decoding the acoustic environment
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PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I pt 2: sensory input ch 2: echolocation in bats bat behavior decoding the acoustic environment hunting bats neural mechanisms moth responses to predation summary PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I pt 2: sensory input ch 2: echolocation in bats bat behavior decoding the acoustic environment hunting bats neural mechanisms moth responses to predation summary SENSORY INPUT 2: SENSORY INPUT 3: CENTRAL PROCESSING 4: MOTOR OUTPUT BEHAVIOR SENSORY INPUT 2: SENSORY INPUT 3: CENTRAL PROCESSING 4: MOTOR OUTPUT BEHAVIOR SENSORY INPUT behavior driven by sensory stimuli external internal survival needs foraging (feeding, predation) shelter (environment, predators) reproduction nervous system evolution specialization for each environment adaptive behavior SENSORY INPUT pt 2: sensory worlds... how nervous systems process sensory information (2 modalities, 3 examples) auditory ch 2: echolocation in bats ch 3: prey location in barn owls visual ch 4: feature analysis in toads SENSORY MODALITIES somatosensory visceral special SENSORY MODALITIES somatosensory touch temperature pressure pain proprioception visceral special SENSORY MODALITIES somatosensory visceral osmolarity pressure specific chemicals temperature special SENSORY MODALITIES somatosensory visceral special olfaction gustation audition vision pheromone SENSORY MODALITIES somatosensory visceral special olfaction gustation audition vision pheromone ECHOLOCATION IN BATS Mammalian order Chiroptera (2nd most numerous) only true flying mammals (flying squirrels glide) most nocturnal 2 suborders Megachiroptera: ~ 150 spp, “big” (eg, flying fox) Microchiroptera: ~ 800 spp, “small” near cosmopolitan distribution many foraging specializations, reflecting... wide range of diet, many insectivorous ECHOLOCATION IN BATS foraging specializations of insectivorous bats outstanding fliers: agile, fast ECHOLOCATION IN BATS foraging specializations of insectivorous bats outstanding fliers: agile, fast eat a LOT (100s) of insects / day ECHOLOCATION IN BATS foraging specializations of insectivorous bats outstanding fliers: agile, fast eat a LOT (100s) of insects / day echolocation, 2 types passive: listen only (stealthy) active: emit ultrasonic pulses, analyze reflection ECHOLOCATION IN BATS documented observations for centuries Spallanzini (1794) studied mechanism of navigation deprived vision no problems deprived hearing failed to navigate ECHOLOCATION IN BATS Griffin (+ colleagues, 1938...) “bat detector” listening device for high frequency sound flying bats emit pulses (field & lab), use to navigate & capture prey... “echolocation” navigate a web of nylon fishing line in dark lab block auditory signal (2 ways) impaired function discriminate thrown edible items from nonedible ECHOLOCATION IN BATS echolocating bat capturing a prey item (meal worm) DECODING THE ACOUSTIC ENVIRONMENT bats use echolocation to discriminate object... position size texture movement ~ we use vision how is this achieved ? what features of sound are used ? DECODING THE ACOUSTIC ENVIRONMENT physical aspects of sound & sound modulation amplitude ( = volume, decibels [ db ]...) Y-axis frequency ( = pitch, cycles/s [ kHz ] ) ... X-axis pulse duration ( time [ t ] ) interpulse interval ( time [ t ] ) } db ~ light and vision t DECODING THE ACOUSTIC ENVIRONMENT 2 functions necessary for active echolocation sending receiving 2 mechanisms linked by... purpose (why) co-evolution or independent events ? nervous system (how) DECODING THE ACOUSTIC ENVIRONMENT bats emit 2 types of ultrasonic signals frequency-modulated (FM) sweep constant frequency (CF) DECODING THE ACOUSTIC ENVIRONMENT bats emit 2 types of ultrasonic signals frequency-modulated (FM) sweep or broadband short pulse (<5 ms) range of frequencies (100 Hz – 25 kHz) eg, big brown bat (Eptesicus) DECODING THE ACOUSTIC ENVIRONMENT bats emit 2 types of ultrasonic signals constant frequency (CF) longer pulse (5 – 30 ms) ~ no frequency modulation eg, horseshoe bat (Rhinolophus) DECODING THE ACOUSTIC ENVIRONMENT bats emit 2 types of ultrasonic signals frequency-modulated (FM) sweep or broadband constant frequency (CF) combined FM-CF pulses 3rd signal category DECODING THE ACOUSTIC ENVIRONMENT bats use 2 additional features of emitted sound fundamental frequencies + harmonics pulse rate (rate as distance ) DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation distance subtended angles (angular size) absolute size azimuth (lateral position ~ receiver) elevation velocity DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation distance time between pulse emitted & echo received rapid FM sweeps gives other info as well pulse-echo determination at >> frequencies DECODING THE ACOUSTIC ENVIRONMENT distance information obtained through echolocation test echo-delay theory train bats to feed at different perches (A) can discriminate very short distances (5 cm) DECODING THE ACOUSTIC ENVIRONMENT distance information obtained through echolocation test echo-delay theory replayed phantom echos with variable delays (B) correct choice of phantom target discriminate 60 s ~ 10delay – 15 ~mm distance very accurate ! DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation subtended angle or angular size (size component) loudness or amplitude of echo amplitude can when target large but distant small but near DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation absolute size computed from distance (pulse-echo delay) angular size (amplitude) DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation azimuth computed from binaural cues compare delays received in both ears ~ triangulation some information processed in each ear DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation elevation computed from two cues, compare echos received when ears are moved to various positions ear flaps in pinnae are opened variably DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation velocity, absolute & relative to self computed from Doppler shift of echo frequency sound frequency perceived (by the bat) shifts on approach, waves “compress” on retreat, waves “expand” DECODING THE ACOUSTIC ENVIRONMENT target information obtained through echolocation velocity, absolute & relative to self CF suited for Doppler analysis long pulses (10 – 100 ms) “narrow band” (not FM) higher energy locate distant targets acoustic fovea auditory system sensitive to narrow band width around CF signals DECODING THE ACOUSTIC ENVIRONMENT Doppler analysis: Doppler shift compensation Rhinolophus CF signal & acoustic fovea both tuned ~ 83 kHz Doppler shifted echo ~ 83 87 kHz in flight Doppler shift compensation = bat lowers CF frequency echo ~ 83 kHz echo returns in sensitive range, more easily distinguished from call at less audible frequency DECODING THE ACOUSTIC ENVIRONMENT Doppler analysis: Doppler shift compensation mustached bat CF signal & acoustic fovea both tuned ~ 61 kHz bat on swing DSC occurs when swinging forward only DECODING THE ACOUSTIC ENVIRONMENT Doppler analysis: target flutter generated by flying insects accoustic glint from reflected signal @ 90° ~ insect wing weak echo from angles echo subtle frequency & amplitude modulation horseshoe bat can discriminate 30 cycles/s (eg 83,000 Hz vs 83,030 Hz) DECODING THE ACOUSTIC ENVIRONMENT Doppler analysis: target flutter stationary horseshoe bats long CF for flutter only then track position and capture prey FM DECODING THE ACOUSTIC ENVIRONMENT pulse-echo delay analysis: jitter variation of playback expt. train bat to detect target that appears to rapidly switch between 2 distances (jitters) reduce intervals between jitters, measured threshold for perceiving such movements DECODING THE ACOUSTIC ENVIRONMENT pulse-echo delay analysis: jitter bats could perceive delay 10 – 12 ns... ~ 2 m distances bats may use such acute temporal resolution in signal perception to characterize fine-grained target texture HUNTING BATS stroboscopic images of hunting bats 3 stages of hunting and capture search approach terminal HUNTING BATS stroboscopic images of hunting bats 3 stages of hunting and capture search habitat-dependent FM in clutter, distance info CF in open, long range HUNTING BATS stroboscopic images of hunting bats 3 stages of hunting and capture approach orient toward target pulse rate (~50/s) CF FM HUNTING BATS stroboscopic images of hunting bats 3 stages of hunting and capture terminal pulse rate FM bats (~200/s) CF bats (~100/s)
