meaning

[chrysanthemum]

American critic Hal Foster thinks he knows why installations are everywhere in modern art. He reckons that the key transformation in Western art since the 1960s has been a shift from what he calls a "vertical" conception to a "horizental" one. Before then, painters were interested in painting, exploring their medium to its limits. They were vertical. Artists are now less interested in pushing a form such as painting or sculpture as far as it will go, and more in using their work as a terrian on which to evoke feelings or provoke reactions.
Can you explain the meaning of the underlined part. I can't understand it.

 

[White Hat]

American critic Hal Foster thinks he knows why installations are everywhere in modern art. He reckons that the key transformation in Western art since the 1960s has been a shift from what he calls a "vertical" conception to a "horizOntal" one. Before then, painters were interested in painting,exploring their medium to its limits. They were vertical. Artists are now less interested in pushing a form such as painting or sculpture as far as it will go, and more in using their work as a terrain on which to evoke feelings or provoke reactions.

The idea of "vertical conception" versus "horizontal "conception" implies that in the past artists were involved in art production more in purely aesthetic, selfless, ways, in the spirit of, say, Michelangelo or Raphael.

"exploring their medium to its limits" implies that they were really into, highly enthusiastic about, what they were doing, perfecting the craft itself by learning and studying it thoroughly.

"Artists are now less interested in pushing a form such as painting or sculpture as far as it will go" implies that today's artists have become lazy and inefficient and more often regard art as a means of manipulating people's perceptions.