PS1080 - Hearing and Language

• Auditory perception


  Perceptual basis of harmony

  
  

  Recognition of voices

  
  

  Separating signal sources

  
  

  Influence of experience and knowledge
• Emotional imbalance: Misophonia


  - Eating sounds making people angry

  - Noisy eating --> physiological distress responses
• The nature of sound


  A sound source is emitting (repeated) circular pressure waves in the air (shells of air compression) >> tuning fork

  
  

  Similar to dropping a pebble into a still pond
• Properties of sound waves


  A pure tone is represented by a singular sinewave (air pressure as function of space/time)

  
  

  Amplitude and frequency

  
  

  Corresponding to perceived loudness and pitch

  
• Measuring perceived loudness


  Perceived loudness is measured by comparing successively presented tones (of different frequency)

  
  

  - Intensity of comparison tone is adjusted until the same 'subjective' loudness as matched to the reference tone

  - Comparing many frequencies >>> curves of equal loudness

  
  

  Physical intensity (SPL= sound pressure level) is recorded as 'perceived loudness
• The spectrum of human speech


  - Speech sounds cover a wide range of the audible spectrum

  - Vowel sounds are mainly in the lower frequency region

  - Consonants cover almost the entire range

  - Telephone systems used to cut off the upper part of the spectrum with minimal effects on speech recognition
• Forms of hearing impairment


  There are a wide range of different auditory impairments AF, including complete deafness

  
  

  Presbycusis: selective high-frequency hearing loss with age (ongoing)

  
  

  Noise exposure can lead to temporary threshold shifts (auditory fatigue) and permanent (partial) deafness

  
  

  Tinnitus: continuous humming or ringing >> leads to suppression
• Sound in time - sonogram


  - A melody is a sequence of tones in time, such a simple a chord

  - To display and analyse real sounds, scientists use 'spectrograms' or 'sonograms': frequency as function of time

  - The chord shows in the schematic spectrogram as sequence of different fundamental & harmonic frequency clusters
• The complexity of a spoken word


  Sonogram of a simple phrase: a complex sequence of frequencies

  
  

  Each spoken word generates a complex pattern of frequency and intensity (spectrum), which is modulated as function of time

  
  

  Recorded as: - Spectrogram (time, frequency, intensity) - Waveform envelope (microphone)

  
  

  Broca's area in frontal lobe: speech production

  
  

  Wernicke's area in temporal lobe: fluent aphasia (phrases without meaning)
• Sound localisation


  - There is no direct representation of auditory space: location needs to be calculated from a number of cues

  - Pinnae: crucial for sensation of space (earphones); locate elevation (up-down)

  - Inter-aural processing to find azimuth (left-right) of sound source

  - Intensity differences: acoustic 'shadow' of the head

  - Temporal or phase differences: inter-aural delays
• Masking


  The detection of a tone is impaired if another tone or noise is presented at the same time
• Binaural masking


  Spatial distance and difference in frequency support separation < difference between ears