Frequency Selectivity and Speech Perception

• what is frequency selectivity? what does it separate, and what does it depend on?

  the ability to separate out sounds with different frequencies that occur at the same time, determined by properties of the basilar membrane
• When can tuning be seen?

  LI, SUR, Psy

  - on the basilar membrane (laser interferometry)

  - in the fibres of the auditory nerve (single-unit recordings)

  - in the whole system (psychophysically)
• Why is the basilar membrane selective, and what does laser interferometry measure?

  → The basilar membrane is selective because the velocity of the membrane at the tested location depends on the frequency of the tone

  → laser interferometry measures the responsiveness of the basilar membrane in terms of the speed of its movement

  → the change in the frequency to which this place on the membrane responds most strongly

  → frequency selectivity interacts with sound intensity in complex ways

  
  

  → easier to hear multiple instruments when they are separate instead of the same

  → excite different places on basilar membrane
• Why does each auditory nerve fibre only respond to a narrow range of frequencies?

  → the reduction and shift of frequency specificity as a function of intensity

  When tone is not resolved from the noise it is difficult to hear.
• What is a psychophysical tuning curve; what does the masker do?

  Psychophysical tuning curves (how we detect different pitches)

  
  

  a way to measure how sensitive a person's senses are to different stimuli.

  Imagine you're trying to figure out how well someone can hear different pitches of sound. You would play tones at various frequencies and ask the person to indicate whether they can hear them or not. By plotting their responses on a graph, you can create a tuning curve that shows their sensitivity to different frequencies.

  Basically, it's a way to map out how our perception changes based on the intensity or frequency of a stimulus, helping researchers understand the limits and capabilities of our senses.

  → the level of the masker is adjusted until it just prevents the listener from detecting the test tone

  → this is done with the masker tone at many different frequencies

  → the closer the masker is in frequency to the test tone, the lower the level of the masker needed to mask the test tone; indicating frequency selectivity
• What is needed for vowel sounds to be produced? What are they characterised by, and what does this correspond to?

  Production of vowel sounds: spectrum of sound from larynx, profile of vocal tract, and spectrum of resonances of vocal tract and radiated from lips.

  
  

  → Vowels in speech are characterised by patterns of peaks and valleys in their spectra

  → the peaks correspond to specific areas of resonance in the vocal tract and are called 'formants
• What are the main cues that distinguish vowels, and how can this be demonstrated?

  → the main cues that distinguish vowels in English are the frequencies of the first two formants

  → we can demonstrate that by simplifying the spectra of vowels to contain just two pairs of harmonics with one pair indicating the frequency of the first formant and the other pair indicating the frequency of the second formant.

  → these simplified sounds are heard as the vowels on which they were modelled
• What is the typical approach to sound perception, and a contrasting view?

  Bottom up approach to sound perception (BM, FS, auditory nervous system)

  Ascending and efferent connections

  Cochlea → CN → SO → IC → Cortex

  HOWEVER

  Language knowledge provides top-down support for speech sound (phonemes) and word identification
• What is the ganong effect and the locus of it?

  Amibigous


  Ganong effect → The "Ganong effect" is the tendency to perceive an ambiguous speech sound as a phoneme that would complete a real word, rather than completing a nonsense/fake word.

  Locus of top-down effect: lexical knowledge
• What is the phoneme restoration and the locus of it?

  eel/heel/

  Phoneme restoration → The phonemic restoration effect refers to the tendency for people to hallucinate a phoneme replaced by a non-speech sound (e.g., a tone) in a word. This illusion can be influenced by preceding sentential context providing information about the likelihood of the missing phoneme. Such as hearing eel with table, heel with shoe

  Locus of top-down effect: lexical knowledge
• What is the sound and word reduction and the locus of it?

  Sound and word reduction → shortened in features such as duration and pitch. It connected speech, words are acoustically reduced. Locus of top-down effect: Syntactic and semantic knowledge
• What is the mcgurk effect and the locus of it?

  lips

  McGurk effect → The McGurk effect is a perceptual phenomenon which happens when a person perceives that the movement of another individual's lips do not match up with what that individual is actually saying. Misleading phonemes. See something but hear different.

  Locus of top-down effect: articulatory knowledge
• What is the sine wave speech and the locus of it?

  pure tone


  Sine Wave speech → Speech signal in which the formants of speech have been replaced with pure tones tracking the intensity modulations of those formants over time.

  Locus of top down effect: phonological, lexical, syntactic, semantic knowledge. Fast recalibration.
• Where do top down effects take place?

  Top down effects on sound perception such as those described take place on a cortical level. Beyond the auditory area. Little evidence for top down effects on lower level neural regions.
• What are the effects of selective attention during speech perception?

  affect brainstem activity; inattentional deafness → reduced sensitivity to auditory stimuli when attention is engaged in another task, such as reading
• When does auditory evoked brainstem response decrease?

  cochlea, superior olive


  Auditory evoked brainstem response to task irrelevant sound decreases as a function of working memory load.

  → there is also evidence for top-down connections from the superior olive to the cochlea during selective attention

  → sharpen responsiveness of inner hair cells in the cochlea
• what else do the top down connections lead to? what is there evidence for?

  cochlea/super olive

  purpose, reduction

  → helps detect tones in noise by enhancing frequency selectivity

  → some evidence for a control loop between the cochlea and superior olive to reduce cochlear responsiveness in response to sharp noises (medial olivo-cochlear reflex)
• What does hearing involve? summary

  Hearing involves both bottom-up and top-down processes

  → lexical and contextual effects allow for quick and effective language comprehension

  → cortical levels

  → do not create "genuine" auditory hallucinations

  → top down effects to subcortical and cochlear levels are observed during selective attention (speech in noise)
• What is a test tone, marker tone, and tone masker?


  A test tone is theoretically a constant pure wave of the desired waveform.

  A marker tone is a tone indicator

  
  

  A tone masker - when the perception of one sound is affected by the presence of another sound.

  Auditory masking in the frequency domain is known as simultaneous masking, frequency masking or spectral masking.