WEEK 11 - Auditory Cognition Pt2.

• Why is it difficult to tell where a sound is coming from in space?

  unlike retina, we cannot localise information based on part of cochlea that is stimulated as information is not layed out spatially in the organ - instead it is layed out according to frequency
• How do researchers study how sounds are localised in space?

  1. azimuth coordinates - position left to right
  2. elevation coordinates - position up and down
  3. distance coordinates - position from observer
• On average, people can localise sounds:

  1. directly in front of them most accurately
  2. to the sides and behind their heads least accurately
• What cues can we distinguish about sound localisation?

  1. binaural - cue for both ears to extract

  2. monaural - cue for either ear extracted independently
• how do we detect Azimuth coordinates?

  binaural cues

  1. interaural time difference
  2. interaural level difference

  arc because every distance is the same from observer ** azimuth = everything along the curving arc

  
• What is interaural time difference?


  considers difference between the time at which sounds reach the two ears (considers that sound travels slower than light hence small detectable difference in which sound behind our head arrives vs when sound in front of us arrives) e.g. Sound A travels faster to left ear vs sound B reaching left ear

  
• What is interaural level difference?

  difference in sound pressure level reaching the two ears

  e.g. reduction in intensity/ loudness occurs for high frequency sounds for far ear because head casts and acoustic shadow - helps us judge azimuth

  slight difference in pressure level reaching one ear vs the other for sounds in azimuth space

  
• more azimuth = more interaural level difference
• What is not effective for judgements of elevation?

  interaural difference and time difference as in many locations, these differences may = 0 (cone of confusion) - everything in the cone has same interaural time and level difference

  
• What are monaural cues for elevation?

  reflections of high frequencies from convolutions of the pinnae produce elevation and front-back-dependent spectral transformations

  Pinna spectral transformation are the only cues for vertical sound localisation

  There are individual differences in pinna/size shape thus patterns in spectral transformations
• paths of sound into our auditory canal: ways in which reflected and direct sound combine - interfere and interrupt with one another, characterizing the overall spectra/frequency profile of the sound

  
• Why are ways in which sound distorted by pinna good cues for elevation?


  different things sounds bounce off are different depending on where the sound is coming from
• blue grid = where actual sounds are

  red grid = where people are able to localise where sounds are coming from

  observation - people can localise sound accurately, but when spectral cues are disrupted (via mold), localisation is changed as they cannot judge elevation - but can still judge azimuth

  
• after wearing pinna molds over time, mind is able to work out new spectral cues from mold and elevation judgement improves

  
• What is an auditory scene?

  array of all sound sources in the environment
• what is auditory scene analysis?

  cognitive process by which sound sources are separated into individual perceptions/ auditory streams
• Why does auditory scene require cognitive processing?

  pattern of vibration of basilar membrane is influenced by all sound sources simultaneously - hence no information of different sources of those sounds in basilar membrane
• How does our mind auditory group/ analyse?

  a number of heuristics that help our minds do this

  1. onset time - sounds that start at different times are likely to come from different sources
  2. location - single sound source tends to come from location and move continuously
  3. similarity - similar sounds (timbre and pitch) tend to be grouped together
  4. rhythmicity - sounds with a rhythmically component can be grouped together
• What did Bregman and Campbell find?

  stimuli were sequences of alternating low-frequency and high-frequency tones

  when played slowly, the perception is of high and low tones, alternating with one another in a galloping pattern

  when sped up however, listener hears 2 streams - 1. high pitched, 2. low pitch - as our auditory processing has changed

  
• What is compound melodic lines?

  same instrument playing alternating notes rapidly, there is segregation of streams to make it sound as if the same instrument is playing 2 different sounds at the same time - auditory stream segregation allows us to perceive these separately
• what is the acoustic signal?

  produced by air pushed from lungs through vocal cords into the vocal tract
• Difference between normal speech vs whispering?

  normal speech - vocal cords vibrate

  whispering - no vibration
• How are speech sounds produced?

  1. acoustic signal
  2. articulators
• what are articulators?


  parts of vocal tract that can be moved around to make different sounds e.g. tongue, lips, teeth, alveolar ridge (roof of mouth behind teeth), soft palate, uvula, pharynx, glottis

  
• What is the distinction between vowel vs consonants?

  how much is the air that is leaving our lungs obstructed as it passes through our mouths

  obstruction of air = consonants

  little to no obstruction of air = vowel
• what are nasal consonants?

  technically classed as consonants but vowel like as no air flowing from mouth but coming from nose e.g. "n" "m"
• How are different vowel sounds created?


  changing the shape of the vocal tract hence changing articulators to create different resonant properties = diff vowels

  
  

  most work done by tongue but shape of lips also matters
• What are vowels distinguished by?

  1. closeness of tongue to roof of mouth
  2. backness is where peak of tongue is
  3. roundness of the lips

  
• In English, front vowels are typically unrounded and back vowels are typically rounded but this is not true of all languages
• Difference between vowels

  
• How are consonants distinguished?

  1. how articulators obstruct air / manner of articulation
  2. their place of articulation/ where air is obstructed
  3. whether they are voiced or voiceless
• What is manner of articulation?

  describes how the articulators are brought together to disrupt the flow of air through the vocal tract
• what is the place of articulation?

  part of vocal tract articulators come together to create a consonant sound
• what are voiced consonants?

  vocal cords vibrating while air is being forced through the voal tract
• during voiceless consonants the vocal cords do not vibrate
• what does a sound/speech spectrogram show?

  how amplitude/frequency changes over time
• each vowel has different pattern of high intensity/ frequency bar

  
• the first formant = lowest frequency

  second formant = next highest frequency
• roy read the will - has vowels and consonants

  
• vowels are identifiable by formant frequencies

  consonants are identifiable in formant transitions