Mentally transformed representations in memory are linked to their originals

Abstract

Working memory is an active workspace for manipulating encoded information. Neural decoding studies show that following mental transformation, the encoded original remains represented alongside the transformation product despite offering little to no functional merit. To test why, we employed multivariate EEG-decoding while participants mentally rotated a memorized orientation grating, encoded an additional grating, and were finally retro-cued whether the rotation product or the additional item would be probed. This tested whether retention of the original reflected (1) perceptual encoding, (2) deep encoding and persistent storage, or (3) a link to the transformation product. The original was decodable after rotation, and encoding an additional item, suggesting its retention was not merely perceptual. Next, contingent on the retrocue, the original and rotation product were retained or dropped together: the original remained decodable only when the rotation product was selected. Therefore, the original did not persist because it was deeply encoded; its retention depended on attentional selection of the transformation product. Yet, we found no evidence that retaining the original was beneficial. Our results show that mental transformation links the transformation product to its source representation, reflecting a dependent representational structure. We speculate that this structure may afford behavioral flexibility in dynamic environments.