A mechanical task for measuring sign- and goal-tracking in humans: A proof-of-concept study

Abstract

Cue-based associative learning (i.e., Pavlovian conditioning) is a foundational component of behavior in almost all forms of animal life and may provide insight into individual differences in addiction liability. Cues can take on incentive-motivational properties (i.e., incentive salience) through Pavlovian learning. Extensive testing with non-human animals (primarily rats) has demonstrated significant variation among individuals in the behaviors this type of learning evokes. So-named "sign-trackers" and "goal-trackers" have been examined in many studies of non-human animals, but this work in humans is still a nascent area of research. In the present proof-of-concept study, we used a Pavlovian conditioned approach task to investigate human sign- and goal-tracking in emerging adults. Conditioned behaviors that developed over the course of the task were directed toward the reward-cue and toward the reward location. Participants' eye-gaze and behavior during the task were submitted to a latent profile analysis, which revealed three groups defined as sign-trackers (n = 10), goal-trackers (n = 4), and intermediate responders (n = 36). Impulsivity was a significant predictor of the sign-tracking group relative to the goal-tracking group. The present study provides preliminary evidence that a simple procedure can produce learned Pavlovian conditioned approach behavior in humans. Though further investigation is required, findings provide a promising step toward the long-term goal of translating important insights gleaned from basic research into treatment strategies that can be applied to clinical populations.

Keywords: Addiction; Associative learning; Incentive salience; Incentive sensitization; Pavlovian conditioned approach; Sign-tracking.

Figure 1.

Human Pavlovian conditioned approach (PavCA) apparatus and task A. Photograph of human Pavlovian conditioned approach apparatus: Reaching into the magazine (“goal”) to retrieve the token (left) and location from which the lever (“sign”) extends (right). The small black and white squares are eye-tracking markers used for area of interest measurement. B. Task schematic and timeline: (1) 18–22 sec (M = 20 sec) intertrial interval (ITI), (2) The lever then extends for 3 sec and participants can press it as many times as they would like (black rectangle on right), (3) Immediately after the lever retracts, a token is delivered into the magazine on 32% of trials, at which time participants can retrieve the token and place it in a cup (black square on left).

Figure 2.

Mean indicator variables by most likely group Mean z-scores on the three indicator variables from the Pavlovian conditioned approach (PavCA) task are shown (magazine gaze, lever gaze, and lever presses), organized by most likely group assignment. Bars indicate +/− 1 standard error.

Figure 3.

Trial-by-trial data to assess learning over the session Data are shown over the entire session on a trial-by-trial basis for sign-trackers (Class 1), intermediate responders (Class 2), and goal-trackers (Class 3). A. Magazine gaze duration, B. Lever gaze duration, C. Magazine gaze latency, D. Lever gaze latency, E. Lever presses. Error bars are +/− 1 standard error. See Table 5 and Supplemental Table 2 for linear mixed model results.