Parameter selectors are activated when the applied refactoring allows you to customize a method's parameters individually. It allows you to change the selected parameter and perform particular actions on the currently selected one. For instance, this functionality is available when using the Create Overload and Reorder Parameters refactorings.
When parameter selectors are available, you can perform the following actions:
The Refactor! folder in the IDE | Shortcuts page in the Options dialog.
The Editor | Refactoring | Selectors page in the Options dialog.