It seems like the input field for writing your messages in a chat application is always placed at the bottom of the conversation.
Do we have any argument for this seen in a UX perspective?
People read from left to right and from top to bottom. Chat applications normally place texts from top to bottom. The newest chats placed at the bottom. Placing the input at the bottom, therefore, is logical.
With this answer I didn't mean ALL people. For example, Arabic is read from right to left. But considering this websites' audience and the OPs background I generalized it a bit.
I don't see it as more than logical.
If the text is displayed in the main window from top to bottom, then the input box for your reply is on the bottom, because that's where your text will end up.
While in another situation, like a comment thread on a blog, the most recent entry can be on top.
Then the input field for new entries is above that, again, because that is the spot where the new text will be.
Both situations feel natural for me. Note that my example is with left to right text, but I'm sure it would be very similar with right to left text.
When multiple messages are ordered in order of writing, it is natural to put the latest one at the bottom. This mimics how physical writing works - imagine a long paper sheet or a guestbook where people come by from time to time and leave a note.
Everyone would write their note just under the last note, and it would end up automatically ordered from oldest to newest.
Thus, it is natural to put the input closest to where the result will appear, so the text box goes to the bottom.
You could argue against the "latest last" ordering. For instance, Facebook orders its feed "latest first". Interestingly, with comment threads of individual posts, the comments are ordered "latest last" despite that.
The reason is not related to any language but the nature of the information and the focusing point for getting a general overview of changing any situation.
Conversation is not a static information like the text in book. Placing text on the bottom will let user to get the latest message and ongoing conversation.
The computer console is also working with the same logic the last written piece of information is the last and newest information. From my point of view, there are also other implementation of the same concept.
The stock information or latest news will be positioned to the bottom of the screen because it is the best place that you can keep focal point to the changing information while having a general overview information.
Subtitles are also performing better if it is positioned at the bottom of the page than putting it the top of the screen, and Japanese are also using the same way. Do you mind if we are going to move the subtitles above the screen? Are you going to perform better in that case?
I do not have data but definitely have some connection with that too.
English speakers read from top to bottom.
In order to comment on a Discussion, it is advisable to read the conversation before commenting. By placing the conversation before the input field, we increase the likely-hood that users read before commenting.
In some websites, it is the opposite - The input field is first, then the most popular comment is after it and comments follow in popularity order. The reason for this design is that the website wants the most distinct possible comment threads (they want everyone to state their opinion). After stating your own opinion, you will read others opinions and +1/agree/disagree with them.
Because in all instances, people read from top to bottom - unless you are reading upside down. A chat is context sensitive. Like a conversation, you need to know what happen before in order to contribute your two cents or form a reply or challenge a statement etc. So having the input at the bottom is only akin to what happens to a chat in real life.
As oppose to search.. you really don't care what has happened, you just want that information you are searching for NOW! - I wish real life could be like that.
One aspect that has not been mentioned in the other answers is that there may be some form of 'race memory' going on from the days before VDUs when teleprinters were the norm.
In the case of teleprinters / early computer terminals, the most recent text was printed on the current line and the paper scrolled upwards so you could see it. This was my first experience of communicating with a computer, and I'm still coding, so data entry at the bottom is quite natural for me.
While a small proportion of the population would have used computer terminals at the time, the concept was very familiar to a wide population from the humble typrewriter, telex machines in offices, TV shots of football results coming up on a teleprinter, and visual references in films set in that time.
Whoa! People who are conversant with certain written languages will read from left-to-right, and from top-to-bottom. Other written languages do things differently. This arrangement is only natural for people who read/write certain kinds of languages. I suspect that the input-at-the-bottom started with GUI coders who happened to read/write one of these languages (like English). And, that it continued, because a lot of people just copy what they see others do.
I think it's due to:
It would probably work ok to have the input box at the top, if messages scrolled downwards - but it would feel a bit surprising.