1. A computer system for determining a topic change of a communication, the computer system comprising: one or more computer processors; one or more computer readable storage media; and program instructions stored on the computer readable storage media for execution by at least one of the one or more processors, the program instructions comprising: program instructions to monitor a communication including a first span; program instructions to determine the communication containing a set of dialog statements, wherein the first span of the communication includes one or more dialog statements of the set of dialog statements; program instructions to determine if the one or more dialog statements of the first span include one or more indicators of a topic change, wherein the one or more indicators are identified by at least one detector of a learning model, wherein each of the one or more indicators of the topic change within the first span includes at least one of: a particular key phrase, a pause of particular duration, a particular activity on a participant's communication device, and a particular duration of the first span; responsive to determining the first span includes the one or more indicators of the topic change, program instructions to generate a score for the one or more indicators, based on the learning model; responsive to the score for the one or more indicators triggering a threshold condition, program instructions to determine a topic change within the first span, wherein the threshold condition is based on a determination of the topic change within the first span of the communication during training of the learning model, and wherein the threshold condition determined during training of the learning model includes: program instructions to determine a weighted value for the at least one detector, based on heuristics, program instructions to receive input of labelled communication dialog statements, wherein the labelled communication dialog statements include one or more topic change indicators that are known, the one or more topic change indicators corresponding to the at least one detector, program instructions to adjust the weighted value of the at least one detector in response to a delta between an output of scores of the at least one detector of the learning model and scores of the one or more topic change indicators that are known, and program instructions to determine the threshold condition in response to achieving an acceptable minimum for the delta between the output of the scores which are determined by the at least one detector of the learning model and the scores of the one or more topic change indicators that are known; program instructions to generate a second span based on adjusting boundaries of the first span by performing at least one of, adding to the first span one or more dialog statements of the set of dialog statements not included in the first span, and removing one or more dialog statements from the first span; program instructions to determine a score for the first span and a score for the second span, wherein the score for the first span and the score for the second span is based on a topic of the first span and a topic of the second span, respectively; responsive to the score of the second span being more favorable than the score of the first span, program instructions to extract one or more features from the one or more dialog statements of the second span not included in the first span, wherein extracting the one or more features from the one or more dialog statements of the second span, includes classifying the one or more features to correspond with the at least one detector of the learning model; and program instructions to train the learning model to determine a topic change, based, at least in part, on including the one or more features from the one or more dialog statements of the second span, in at least one detector of the learning model.