Get / Set Composite Type Fields within triggers

Hi

This is my first question, so, forgive me if it's a newby issue but I
couldn't find an answer googling.
I have a simple composite type

CREATE TYPE info_base AS
(by text,
at timestamp without time zone);

I want to use it as the data type of created, modified and deleted fields.
I already know hot to index, update and select a sub-field like

CREATE INDEX ix_created_by ON xxx.yyy ((created).by);
UPDATE xxx.yyy SET created.by = 'user';
select * from xxx.yyy where (created).by = 'that user';

My problem is inside triggers: How can I set or get type field values for
NEW or OLD? (I need it to check users permissions at row level, etc.)

I tried NEW.((created).by), NEW.(created.by), NEW.created.by and nothing
works...

Could you help me please?

Thanks in advance.
Martin