Storyboard

Estimating distance and depth is critical for navigation, capturing prey, and avoiding obstacles. The physical mechanisms available are: time of flight (active, echolocation), binocular disparity (passive, stereoscopic vision), motion parallax (passive, optic flow), texture gradient (passive, monocular signal) and blur.

Echolocation (ToF) is the most accurate method at close range: the distance resolution d = c_s·t/2 depends on the temporal resolution t. Bats with 1 ms pulses have d 17 cm; dolphins with 50 s pulses have d 3.75 cm. The sonar equation (RL = SL - 2·TL + TS) determines the maximum detection range.

Binocular disparity exploits the separation between the two eyes (baseline b). For an object at distance d, the disparity disp = f·b/d: close objects have greater disparity. The stereopsis acuity _stereo d²·_ang/(f·b) shows that accuracy decreases with d²: stereopsis is useful up to ~10 m in humans (b = 6.5 cm, _ang 20 arcsec).

Motion parallax is the primary depth cue in monocular animals (many birds and insects). Closer objects produce greater optical velocity v_opt = v_self/d on the retina. Bees and locusts actively use head movement to generate this parallax and estimate distances.

Blur is a monocular distance signal: photoreception of out-of-focus objects produces a circle of confusion c_blur proportional to the distance from the focal point. Animals with very aspherical pupils (octopuses, mantis shrimp) actively exploit spectral blur (chromatic aberration) to estimate distances without the need for movement.

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ID:('ky', 581)

Description

ID:(0, 581)