I always called them 'suicide levers' because getting leverage to activate them required hunching over the bars, which put your weight forward. Upon braking, the rider was catapulted you over the bars and onto their head. The modern version is 'interruptor' type levers and are much safer because you can activate them while still keeping your weight back.

Suicide levers were generally only found on low-end models since they were marketed toward beginners who liked the idea of keeping their hands near the stem. The same bikes often had stem-mounted shifters, too.