Patent GB-1098895-A (GB)
Title: Pattern recognition system
IPC: G06N20/00
Filed: 1966-06-28
Abstract: 1,098,895. Pattern recognition. GENERAL ELECTRIC CO. June 28, 1966 [July 8, 1965], No. 28998/66. Heading G4R. Pattern recognition apparatus includes means for converting patterns of known origin from different classes into corresponding digital codes, means for tabulating for each code the frequencies of occurrence of particular digital words in the code and for comparing said frequencies so as to identify a limited number of digital words which are most suitable for distinguishing patterns coming from different classes and using them for recognizing unknown patterns. As described, the pattern may be a waveform representing speech, jet engine noise for fault diagnosis, electrocardiogram or lie detector output. Learning phase. In the main embodiment, waveforms from known classes (two classes A, B) are applied to the apparatus in turn, each being sampled at a constant rate, the sampling output being 1 or 0 for positive and non- positive amplitude respectively. These bits are shifted into a shift register 31 (Fig. 5-2), particular patterns of adjacent and/or non- adjacent bits, selected at 32, being tested for by AND gates at 33 during shift-in. For each selected bit pattern, the frequency of occurrence c is obtained for each waveform separately by a counter 37 respective to the pattern, the results being stored in a matrix 42 or 43, respective to the class (Fig. 5-3), and also fed to a circuit 4 (see Fig. 5-2) which calculates the mean M and standard deviation # of the frequency of occurrence coefficients of the given bit pattern over the waveforms of each class A, B separately. The mean is obtained by a counter 48, fed direct from the AND gate, and the standard deviation is obtained from the mean and the output of the counter 37. The mean M and standard deviation # for the two classes are stored in the respective matrices 42, 43. The stored results for the various bit patterns used are read out in turn, the socalled " m/d ratio " viz. being calculated at 6 for each bit pattern. When the ratio exceeds a threshold at 63, the corresponding frequency of occurrence coefficients c converted to Gray code 64 and passed to categorizing means 7 wherein variable resistors are adjusted in accordance with the coefficients to maximize discrimination between the classes. The categorizing means 7 estimates the projected accuracy of discrimination and if this is not sufficient, further bit patterns are chosen at 32 and the learning process repeated. The further patterns may be those obtained from the patterns previously used by adding a bit before or after. When the projected accuracy is sufficient, test waveforms are applied and recognition (classification into classes) attempted, different bit patterns being tried as above if the success rate is insufficient. In a modification (Fig. 7, not shown), for speech recognition, the waveform is sampled whenever its slope is zero instead of at regular intervals, and the frequency of occurrence counts at 37 are done by RC networks and each count continues through the duration of one speech event i.e. the period during which the rate of zero-crossings remains approximately constant. Recognition phase. The outputs of the counters 37 are fed direct to the categorizing means 7, previously set during the learning phase, to indicate the class A or B.