Eye-tracking was used to investigate the attentional processes whereby different types of focus on form (FonF) instruction assist learners in overcoming learned attention and blocking effects in their online processing of second language input. English native speakers viewed Latin utterances combining lexical and morphological cues to temporality under control conditions and three types of explicit FonF: verb grammar instruction, verb salience with textual enhancement, and verb pretraining. Chinese native speakers were also tested on control and verb grammar conditions. All groups participated in three phases: exposure, comprehension test, and production test. Verb grammar participants viewed a short lesson on Latin tense morphology prior to exposure. Verb salience participants saw the verb inflections highlighted in bold and red during exposure. Verb pretraining participants took part in an additional introductory phase in which they were presented with solitary verb forms and were trained on their English translations. Instructed participants showed greater sensitivity to morphological cues in comprehension and production. Eye-tracking revealed how FonF affects learners' attention during online processing and thus modulates long-term blocking of verb morphology.