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NEURAL sensory-memory representations that encode physical properties of incoming stimuli can be probed by recording the change-specific mismatch negativity of the event-related potential (ERP). The present study was aimed at determining whether invariant stimulus features, abstracted from the continuously changing acoustic environment, are encoded in these sensory-memory representations. Regularly descending tone sequences with an occasional ascending tone or tone repetition were presented to reading subjects. A significant MMN was elicited by the ascending tones. When instead of simple tones, Shepard tones creating an illusion of a continuous pitch decrement were used in the same paradigm, the MMN was elicited by both ascending and repeating tones. It was concluded that besides physical stimulus properties, abstract stimulus features are also encoded in the neural representations of sensory memory.