Clustering is a core building block for data analysis, aiming to extract otherwise hidden structures and relations from raw datasets, such as particular groups that can be effectively related, compared, and interpreted. A plethora of visual-interactive cluster analysis techniques has been proposed to date, however, arriving at useful clusterings often requires several rounds of user interactions to fine-tune the data preprocessing and algorithms. We present a multi-stage Visual Analytics (VA) approach for iterative cluster refinement together with an implementation (SOMFlow) that uses Self-Organizing Maps (SOM) to analyze time series data. It supports exploration by offering the analyst a visual platform to analyze intermediate results, adapt the underlying computations, iteratively partition the data, and to reflect previous analytical activities. The history of previous decisions is explicitly visualized within a flow graph, allowing to compare earlier cluster refinements and to explore relations. We further leverage quality and interestingness measures to guide the analyst in the discovery of useful patterns, relations, and data partitions. We conducted two pair analytics experiments together with a subject matter expert in speech intonation research to demonstrate that the approach is effective for interactive data analysis, supporting enhanced understanding of clustering results as well as the interactive process itself.

In two speeded acceptability experiments we tested which combination of prenuclear accent, nuclear accent and f0-interpolation between them is best suited to signal a double contrast in German (i.e., a contrastive topic followed by a contrastive focus). The experimental utterances differed in the prenuclear accent (medial- vs. late-peak, i.e., L+H* vs. L*+H), the nuclear accent (early- vs. medial-peak, i.e., H+L* vs. H*) and the f0-interpolation between them (high or dipping). All utterances were judged for their acceptability in a contrastive (Experiment 1) and a non-contrastive context (control Experiment 2). Our results showed that the combination of a late-peak prenuclear accent (L*+H) and an early-peak nuclear accent (H+L*) is best suited to signal a double contrast, independent of the f0-interpolation. The reaction time data also support the view that the f0-interpolation is not necessary for the interpretation of a double contrast.