General Settings. Go to Preferences > Notifications to edit general settings.
Task-Specific Settings. If under preferences > notifications, you have chosen “notify about selected tasks only”, then the default setting for “Notify me” (for each task) is unchecked. You may check or uncheck “Notify me” for any individual task.
Warning. If under preferences > notifications, you chose “notify me about ALL tasks”, then you cannot unselect “Notify me” for any particular task.