Table of Contents
Echolocation, also referred to as biosonar, is the phenomenon whereby certain organisms have the ability to use echoes of their own sound for location of food and danger, navigation, determination distance and analysis of their environment in general for their survival. This characteristic is mainly common in members of Cetacea (Dolphins and Whales), of these, bottlenose dolphins have seen to be more sophisticated. Some mammals, mainly bats have also been seen to posses this ability (Thomas, et al. 2004). In echolocation, an organism makes certain noise which is later generates echoes that the animal analyzes for different purposes as discussed above.
Bottlenose Dolphin biosonar is very complex and sophisticated ultra-performance system that no man-made system has been able to simulate. Research has indicated that this system uses very complex signal receiving and generation system, as well as an equally complex system for extraction of information. Both anatomical and neurological adaptations have enabled these creatures to have these extra-ordinary capabilities.
The neurological plan in Dolphins is similar to that of other mammals. Nevertheless, different adaptations have taken place to this system. For example the paleocortex of the dolphin’s cerebral cortex has been preferentially allocated more volume, relative to other brain portions, as compared to other mammals. According to Thomas, et al (2004) studies by Gurevich and Bullock indicated that the medial geniculate of dolphins is 7 times larger relative to those other mammals, specifically humans. The study also elucidated that the dolphin’s inferior colliculus is twelve times larger as compared to that of humans. The lateral lemniscus nucleus is more two hundred and fifty times larger relative to the human analog. The nucleus of the cochlear is also very huge relative to those of humans. These structures are located in the “old brain”, the pleocortex unlike the cerebral cortex. These structures are paired in dolphins as is the case with other mammals.
Dolphins use a precision biosonar/echolocation system that resembles precision optical system, present both in other mammals and in the dolphin itself. It plays a central in determination of angular direction and range to a specific target virtual to the dolphin. A large section of the precision echolocation system is located in the paleocortex portion of the brain, in conjunction with the precision optical system.
In dolphins, the direct acoustic energy delivery to the vestibule, coupled with the inner ear and labyrinth, is carried out by the conformal outer ears. Since dolphins live in an aquatic environment, the functions of the middle ear as surface/air-to-fluid transformer (impedance transformer) are not required. The dolphin’s cochlea is almost analogous the outer and inner human hair cells arrangement and operation. Cochlea’s variable curvature scatters the acoustic energy as a frequency function. The dispersion process is meant to eliminate any requirement for the presence of any kind of resonant circuits in the cochlea as hypothesized in most cases. Analogous to the human cochlea, there is generation of two distinct signal streams, one on the basis of signal’s tonal characteristics and another one on the basis of applied signal envelope or temporal characteristics by employing the outer hair cells (Whitlow and Hastings, 2008).
The acoustic energy incident to cochlea’s tonal neurons is crinkled into an array of multiple dimensions in the perigeniculate nucleus’s correlator. The data in the correlator is detected or sensed by various sensing neurons existing in a vertical arrangement. The output of these vertically arranged neurons is transferred to hypothalamus’ pulvinar for further signal manipulation.
Analogous to some of the neurons emerging from the spiral ganglia connected with the cochlea in humans, some of its neurons have the ability to transmit bandwidths as high as 1000HZ. Most of these neural paths are employed for specific determination of range in the lateral lemniscus and inferior colliculus.
The dolphin’s huge lateral lemniscus relative to the land mammals (specifically humans), indicates it is the central seat in manipulation of signals associated to the dolphins’ active echolocation. Similar to other mammals, the contiguous inferior colliculus is suspected to be central seat of passive echolocation.
Other neurons emerging from spiral ganglia, like those of humans, can only hold a maximum of 250Hz bandwidths and are used for provision of accurate data or information on the cochlea energy dispersal but lacks the actual frequency in the context of the stimulus.
Circuits dedicated to information extraction i.e. circuits of acoustic perigeniculate nucleus (part of the medial geniculate nucleus vital in precision determination) and lateral lemniscus employ very complex associative correlators to dig out information that is multidimensional in nature from data identifying the scene of the target (Whitlow and Hastings, 2008).
The circuit systems employed by dolphins for echolocation nearly resembles those in utilized by higher mammals, including humans for vision. The combined hearing capabilities and ultra high frequency vocalization characteristic of dolphins especially the bottlenose dolphins are incomparable in Kingdom Animalia