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Senses
Perception · Active sonar

Seeing with sound.

A bat clicks at 100 kilohertz, listens for the returning echo within a microsecond, and steers itself around a single twig in the dark. A dolphin clicks underwater at 150 kilohertz and tells a sardine from a herring at twenty metres. Both arrived at the same protein in their cochleas through completely independent evolutionary paths. Click on the dark zone below to place a target, then watch the pulse expand, reflect, and return — and hear the echo with the real time-of-flight delay.

Echo simulator
Mode
Phase
6 Hz
Four very different sonars

  • Big brown bat

    Eptesicus fuscus

    Freq.
    20-100 kHz FM sweep
    Range
    5-15 m
    Res.
    0.2 mm (time of flight)

    Three-phase hunt: search clicks at ~5 Hz, approach at 50 Hz, terminal buzz at 200 Hz right before the catch.

  • Bottlenose dolphin

    Tursiops truncatus

    Freq.
    0.2-150 kHz clicks
    Range
    ~100 m
    Res.
    Steel sphere 7.6 cm vs 8.9 cm at 8 m

    Water carries sound four times faster than air. Their melon focuses the click beam; the lower jaw receives returning echoes through fat-filled cavities.

  • Sperm whale

    Physeter macrocephalus

    Freq.
    0.1-30 kHz
    Range
    1-2 km depth
    Res.
    230 dB · loudest biological sound on Earth

    The largest acoustic apparatus in the animal kingdom — the spermaceti organ in the head focuses click trains downward into the dark deep.

  • Trained human

    Homo sapiens · echo experts

    Freq.
    Tongue clicks 2-10 kHz
    Range
    ~3 m
    Res.
    Objects ~3 cm at 1 m

    Daniel Kish has used clicks since infancy to map the world. Thaler et al. 2011 found expert blind echolocators activate the visual cortex when listening to echoes.

How the visualisation works

The echo simulator is drawn live on a canvas with a real-time animation. Sound speed in air (343 m/s) and water (1500 m/s) is honoured at scale — the pulse and echo travel at proportionally correct speeds for each mode, just slowed down by a constant factor so the geometry is visible. The audio engine uses the Web Audio API to synthesise pulse clicks at adjustable frequency and to play back the matching echo after the simulated time-of-flight delay. Pulse rates per phase follow Schnitzler & Kalko 2001 for bats. Species comparison values from Au 1993 (dolphins), Madsen et al. 2002 (sperm whales), Surlykke & Kalko 2008 (bat output), Thaler et al. 2011 (humans).

Hearing as a way of seeing

Four readings of one returning sound.

  1. Time of flight — distance from delay.

    The core trick of biological sonar is elementary physics. Emit a sound, wait for it to bounce back, multiply by half the speed of sound, divide by the elapsed time — and you have the distance to the reflector. Bats can resolve this delay with a precision below one microsecond, which translates into spatial resolution better than a third of a millimetre. A moth in the dark stops being a vague threat and becomes a precisely tracked target.

  2. Three phases of the hunt.

    Schnitzler and Kalko (2001) described the canonical three phases of insectivorous bat hunting. In the search phase, clicks are long and slow — five to ten per second — scanning a wide field. Once prey is detected, the approach phase begins: shorter, faster clicks at fifty per second narrow the acoustic beam. In the final terminal buzz, just before contact, pulses reach two hundred per second — almost a continuous stream — for maximum spatial-temporal resolution. The bat is solving a tracking problem in real time, at a sampling rate no human-engineered radar matches.

  3. Convergent evolution at the molecular level.

    Bats and toothed whales evolved echolocation independently — they share no common ancestor with the trait. Yet Liu et al. (2010) found that fourteen specific amino-acid substitutions in the Prestin protein, which sits in the outer hair cells of the inner ear and tunes high-frequency hearing, are identical between echolocating bats and dolphins. This is one of the cleanest molecular examples of convergent evolution known. Two completely separate evolutionary paths arrived at the same protein-level solution to the same problem.

  4. Humans can learn it too.

    Daniel Kish lost both eyes to retinoblastoma at thirteen months old and has been clicking ever since. He navigates cities by bicycle, hikes, leads his own organisation, World Access for the Blind. Thaler, Arnott and Goodale (2011) put expert blind echolocators in an fMRI scanner and recorded their brain activity while they listened to recorded click-echoes. The auditory cortex lit up as expected — and so did the calcarine cortex, which in sighted people processes visual input. The brain repurposed visual machinery to spatial sound. The capacity is in all of us; very few of us train it.

Sources