Unit 10 Auditory Perception Flashcards
perceptual process with hearing
auditory perception the distal stimulus produces pressure changes in the air
-> pressure detected in the ears, which are converted into a neural signal that is sent to the brain
-> Brain uses neural info to produce a perception
Hearing
auditory perception relies on auditory information that can travel around corners, offering information about objects or events that may be invisible -> adds richness to our lives -> and safety alerts if needed
sound waves
sound stimulus is produces when the movement or vibration of an object cause pressure changes in the air (or in water, and other mediums that TRANSMIT VIBRATIONS)
A speaker-> it’s diaphragm moves back and forth moving CONDENSING molecule (pushing air molecules close together) and RAREFACTING molecules (pushing them further apart)
are sound waves made of air molecules moving to the ears of observer?
no, a speaker pushed change in air pressure towards the observer, which is what is detected by the observer’s ear
visualisation of sound waves
mathematically it is called a sine wave
-> they are measured by frequency and amplitude
frequency: number of cycles completed in one second (Hz)
amplitude: measured as the difference between the high and low peaks of the wave (dB)
high freq: higher pitch
greater amplitude : greater loudness
Loudness
-> how loud we perceive a sound stimulus to be
-> depends on both the amplitude and the frequency (as shown is the audibility curve)
-> 0 -10 decibels (dB) (and ) barely detectable
-> 120 db is extremely loud (potential ear damage
humans perceive - 20 to 20,000 Hz
-> we can easily hear when frequency has a lo dB
-> harder to hear some frequencies when it is played with a high dB
audibility curve
describes our sensitivity or threshold of hearing sounds of different frequencies
- we mostly hear frequencies between 2000 to 4000 Hz -> also the range of frequency of speech
-> we detect 4000Hz sounds even when they are played very quietly
we can only detect 100Hz sounds when it is played much louder
we CANNOT hear sounds between (20Hz, 75dB) and (500Hz, 5dB)
we can FEEL in the area of the threshold of feeling; they can produce discomfort and can cause damage
equal loudness curves on the audibility curves
these curves indicate the sound levels that create the same perception of loudness at different frequencies
The shape of the equal loudness curves is not uniform at different frequencies and dB: the “80” curve is much flatter than the “40” curve
loudness is not straight forward
PITCH
we perceive sounds as “high” and “low”
We tend to perceive high frequency sounds as high-pitched and low frequency sounds as low-pitched
like on a piano and its scales Left=Low, right=high
-> relationship between pitch (subjective perception) and frequency (objective measurement units)
fundamental frequency
a sound with a measurable
-> lowest note (A0) has a frequency of 27.5 Hz, and the highest note (C8) has a frequency of 4166 Hz
With increasing fundamental frequency, we perceive increasing pitch (also called tone height)
Tone Chroma
notes of the same letter sound similarly
-> every time we pass the same letter we go up an octave
Tones separated by one octave have the same tone chroma, and therefore sound similar w/ different pitch
Timbre
When two sounds have the same pitch, loudness and duration but sound different
->the different sound waves
pure tone: the sine wave (rarely appear in nature)
complex tones: more than one pure tone is added together to produce complex waveform
harmonics = component of pure tones that make up the complex tone
complex waveforms
different timbre happens bcs CWF produced by each sound consists of a different combination of harmonics
timbre is determined by
attack and delay
a: build-up of a sound until it reaches a steady intensity
d: the decrease in intensity at the end of a sound (the rate at which a sound fades to silence)
auditory localisation
allows us to determine the sources of sounds in the environment
-> The problem the auditory system faces is that sounds, unlike visual stimuli, do not stimulate hearing receptors based on their spatial location
-> Therefore, the auditory system must use other location cues to discern where sounds are originating from. These cues are created when sound waves interact with the ears and head
Binaural cues
information from both ears that help determine the lift-right position of sounds
-> cues involve comparing the sound signals that reach each ear
interaural level difference
the difference in sound pressure intensity of the signal detected at each ear
-> difference in intensity happens because the head produces an ACOUSTIC SHADOW
sounds originating from one side of the head will reach the opposite side of the head with lower intensity
acoustic shadow
only happens for high frequency sounds and not low-frequency sounds
human head is larger than the distance between high-frequency soundwave cycles which cause disruptions of the sound waves = producing a shadow
low soundwaves cycles are bigger than the human head
Interaural time difference - binaural cues
the time difference between when the sound reaches each ear
-> sounds reaching our right ear faster than our left ear are perceived to be located to the right of us
Auditory Localisation: Monaural Cues
monaural cues give us information about up-down (elevation) location, and only depend on one ear
- spectral cues: main source of monaural information
sounds originating from different elevations stimulate hearing receptors in the inner ear with different intensities depending on their frequency
pinnae
before the sound enters the auditory canal it bounces around the folds of the pinnae, altering the sound
-> Sounds from different elevations bounce around the pinnae in a different way, causing different frequencies to enter the auditory canal with different intensities. Therefore, a sound presented higher up sounds different to when it is presented lower down
placing mold to change the pinnae shape disrupts our ability to detect location of noise
Direct and indirect sounds
-> auditory perception depends whether we are indoor or outdoors, and on the obj inside the indoor space
outdoor direct sound: the sound travels directly from the source to your ears
indoor - based on direct sound + indirect sound: the sound also bounces off other objects before reaching your ears
auditory system’s problem
the sound reaches the ears from different locations and at different times and it must decide where the location of the original source of the sound is
fixes this problem = playing the same sound from two speakers at slightly delayed times
precedence effect
if the delay between of sound at 100ms or longer it is percieved as two sounds.
If the delay is 5-20ms the sound from the first speaker is percieved
direct sound will reach our ears before indirect sounds, we correctly perceive the location of the sound as coming from where it originates
precedence effect in larger rooms
In larger rooms (e.g. concert halls) the delays are longer: even though the perception of the location of the sound is still determined by the direct sound, the indirect sounds can affect the quality of the sound
* In cases where the delay is very long (e.g. in cathedrals), we even perceive an echo, making it very difficult to localise the original source of the sound
architectural acoustics
study of how sounds are reflected in rooms, and is applied to optimise the sound quality in concert halls
If most of the sound is absorbed by the materials in the room, there is less indirect sound, and the shape of the room determines the direction in which sounds are reflected
- The amount of indirect sound is measured in reverberation time: the time it takes for the sound in a room to decrease to 1/1000th of its original pressure (or to decrease to 60 dB)
concert halls
These kinds of concert halls have reverberation times of ~2 s, which is the standard that engineers aim to achieve
* However, achieving 2 s reverberation time does not guarantee success: the New York Philharmonic Hall opened in 1962 with a reverberation time of 2 s, but was heavily criticised (especially by the musicians) for having an apparently short reverberation time - it sounded “dead”
* They destroyed the hall and rebuilt it in 1992 and it still sounded terrible, and is currently waiting to be remodeled again…
Organisation: Separating Sound Sources
multiple sources in the environment, the sounds from different sources combine into a single complex waveform
problem: determine which parts of the complex waveform belong to each source in the environment
Principles of Auditory Scene Organization
- The auditory system uses various cues to organize sounds in the environment.
Location cues: Interaural level difference and interaural time difference help distinguish different sound sources based on spatial separation. - Onset time: Sounds starting at slightly different times usually come from different sources.
- Timbre and pitch: Sounds with the same timbre and pitch are often from the same source.
- Auditory continuity: Constant or smoothly changing sounds are perceived as from the same source.
- Experience: Past experiences influence our perception of sounds.
Key Experiments and Findings
- Scale illusion task (Deutsch, 1975, 1996): Subjects heard high notes in one ear and low notes in the other, perceiving continuous scales, showing grouping by pitch.
- Auditory continuity (Deutsch, 1999): Sounds with constant or smoothly changing frequencies are perceived as continuous even with interruptions.
- Effect of experience: Recognition of melodies despite octave jumps is enhanced by prior exposure to the original melody (Goldstein, 2017).
