One theory by Goldberg (1990) argues the dynamic relationship between overlap and power over the conversation by suggesting that two types of overlap are power interruptions and displays of rapport. During conversation, a listener has an obligation to support the speaker. An interruption impedes upon this obligation by infringing upon the wishes of the speaker (which is to be heard). The difference between a power interruption or rapport is the degree to which the speakers' wishes are impeded upon. Rapport interruptions contribute to the conversation in that they ultimately cooperate and collaborate with the speaker in order to reach a mutual goal of understanding. Power interruptions are generally hostile and do not cooperate with the speaker. The goals of the power interruptor are both divergent from and regardless of the goals of the speaker. Power interruptions are further categorized into two types: process control interruptions and content control interruptions. Process control interruptions involve attempts to change the topic by utilizing questions and requests, and because they return control to the original speaker are generally seen as the less threatening of the two. Content control interruptions involve attempts to change the topic by utilizing assertions or statements that are unrelated to the current topic. Content control interruptions are viewed as problematic and threatening since they seize control of both the topic and attention away from the speaker. However, while overlaps have the potential to be competitive, many overlaps are cooperative. Schegloff concludes that the majority of overlaps are non-problematic. Konakahara et al. explores cooperative overlap by observing 15 graduate students from 11 different lingua-cultural backgrounds in an ELF (English as a lingua franca) conversation, or an English-based conversation among individuals of multiple native languages. Two types of overlap were observed: overlaps that were continuers or assessments and did not substantially contribute to the conversation or demand attention away from the speaker, and overlaps that were questions or statements and moved the conversation forwards. The majority of overlap during the study consisted of continuers or assessments that were non-interruptive. Overlapping questions and their interactional environment were analyzed in particular. It was found that overlapping questions demonstrate the speaker's interest in the conversation and knowledge of the content, act as clarifiers, and progress the conversation. In response, speakers who are interrupted by overlapping questions continue on to clarify their meaning. This suggests that overlapping questions, while interruptive in the fact that they demand attention away from the speaker, are cooperative in nature in that they significantly contribute to achieving mutual understanding and communication. While Goldberg's study primarily focuses on the distinctions and characteristics between power interruptors and displays of rapport, Konakahara et al. explores the ways in which overlap, in particular overlapping questions, can be collaborative and cooperative.