In the English lexicon, laryngeal alternations in the plural (e.g. leaf ~ leaves) impact monosyllables more than finally stressed polysyllables. This is the opposite of what happens typologically, and would thereby run contrary to the predictions of INITIAL-SYLLABLE FAITHFULNESS. Despite the lexical pattern, in a wug test we found monosyllables to be impacted no more than finally stressed polysyllables were—a 'surfeit of the stimulus' effect, in which speakers fail to learn a statistical generalization present in the lexicon. We present two artificial-grammar experiments in which English speakers indeed manifest a universal bias for protecting monosyllables, and initial syllables more generally. The conclusion, therefore, is that speakers can exhibit spontaneous learning that goes directly against the evidence offered by the ambient language, a result we attribute to formal and substantive biases in phonological acquisition.