Week 5 - Hearing & Sound Flashcards
Define Amplitude
Amplitude = loudness of a sound. How high a wave goes. When we say high, it actually means being pushed further away from you.
Define Frequency?
Frequency = pitch. How many cycles a wave goes through in a unit of time.
Define Phase?
Phase - position within a cycle. Peaks on the sound wave
Define Sine Wave
Sine wave = pure tone. The simplest sound wave.
What is the range of human hearing?
20- 20 000 HZ
What is a pure tone?
A pure tone is essentially 1 frequency. However, real sounds in the environment are a combination of many frequencies & amplitudes.
What is Fourier Analysis?
Decomposing complex sounds into their sine waves
What is a Fundamental?
Fundamental = lowest frequency component of a complex sound. Adding harmonics together in a sound wave. Sound waves are composed of fundamentals and their harmonics.
What are the biological parts of the outer-ear?
Pinna
External Auditory Canal
Eardrum (tympanic membrane)
What does the Pinna do, and where is it located?
Pinna = increases the sound amplitude (crack around edge of your outer ear). Important in catching sound waves. Helps determine direction from which a sound is coming. The pinna can distinguish front/ back.
What is the external auditory canal and where is it located?
External auditory canal = the outer-ear. provides protection, increases sound amplitude. Right before the eardrum. Pressure increases and sound needs to travel through your small ear canal.
What is the Eardrum (tympanic membrane) and where is it located?
Eardrum = in outer ear. Vibrates in response to sound waves. First point of contact, moves bones in middle ear and transports throughout ear structure.
What are the parts on the Middle Ear?
Ossicles (collectively):
- Malleus
- Incus
- Stapes
Smallest bones in the human body. They transmit the vibration of the eardrum into the cochlea. Further amplifies sound and provides protection against high amplitude sounds at the same time.
What parts are in the Inner Ear?
Cochlea = contains auditory sensory receptors. Oval window/ spiral part of the inner ear.
- Starts vibration of the eardrum, transmitted to oval window where the cochlea is.
- 3 canals in cochlea separated by membranes.
~ Reissner’s membrane, Basilar membrane, (on which auditory receptor cells/ hair cells, converts vibrations into neural signals in the cochlea duct).
~ Physical waves in external environment need to be converted into neural signals - the cochlea is where this occurs.
Central Auditory Pathways. What are the different parts involved?
Nerve fibres from each cochlea synapse in a number of sites on the way to the primary auditory cortex:
~ cochlea nucleus
~ Superior olivary nucleus
~ inferior colliculus
~ Medial geniculate nucleus
Signal arriving at cochlea nucleus splits & goes to each of the superior olivary nuclei 0 beyond this point input from both ears is present in both hemispheres. Beyond the point of the cochlea nucleus, the auditory information splits and involves both sides of the head (two ears).
Cortex is central. Studies reveal tasks which cannot be performed without the cortex: duration of sounds, tones of sounds (REFER TO SLIDES)
What is the Basilar Membrane?
Basilar membrane has a unique shape - narrow and stiffer at base, wider at apex. travelling waves move along the basilar membrane & peak at different points, depending on the frequency of the sound.
Each hair cell has its own preferred frequency.
Base of membrane = higher. frequency
Apex of membrane = lower frequency
What are tonotopic maps?
Tonotopic maps = present in the auditory system. Organisation is seen repeatedly in the auditory pathways - auditory neurons are arranged in an orderly matter.
Primary visual neurons in primary visual cortex are organised in an orderly matter. Not according to spatial location, but according to frequencies of the sound (tonotopic map).
Pitch perception: does one ear do all the work, or do we require two?
Perception of a missing fundamental = when high-order harmonics are present in the absence of the fundamental (first harmonic), the missing fundamental is ‘filled in’
A missing fundamental is perceived even when harmonics are presented to different ears.
What do you know about loudness perception?
Loudness perception = how strongly hair cells fire & overall firing rates.
Sound duration - longer = louder
The important factor here is frequency (higher = louder sound). E..g lower sounds (lower frequency) quieter.
Describe what is involved in auditory space perception:
You try to determine a sounds:
~ horizontal direction (azimuth)
~ vertical direction
~ distance
Vision provides more precise information about an object’s location. Nothing on basilar membrane directly indicates sound locations.
What is auditory space perception classified as?
A binaural process;
- Interaural time difference (onset difference & phase difference)
- Interaural intensity difference
What is Interaural Time difference?
When sound reaches two ears at different times (unless directly in front of behind you - which is onset differnce)
What is onset difference?
Detected by “delay line”
What is the role of head movements?
Head movements are generally helpful for auditory localisation.
By changing the position of the ears, you can experience changes in interaural time/ intensity differences.
Explain a little bit about Horizontal VS Vertical direction?
humans perceive horizontal directions better than vertical directions through auditory cues
- Pinnae are more effective in distinguishing front/back than above/ below
- Ear positions can be varied more freely along the horizontal direction
What are some limits of auditory localisation?
Most of the auditory localisation cues are dependent on the distance between a sound source and ears. As a result, it is difficult to distinguish locations of sounds that are equidistant to an ear - cone of confusion
What are the (2) cues for auditory distance perception?
Loudness
Energy ratio of direct & reverberant sound
