The phrase "a flat affect" is correct and usable in written English.
It is typically used in psychological or medical contexts to describe a lack of emotional expression or response.
Example: "The patient exhibited a flat affect during the evaluation, showing little emotional response to the questions asked."
Alternatives: "an emotionless demeanor" or "a muted emotional response".
He had a flat affect and an arid wit, and did not open up right away.
Former classmates here described him as nervous, with a flat affect.
Beth sings in an almost full voice, but with a flat affect, "I am here and there at the same time.
He may rap with a flat affect, but he's coolly percussive, delivering lyrics in triplet and eighth-note patterns that are his only claim to dynamism.
Schwartzman, a slight man with a flat affect and a speaking voice that's a light-tenor monotone, pulls off this self-absorption not with hiself-absorption notudience.
Schwartzman, a slight man with a flat affect and a speaking voice that's a light-tenor monotone, pulls off this self-absorption — not with his ex but with the audience.
On the DailyKos, a blogger who identified himself as having Asperger syndrome worried that the actions of Mr. Lanza, 20, who killed 20 young children and 7 adults, including his mother, and was described by a classmate as having a "very flat affect," might be how "people with this disability are defined in the popular imagination".
The frontman Robbie Furze sang it with a disarmingly flat affect, delivering it as the ramble of a neurotic.
Jon Caramanica of The New York Times commented that The Big Pink's version of "Sweet Dreams" had a "disarmingly flat affect, delivering it as the ramble of a neurotic" when compared to the original recording sung by Knowles.
One former classmate who said he was familiar with the disorder described Mr. Lanza as having a "very flat affect," adding, "If you looked at him, you couldn't see any emotions going through his head".
Instead, Costa was getting Jerry Sandusky to open up and say (with a disturbingly flat affect), "I shouldn't have showered with those kids".
