Auditory Cues and Ecolocation

Sound

  1. Intensity
  2. Frequency
  3. Direction
Prey detection

Object localization

Owls

Vision & hearing

Home ranges If target detected:

The hunting technique of an owl, drawn from photographs of Tengmalm's owl, Aegolius funereus, in its natural habitat. (a) The owl about to strike the prey with its talons, after flying down from an observation perch. (b) The owl on its perch immediately before striking, with a diagram showing the erros involved in localising prey by hearing. The prey (o) is observed at a shallow angle (alpha), with the result that a given angle of error converts into a greater distance along the ground for a vertical (elevation) error than for a horizontal (azimuth) error. (Modified after Norberg, 1970. 1977). (From: Young, 1989, p. 189.)
Horizontal (azimuth) and vertical (elevation) Can orient in full darkness by sound

Greatest accuracy 6 to 9 kHz

Experimental apparatus

Appratus used to measure accuracy of owls in localization of sounds from different positions in space. (From: Young, 1989, p. 191.)
Do not localize through approximations Relatively low error rate

Localization of sound accuracy as a function of sound position in space, showing mean degree of error in localization of sound target in horizontal (left) and vertical plane (right) for an individual owl. (From: Young, 1989, p. 191.)

Intensity difference between ears

Intensity --> elevation information Ear plug experiments Facial asymmetries

Barn owl's ability to localize sounds in elevation. (a) Plot of auditory space in front of owl in degrees of azimuth (L and R) and elevation (+ and -). (b) Facial ruff of the barn owl. (From Young, 1989, p. 192.)
Ruff removed Time differences between ears Time difference --> azimuth direction Earphones

  • Owl Brain Structure for Audition

    Optic tectum

    Neuronal map of auditory space in the midbrain of the barn owl. The bottom element of the figure depicts the receptive fields (bold rectangles) of 10 neurons recorded in three separate electrode penetrations. (From: Young, 1989, 195.)
    Inner region interneurons Outer region interneurons Limited-field neurons

    Receptive fields of auditory interneurons in midbrain of the barn owl. (From: Young, 1989, p. 194.)

    Sonar

    SOund NAvigtation Ranging Detect underwater objects Transmitter Receiver Time for echo to return --> depth

    --Fig 16.27 (Physics)--

    Bat Ecolocation

    20-200 kHz sounds Frequency Modulated (FM) Constant Frequency (CF)

    Echolocating and Non-Echolocating Bats

    Echolocating bats have special external physical adaptations that allow them to reacquire the ecolocation pulse they send out. These adaptations are generally seen in the ears and face of echolocating bats. Notice that the ghostfaced bat has forward facing ears mounted low on its head and a highly sculpted face (i.e., it looks like it has been hit in the snout with a two-by-four). These facial ridges help deflect the returning echolocation pulse towards the ghost faced bat's ears. The fruit eating bat, by contrast, lacks these specializations. Notice the larger eyes and the unmodified snout. While this fruit eating bat does have fairly large ears they are not positioned well for the receiving of returning echos.

    Echolocating Ghost Faced Bat

    Non-Echolocating Fruit Eating Bat
    Horseshoe bat

    Long CF pulses

    Doppler Effect

    Approaching sound: high frequency Retreating sound: low frequency

    Sound source & observer

    Stationary and moving sounds

    Doppler shifts measure velocity of targets

    FM pulses good for
    1. Target description
    2. Range information
    CF pulses good for
    1. Prey detection
    2. Increasing maximum range

    Stages of Bat Flight

    Search stage Approach stage Terminal stage

    Neurophysiology of Bat Auditory System

    Typical mammalian ear

    Auditory nerve to:

    1. Coclear nucleus (hindbrain)
    2. Inferior colliculus (midbrain)
    3. Auditory cortex (forebrain)
    Specialisations
    1. Bat's hearing sensitive to frequency of its own sounds
    2. Hearing highly directional
    3. Higher levels of auditory pathway for pulse-echo delays
    4. Reduce sensitivity to other sounds (e.g., muscular contraction of middle ear prior to pulse; partially decouples inner ear from tympanum)
    5. Doppler shift neurophysiology
    Maximally sensitive to a 60 degrees forward cone

    Neural recovery of auditory system

    Pulse return in 30 ms Full recovery within 2 ms

    Auditory cortex

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