Jenkins, W. O. (1943). Studies in the spread of effect. II. The effect of increased motivation upon the bi-directional gradient. Journal of Comparative Psychology, 35(1), 57-63.
http://dx.doi.org/10.1037/h0053668
"After preliminary training, 25 male albino rats were tested on a series of 20 units consisting of alternative pathways, both of which were open… . The motivation employed was 71 hours of food privation, and results were compared with a previous study in which a 23-hour period of starvation was used." A bi-directional gradient of repeated choice was found, extending 4 points preceeding reward and 3 points following. "The conclusion that an increase in drive resulted in a higher frequency of repeating responses was supported by the fact that the increased drive group showed a reliably greater frequency of repetition at 8 of 10 points as compared with the standard group. A change in the shape of the curve under conditions of increased motivation was also suggested by the data." (PsycINFO Database Record (c) 2016 APA, all rights reserved)