directly; head-on; right in front
Describes facing something squarely, without avoidance; often used with verbs like 向き合う, 受ける, ぶつかる.
See also: まとも
彼はまともに私の目を見て話した。
He spoke looking me straight in the eye.
台風がまともにこの地域を襲った。
The typhoon hit this area head-on.
properly; normally; in a normal way
Used when something is done in a proper, expected, or normal manner; often appears in negative sentences like まともに～ない.
風邪でまともに声が出ない。
I can't speak properly because of a cold.
Implies taking something seriously, dealing with it honestly, or in a fair/decent manner; often used with verbs like 取り合う, 相手にする, 考える.
彼はまともに仕事ができない。
He can't do his job properly.
You shouldn't take his jokes seriously.
まともに考えれば、その計画は無理だとわかる。
If you think about it seriously, you'll see that plan is impossible.
ろくに is used only with negative verbs to mean 'not properly', while まともに can appear in both positive and negative sentences to mean 'properly' or 'seriously'.
Adverbial form of the na-adjective まとも (proper, straight). The kanji 正面 are rarely used; the word is now almost always written in kana.