Abstract
Despite the virtually unlimited capacity of visual long-term memory (VLTM) (e.g., Brady et al., 2008), not all visual information that we wish to remember gets encoded into VLTM. One robust way to enhance VLTM encoding is to encode the visual information over multiple opportunities; known as the multiple encoding benefit (MEB). However, it is unclear whether it is the number of encoding opportunities or the total encoding duration that underlies the MEB, because as the number of encoding opportunities increases, so does the encoding duration. Thus, we dissociated the contributions of the number of encoding opportunities and the encoding duration and measured their impacts on objective memory recall precision as well as subjective memory recall confidence. Specifically, we had participants encode a series of 360 pictures of real-world objects presented in a solid colour drawn from a 360° colour wheel (Brady et al., 2013). During the serial presentations, baseline pictures were presented once for 500ms, while some were presented once for 1000ms, and other pictures were presented twice for 500ms each with variable lags between the two presentations. Here we found that while elongating encoding duration benefited both objective and subjective memory recall performance, there was also a unique benefit of additional encoding opportunities on both measures of memory performance. Importantly, the magnitude of this additional benefit amplified as a function of the lag between the two encoding opportunities. Therefore, the MEB is not just due to the increase in total encoding duration but is driven by the increase in the encoding opportunities.