Tulving and others have suggested that humans may have multiple memory systems.(see some possible examples in the figure below) One might gain efficiency by using different representations in different memories acted on by different algorithms. The simplest example might be 2 dimensional arrays to store visual information and 1 dimensional lists to store audio information. The simplest implementation in Asa H might be to use 2 copies of Asa H on the lowest level in the hierarchy, one with NM=1 for audio input and one with NM set equal to the number of pixels in an image for visual input. (see my blog of 10 Feb 2011 for an example of simple code) At some higher level in the Asa hierarchy the outputs of these two sensory modalities would then be combined together.(concatenated) Things like translation, rotation, and reflection operations would only be applied to the visual memory. Things like time dilation would be applied to both. More complex examples of the use (and usefulness) of multiple memories are also under study.