Once a controller issues a visual approach (provided the pilot has reported either the airport or traffic to follow in sight) the ONLY restriction to the pilot is noise abatement.
At times, a controller may include a restriction within the visual approach clearance, such as "not below 2000' until final" or "turn final no closer than 6 miles". For non-local pilots, he may even include noise abatement restrictions within the visual approach, such as "cleared visual, not below 3000 until over the lake"
In the example given in the first post, where the controller says 'track towards right base' the aircraft is still either on radar vectors or some form of IFR navigation, and hasn't been issued a visual just yet. So 'track towards right base' is ambiguous at best, and as a pilot I would definitely stay at my last assigned altitude.