Bass Guitar is a playable instrument in all Guitar Hero. In pre-Guitar Hero World Tour games, bass was only playable in practice or Cooperative mode. In Guitar Hero World Tour and it's successors the bass guitar was made playable in single player.
Similarly to regular Guitar the highway is made up of five targets and the note to be played must be matched with it's respective target. Bass guitar is used to keep the rhythm of a song so the player will encounter the same beat. Unlike guitar, bass guitar is less likely to contain chords though some of higher tiered songs do contain chords. Tap notes and extended sustains are still part of bass.
Star Power is gained by hitting all star power notes in a star power sequence. Star power can also be gained by using whammy on star power sustains. Star power can be activated by tilting the guitar up or by pressing the select button.
In Guitar Hero: World Tour and onwards a new type of note is present: the open note. The open note is purple in appearance and spreads across the highway. Because it doesn't match up to a target the open note is played without holding any fret buttons. Open notes can also be hammered-on. Hammer on open notes appear white. The open note can be considered the easiest type of note to hit but can be difficult when played along with regular colored notes.
Another modified form of the open note exists in Guitar Hero: Warriors of Rock. This is the open sustain. The open sustain is played just like a regular open note. Since no buttons correspond to it, no buttons must be held to sustain it.