It is well known that recent sensory experience influences perception, recently demonstrated by a phenomenon termed “serial dependence”. However, its underlying neural mechanisms are poorly understood. We measured ERP responses to pairs of stimuli presented randomly to the left or right hemifield. 17 male and female adults judged whether the upper or lower half of the grating had higher spatial frequency, independently of the horizontal position of the grating. This design allowed us to trace the memory signal modulating task performance and also the implicit memory signal associated with hemispheric position. Using classification techniques, we decoded the position of the current, previous stimuli and response from voltage scalp distributions of the current trial. Classification of previous responses reached full significance only 700 ms after presentation of current stimulus, consistent with retrieval of an activity-silent memory trace. Cross-condition classification accuracy of past responses (trained o...