Development of Auditory and Sound Mechanisms in Dolphins

Bottlenose dolphins are among the most vocal of the nonhuman animals and exhibit remarkable development of the sound production and auditory mechanisms. This can be seen in audition, which is shown in the animal¡¦s highly refined echolocation ability, and in tightly organized schools in which they live that are made up by sound communication. In testing the communication skills of dolphins, extensive studies have been done on vocal mimicry, in which the animal imitates computer-generated sounds in order to test motor control in terms of cognitive ability. Language comprehension on the other hand has been tested through labeling of objects, which has proven to be successful regarding the association of sound and object stimulus.

The biggest question in dolphin communication, is whether or not the species is capable of intentional communicative acts. Though results from studies have been debatable, the key to understanding the extent to this ¡§language¡¨ is to determine whether they have a repertoire of grammatical rules that generate organized sequences. In determining this, the greatest accomplishment for both the scientist and all of humanity, would be to accomplish interspecies communication, creating a bridge between humans and animals which could open up a new understanding of the unknown world of wildlife. Most importantly, it is necessary to understand the incredible aptitude of dolphin communicative skills, and the impressive intelligence the animal possesses which allows for a great deal of intraspecies and interspecies communication (Schusterman, Thomas, & Wood, 1986).

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The acoustical reception and processing abilities of the bottlenosed dolphins have generally been shown to be among the most sophisticated of any animal so far examined (Popper, 1980 as cited by Schusterman et al. 1986). In order to understand the complexity of these highly mechanized acoustic systems, it is necessary to learn the process for which the dolphin hears. In most water-adapted cetaceans, tissue conduction is the primary route of sound conduction to the middle ear.

The isolation of the bullae shows an adaptation for tissue-conducted sound. The lower jaw contains fat that is closely associated with the impedance of seawater. The lower jawbone of most odontocetes becomes broadened and quite thin posteriorly, and the fat forms an oval shape that closely corresponds to the area of minimum thickness of the jaw. This fat body leads directly to the bulla, producing a sound path to the ear structures located deep within the head. Paired and single air sacs are scattered throughout the skull, which serve to channel these tissue-conducted sounds (Popov & Supin, 1991). Other than this description, there are still more studies needed to determine the function of the middle ear and the type of bone conduction that occurs within the bulla.

Due to detailed audiograms, dolphins have been shown to have the ability to detect high-frequency sounds. In an experiment by Johnson (1966) as cited in Schusterman et al. (1986), sine-wave sounds ranging in frequency from 75 Hz to 150 Hz were presented to a bottle-nosed dolphin. The animal was trained to swim in a stationary area within a stall and to watch for a light to come on. Following the light presentation a sound was sometimes presented. If the dolphin heard the sound, its task was to leave the area and push a lever. Sound intensity levels were varied by a staircase method of 1, 2, or 3 dB steps.

The resulting audiogram, compared to the human aerial audiogram, showed that at regions of best sensitivity for each, thresholds for human and dolphin are quite similar, but separated by about 50 kHz in frequency, showing that the animal¡¦s inner ear function is very similar to a human. The experiments done on dolphin auditory functions have generally shown a finely adapted sound reception system. This would be expected due to the highly adapted echolocation ability of the bottlenosed dolphin and other cetaceans. Results of work on absolute thresholds, critical bandwidths, frequency discrimination, and sound localization all indicate that the dolphin auditory system is at least as good or better than the human system. This is in spite of the fact that sound travels five times as fast under water as it does in air (Popov et al. 1991).

The bottlenosed dolphin in captivity produces two categories of vocalizations: (a) narrow-band, frequency-varying, continuous tonal sounds referred to as ¡§whistles¡¨ and (b) broad-band pulsed sounds expressed as trains of very short duration clicks of varying rates (Evans, 1967, as cited in Schusterman et al. 1986). The pulsed sounds are used for both communication and echolocation, and the whistles are found to be used primarily for communication (Herman & Tavolga, 1980, as cited in Schusterman et al. 1986).

Descriptions in literature emphasizing either the whistles or the pulsed sounds have led to contradictory hypotheses concerning the communication system of the dolphin. It has been reported that individually specific whistles often make up over 90% of the whistle repertoire of captive bottlenosed dolphins (Popov et al. 1991). A number of observations of apparent vocal mimicry have been made, though with no systematic investigation of the degree of vocal flexibility. The observed variability in the whistles, combined with the difficulty of identifying individual vocalizing dolphins in a group, has led to speculation that the whistles might be a complex, shared system, in which specific meanings could be assigned to specific whistles.

Consideration of vocal mimicry has been taken to understand its relation to cognitive complexity, and to the potential use of vocal response for communication in an artificial language. In one study done by McCowan, Hanser, & Doyle, (1999), the dolphin was able to learn to mimic a number of computer-generated model sounds with high fidelity and reliability.

The dolphin using its whistle mode of vocalization imitated all of the sounds, and all were distinct from the unreinforced whistles produced prior to training. The large majority of each dolphin¡¦s whistle vocalizations were individually specific acoustic patterns, described as a ¡§signature whistle¡¨; the rest of the whistles were short chirps. The results of the mimicry training have shown that dolphins can mimic tonal sounds with frequencies between 4 and 20 Hz. Due to this research, scientists can now learn from these mimicry skills how to understand and develop natural communication based on a stronger emphasis on the animal¡¦s cognitive abilities (Brecht, 1993).

In object labeling, the dolphins seemed to understand the task of associating model sounds with displayed objects. Progress was most rapid when the model sound was always presented at full intensity, but the probability of its being presented on any given trial was systematically decreased over successive trials. There wasn¡¦t any confusion of the objects themselves, but only a tendency to drift in the quality of the rendition of the labels.

This demonstration of symbolic use of vocalizations could lead to the investigation of the potential of animals to form referential concepts, thus creating a new understanding of dolphin communication and its uses in the wild. The main purpose of study in dolphin language, is the interest in whether the animal¡¦s speech is intentional communication like our own human speech. The fact that awareness as applied to the phenomena of human communication also implies something we would not attribute to animals-and this is the awareness that communicative acts are behaviors about behaviors (Crook, 1983, as cited in Schusterman et al. 1986).

Language, as we know it, could not exist without the capacity for intentional communication, as all linguistic communications are, by definition, intentional. Dolphins have been observed to have some of these intentional communication characteristics, as their behaviors have shown in captivity. For example, dolphins have been observed to squirt or splash water at strangers who come near their tank. After squirting the water the dolphin will raise itself out of the water to curiously observe what effect their behavior had on the stranger. Although this behavior is not communitive, nonetheless, it seems to suggest that the dolphin is aware of the effect of its behavior on others, showing that it has the cognitive ability for intentional communication (Erickson, 1993).

Communication between humans and dolphins occurs mostly through a gestural language that borrows some words from American Sign Language. The trainers make the gestures with big arm movements, asking the animal to follow commands such as ¡§person left Frisbee fetch,¡¨ which means ¡§bring the Frisbee on the left to the person in the pool¡¨. In one study, two bottlenosed dolphins were tested in proficiency in interpreting gestural language signs and compared against humans who viewed the same videos of veridical and degraded gestures.

The dolphins were found to recognize gestures as accurately as fluent humans, and the results suggested that the dolphins had constructed an interconnected network of semantic and gestural representations in their memory (Herman, Morrel-Samuels, & Pack, 1990). Such requests probe the dolphins understanding of word order and test the animal¡¦s grammatical competence. It has also been determined that dolphins can form a generalized concept about an object: they respond correctly to commands involving a hoop, no matter whether the hoop is round, octagonal, or square.

The animals seem to have a conceptual grasp of the words they learn, showing an understanding of the core attributes of human language, those being semantics and syntax (Erickson, 1993). Though this information seems compelling for dolphin language abilities, to determine whether or not they are capable of complex intentional communications, researchers must continue to investigate their receptive capacities, and to attempt to provide them with a communication system that would tap their productive capacities. Is interspecies communication possible? Could we someday be having philosophical discussions with a bottlenosed dolphin? Though these questions seem ridiculous, there was much debate over these questions when a medical doctor named John Lilly came out with hopeful findings of dolphin intelligence in the 1960s (Shane, 1991).

In the first true research of dolphin communication and intelligence, Lilly set out to show that through the correlation of brain size and IQ, the bottlenose dolphin was perhaps smarter than humans and began a growing interest in dolphins and their language through whistles. Though dolphins are exceedingly intelligent creatures, no real scientific evidence has yet been found to totally support the many conceptions about the animal¡¦s intelligence.

Lilly (1966) states, ¡§A dolphin . . . naturally uses other sounds to convey and receive ¡¥meaning¡¦: creaking for night-time and murky-water finding and recognition, putt-putting and whistles for exchanges with other dolphins, and even air wailing to excite human responses in the way of fish or applause. If a dolphin is copying our speech, he¡¦ll copy that part of what he hears which in his ¡¥language¡¦ conveys meanings.¡¨ Although this excerpt shows an incredible capability for dolphins to produce intelligent communication, it is findings such as these, which lack scientific support and have lost credibility among other dolphin researchers in the past few decades. Though his findings lack support, Lilly was important in bringing forth interest among people and therefore funds towards more scientifically based research and experiments that have helped us learn more about communication skills and intelligence of dolphins (Tyack et al. 1989).

In order to clearly understand if dolphins are creating intentional, intelligent communicative sounds and meanings, it is necessary to break down the vocal signals into repertoires and analyze those individually. The breaking down of dolphin signaling into component units has just now begun and the task will be to discover if, when, and to what extent they structure formalized sequences of signal units. To determine whether they have a repertoire of grammatical rules that generates organized sequences will be difficult, and it will be necessary to obtain extended and continuous recordings.

Patterns must be found and compared to other dolphin recordings in order to obtain the most accurate and universal findings for language among bottlenose dolphins (Herman, Kuczjac II, & Holder, 1993). Through many more years of careful study of these sounds, it is hopeful that our scientists can determine capacities and meanings behind dolphin language. Though interspecies communication seems unlikely at this point in time, through new studies being conducted our conception of dolphins as communicative animals seems more possible. Intentional communication through gestural understanding is the best finding so far in the study of these intelligent animals, and leads many to believe there is a lot more to dolphin¡¦s communication skills than has yet been uncovered.

In tests done in mimicry and labeling of objects, it seems that the capacity the bottlenose dolphin has for learning and understanding is large enough to make taught communication a realistic goal in the future of dolphin training. The highly specialized auditory and vocal mechanisms of the animal have helped lead the way to a better understanding of cetacean ear anatomy and sound production mechanisms, and these functions can now be seen as complex structures unlike any found above water. Though more research needs to be done before any true conclusions can be made about dolphin language, from what we do know the bottlenose dolphin is among the most vocal of nonhuman animals and exhibits remarkable development of sound production and auditory mechanisms (Schusterman et al. 1986).


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11.Tyack, P. L.,& Sayigh, L. S. (1989). These Dolphins Aren¡¦t Just Whistling in the Dark. Oceanus, 32, 80-83.


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Development of Auditory and Sound Mechanisms in Dolphins. (2018, Jun 26). Retrieved from