Patent GB-939134-A (GB)
IPC: G06V30/194
Abstract: 939,134. Learning circuits; automatic speech and character recognition. STANDARD TELEPHONES & CABLES Ltd. Sept. 22, 1961 [Sept. 23, 1960], No. 34045/61. Class 106 (1). An electric circuit adapted to assign to each of a number of input signal patterns a corresponding meaning comprises a matrix of intersecting row and column leads and elements at the cross-points coupled to the row and column leads, the input signal patterns being applied repeatedly to the column leads while a signal is also applied to the row leads corresponding to the meanings so that a change is made in the electrical characteristics at the cross-point elements associated with certain input and output leads so that subsequently upon applying an input pattern to the column leads the corresponding row lead receives a signal and vice versa. In Fig. 1 the input patterns 1, 2, 3 and 4 are derived from an array of six photocells and there are for each cell mark and space leads, e.g. e 1  and e 1 . For each of the four patterns the corresponding row lead is energized thereby modifying certain ones of the cross-point elements along the row wire to cause the intersecting wires to be electrically connected. Subsequently the application of one of the input patterns will produce signals on all the row wires, the magnitude of the signal representing the match between the pattern set up in that row and the input pattern. Each row wire is connected to a relay B 1 -B 4  and the row producing the highest signal causes the associated relay to operate before the others. As soon as the first relay operates, the others are disabled to prevent more than one output signal. The cross-point elements may be adapted to build up to full conductance on successive applications of the input signal with the corresponding row signal so that each element in effect registers the correlation between a column signal and a row signal for a succession of input patterns all of which are assumed to correspond to a particular meaning. The elements may be reversible, i.e. their conductance may be reduced by a number of input patterns applied during the learning phase which disagree with previous patterns. The elements may also gradually lose their conductance if it is not re-established from time to time. This corresponds to a " forgetting " faculty, the connection between an input pattern and the corresponding row gradually fading until there is no stored association. The cross-point elements may be electro-chemical and consist either of a pair of electrodes of silver coated with silver bromide. During the learning phase currents are made to flow between row and column wires and this causes silver threads to stretch from the cathode to the anode until metallic contact is established. This produces an irreversible conductance. Graphite may replace silver for the anode. In the form of Fig. 9c, tantalum coated with tantalum pentoxide is used for one electrode and graphite for the other. The whole is immersed in an electrolyte. The current passing during the learning phase causes the pentoxide to be decomposed into metal and the process is reversible. Alternatively, instead of electrochemical, elements, magnetic cores may be used. In Fig. 10, a simple core is used which is set positively or negatively by a series of coincidences or anti-coincidences. In the recognition phase the input pattern is applied as a pattern of high frequency currents. The magnetization of the cores is not destroyed by this current but the signal induced in the output wires represent by phase shift the state of the core. In other core arrangements transfluxors are used.