Maintaining student concentration in lectures has long been a challenge for lecturers. Pedagogical research consistently finds a drop in attention between 10 and 30 minutes into the lecture, which has been associated with the passive nature of the standard format, and has consequences for learning approaches and outcomes. A similar phenomenon has been observed in ergonomics for some time, known as the vigilance decrement. In this article, we present an exploratory effort to detect the vigilance decrement in four different lecture formats, by adopting an ergonomics measurement tool which has been related to vigilance, and relating the findings to students' assessment results. It was found that standard lecture formats do induce a vigilance decrement, and this can adversely affect learning of the material. Conversely, vigilance degradation is avoided when presentation is varied, though this is not necessarily associated with interactive participation techniques. Implications for lecturing styles, learning approaches and pedagogical research methods are discussed. (Contains 4 figures and 1 table.)