What rhetorical choices does Frederick Douglass use to convince his reader of the psychological trauma that children who were slaves experienced?

One of the reasons that Frederick Douglass was an effective anti-slavery advocate was because he was a powerful speaker and writer who mastered rhetorical tools and was able to use them to convey the realities of slavery to people who had either never experienced or had experienced slavery from the perspective of the slaveholder, rather than the perspective of the slave. 

Douglass uses simile, comparing most slaves’ knowledge of their birthdays to what a horse would know of its birthday.  Given that slaves were often compared to beasts of burden; this may not seem like a rhetorical device that would highlight their humanity.  However, he goes beyond that to explain why slaveholders kept slaves ignorant of their birthdays, which subtly challenges some of the then-existing stereotypes about race and intelligence.

At first blush, it appears that Douglass uses meiosis when describing his mother’s absence from his life and his reaction to her death.  His feelings about missing her and his lack of a reaction when she died are both far from what one would expect from the death of a parent, which makes it seem like it is an understatement.  It certainly highlights the point that he is making, which is that slaveholders separated mothers from their children in order to blunt the natural affections between parent and child, thus weakening societal and communal links among the slaves.  However, upon further reflection, it is really difficult to tell whether or not this is a rhetorical device or simply Douglass plainly recounting how he felt about the death of his mother.  If it is not deliberately understated, it may not qualify as meiosis.

He uses litotes very effectively when he states that Master was not a humane slaveholder.  When he goes on to describe the behavior, especially how Master treated his aunt, it is clear that Master’s behavior was barbaric, so the understatement highlights the extremes of his behavior.