In this study we employed a 'memory masking' paradigm (Magnussen & Greenlee, 1992) to determine which stimulus attributes are important in the storage of information about moving grating stimuli in visual short term memory (VSTM). Delayed speed discrimination thresholds were measured in the presence of masking stimuli which varied in terms of their spatial frequency or temporal frequency. Our results demonstrate that it is genuinely the speed of the stimulus, as opposed to temporal or spatial frequency content, that is crucial in the retention of information about motion in visual short term memory. The property of speed selectivity exhibited by VSTM mirrors that reported for neurons in area V5/MT, a brain area crucial for the processing of visual motion in primate brain (Perrone & Thiele, 2001). This link between area V5/MT and VSTM for motion is consistent with current views which suggest that there is a close association between the neural mechanisms involved analysis of sensory information and those involved in its retention in short term memory (Pasternak & Greenlee, 2005).