Redwing blackbirds, brown-headed cowbirds, and pigeons were trained with operant conditioning techniques to discriminate the steady-state vowels e, ae, a, and ⊃ from each other. A pulsed train of one of these vowels comprised the background stimulus. Birds were trained to peck on one response key to produce occasional alternations from this standard vowel to one of the three remaining comparison vowels, and to peck on a second response key during these alternations to produce a grain reward. All birds discriminated all combinations of vowel pairs employed when only one comparison vowel occurred during a session. Differences in discriminability emerged when three comparison vowels occurred within each session. For pigeons, increased discriminability (indicated by shorter response latencies and higher rates of correct detections) was directly related to the size of the first or second formant frequency shifts between standard and comparison vowels. For blackbirds, this was only true if the first or second formants shifted to higher frequencies when going from the standard to the comparison vowel. Comparison vowels producing downward formant shifts were not discriminated very easily, and in some cases not discriminated at all by blackbirds.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics