Echolocation (readings)

  • Jones

    • (p.1) our reliance on vision makes it difficult for us to comprehend echolocation (producing sound to determine position)

    • (p.2) Nagel’s “what is it like to be a bat” (philosophy)

    • Echolocation

      • (p.1) Producing images of surroundings using modified versions? Questions of accuracy or inherit need for accuracy (maybe sufficient to have precision)

      • (p.2) Cool! Determining range by measuring time delays between calls and reception; little iffy on the math

      • (p.3) Elevation by interference patterns caused by sounds reflecting from the tragus. Azimuth from intensity of ITD

      • (fig.1) nose leaves that focus sound are interesting

      • (last) the “switch off” of echolocation between airborne and prey among leaves is cool

    • Discovery

      • (p.1) Cuvier’s influence hindered the breakthroughs in research on bat echolocation

      • (p.2) difficult for human’s to fathom bat sounds as their calls are inaudible to human’s (high frequency for small targets)

        • How do the frequencies change for larger targets? or do they?

      • (p.3) Griffin and Pierce used piezoelectric crystals to transform bat ultrasound into frequencies they could hear

    • Diversity

      • (p.2) narrowband calls - for detecting flying insects; broadband calls - for localization

      • (p.3) Cool! switch from narrow to broad while hunting, as well as the “feeding buzz” when approaching prey

      • (p.5) Doppler shift - reducing call frequency as flight speed increases so echo frequency can be heard

      • (p.6) call and echo are separated in time, since bats’ middle ear muscles contract during calling so the bat does not deafen itself

      • (p.7) the noctule uses narrowband calls to anticipate echoes over open space

      • (p.8) Cetaceans produce short calls because sound traveling 5 times slower in water and cannot use Doppler shift

      • (p.9) easier detection for dolphins because of less echoes in water?

      • (p.11) bats: larynx → mouths or nostrils → pinnae; dolphins: phonic lips in nasal passage → waxy melon on forehead → lower jaw

      • (p.12) bottlenose - broadband, harbor porpoise - narrowband, sperm whale - within human hearing range

    • Ultrasonic

      • (p.1) six orders of insects have evolved sensitivity to ultrasound

      • (p.2) certain fish are also sensitive to ultrasound

    • Applications

      • (p.1) info on bat calls used in engineering (connection between neuroethology and society)

      • (p.2) the “ultracane” is a cool concept

    • Challenges

      • (p.3) how do bats navigate over longer distances? (maybe magnetoreception)

  • Goldshtein

    • Summary: Bats can identify their location after being translocated several km from their roost and are able to navigate home using echolocation alone, without relying on other senses.

    • 4 groups: control, visual deprivation, visual and magnetic deprivation, and visual, magnetic, and olfactory deprivation

    • sight does affect navigation (but bats have poor vision)

    • bats relied on distant rather than local visual information

    • acoustic cognitive map

    • bats flew in a correlated random walk until they identified their new location

    • all bats established the localization phase within minutes

    • both control and groups 2 and 3 achieved localization at similar beeline distances of ~ 500 m from the translocation point

    • what is shannon entropy?

    • bats use landmarks with high echoic entropy and high KL distances to provide ample spatial info

      • explains the bats wandering during the localization phase?

    • bats flew near environmental features that provide sufficient information to navigate, regardless of the sensory modality they could use, but did not search for the maximum entropy, probably because this would be less efficient in terms of flight distance and duration