Some years back the US Army did a test, using experienced instrument instructors and pilots, flying UH1s with a safety pilot. The objective was to slow the airspeed down by 10 knots at a time, and see how slow they could fly and maintain control. Some sort of instrumentation was used to record eye movements and where the eyes were looking. In every case, the scan had to be reduced as airspeed slowed and stability was reduced, and by the time 60 kts was reached the AI was basically all any of the pilots had time to scan, and below 60 knots every pilot went into a graveyard spiral and the aircraft had to be recovered by the safety pilot. If you fly into weather and have to go on the instruments, make sure you get the airspeed up immediately. The exact airspeed may differ by model, but the overall effect is likely to be the same, at least with helicopters without AFCS.