Harris Lussenhop, Ajay Rao, Augustus Lee
Service-Learning Course Project as part of DS 4200 F20: Information Visualization, taught by Prof. Cody Dunne, Data Visualization @ Khoury, Northeastern University.
In collaboration with Northeastern University’s NeuroLab, headed by Professor Samuel Chung, this project aims to create effective visualizations displaying neuronal regeneration data in Caenorhabditis elegans (C. elegans). NeuroLab observed a novel form of neuronal regeneration in C. elegans that is independent of common known neuronal regeneration signaling factors. Through the use of an interactive web-based visualization, the goal of this project is to effectively communicate the novel neuronal regeneration data to other researchers and to elucidate key data trends found across the various experimental conditions/groups. The visualization consists of stacked bar charts and dot plots to display the neuronal regeneration data. The linking of the charts enables users to extract key information when examining specific data. Together, the dot plots and the stacked bar charts enable the user to compare novel neuronal regeneration data across the different experimental conditions/groups and to interpret any newly-evident significant data findings.
The current visualization contains linked stacked bar charts and dot plots. The dot plots display the length of axon regeneration given three experimental conditions (wt axon, wt a+d, DLK-1 a+d) for three different cohort groups (L2 cut 12 hr reimage, L2 cut 24 hr reimage, Young adult cut, 24 hr reimage) for a total of nine plots.
L2 and Young Adult refer to the larval stage of the C. elegans worms. The reimage time describes how long after surgery the particular worm was evaluated for data collection. The three experimental conditions describe the genetics and type of regeneration stimulation used on each worm. “Wt” refers to normal, wild-type worms, while “dlk-1” refers to worms that do not have the DLK-1 gene (typically associated with traditional neuronal regeneration). “Axon” refers to the neuronal axon being cut to stimulate regeneration while “a+d” refers to the neuronal axon and the dendrite being cut to stimulate regeneration.
Stacked bar charts are organized below each of the nine dot plots with data displaying the distribution of regeneration types that correspond to the dots in the respective dot plot. When a dot in a dot plot is brushed over, the bar corresponding to that dot’s regeneration type is highlighted. If multiple dots in a dot plot are brushed over, all the respective bars corresponding to the selected dots are highlighted. The linking between the dots in the dot plots and their corresponding regeneration type in the stacked bar charts persists even when selecting dots across different dot plots (i.e. selecting dots in L2 cut, 12 hr reimage and dots in L2 cut, 24 hr reimage). In addition, when dots are selected via brushing, the dots are colored corresponding to their respective regeneration type in accordance with the color scheme in the legend and in the stacked bar charts. The dots are normally filled black if not brushed to allow the user to see the overall data points without the confusion that may be experienced if the user sees many colorful dots in a small viewing area.
When a bar within the stacked bar chart is moused over, the bar becomes highlighted and utilizes a detail-on-demand feature: displaying the relative percentage of the selected bar’s regeneration type in comparison to the other regeneration types found within the dots that correspond with the selected bar. In addition, the bar that is moused over also colors in the dots that correspond to the selected bar’s regeneration type. For example, if a red bar within a stacked bar chart is moused over, the percentage of that regeneration type in relation to all the regeneration types in that group is visible and all the dots that correspond to the red bar are filled in red.
The linking between the stacked bar charts and the dot plots is intended to provide the user with dynamic feedback when exploring the data and should aid the user in analyzing and comparing the data with useful contextual information (i.e. the dot plots data along with the stacked bar charts data should allow for contextualized data results that aid in data interpretation/analysis).
The dot plots contain a tool-tip functionality for the three types of experimental conditions (wt axon, wt a+d, DLK-1 a+d). When the experimental condition is moused over, the tooltip displays a text box that contains more details about the selected experimental condition to aid the user in interpreting the data. The purpose of the tooltip is to reduce any confusion about the contextual significance of the dot plots data. The tooltip is not included for the stacked bar charts since they contain the same experimental groups as the dot plots (repeating the same information is unnecessary).
The legend is positioned to the right of both the stacked bar charts and the dot plots to provide the user an easy reference point when interpreting the color encodings found throughout the visualization. Throughout the visualization, five different colors were used: purple, blue, green, yellow, red. All colors had the same saturation and brightness, only differing in hue. These colors were selected to differentiate the types of regeneration (categorical data) because their stark contrast with each other reduces any ambiguity when a user attempts to visually gauge the regeneration type of a dot or bar. The colors are all distinct from each other, which aids in establishing clear visual differentiations between the different regeneration types. All the colors were given the same saturation and brightness to eliminate any potential data importance/magnitude interpretations of the categorical data. The legend also includes information about the statistical tests performed (denoted by * or **) that are present in the dot plots.
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