Animals have to process quantity of information in order to take decisions and adapt their behaviors to their physical and social environment. They have to remember previous events (learning), to cope with their internal (motivational and emotional) states and to display flexible behavioral responses. From a human point of view it is quite impossible to access all those information, not only because of the sensorial channels used that can vary but also because all the processing phase occurs in the “black box” and non-human animals are not able to express verbally what they think, feel or want. Though useful information might lie in the “collected data” (animal mind), extracting them into insightful knowledge with human-accessible form (clear meaning, no interpretation) presents a demanding and sophisticated undertaking. Several scientists decided to trained different individuals from several species (apes, dolphins, grey parrots, dogs) in order to teach them a new communicative system that they could share with us. Here, the different studies (techniques and species used) are presented, their constrains but also the main findings.
Humans are curious by nature and want to increase their knowledge about their environment. In a developmental and philosophical point of view they are interested in: “what makes human different from other species” and “how this human species evolved”. There is more and more evidence of animal sentience and consciousness nevertheless it is a hard job to know exactly what they want and how they see the world. The interspecific communication is complex and often not complete because of differences regarding modality and integration of the signals.
Several studies have been conducted in ethology, behavioral ecology, comparative psychology and cognition in order to “ask” other species: What do you see? What do you want? Studies in the field, using playback paradigm for instance revealed complex communicative abilities in different species such as birds or primates [
Because scientists still did not find the ring of King Salomon—the object with which the king could talk to the animals—they have tried different (sometimes co plementary and not all fruitful) strategies to teach animals to communicate with people in a human-designed language. Interspecies communication is a powerful mean of studying animal cognition. It also a good opportunity to know how they perceive the world (color, contrast, optical illusion), what are their preferences (food, toys, etc.) and their thought. This system offers the possibility to interact directly, asking questions and also to compare the results between species (included humans). Interspecies communication could also bring some answers about human language roots and evolution. The major constraint is that the communication code has first to be taught, which is time consuming.
The first species, the scientist focus on, where apes because of their genetic proximity. Researchers also work with marine mammals because of their large brain. One scientist decided to work with a parrot. African grey parrots have good vocal mimicry ability. Because birds are able to reproduce exact human words, intonations and even laugh, people invest emotionally and attribute intentions easily. Even infants treat parrot vocal production as human ones [
In this review, different type of techniques used to teach an artificial communicative system will be presented and the species involved. In order to illustrate the diversity and complexity of the behaviors that the scientists observed examples of several studies would be presented.
The first attempts of communication were to raise apes in human family so that they could learn to speak. Gua (chimpanzee of the Kelloggs) was able to imitate motor actions but not human speech [
Scientist decided to use American Sign Language and to teach “words” to apes. Humans produce the sign in front of the apes. The animal learns through observation and also with hand modeling (from humans or other ape). The individual has to shape his hands in a specific way and place and/or move them appropriately for each word. This method, used with deaf humans seems relevant to communicate with another species.
Beatrix & Allen Gardner and then Roger Fouts teach Washoe, a chimpanzee, the simplified American Sign Language [35,36]. Other chimpanzees (Loulis) and bonobos (Kanzi) learned to sign. Francine Patterson did the same with Koko and Michael, two gorillas (Gorilla gorilla) and Lyn Miles with Chantek (Pongo borneo) [
Ernst von Glasersfeld developed the language that Lana learned to use: he coined the term “lexigram”, created the first 120 of them and designed the grammar that regulated their combination at Yerkes National Primate Research Center. Lana was the first chimpanzee that learned to use lexigrams [
Other chimpanzees (Panzee, Sherman) but also bonobos (Panbanisha, Kanzi, Nyota) have been taught (or learned through observation) and tested with this method. Although Kanzi learned to communicate using a keyboard with lexigrams (through observation), he also picked up some American Sign Language. Kanzi & Panbanisha were able to imitate human words but also indicate (by pointing at their mouth and throat) their difficulty to vocalize. So able to control their vocal production, in the same way that they develop some dexterity to sign [
Ann & David Premack used a different method to teach Sarah (chimpanzee) to communicate by writing with magnetized plastic symbol [
Ann & David Premack developed another technique in which the ape has to use a joystick in order to generate the phonemes of English. This technic was two complicated and thus stopped [
Louis Herman and Ronald Schusterman used large-scale arm movments, signs (hand-shaped) and computer-generated sounds with bottlenose dolphins, Puka, Kea, Ake, Phoenix (Tursiops truncates). The animals had to associate specific (artificial) whistles with objects and/or actions. Dolphins were asked also to use (press on) dedicated paddle [40,41]. Scientists used command gestures to teach Californian sea lion (Zalophus californianus), Bertie and Rocky, names and characteristics of objects [42-44].
In the 70s Irene Pepperberg started her work with Alex, an African grey parrot [
More recently a Portuguese team starts to train a dog to use a keyboard in order to ask for food, a walk or to be petted [
In general, all the individuals (whatever species they belong to) have (had) a good understanding of human language (English, French, Portuguese, etc.) [48,56,58].
Possession of (or the ability to acquire) human language or at least some form of a human-based communication code has been posited as a necessary precondition for an organism to organize and process information for certain complex cognitive tasks. Language may help to have abstract representation even if it’s not absolute pre-request as human infants, for instance, could have difficulties label object but not to classify them in same/different categories. Language may reveal inherent abilities rather than enable animal to learn more complex tasks even if animal that have been trained to use human-based language code do better than untrained animals on some tests such as those requiring understanding of analogies, but not for task of spatial representation [
Apes signed and used plastic magnet and lexigram to ask for toys, food, etc., but also for walk and interactions. In few occasions they described their environment [59,60]. Alex learned and use English labels to answer the questions but also to ask for something. Sometimes he even asks questions about objects characteristics or name [
Sofia’s performances at the keyboard was based on the association of a specific sign with a specific desire and that it was part of goal directed sequences similar to those normally displayed by dogs. The dog does not use it when alone, presses in view of the experimenter [
The apes species, dolphins and grey parrot show evidence of both discrete combinatory and category-based rules. The dolphins and Kanzi show knowledge of argument structure (although for Kanzi, only in his comprehension of English). The capacities that underlie these three properties of syntax, then, do not appear uniquely human [
Most of the individuals (apes and parrots) have been observed while babbling. Some individuals also recombine phonemes or sign or even create new ones (e.g. Washoe created a sign for “bib”) [69,70]. These are some example of combination: “ring-ball” combination of bottlenose dolphins [
Animals have been also observed “talking” to themselves [38,73]. This occurred during the learning and consolidation phase but not only. Indeed, parrots enjoy these moments (resting period). They can also “talk” to describe their environment or express what they have to do (e.g. Washoe signed “Quiet” when she sneaked into a forbidden room [
Dolphins can label things and report presence or absent of such object by pressing on specific paddles [
Alex was trained on absence of a difference or similarity “what same?/what different?”, as well as apes. Thus individuals were able to display a zero-like concept—which is the expression of an absence of something (e.g. no difference or none green block) [
Kanzi, Panbanisha and Panpanzee used precursor of morality while pressing the lexigrams “good” and “bad” in appropriate contexts. This suggests a symbolic language processing in the different species but heavily influenced by the value judgments of their human caregivers [
The ability to categorize elements of the environment, i.e. to classify objects according to proprieties they share, is a fundamental aspect of information processing. Conceptual categorization implies two criteria: a rapid generalization over class members of items and a classification of items not necessarily similar perceptually (e.g. “food” vs “tool” items [75,76]). Alex, was able to categorize items according to their color, shape or matter. He was capable of giving the similar and/or different characteristics of the items presented [77,78]. He was also able to identify the number of items according to two modalities [79,80]. Alex’s categorization was noteworthy because he expressed this classification by verbalizing labels. However, Alex received a long training (months to years for various items and/or concepts) before being able to label and categorize correctly the items presented. In a recent study two African grey parrots learning French labels spontaneously categorized items with vocal imitations [
Furthermore, Alex spontaneously established equivalency relations between Arabic numerals and the corresponding sets of items [
A bottlenose dolphin discriminates visual stimuli differing in numerosity [
Kanzi learned through observation (of the adult) how to use lexigram. Loulis (Washoe was his foster mother) was not cross-fostered and learn through interaction with the other chimpanzee to sign. Loulis mastered sign language through watching, babbling and then doing the sign properly [
The same for birds who learn from each other new vocalization and thus new words and then associate the label with the correct object (or characteristic). Irene Pepperberg reports also that Alex vocalized several times “say better” or even giving the (right) answer when another birds was questioned [
Using lexigrams, words or plastic object is also a good way to assess the memory of an individual across the time. Thus Lana, Koko, Kanzi et al. remember the name of object they did not see for several months [37,90].
Irene Pepperberg, taught to employ the vocalization “want” before an object label so as to discriminate functional “labeling” from “requesting” [
In the same way, apes using lexigram or sign language requested for food, toy, tickles, etc using the appropriate signal and also request for “more” or “less” of it. Washoe sign “More” to get more tickling after that the Gardners introduced “More” into a game of pulling [
Four African grey parrots have been tested on their ability to obtain an item suspended from a string such that multiple, repeated, coordinated beak-foot actions were required for success. Only the birds with little training in referential English requests (e.g. “want X”) succeeded. The two others (Alex & Griffin) failed to obtain the reward as they did not try and engaged in repeated requesting “want nut” [
The African grey parrots tested in the French laboratory developed specific asking calls for food [
Apes signed, pressed lexigram or combined object in order to request for food or toy or whatever. In captivity, Chimpanzees have been observed to beg extending an open hand and vocalizing. Loulis for instance produced the sign “Gimme” to request for a preferred food [
Several individuals of very few species have been involved in language-trained studies. Mostly primates but also other mammals such as dolphins, sea lion or dogs and one bird species, the grey parrot. The different experiments have more or less successful according to the technique used (e.g. joystick vs ASL) but also to the individuals [
All these studies provide astonishing results for the scientific community. Animal species are able to comprehend and produce part of a communicative system and able to understand new utterance. The gap between human and non-human species is smaller than expected. These studies have changed the perception humans had from the rest of animal species. Even animals with a brain of the size of a walnut (grey parrots) manage to learn words and describe the characteristics of objects according several modality and also to elaborate complex concept. All the data collected change the way animal consciousness was perceived by humans. This have a direct impact on animal right and the laws for animal welfare.
The different individuals tested have shown complex and diverse competencies. Thanks to the different artificial language systems, the researchers manage to interact directly with the animals and thus access to a part of their own world.
All the experiments presented have raised many questions and critics among the community; critics about the methods used, about the number of animal or the influence of human on the animals’ answers and also the way to validate or not new acquired “word”. Some studies raised also ethic and welfare issues (e.g. activists had released dolphins in ocean) sometimes because of the housing conditions or the difficulty for the animal to adapt a life with conspecific later on (for apes for example). For instance Washoe, sign “black bugs” to designnate conspecifics (seen for the first time) [
The different experiments presented are complex because it takes time to teach animals a new code of communication but also because the results obtained (when obtained), come from only one individual (of one species). This type of study is also costly and time consuming. Most of the species tested are long-living animal species, some of them could be very aggressive or at least represent a danger for human because of their strength. Several people involved in apes studies lost one or more fingers. Thus the dogs—as tested in the recent study—seemed to be a good compromise between all these constrains and the advantages to be able to share a communicative system.
Some individuals had (have) incredible cognitive abilities. For instance Kanzi is able to communicate using lexigram, vocal production and sign language. He also demonstrates a great ability in using tool (motor imitation) [
Scientist would now look to see if this new communicative system is used between individuals and across generations. The scientific community would tend to look to more accessible species such as dog which are already living in human houses! Thus not only we can know (or guess) what an animal think or feel watching its behaviors, social interactions and reactions (in decision making), we can study their ecology to have a better understanding on their natural communicative system but most importantly we can also develop an artificial communicative system to be share with other animal species in order to access the “black box”. Nevertheless the issue of human interpretation still exists even with the artificial communicative system.
All these experiments had also brought information about the roots and the evolution of human language, even if some results are still controversy but more importantly raised other questions such as semantic aspect of the signals sequence.
Though useful information might lie in the “collected data” (animal mind), extracting them into insightful knowledge with human-accessible form (clear meaning, no interpretation) presents a demanding and sophisticated undertaking. Using a human designed language represent a window at the “black box”. The different techniques developed lead to increase our knowledge on how animals perceive the world. Through the different examples presented, we have seen that the individuals (whatever was the species) organized their knowledge and develop strategy in order to solve the problem the experimenter were giving them (mostly answering questions). Scientist look at how animals learns, used and also their errors in order to access the way they are processing information.
I would like to thank Lauriane Rat-Fischer for her help.