by ochiai808

Like that of monkeys, the brain of another animal is thought to be comparable to the brain of humans.  Dolphins are commonly labeled as “smart,” and their levels of intelligence have made them a popular animal of study.  V. Janik, L. Sayigh, and R. Wells followed this trend and conducted their research on the identity calls of bottlenose dolphins.   Identity information, for almost all animal calls, give specific details of species, population, group, family line, and even in some cases individual identity (Janik et al. 8293).  However, dolphins use distinctive calls unique on the level of the individual.  Individual identity information requires a tremendous amount of interindividual variability and is hypothesized to be encoded by the “pattern of frequency modulation over time that gives a spectrographic contour its distinctive shape” (Janik et al. 8293).  Janik et al. however addressed the problem of whether this type of individual discrimination occurs dependently of voice features.  For example, human naming is accomplished dependently of voice features.  You could recognize your name if you heard it in your own voice, in your friend’s voice, or in a stranger’s voice.  We recognize that identity call based on the name itself and not on the voice.  Dolphins can use distinctive call types as descriptive labels in referential communication, however, the research of Janik et al. aimed to see how dolphins do so.

Janik et al. produced “synthetic whistles that had the same frequency modulation but none of the voice features of known signature whistles” in the following manner (Janik et al. 8293).  They recorded adult dolphins and transformed their calls into a synthetic form via SIGNAL 3.1, a program that essentially stripped down the whistles to its basic frequency modulation pattern.  Then, over four seasons between June 2002 and February 2005, they played back these calls and measured the target dolphins’ responses.  Each animal was held in a net by several people such that the dolphin’s head was free to move from side to side.  Fifteen minutes after the dolphin became acclimated to the aforementioned position, the speaker was introduced 2 meters to the side and the calls were played.  Each subject was exposed to a “sequence of synthetic whistles resembling the signature whistle of a related individual (as determined through long-term observations and confirmed through genetic testing) and a sequence of synthetic whistles resembling the signature whistle of an unrelated but known individual” (Janik et al. 3296).  To avoid confounds, the calls were matched between the related and non-related individuals on the levels of approximate age, sex, and time spent together.  Any head turn that was greater than 20 degrees was counted as a turn related to the call.  (Head turns less than 20 degrees were not counted since dolphins naturally move their heads back and forth within this range).

The results of Janik et al. demonstrated that “bottle nose dolphins from Sarasota can recognize structure whistles of individuals [. . .] [through] distinctive frequency modulation patterns [dependent of] voice features” (Janik et al. 8295).  Individual dolphins turned their head more towards the speaker if the playback was the synthetic signature whistle of a close relative rather than that of an unrelated individual.  The whistle modulation contour themselves therefore carry the identity information required.  They addressed the possibility that related dolphins had more similar whistle calls than unrelated dolphins as follows.  Janik et al. tested to see if the response strength of targeted dolphins responded related to stimuli significantly more or less similar to their own whistle, independent of kin relationship, and found no significant differences (Janik et al. 8295).  Therefore, the orienting responses of the dolphins were not due to similarities to their whistle.

As stated before, individual identity information is encoded independent of the signaler’s voice or location such that the frequency modulation pattern of signature whistles is sufficient for individual discrimination (Janik et al. 8295).  It does not mean, however, that dolphins do not have or benefit from voice features specific to each individual.  In their discussion, Janik et al. suggest that their findings support the notion that dolphins are recognizing whistles as opposed to merely discriminating between them.  They define recognition as “perceiving something to be identical with something previously known,” and discrimination as “the comparison of distinctive features that can use, but does not require, such previous knowledge” (Janik et al. 8295).  Therefore, this reveals the complicated abilities dolphins encompass.

I would like to just address one concern.  When they tested the dolphins, they were constraining the subject in an unnatural manner.  Dolphins are free-swimming animals, and I wonder if such methods caused any distress which could therefore alter any results.

In closing, the following is a pictorial representation of the dolphin whistles.  The left side shows the natural original whistles while the right side shows the corresponding synthetic versions.

 

Janik, V., Sayigh, L., & Wells, R. (2006) Signature whistle shape conveys identity information to bottlenose dolphins. Proceedings of the National Academy of Sciences, 103(21), 8293-8297.

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