Our research has shown that the auditory system appears to be selective or tuned for behaviorally informative sound features in natural sounds.  We are researching to what extent this specialized processing is dependent on sensory exposure during early development.  We first performed the same characterization that we did in the auditory forebrain of adult birds in young birds at an age where their audiogram is normal and where they are beginning to produce song.  We found that, although these young birds could hear perfectly well, the responses in the higher level neurons in the young animal lacked the specificity found in the adult (Amin et al, J. Neurophys 2007).   This study did not exclude the possibility that this difference was due to a maturation effect versus an experiential effect but it showed that neural responses in auditory cortex changed significantly during development.

    
We then began a series of experiments where we manipulated the early acoustical environment of developing birds.   In this research we used both males and females (who don’t sing) and changed the environment in three different ways: we isolated birds from their singing father, we cross-fostered zebra finches with Bengalese finches and we raised birds in continuous white noise.  
We failed to observe any differences in responses in the auditory cortex between adult male and female birds, suggesting that the experience of producing a song is not necessary for generating a highly selective auditory cortex (Hauber et al, J Comp Phys, 2007).  Moreover, neurons in father absent females preserved the selectivity for social complex song over matched synthetic sounds that was observed in control females (Hauber et al, J of Ornithology, 2007).  As a result of those studies, we concluded that the experience with song per se is not necessary as long as birds experience an otherwise normal acoustical environment: non-singing young birds and female birds produce many other complex vocalizations used in communication.  
Our results with the cross-fostered bird and birds raised in white-noise were more revealing.  Cross-fostered zebra finches showed a depressed neural response to both zebra finch and Bengalese finch song and we are able to show that this depressed responses leads to a decrease in neural discriminability for songs (Woolley et al, Dev Neurobiology, 2010).  The results from the white noise treatment are even more drastic.  Birds raised in white noise fail to develop the selectivity for conspecific song that is observed in socially raised animals. An information theoretic analysis also shows an increase in redundancy in the ensemble neural code for the representation of song but not complex synthetic sounds (Amin et al).  We can therefore conclude that both social and sound experience is critical for the development of the avian auditory cortex.  In future work, we plan on further investigating potential mechanisms for this developmental plasticity using a combination of modeling and pharmacological studies.