Here's a book suggestion (you've probably read it though):
The Western Way of War by Victor Davis Hanson, 2000.
Connections with modern times:
The Romans seemed to employ training and formation to lessen the impact of death close at hand.
For instance- you knew that if everyone maintained their intervals and the ranks filled as necessary, your actual fighting time could be fairly brief as reinforcements could move up and exhausted troops pull back for a breather. Or, just stick to your job, do it like in drill and concentrate on doing it right rather than worrying about death or injury.
That is why rigid formations were, for so very long, necessary on the battlefield...even after relative killing power made them more dangerous than an open skirmish line.
I would also hazard to guess that delaying stress, just like today, would have had some similar results on the men. Dreams, sweats and mood swings...which if I remember correctly some surviving plays mention as well as some classical histories.
The professional legionaires of imperial times would have had more support from each other than the citizen soldiers of early Rome...being that later legions spent longer and longer terms of service with each other and in ranks of other long term veterans. The citizen soldier experience would have been closer to the greek experience detailed in Hanson's book, imho. A common bond of living and working together, as well as family ties, with other citizen soldiers, but not necessarily the understanding that the more professional legionaires had for each other.
Of course the latter legions were subjected to far more brutal treatment, so that too may have stoked the delayed stress reaction. Maybe delayed stress reaction was a proximal cause in legion revolts since units that had more fighting under their belts had a lower rate of insubordination...implying more experience in dealing with delayed stress. I'll have to see if that thesis holds any water.