Patrice Adret | Operant conditioning, vocal learning, visual discrimination and deprivation in zebra finches

+ OPERANT CONDITIONING AND SONG LEARNING
+ VISUAL DEPRIVATION AND SONG LEARNING
+ DISCRIMINATION OF VIDEO-IMAGE

Among the roughly 10,000 extant species of birds, only parrots, hummingbirds and songbirds have been found capable of vocal learning. Many songbirds like the canary, the nightingale, the white-crowned sparrow and the chaffinch will faithfully reproduce sounds that are played to them - even a little - from a loudspeaker in youth.

In 1969, the late Dr. Klaus Immelmann brought the zebra finch - an Australian representative of grass finches (estrildids) - to the front stage of birdsong research. He showed that young males not only accurately copy their fathers' song (females do not sing) but will also accept the song of another species (e.g. Bengalese finch) if they are raised by foster parents of that species. However, unlike the above-mentioned songbirds, zebra finches were found particularly resistant to imitate their own species' song played from a tape.

Would young male zebra finches learn from a loudspeaker if one let them turn on the tape-recorder? The idea arose as I was watching a bird relentlessly pecking at a plastic lid stuck in the wire mesh of its cage, as if expecting something to happen in return.

photo: (top and below) Univ. St-Andrews

The experimental set-up I developed in 1991 to investigate song learning and song preferences in zebra finches (Adret, 1993). The experimental bird (right) has access to a response panel displaying two keys. Pressing either one results in the playback of a song model for 15sec (here, song is the reward) broadcast simultaneously in an adjacent cage. The control bird receives the same amount of auditory stimulation but only in a passive way. Compared to the controls, experimental birds were found to achieve better imitations of the song model, perhaps as a result of increased attention to the details of the stimulus. This work, performed in Dr. Peter J.B. Slater's laboratory, points to the importance of social interaction in vocal learning.

Subsequent work in Dr. Carel ten Cate's laboratory could not replicate this result; the birds did learn, albeit to the same extent in both groups. More recent implementations by Dr. Ofer Tchernichovski at CUNY showed that, with such techniques, limited exposure to a model song - rather than having continuous access to it - leads to better learning in zebra finches. On the other hand, Dr. Katharina Riebel at Leiden University took advantage of these operant techniques to further explore song preferences, particularly in female songbirds.

Young male zebra finches blindfolded over the sensitive phase for song learning (35-65 days post-hatch) imitated from a live tutor that shared the same cage. The accuracy with which the blindfolded birds copied the tutor song was found to increase in the presence of a non-singing conspecific female. Controls without eye caps and kept separated from the tutor by an opaque partition imitated poorly. Physical contact, not sight, appears to be an important factor in the song learning process of zebra finches. Conspecific females prove to be influential in this process.

The operant set-up I used for testing the ability of zebra finches to discriminate video images. Here, key pecking resulted in the presentation of one randomly selected moving image displayed for 15 sec "without sound" on a cathode ray tube (CRT) video monitor.

Adult males sang directed song in response to video clips featuring whole images of birds (# 1, 6, 8, 11) but refrained from singing while viewing non-bird pictures.

When tested with sections of bird images, subjects sang vigorously in response to the head portion of a male zebra finch exhibiting beak movements associated with singing (#5). Judging from their overall song performance, however, the birds failed to discriminate between heads and bodies.

The advent of thin film transistor (TFT) liquid crystal technology has enabled Dr. Kazuo Okanoya and his colleagues to investigate further directed singing in grass finches. A major advantage is that TFT monitors provide more realistic moving stimuli, devoid of the flicker that birds can naturally perceive when using the older CRT technology.

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