Hi DozyWannabe,
...and the same could be said of the Airbus auditory/visual warnings. Unsurprisingly, in training situations, pilots respond well to both.
Please see Page 105 of the final report:
"1.16.8.3 Response to aural warnings
Numerous studies have been conducted on insensitivity to aural warnings and they showed that the aggressive nature, rarity and unreliability of these warnings may lead operators to ignore these signals [1, 2]. In particular, in the event of a heavy workload, insensitivity to aural warnings may be caused by a conflict between these warnings and the cognitive tasks in progress. The ability to turn one’s attention to this information is very wasteful as this requires the use of cognitive resources already engaged on the current task. The performance of one of these tasks (solving the problem or taking the warning into account) or of both would be affected [3].
In addition, studies on the visual-auditory conflict show a natural tendency to favour visual to auditory perception when information that is contradictory and conflicting, or seen as such, of both senses is presented [4, 5, and 6]. Piloting, calling heavily on visual activity, could lead pilots to a type of auditory insensitivity to the appearance of aural warnings that are rare and in contradiction with cockpit information.
A recent study in electrophysiology on a piloting task seems to confirm that the appearance of such visual-auditory conflicts in a heavy workload situation translates into an attention selectivity mechanism that favours visual information
and leads to disregarding critical aural warnings [7]."
Having the stall warning alert only via the auditory channel is not a good design during high work load situations.
If you were busy arguing with Lyman in a noisy party and I wanted to get your attention, the most effective way would be by touch (on your arm or shoulder say). It's a completely separate channel with no competition from any other warning - as is the stick shaker.