Early visual deprivation induces structural plasticity in gray and white matter

discovered that certain fish are also sensitive to ultrasound. Cod may be able to detect echolocating odontocetes at 10–30 metres, and shad may detect their main predators, dolphins, at a range of 180 metres. Blueback herring swim away from echosounders used to survey them, raising the possibility that fish may exhibit negative phonotactic behaviour in the way that moths do. Some clupeid fish even show movements interpreted as escape manoeuvres when subjected to ultrasound. Applications Echolocation is obviously a remarkable way of sensing the world: bats may be able to detect differences in target range that require time difference discriminations of 10–12 nanoseconds, an ability that some physiologists refuse to believe is possible. Can humans learn anything from biosonar? There are remarkable similarities between bat calls and signals developed by engineers working in the fields of sonar and radar. Doppler shifts are exploited in radar speed-traps to measure velocity, and broadband echolocation calls have certain parallels with signals used in chirp radar. Dean Waters, a scientist working on bat echolocation at the University of Leeds, recently helped to develop a walking stick which emits ultrasonic signals through four sensors. A small computer calculates the direction and relative range of an object, and sends information to four vibrating buttons on the handle. The walking stick is now marketed as an 'ultracane', and has received excellent reviews from visually impaired users. Challenges Recent advances in portable devices that can record ultrasound in the field, combined with imaging methods such as multiflash photography have permitted great advances in understanding how bats use echolocation in natural conditions over the past 15 years or so. Until recently, our understanding of cetacean echolocation was largely restricted to studies on trained laboratory animals. This imbalance is now changing because archival tags that monitor sound, depth and acceleration can be fitted to diving cetaceans. In the same way that simultaneous multiflash photography and the recording of echolocation calls allowed a better understanding of prey capture behaviour in bats, it is now possible to understand how foraging cetaceans are moving through the ocean in relation to the sounds they produce. Field studies on interactions between tympanate insects and echolocating bats have revealed some remarkable sensory battles between predator and prey, and the potential for similar studies in fish–dolphin interactions is exciting indeed. Although ultrasound is well suited for the detection of small targets such as insects at night, it …