Explanations for the well-documented second language (L2) learning challenge of the English regular past include verb semantics (Bardovi-Harlig, 2000), phonetic properties (Goad, White, & Steele, 2003), and frequency factors (Collins, Trofimovich, White, Cardoso, & Horst, 2009). Difficulty perceiving past-tense morphology (i.e., hearing "-ed" in the input) has received less research attention. In this study, we explored the roles of three perceptual factors (phonological environment, speech rate, semantic clues) among 106 L2 learners and 81 English speakers of a similar age. Experiment 1 was a forced-choice auditory identification task contrasting perceptually "easy" ([?d] + vowel) and "hard" ([t] or [d] + consonant) regular past contexts at normal conversational speed. Experiment 2 contrasted easy and hard contexts at a slowed-down speech rate. Experiment 3 included time adverbials that matched or mismatched the tense marker (e.g., "walked the dog now" vs. "walked the dog yesterday"). The L2 learners behaved at just above chance at normal conversational speed in both contexts, and slowing speech down helped them in easy contexts only. The English speakers were more accurate in easy than in hard contexts regardless of speech rate. Both L2 learners and English speakers also relied on adverbials at the expense of the phonetic cue to past morphology ("-ed"). Implications of these findings for the roles of input and frequency in L2 learning, and for pronunciation teaching (i.e., setting reasonable learning goals) are discussed.