Some people might consider them the “rats of the air”, but if so they are very smart rats. Pigeons can not only recognize words, but process them in ways similar to primates, learning patterns that help them detect whether strings of letters are more likely to be real words they don’t know, or gibberish.
Researchers led by Dr Damian Scarf of the University of Otago, New Zealand trained 18 pigeons to distinguish words from random strings of letters. The birds were introduced to 308 four-letter words (no, not those ones) that baboons had learned to recognize in a previous study, mixed in among thousands of random strings of letters. Birds were trained to peck at a symbol when shown a word.
In each session pigeons were introduced to a new word, followed by refresher sessions on words they had learned before. Birds were considered to know a word when they could identify it more than two-thirds of the time.
After eight months the four brightest pupils had learned an average of 14 words. The other birds averaged just four, and Scarf saved resources by limiting further work to his four stars.
In Proceedings of the National Academy of Sciences, Scarf reports that the star pupils, after more intensive training, learned between 26 and 57 words. The birds did not learn meanings, only to distinguish real words from gibberish. The numbers are well short of the baboon average of 139 but still show considerable facility for reading.
Remarkably, once the pigeons had learned a number of words they were quicker to start to recognize a new unfamiliar word, compared to four random letters. "At a minimum," the authors write, "this transfer suggests that during training, the pigeons derived some general statistical knowledge about the letter combinations that distinguish words from nonwords." The pigeons appeared to pick up the fact that certain pairs of letters, such as "TH" and "AL" appear more often together in English words than random chance would suggest, and were quick to learn words that include such pairs.
Scarf used the last observation to reject the idea the pigeons were just learning words by rote. Instead, the paper argues the birds were generalizing from patterns in the words they had already learned.
No matter which language we use, humans activate an area of the brain, known as the visual word form area (VWFA), when reading. Neuroscientists are puzzled by the fact that writing is such a recent human development, yet the VWFA has clearly been around for far longer. One theory holds that the VWFA evolved to code other visual stimuli, but happened to be very well suited to the subtitles of writing.
Scarf and his colleagues hoped to see whether creatures with brain structures so different from those of primates could perform the same functions. As the paper notes, the last common ancestor of humans and pigeons was 300 million years ago, and both sets of brains have done plenty of evolving since.