Distinguishing different sounds
- many listeners find it easier to distinguish a cello from a flute because they excite a different- place on the basilar memb
- when 2 cellos at different pitch played they excite same region of basilar memb (BM) = hard to distinguish
Frequency selectivity definition
- Ability to separate out sounds with different frequencies that occur at the same time
- good for speech perception
selectivity of the basilar membrane
- Laser interferometry - measures responsiveness of BM in terms of speed of its movement (Velocity)
- BM is selective p because velocity at tested location depends on frequency of tone
- measure vibrations at different locations
- Drop glass bead on BM, shine laze on bead allows us to measure amplitude when pure tones are played
Frequency selectivity + intensity
- Lower frequency at higher intensities
- Higher frequency at low intensities
- suggests frequency selectivity interacts with intensity
Auditory nerve tuning
-each auditory nerve fibre responds only to a narrow range of frequencies
- reduction + shift of frequency specificity as a function of intensity - insert 1 microelectrode into 1 single auditory fibre of rat
- when increasing intensity of sound = less selective + responds to larger range of frequencies
Psychoacoustic demo of frequency selectivity
- warbling tone centred on 500 Hz (wobbles)
- Band of noise = random energy within a band of frequencies centres around a specific frequency
- known as mask
When near it against noise = tone resolved from noise + is easy to distinguish when played with masker - When same frequency = masked both activate same part of BM
Psychophysical tuning curves
- play test tone at fixed level of intensity
- play masker tone simultaneously with test tone changing intensity of masker till you can’t hear test tone = threshold
- repeat for multiple frequencies
- Collect intensity of masker tone so test is no longer distinguished
- closer Masker is in frequency to test , lower level of masker needed
- indicates frequency selectivity of whole system
where is frequency selectivity found
- Basilar memb
- Auditory nerve
- Entire system
Spectrogram: frequency vs time
-is intensity as a function of frequency
- representation of sound over time as a function of frequency
- intensity = darkness of trace
- dark bands are lots of energy across entire frequency selection
- fricative sounds: s, sh, z -> have energy in high frequencies (sometimes low)
- formants -> band of energy in conc area - make vowels which project energy at diff locations on BM
- Bottom of spectrogram = apex of BM
Production of vowel sounds
-peaks = formants (specific areas of resonance in vocal tract)
- same sound source from vocal chords + you change it to create formants
- spectrum of resonance of vocal tract + radiated from lips
- To distinguish English vowels only need to near frequencies of first 2 formants
- simplify spectra of vowels to contain just 2 pairs of harmonics
- First harmonic/fundamental frequency determines pitch of sound
Top-down effects on hearing
- lang knowledge provides top- down support for speech sand (phonemes) + word identification
- allows US to deal with uncertainty if there’s background noise + gaps can fill it but can cause illusions
Ganong effect -Top-down
- Ability of linguistic knowledge to perceive a sound in 1 way or another
-randomise syllables + ask to identify the letter they heard - when its clearly g, very few say k
-when make it giss or kiss people report more k even though nothing Changed in the signal
-k is compatible with iss - want it to make sense
-Locus of top-down effect: lexical knowledge
phoneme restoration - Top down
- Restoration effect (warren)
- Hear nothing but we restore the sound to make it meaningful
- want to hear word with missing letter to make sense of it
- LoCuS of top-down effect: Lexical knowledge
- when you play a sentence with a cough people hear the word needed to make sense of it conceptually
- creating position of uncertainty on auditory system but fill it 50 it mares sense
- Locus of top-down effect: semantic knowledge
sound + word reduction - Top down
- in conversation words often acoustically reduced sometimes you don’t know what was said
-when reduced word is played in isolation can’t make sense, when its in a sentence we can - is a impoverished version of What we think we are hearing
- LocUS of top-down effect: syntactic + semantic Knowledge
McCurk effect - Top down
- Effects of vision on audition
- Effect of seeing speech on hearing speech
- Auditory perception influenced by vision
-illusions occur when they clash - vision has ability to hijack auditory system
-intertwined - Locus of top-down effect: articulatory knowledge
sinewave speech-Top down
- speech signal which formants of speech replaced with pure tones
- Distorted + simplified version of speech
- Nothing changes on cockled level but auditory system imposed structure g meaningless pattern of activation on BM
-locus of top-down effect: phonological, lexical, syntactic, semantic - can train ppts to understand sine wave speech with repeated sentences which can be transferred to new sinewave sentences
Top-down effects in the brain
- Take place mostly at cortical level
-auditory hallucinations are ASsOC with early-episodes of psychosis - However inner voice PVC isn’t activated but hallucinations are
Effects of selective attention during speech perception affects brainstem activity
- inattentional deafness= reduced sensitivity to auditory stimuli when attention is engaged in another task
- auditory -evoked brainstem response to task-irrelevant sound decreases as function of WM load
-level of activation decreases as a function of complexity of wM increases
top- down connections in the ear + inner hair cells
- from superior olive to cochlea during selective attention
-connections sharpen responsiveness of inner hair cells
-Help detect noise by enhancing frequency selectivity
-detect high frequency sound = aper inner hair cells toned down + base tuned up
Hearing = bottom-up + top-down processes
-lexical + contextual effects allow quick + effective Comprehension of lang
- affect interpretation
- subcortical + cochlear level effects observed during selective attention (speech)
