Discrimination of natural, sustained vowels was studied in 5 budgerigars. The birds were trained using operant conditioning procedures on a same-different task, which was structured so that response latencies would provide a measure of stimulus similarity. These response latencies were used to construct similarity matrices, which were then analyzed by multidimensional scaling (MDS) procedures. MDS produced spatial maps of these speech sounds where perceptual similarity was represented by spatial proximity. The results of the three experiments suggest that budgerigars perceive natural, spoken vowels according to phonetic categories, find the acoustic differences among different talkers less salient than the acoustic differences among vowel categories, and use formant frequencies in making these complex discriminations.
