Participants wore a smartphone, which collected GPS, audio, accelerometry and image data, in a pouch around their necks for a period of two weeks. After a retention interval of one week, they were asked to judge the specific day on which each of a selection of images was taken. To account for people’s judgements, we proposed a mixture model of four processes - uniform guessing, a signal detection process based on decaying memory strength, a week confusion process and a event confusion process in which the sensor streams were used to calculate the similarity of events. A model selection exercise testing all possible subsets of the processes favoured a model that included only the event confusion model. GPS similarities were found to be the most significant predictors, followed by audio and accelerometry similarities and then image similarities.