studying barn owls in the laboratory sound intensity cues sound timing cues

studying barn owls in the laboratory sound intensity cues sound timing cues

neural pathways for sound location auditory space interaural time differences delay lines & coincidence detectors

visual calibration of the auditory world summary

PART 2: SENSORY WORLDS#07: PREY LOCATION IN BARN OWLS I

studying barn owls in the laboratory sound intensity cues sound timing cues

neural pathways for sound location auditory space interaural time differences delay lines & coincidence detectors

visual calibration of the auditory world summary

PART 2: SENSORY WORLDS#07: PREY LOCATION IN BARN OWLS I

Intensity differences

Timing differences

high frequency ...

short wavelength

low frequency ...

long wavelength

AUDITORY CUES

Tyto alba, hunt using auditory cues height: 1-1.5 ft wing span: 3 ft velocity: 4-8 m/s forms pair bonds hunting nocturnal

& crepuscular small rodents > other

small animals prey of great horned

owls restricts barn owl hunting to deep night

BARN OWL BIOLOGY

Tyto alba, hunt using auditory cues locates prey in space

horizontal vertical relative to self

prey capture... FIG 1

how to determine the cues? not visual (test in dark) heat, olfactory, auditory ? early mouse/paper expt.

p.63 fig.3.1

BARN OWL BIOLOGY

1st important behavioral observation...

owls turn their heads rapidly toward sound

bring source to center

tested experimentally...

p.63 fig.3.1

BARN OWLS IN THE LABORATORY

monitor head orientation behavior

used “search coil” weak electric field

signal magnitude + sign head position

~ sounds

no echoes

total darkness

sound & head positions correlated by computer

p.64 fig.3.2

BARN OWLS IN THE LABORATORY

features of barn owl auditory system

face covered with rows of stiff feathers... facial ruff

sound-collecting surface auditory canals

ears asymmetrical right ear & opening directed , sensitivity head left ear & opening directed , sensitivity head

BARN OWLS IN THE LABORATORY

2D mapping of sound dimensions

azimuth horizontal

elevation vertical

can target soundwithin 1°-2°

3x human accuracyin vertical dimension

p.65 fig.3.3

BARN OWLS IN THE LABORATORY

2D mapping of sound dimensions

most sensitive tosound in front

frequency range100 Hz - 12 kHz

azimuth: accurate within 1 - 9 kHz

elevation: accuratewithin 3 - 10 kHz p.65 fig.3.3

BARN OWLS IN THE LABORATORY

experiments identified 2 critical auditory cues...

sound intensity cues elevation dimension

sound timing cues azimuth dimension

BARN OWLS IN THE LABORATORY

attenuated sound, blocking ears with 2 types of plugs soft modest hard severe

sound location... recall that the ears are asymmetrical...

right ear & opening directed , sensitivity head left ear & opening directed , sensitivity head

interaural intensity differences to target elevation, also called interaural level differences (ILD)

SOUND INTENSITY CUES

attenuated sound, blocking ears with 2 types of plugs soft modest hard severe

sound location error... elevation some azimuth

not sufficient to explain accuracy

p.67 fig.3.4

SOUND INTENSITY CUES

removed facial ruff

sound location error... mostly elevation (head oriented @ horizontal plane) azimuth OK ruff amplifies directional asymmetry of ears

SOUND INTENSITY CUES

sounds arrive @ different times to each ear difference in time = temporal disparity

barn owls can distinguish 10 ms temporal disparity interaural time difference (ITD) use ITD for azimuthal sound source determinations

p.68 fig.3.5a

SOUND TIMING CUES

sounds arrive @ different times to each ear 2 types of temporal disparity

transient (onset / offset) ongoing

can use both which is used ?

p.68 fig.3.5b

SOUND TIMING CUES

implanted miniature speakers decouple disparities

measured orientation ~ ongoing temporal disparity range of 10 - 80 s head movement to target represented by disparity

orientation not ~ transientdisparity

p.69 fig.3.6

SOUND TIMING CUES

anatomical structures

basilar mem. / inner ear frequency coding phase locking intensity coding

cranial nerve VIII

cochlear nuclei NA NM p.71 fig.3.7

NEURAL PATHWAYS FOR SOUND LOCALIZATION

anatomical structures

cochlear nuclei NA NM

NL

LL

higher auditory centers ICC (~ mam. IC) ICX p.71 fig.3.7

NEURAL PATHWAYS FOR SOUND LOCALIZATION

p.72 fig.3.8a

external nucleus (ICX) neuron response

frontal sound

ICX space-specificneurons

AUDITORY SPACE

p.72 fig.3.8b

external nucleus (ICX) neuron response

frontal sound

ICX space-specificneurons

map

AUDITORY SPACE

p.73 fig.3.9

external nucleus (ICX) neuron response

frontal sound

ICX space-specific neurons

map

2nd roving speaker

excitatory (peaks) & inhibitory (trough) regions

AUDITORY SPACE

p.74 fig.3.10

2D field

space-specific neurons are binaural

driven by bilateral stimuli

eg, neuron peak response...

response ILD & ITD specific

ILD ~ 11 dB

ITD ~ 32 s

AUDITORY SPACE

cochlear nuclei ICX

NM time info ITD azimuth phase sensitive intensity sensitive

NA intensity info ILD elevation intensity sensitive

p.71 fig.3.7

AUDITORY SPACE

cochlear nuclei ICX... parallel pathways ?

inject reversible local anesthetics, record from space-specific ICX neuron, sound target stimuli

NM disruption selectivity for time disparity no effect on level disparity

NA disruption selectivity for level disparity no effect on time disparity

AUDITORY SPACE

Jeffress’s neuronal circuit model for encoding time

coincidence detector C fires best with L & R coincident signals

delay line L (eg) codes R delay

p.77 fig.3.11

INTERAURAL TIME DIFFERENCES

Konishi model built on Jeffress for encoding ITD

coincidence detector neuron arrays variable delays

features encodes ITD neurons encode different ITDs but... = output ITD place code p.78 fig.3.12

INTERAURAL TIME DIFFERENCES

does the owl use this mechanism ? ... evidence

anatomy... NM NL (putative neural substrate for model) ipsilateral & contralateral innervation of NL innervation parallel

p.79 fig.3.13

DELAY LINES & COINCIDENCE DETECTORS

does the owl use this mechanism ? ... evidence

physiology... NL neurons phase-lock to binaural stimuli delay asymmetry delay ~ temp. disparity NL neurons = coincidence detectors p.79 fig.3.13

DELAY LINES & COINCIDENCE DETECTORS

does the owl use this mechanism ? ... evidence

anatomy + physiology... each ITD encoded by different delays space-specific neurons NL position info ICX

p.80 fig.3.14

DELAY LINES & COINCIDENCE DETECTORS

does the owl use this mechanism ? ... evidence

anatomy + physiology... each ITD encoded by different delays space-specific neurons NL position info ICX

p.71 fig.3.7

DELAY LINES & COINCIDENCE DETECTORS

ILD (intensity) processing ? ...

poorly understood

v. nuc. lat. lemniscus

spatial organization ~ ICX

bicoordinate signatures not yet elucidated

p.71 fig.3.7

DELAY LINES & COINCIDENCE DETECTORS

integration with other sensory input

ICX optic tectum sensory space maps

optic tectum brain stem

p.84 fig.3.16

sens

orymoto

r

sensory motor

br stem tegmentum 3D map of head position distinct circuits

AUDITORY SPACE