It was called "Virtual Arranger" on my 8000 and I believe the PSR 730/740.

According to manual...

When the Virtual Arranger* function is turned on, the Auto-accompaniment feature will play a more complex "arrangement" which provides livelier, more melodic accompaniment.

The Virtual Arranger is only effective when Auto-Accompaniment is On and the Full Keyboard or Manual Bass fingering mode is not selected.

* The Virtual Arranger will not work with custom styles


Present day Groove and Dynamics aren't as simple to use as the presets in Virtual Arranger, but they offer far better (deeper) editing choices and they work on all styles...not just the factory ones.

Session styles, presently on the later Yamaha act a bit like the old Virtual Arranger styles in that you have to be careful with your chording.

Ian