speech
Detection and Loudness
• Sound level is measured in decibels (dB)
- a measure of the amplitude of air
pressure fluctuations
Detection and Loudness
• Sound level is measured in decibels (dB)
- a measure of the amplitude of air
pressure fluctuations
• dB is a log scale (small increases in dB
can mean very large increases in
pressure)
Detection and Loudness
• Sound level is measured in decibels (dB)
- a measure of the amplitude of air
pressure fluctuations
• dB is a log scale (small increases in dB
can mean very large increases in
pressure)
• We have a dynamic range that is a factor
of 7.5 million!
Detection and Loudness
• minimum sound level necessary to be heard
is the detection threshold
Detection and Loudness
• detection threshold depends on frequency
of sound:
• very high and very low frequencies must have
more energy (higher dB) to be heard
• greatest sensitivity (lowest detection threshold) is
between 1000 hz to 5000hz
Detection and Loudness
• Detection can be compromised by a
masking sound
• even masking sounds that are not
simultaneous with the target can cause
masking (forward and backward
masking)
Detection and Loudness
• Loudness is the subjective impression of
sound level (and not identical to it!)
Detection and Loudness
• For example,
tones of different
frequencies that
are judged to be
equally loud
have different
SPLs (dB)
Detection and Loudness
• Hearing loss due to exposure to high-intensity
sounds (greater than 100 dB) can last many
hours
Localization
• recall the lake analogy: task is to localize
the positions of the boats on a lake using the
pattern of ripples at two points on the shore
Localization
• All you have is a pair of instruments
(basilar membranes) that measure air
pressure fluctuations over time
Localization
• There are several clues you could use:
Localization
Left Ear
Right Ear
Compression
Waves
Localization
•
There are several clues you could use:
1
arrival time - sound arrives first at ear
closest to source
Localization
Left Ear
Right Ear
Compression
Waves
Localization
•
1.
2.
There are several clues you could use:
arrival time
phase lag (waves are out of sync) - wave
at ear farthest from sound source lags
wave at ear nearest to source
Localization
Left Ear
Right Ear
Compression
Waves
Localization
•
There are several clues you could use:
1.
2.
3.
arrival time
phase lag (waves are out of sync)
sound shadow (intensity difference)sound is louder at ear closer to sound
source
Localization
•
What are some problems or
limitations?
Localization
•
Low frequency sounds aren’t
attenuated by head shadow
Sound is the same
SPL at both ears
Left Ear
Right Ear
Compression
Waves
Localization
•
Left Ear
Right Ear
High frequency sounds have
ambiguous phase lag
Left Ear
Right Ear
Two locations, same phase information!
Localization
•
These cues only provide azimuth
(left/right) angle, not altitude
(up/down) and not distance
Left Ear
Right Ear
Azimuth
Localization
Additional cues:
Localization
Additional cues:
Head Related Transfer Function:
Pinnae modify the frequency
components differently depending on
sound location
Localization
Additional cues:
Room Echoes:
For each sound, there are 6
“copies” (in a simple
rectanguluar room!).
Different arrival times of
these copies provide cues
to location of sound
relative to the acoustic
space