Songbirds are excellent auditory discriminators, irrespective of age and experience

Abstract

Human infants but not adults possess the ability to perceive differences between non-native language phoneme categories. The predominant explanation for this age-related decline in discriminative ability is the effect of statistical learning driven by sensory exposure: phoneme categories of the native language take precedence, have a higher frequency of occurrence and may encompass category distinctions in non-native languages. Alternatively, one could explain the decline through a reduction in discriminative abilities attributable to ageing. Thus, to what extent is auditory perception influenced either by experience or by age-related processes? Here, we attempted to answer this question, which cannot easily be disentangled in humans, in songbirds, which share many properties with humans: both learn the statistical distribution of sounds in their environment, both possess neural circuits to process vocalizations of their own species and plasticity in these circuits is subject to critical periods. To study the effects of experience and ageing, we trained zebra finches, Taeniopygia guttata, to discriminate short from long versions of a single zebra finch song syllable type. Birds in four groups distinguished by their age (old versus young) and level of auditory experience (with song experience versus completely isolated from song) could learn to discriminate arbitrarily fine differences between song syllables, although we found a trend that upholds the statistical learning hypothesis: birds with song experience performed better than birds with no experience. Furthermore, birds in all groups were able to generalize their learning to new stimuli of the same type, and they were able to rapidly adapt their learned discrimination boundaries. Finally, we found that songbirds could accurately discriminate randomly selected renditions of a stereotyped adult song syllable, revealing a flexible ability to discriminate conspecific vocalizations.