These are modified versions of the implicit probabilistic reward task based on the work of Pizzagalli (Heerey, Bell-Warren, & Gold, 2008; Pizzagalli et al., 2005), here termed IPILT-Positive (IPILT-P) and IPILT-Negative (IPILT-N), to assess gain and loss responsiveness respectively. We developed five different sets of stimuli:

1. mouth long or short (the original stimulus type in Pizzagalli et al (1);
2. nose long or short (2);
3. mouth thick or thin;
4. nose thick or thin;
5. eyes big or small.

On each trial, participants perform a perceptual discrimination in which they indicate which of two variants of a stimulus was briefly presented (e.g., short or long mouth). For the IPILT-P, ~40% of correct responses receive gain feedback while, for the IPILT-N, a portion of incorrect responses receive loss feedback. For both tasks, one of the two responses (termed the RICH response) is scheduled to receive three times the amount of feedback as the alternative (LEAN) response. Each trial starts with a fixation cross for 500 ms, followed by a face without the critical stimulus for 500 msec. The critical stimulus is then presented for 100 ms, followed by a noise mask (#######). Participants have up to 8000 ms from onset of the critical stimulus to respond. On the IPILT-P, if it is a feedback trial and they respond correctly, they see "Correct! You win!," The initial instructions indicated that this means that they earned $0.05. On the IPILT-N, participants are told that they start with an endowment of $3.60. If it is a feedback trial and they respond incorrectly, they see "Sorry. You Lose," The initial instructions indicate that this means that they lose $0.05. In both versions, if they do not respond within 8000 ms, they see "Too slow – please respond faster." Instructions about the response mappings remain on the bottom of the screen throughout the task. In both tasks, feedback is presented in a pseudorandom order, such that no more than three trials in a row can receive feedback. A counter, reshuffled for each block, determines which RICH or LEAN response was scheduled for feedback. If a correct/incorrect response (IPILT-P/N respectively) is not made on a trial scheduled to receive feedback, feedback is delivered on the next available trial of that type. The button (left or right) used for the RICH or LEAN response is counterbalanced across participants, as is the variant of the stimulus (e.g., short or long mouth) that was designated as RICH or LEAN. Trials are presented in three blocks of 60 trials each, with a brief break in between blocks and the same ratio of RICH to LEAN trials within each block.

 

References

1. Pizzagalli DA, Jahn AL, O'Shea JP. Toward an objective characterization of an anhedonic phenotype: a signal-detection approach. Biological Psychiatry. 2005;57(4):319-27. PubMed PMID: 15705346.
2. Bogdan R, Pizzagalli DA. Acute stress reduces reward responsiveness: implications for depression. Biol Psychiatry. 2006;60(10):1147-54. PubMed PMID: 16806107.