A reaction-time paradigm to measure reward-oriented bias in rats.

The authors devised a nose-poke task with asymmetric position-reward mapping to distinguish between effects of bias and sensitivity in reaction times of rats. In all trials, the rats had to poke their noses into the hole to the left or to the right of center, corresponding to the side at which 4 lights were illuminated, while ignoring distracters on the other side. Reaction times were faster for large-reward trials than for small-reward trials. In large-reward trials, there was no influence of the number of distracters, whereas in small-reward trials, distracters produced an increase in reaction time. Analysis of reaction-time distributions according to a linear model of decision making suggests that most of the systematic variability was due to a reward-oriented bias.