Anthropogenic noise negatively affects wildlife in a wide range of taxonomic groups. Especially for birds, a substantial number of observational studies have now shown negative associations between... Show moreAnthropogenic noise negatively affects wildlife in a wide range of taxonomic groups. Especially for birds, a substantial number of observational studies have now shown negative associations between noise pollution and abundance and diversity along roadsides. Researchers investigating birds’ behavioural responses to high level noise to date have mostly focused on the immediate adjustment of vocal signalling behaviour. However, there is more than one mechanism by which birds might cope with increasing noise levels. They may show immediate behavioural reactions, such as spatial avoidance and/or vocal adjustment, but also more ontogenetic adjustments with long-term consequences like changes in sensory and personality traits. To test these potential effects of traffic noise on birds, I conducted a series of experiments using zebra finches. I have demonstrated that traffic noise per se can contribute to spatial avoidance in birds and cause variation in parental behaviour, and that there can be changes in noise avoidance behaviour in the course of a lifetime. These results provide new insights into the potential impacts of noise on birds. Show less
Speech sound categorization in birds seems in many ways comparable to that by humans, but it is unclear what mechanisms underlie such categorization. To examine this, we trained zebra finches and... Show moreSpeech sound categorization in birds seems in many ways comparable to that by humans, but it is unclear what mechanisms underlie such categorization. To examine this, we trained zebra finches and humans to discriminate two pairs of edited speech sounds that varied either along one dimension (vowel or speaker sex) or along two dimensions (vowel and speaker sex). Sounds could be memorized individually or categorized based on one dimension or by integrating or combining both dimensions. Once training was completed, we tested generalization to new speech sounds that were either more extreme, more ambiguous (i.e., close to the category boundary), or within-category intermediate between the trained sounds. Both humans and zebra finches learned the one-dimensional stimulus-response mappings faster than the two-dimensional mappings. Humans performed higher on the trained, extreme and within-category intermediate test-sounds than on the ambiguous ones. Some individual birds also did so, but most performed higher on the trained exemplars than on the extreme, within-category intermediate and ambiguous test-sounds. These results suggest that humans rely on rule learning to form categories and show poor performance when they cannot apply a rule. Birds rely mostly on exemplar-based memory with weak evidence for rule learning. Show less
Animal models, songbirds particularly, are increasingly used to study the human capacity for speech and language. In the light of understanding both language evolution and individual language... Show moreAnimal models, songbirds particularly, are increasingly used to study the human capacity for speech and language. In the light of understanding both language evolution and individual language acquisition these models are highly valuable, provided that they are studied within a valid comparative framework. In the past few decades, non-invasive methods such as functional Magnetic Resonance Imaging (fMRI) and Near-InfraRed Spectroscopy (NIRS) have become available for human as well as animal brain research. In the studies discussed in this thesis, fMRI is employed to unravel the neural correlates of vocal learning in the human and songbird brain. Specifically, fMRI in both songbirds and humans is used to study the neural mechanisms underlying birdsong learning and human artificial grammar learning. In a series of fMRI studies investigating these neural mechanisms in adult and juvenile zebra finches and human adults, this thesis compares the neural substrates of song learning in birds with those of language learning in humans. Studies in both species show correlations between behavioral learning of song or speech and neural activity. These results contribute to the songbird model for human vocal learning. Show less
The aim of this thesis is to shed light on whether some capacities that are considered linked to, or characteristic for, language are shared between humans and nonhuman animals, which can help to... Show moreThe aim of this thesis is to shed light on whether some capacities that are considered linked to, or characteristic for, language are shared between humans and nonhuman animals, which can help to understand the basic cognitive abilities from which the evolution of human language may have arisen. The thesis starts with comparing human language with other communication systems. Then Chapter 2 addressed the question: what mechanisms are involved in learning a sequence of vocal items in zebra finches. Chapter 3 addressed whether zebra finches are able to discriminate between, and generalize, affixation patterns. Chapter 4 dealt with a controversial topic that is recently getting a lot of attention: whether animals show the ability to learn __algebraic__ rules that are relevant to syntax learning in humans. Chapter 5 examined the ability of zebra finch to learn nonadjacent dependency that is important for learning the hierarchical structure of languages. Altogether, this thesis provides positive evidence for similarities between humans and songbirds in using transitional information, generalizing surface transformations of human affixation patterns and detecting nonadjacent dependencies. Show less
Birdsong and human speech are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. The most important parameters in human... Show moreBirdsong and human speech are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. The most important parameters in human speech are vocal tract resonances, called formants. Different formant patterns characterize different vowels and are produced by moving articulators such as tongue and lips. However, not much is known about the production and perception of vocal tract resonances by birds. In this thesis I show that both songbirds and parrots use different articulators, comparable to humans, to modify the sound produced. While in songbirds beak gape and the expansion of the oropharyngeal-esophageal cavity are the most important articulators, parrots exhibit prominent tongue movements which also might explain their sophisticated ability to mimic human speech. Regarding formant perception I show that zebra finches can discriminate human words differing only in their vowels and categorize these words independent of speaker identity. To do so the birds employ, just like humans, a combination of intrinsic and extrinsic speaker normalization. Furthermore, when tested for a cue weighting bias both zebra finches and Dutch adults weight higher frequencies stronger. These results indicate that the mechanisms underlying vocal production and perception in birds and humans exhibit more similarities than realized before and studying birdsong will increase our knowledge about the emergence of these mechanisms and might even shed light on the evolution of human speech. Show less
