Common coding of auditory and visual spatial information in working memory

We compared spatial short-term memory for visual and auditory stimuli in an event-related slow potentials study. Subjects encoded object locations of either four or six sequentially presented auditory or visual stimuli and maintained them during a retention period of 6 s. Slow potentials recorded during encoding were modulated by the modality of the stimuli. Stimulus related activity was stronger for auditory items at frontal and for visual items at posterior sites. At frontal electrodes, negative potentials incrementally increased with the sequential presentation of visual items, whereas a strong transient component occurred during encoding of each auditory item without the cumulative increment. During maintenance, frontal slow potentials were affected by modality and memory load according to task difficulty. In contrast, at posterior recording sites, slow potential activity was only modulated by memory load independent of modality. We interpret the frontal effects as correlates of different encoding strategies and the posterior effects as a correlate of common coding of visual and auditory object locations.