<p> Vowel harmony has been of great interest in phonological research. It has been widely accepted that vowel harmony is a phonetically natural phenomenon, which means that it is a common pattern because it provides advantages to the speaker in articulation and to the listener in perception. </p><p> Exceptional patterns proved to be a challenge to the phonetically grounded analysis as they, by their nature, introduce phonetically disadvantageous sequences to the surface form, that consist of harmonically different vowels. Such forms are found, for example in the Finnish stem <i>tuoli</i> 'chair' or in the Hungarian suffixed form <i><b>hi:d-hoz</b></i> 'to the bridge', both word forms containing a mix of front and back vowels. There has recently been evidence shown that there might be a phonetic level explanation for some exceptional patterns, as the possibility that some vowels participating in irregular stems (like the vowel [i] in the Hungarian stem <i> hi:d</i> 'bridge' above) differ in some small phonetic detail from vowels in regular stems. The main question has not been raised, though: does this phonetic detail matter for speakers? Would they use these minor differences when they have to categorize a new word as regular or irregular?</p><p> A different recent trend in explaining morphophonological exceptionality by looking at the phonotactic regularities characteristic of classes of stems based on their morphological behavior. Studies have shown that speakers are aware of these regularities, and use them as cues when they have to decide what class a novel stem belongs to. These sublexical phonotactic regularities have already been shown to be present in some exceptional patterns vowel harmony, but many questions remain open: how is learning the static generalization linked to learning the allomorph selection facet of vowel harmony? How much does the effect of consonants on vowel harmony matter, when compared to the effect of vowel-to-vowel correspondences?</p><p> This dissertation aims to test these two ideas --- that speakers use phonetic cues and/or that they use sublexical phonotactic regularities in categorizing stems as regular or irregular --- and attempt to answer the more detailed questions, like the effect of consonantal patterns on exceptional patterns or the link between allomorph selection and static phonotactic generalizations as well. The phonetic hypothesis is tested on the Hungarian antiharmonicity pattern (stems with front vowels consistently selecting back suffixes, like in the example <i>hi:d-hoz</i> 'to the bridge' above), and the results indicate that while there may be some small phonetic differences between vowels in regular and irregular stems, speakers do not use these, or even enhanced differences when they have to categorize stems.</p><p> The sublexical hypothesis is tested and confirmed by looking at the disharmonicity pattern in Finnish. In Finnish, stems that contain both back and certain front vowels are frequent and perfectly grammatical, like in the example <i> tuoli</i> 'chair' above, while the mixing of back and some other front vowels is very rare and mostly confined to loanwords like <i>amat&oslash;&oslash;ri </i> 'amateur'. It will be seen that speakers do use sublexical phonotactic regularities to decide on the acceptability of novel stems, but certain patterns that are phonetically or phonologically more natural (vowel-to-vowel correspondences) seem to matter much more than other effects (like consonantal effects).</p><p> Finally, a computational account will be given on how exceptionality might be learned by speakers by using maximum entropy grammars available in the literature to simulate the acquisition of the Finnish disharmonicity pattern. It will be shown that in order to clearly model the overall behavior on the exact pattern, the learner has to have access not only to the lexicon, but also to the allomorph selection patterns in the language.</p>