Since the question is referring to tasks, this is controlled by metadata roles. Access permissions would apply to accessing content, such as tables, stored processes, (metadata content). Roles have to do with what menu choices, tool bar icons (tasks) that are available through the interface. For example, a user may have the readmetadata permission to see/access a table, but may be in a role that doesn't allow for him/her to run certain tasks against that table (statistical procedures) as it isn't a menu choice available.