Neural signals responding to motions of the basilar membrane show responses in one direction as in rectification. At all but low frequencies, the neural measure averages over multiple cycles to give the equivalent of rectification followed by averaging (low-pass filtering). Over the entire cochlea, response shows as a pattern that varies more slowly that the applied frequency but that does follow the envelope of the applied signal. Each group of cells can give rise to a semi-periodic wave that can be analyzed by neurons in the brain. The total pattern that arises from a sound can thus be thought of as a two-dimensional pattern in time with one axis being the distance along the basilar membrane and the other being distance along some sequence of neurons. These patterns, varying at rates less than lower audio frequencies, have shapes that can be identified much like patterns in vision. The concept of the "neural analyzer" as an extension of cochlear patterns is discussed in , "Speech Bandwidth Compression System", June 4, 1968 (filed in 1964).