Both 'automatic reaction' and 'automatic response' are correct and usable in written English.
You can use it to describe an immediate or instinctive reaction that you or someone else has to a particular situation. For example: "The sound of a gunshot immediately triggered an automatic reaction in me, and I ducked for cover."
When you get used to looking nice all day, you will begin to automatically think 'I look nice' as an automatic reaction, and you will interact with other people with confidence.
After a while that became an automatic reaction".
The automatic reaction when a police officer starts questioning you is to feel inexplicably guilty.
"There's an automatic reaction on the part of institutions to sell stocks involved in a merger.
"If one plays with sound and image in a too-unconventional way, people yell — it's an automatic reaction," Truffaut said.
When a customer or a potential customer becomes frustrated, the automatic reaction is to never deal with that company again.
Controlled processing can override our automatic reactions, but we have to think about it, and it requires effort.
Another is that her patients will learn to be aware of the changes in their bodies — automatic reactions similar to salivating — before or during sex.
Booing can seem a healthy contrast to the automatic reactions of Broadway audiences who give nightly standing O's to almost every show, no matter how dull, inept or commercial.
Pictures of the burning towers and of the noble rescuers trigger automatic reactions of sorrow, admiration and anxiety, but the real human ache comes from the homely details of those who died or survived.
We suggest that humans use both mechanisms: simple, fast sensor fusions with thresholding for automatic reactions (default mechanism), and more complex methods for voluntary movements.
