Basic Auditory Func0ons Pitch Loudness Localiza0on Pitch Percep0on •  Place theory –  Helmholtz (harp) –  Von Békésy (cadavers) •  Temporal theory –  Rutherford (telephone) Traveling Waves Basilar Membrane Mo0on •  hGp://www.youtube.com/watch?
v=dyenMluFaUw Place Theory •  cochlear map of maximum displacements •  s0mula0on deafness experiments (chinchillas) •  natural s0mula0on deafness studies in humans (terminally ill in hospital) •  Mössbauer technique (radioac0ve isotope on BM in live animals) sharp wave •  tonotopic map (place on basilar membrane and place in brain) •  tuning curves for auditory nerve cells Cochlear Map of Frequencies Traveling Wave Auditory Tuning Curves Place Theory •  But what about… –  Ability to discriminate low frequency sounds (with similar envelopes)? –  Missing fundamental? Temporal Theory •  The basilar membrane does vibrate at a rate consistent with the incoming frequency •  But how fast can neurons fire? (1 kHz) •  Could neurons work together to encode higher frequencies? (Wever – volley principle) •  But phase locking only works to ~5 kHz •  Frequencies above 5 kHz aren’t “melodic” so maybe that doesn’t maGer How do we perceive pitch? •  Lower frequencies: temporal informa0on •  Higher frequencies: place informa0on •  Most current theories emphasize temporal informa0on •  But Oxenham et al. (2004) shi`ed the temporal informa0on for a low-­‐frequency tone so that it mimicked a high-­‐frequency tone—but place was s0ll important! Ways to use the missing fundamental •  Pitch can emerge beyond the inner ear! •  Houtsma and Goldstein used a missing fundamental-­‐type study, with one harmonic to the le` ear and a higher harmonic to the right ear. People heard the missing fundamental pitch…even though it wasn’t present in either ear. •  Neurons respond as though the missing fundamental is present (so encode pitch and not frequency) Complex rela0onship between frequency and pitch •  Experience maGers: musicians and blind more sensi0ve •  Missing fundamental: diff freqs give rise to same pitch •  High freqs (above 5k) not heard as pitch •  Brief dura0on heard as clicks It’s complicated… •  First, present this complex: –  200 Hz + 400 Hz + 600 Hz + 800 Hz + 1000 Hz •  Then, replace 800 Hz with 900 Hz –  Perceived pitch of the complex goes up •  Instead, first present a 900 Hz tone •  Then add 200 Hz + 400 Hz + 600 Hz + 1000 Hz •  People hear two tones: 900 Hz and a complex tone with a 200 Hz fundamental It’s complicated… •  Shepard Tones •  Octave Illusion (Need Headphones-­‐Music Video) •  Tritone Paradox •  Mysterious Melody Octave Illusion Loudness •  Loudness is a psychological phenomenon (phon or sone) related to sound pressure intensity (dB of SPL) •  Percep0on of loudness is likely due to a summa0on of firing across a number of neurons •  Loudness varies with frequency (Fletcher-­‐
Munson curves) Loudness Localiza0on Localiza0on in space How do we localize sounds? •  Timing informa0on (inter-­‐aural 0ming differences): onset and phase differences •  Intensity informa0on (inter-­‐aural intensity differences) •  Minimum audible angle (MAA) Illustra0ng ITD and IID Intensity differences depend on frequency (best for high) Onset differences work well, but some sounds are con0nuous… Webster-­‐Jeffress Model For con0nuous sounds, we rely in phase differences to localize sounds Works best for low frequency sounds Owls Owls and auditory localiza0on •  Evolved in a niche without compe00on and with rela0vely few predators •  Can localize well in both azimuth and eleva0on (due to ear asymmetries) •  Rely solely on auditory localiza0on in the dark (mouse example)…so prey learn to tread so`ly •  Wing noise can be heard by some prey…
kangaroo rats have evolved the ability (study) Kangaroo rat—how to avoid becoming a meal hGp://www.youtube.com/watch?v=o2GNHxlEnXg Owls and auditory localiza0on Same localiza0on cues The owl’s brain •  Konishi and Knudsen were able to iden0fy an area in the midbrain of the birds containing cells called space-­‐specific neurons—about 10,000 in all—which would fire only when sounds were presented in a par0cular loca0on. Astonishingly, the cells were organized in a precise topographic array. Echoloca0on •  Rather than simply hear (and localize) sound sources in the dark…some animals (e.g., bats and dolphins) produce sounds to provide informa0on about the world around them Bats Bats and echoloca0on •  Spallanzani (1729-­‐1799) blinded bats and observed that they could s0ll fly and avoid obstacles…couldn’t figure out how •  “Blind as a bat” NO! Use sight when leaving cave (plexiglass study) •  Can detect .5 mm (thread) •
•
hGp://www.youtube.com/watch?v=Hr-­‐Y2Tt8gFE hGp://www.youtube.com/watch?v=gZxLUNHEmPw Bat Sounds •
•
•
•
•
•
CF-­‐FM vs. FM calls Big Brown Bat Mexican free-­‐tail Myo0s bat Western Mas0ff Western Pipistrelle •  Doppler shi` (e.g., emit at 20kHz, but returning sound could be 60 kHz) Predator-­‐Prey rela0ons •  Some moths “jam” sonar by emixng a sound that may confuse some (especially young) bats •  Others just stop flying (drop) •  hGp://www.youtube.com/watch?v=p08Y0oRAX3g •
•
•
•
Pheromone to aGract moth Then bat sonar “To mate or not to mate” Frog ma0ng calls Dolphins Dolphins and echoloca0on Dolphins and echoloca0on hGp://www.youtube.com/watch?v=ZoNDW0zSRNo Combining visual and auditory informa0on •  Visual capture (Bertelson & Radeau) Audio-­‐Visual research •  We’re all lip readers! •  Which sensory informa0on do we “trust” more? The one that provides beGer informa0on! •  For example, audi0on is beGer for temporal informa0on (e.g., rate of tapping), so if it differs from a light flashing, we trust auditory informa0on (unless it is degraded) Simultaneous Sounds -­‐ Beats •  Binaural beats (lab) Sequen0al Sounds -­‐ Masking •  Masking –  More intense sound masks less intense sound –  Cri0cal band = range of frequencies that can be masked by a sound (equal or higher frequencies) –  Forward masking is more effec0ve than backward masking Noise •  Unwanted sounds (with adverse effect) •  Noise abatement programs