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)

• 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

Some Themes

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:

• Notice it requires both fact regurgitation and some reasoning.

When a sound source is moving toward When a sound source is moving toward you, the spacing between the regions of you, the spacing between the regions of compression and rarefaction is smaller compression and rarefaction is smaller than when it is moving away from you, than when it is moving away from you,

what effect does this have on the percept what effect does this have on the percept of the sound ?of the sound ?

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

• Revisit the lecture slides online

• Use Sensation and Perception text as a resource!

• Talk to me after class or by appointment

What if you’re not getting it? Try these (in this order):

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

• 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

Localization

Left Ear

Right Ear

CompressionWaves

• There are several clues you could use:1 arrival time - sound arrives first at ear

closest to source

Localization

Localization

Left Ear

Right Ear CompressionWaves

• There are several clues you could use:1. arrival time

2. phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source

Localization

Localization

Left Ear

Right Ear CompressionWaves

• There are several clues you could use:1. arrival time

2. phase lag (waves are out of sync)

3. 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

Localization

Left Ear

Right Ear CompressionWaves

Sound is the sameSPL at both ears

• High frequency sounds have ambiguous phase lag

Localization

Left Ear

Right Ear

Left Ear

Right Ear

Two locations, same phase information!

• These cues only provide azimuth (left/right) angle, not altitude (up/down) and not distance

Localization

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