Temporal limits of spatial working memory in humans

An essential feature attributed to working memory is the labile and transient nature of its representations. Using an oculomotor task, we examined the stability of spatial working memory in 16 normal human subjects, Eye movements towards remembered spatial cues (memory-guided saccades) were electro-oculographically recorded after memorization delays that varied unpredictably between 0.5 and 30 s. A peaked time-course of saccadic targeting errors, with maximal errors around 20 s delay, was found, showing that delay-dependent decay of spatial information in working memory occurs, but is time-limited and reverts significantly beyond delays of about 20 s. These data (i) indicate temporal limits of spatial working memory and (ii) provide the first behavioural evidence for the existence of two parallely generated mental representations of space that successively control memory-guided behaviour in humans.