Reed, P., Szczudlo, V., Willis, A., & Hall, G. (1993). The influence of brief stimuli uncorrelated with reinforcement on choice between variable-ratio schedules. Animal Learning & Behavior, 21(2), pp. 159-167. doi:10.3758/BF03213396

Reed, Phil, Val Szczudlo, Alan Willis, and Geoffrey Hall. "The Influence of Brief Stimuli Uncorrelated With Reinforcement On Choice between Variable-ratio Schedules." Animal Learning & Behavior 21, no. 2 (1993): 159-167.

Reed, Phil, Val Szczudlo, Alan Willis, and Geoffrey Hall. "The Influence of Brief Stimuli Uncorrelated With Reinforcement On Choice between Variable-ratio Schedules." Animal Learning & Behavior 21.2 (1993): 159-167.