A random-walk interpretation of incentive effects in visual discrimination

Previous studies have shown that changes in stimulus discriminability and changes in reward density affect pigeon reaction-time (RT) distributions in different ways. A random-walk model ("RWP") accounts for these differences and assigns a single parameter to each of the independent variables. This paper briefly reviews the model and illustrates its findings with hue discrimination data. A new analysis then presents fits to data showing that increased reward for stimulus "A" lengthens RT of pecks to an alternative stimulus "B", and that this effect on RT distributions is much the same as the effect caused by reduction of reward to B. RWP account for both effects by changes in its "bias" parameter. The remainder of the paper comments on the relations between reward, RT, incentive and bias.