How to create surface variables
Surface variables have a value for each tile in a set of rectangular tiles which fill the surface of the arena. In the resulting scrollsheet, surface variables are represented as double columns with one row per tile. For example, a surface variable may report the time spent inside each rectangular tile, or the average speed while traversing it. The first column whose name bears the prefix "v" lists the variable values for each tile. The second one whose name bears the prefix "n" lists the number of cases contributing to the corresponding value in the "v" column. As you later process the variable definitions, Wintrack leaves you a choice of either analyzing all trials in a case document or only a selection of trials. Defining a profile variable requires the following sequence of statements:
- Create an active data matrix and selection mask using an appropriate combination of Matrix, Memory, Transform, Include and Exclude statements.
- If you wish to limit the analysis to just a portion or time window of the trials, use the Window statement to set that window. If you omit the Window statement, all data points will be considered.
- Use the Surface statement to compute a data surface from the active data matrix. Each cell of a data surface stands for a rectangular tile within the arena. The arrangement of the cells in rows and columns represents the vertical and horizontal arrangement of the tiles in space and the cells of the data matrix are mapped onto cells of the data surface according to the x- and y-position coordinates of the corresponding data points. Data surfaces representing case documents with more than one trial have multiple trial planes. You can have Wintrack compute a trial plane for each trial in the case, or only for a selection of trials. In order to allow for a maximum of flexibility, this selection of trials can be further restricted when later processing the variable definitions with the Analyze Case Document command. Wintrack provides storage for 5 data surfaces, referred to as s1-s5. Executing a Surface statement does not destroy the active data matrix. You can use the statement repeatedly to create several data surfaces from the same active data matrix.
- Use the Tabulate statement to create a surface variable. Each Tabulate statement will add two new columns to the resulting scrollsheet and each tile will be represented by the average of all computed trial planes. At the beginning of the analysis, Wintrack will automatically create two columns listing the horizontal and vertical tile position for each row.
- You may repeat steps 1-4 as many times as you wish, in order to create a set of profile variables that report data from different matrices, for example speed and distance from a reference point.
Note that...
Surface variables are the only variables whose values can represent data from more than one case. For example, a surface variable may represent the total occupancy of the trained goal quadrant during the probe trial of an entire group of mice. It is the information in the "n" column which permits successive averaging as more cases are added to the surface.
Instead of using a data surface to compute a surface variable, you may also use the Collect statement to compute a data value which represents a particular aspect of the data surface, e.g. the largest cell value or the average of all cell values. Once computed, this data value can serve as source for the Tabulate statement to create a case variable.
Additional information...
- Managing custom variable definition files provides general information on the management of custom variable definition files.
- There is a topic describing how to build a custom variable definition file.
- The Flowchart of advanced data analysis gives a synopsis of data and variable types.
- There is a list of all available variable definition statements.
- Using the Memory statement you can build collections of data matrices and selection masks for later reuse in other variables.
- See the topic Analyze Case Document command for basic information on that command.
- Managing custom setup files provides general information on these files.
- Inside case documents provides advanced information on case documents.
