Prior to DEC's PDP-1, of 1959, there would be MIT's TX-2 of 1958 - after all, the PDP-1 (and DEC itself), was a spin off of this project (and team). That said, it was only a single machine and a research project, not anything commercial available.
Before that, there was the SAGE system, operational in 1958, which was used for RADAR surveillance. Images from this system are maybe what you had in mind. The displays were completely synthetic (computer-generated) on hardware made by IBM based on the 740/780 linage.
Thus I'd say, an IBM 740 system, and here especially the IBM 780 CRT Display, qualifies as first. Likewise in display capabilities, as well as being commercial available since 1954. Connected to a 701 (or similar machine), interactive computer displays could be generated.
That is, of course, not counting the Williams Tube used by the 701 itself - and before that with the Manchester Baby, in 1948 (and Mark 1 in 1949). Both, without a doubt, could be used to display patterns including characters. And for sure it was a direct reaction :)
... I guess that's as far as the 'first' stuff can go in this context :))