A modified sequential recognition machine using time-varying stopping boundaries

The problem of optimally terminating the sequential recognition procedure at a finite time prespecified by the designer is considered. The application arises, in practice, when the receptor (feature extraction) part of a sequential recognition machine has only a finite number of suitable features available to the categorizer (decision) part, or the cost of taking observation is found too high as the recognition process exceeds a certain time limit. In either case, the urgency to terminate the recognition procedure becomes greater when the available measurements are to be exhausted. The problem is studied by considering time-varying stopping boundaries for the sequential procedure such that by a preassigned length of time, the acceptance and rejection regions meet and, therefore, one of the pattern classes has to be accepted as the terminal decision. The idea of varying the stopping rules as a function of time enables us to investigate the behavior of a modified sequential test as compared to the standard Wald test with constant stopping boundaries. Computer simulation of English character recognition using the modified sequential test procedure indicates very satisfactory results.