  Action selection from many options with few constraints is crucial for
improvisation and co-creativity. Our previous work proposed creative arc
negotiation to solve this problem, i.e., selecting actions to follow an
author-defined `creative arc' or trajectory over estimates of novelty,
unexpectedness, and quality for potential actions. The CARNIVAL agent
architecture demonstrated this approach for playing the Props game from improv
theatre in the Robot Improv Circus installation. This article evaluates the
creative arc negotiation experience with CARNIVAL through two crowdsourced
observer studies and one improviser laboratory study. The studies focus on
subjects' ability to identify creative arcs in performance and their preference
for creative arc negotiation compared to a random selection baseline. Our
results show empirically that observers successfully identified creative arcs
in performances. Both groups also preferred creative arc negotiation in agent
creativity and logical coherence, while observers enjoyed it more too.
