All experiments were performed in accordance with relevant guidelines and regulations, including the Declaration of Helsinki.
Experiment 1: We followed the same general design as Crump and colleagues (4), with some modifications. While they (4) used simple shapes (circle and square) as cue and outcome events, and a relatively fast 100 ms frame rate to present all cue-outcome events in each streamed-trial, we aimed to ensure that their results were not idiosyncratic to those conditions, and modified both the visual depictions of cues and outcomes as well as frame rate. First, cues were pictures of foods and outcomes were cartoon depictions of allergic reactions. Second, we used two frame rates, presenting cue-outcome events for either 100 ms or 300 ms at a time. The slower frame rate makes the procedure more similar to standard contingency tasks that present event pairs one trial at a time. Similarly to Crump and colleagues (4), we had subjects rate the contingency between a cue and outcome in four conditions: ∆P zero/ outcome density low, ∆P zero/ outcome density high, ∆P medium/ outcome density low, and ∆P medium, outcome density high. The primary question was whether subjects would give negative contingency ratings for zero contingency/low outcome density conditions.
Participants. Ten students from Vanderbilt University took part. All subjects were compensated with research participation credit for a psychology course. All subjects had normal or corrected-to-normal vision, and provided written informed consent. All experimental protocols were approved by the Vanderbilt University Institutional Review Board.
Apparatus & Stimuli. The experiment was controlled by PCs running in-house LIVECODE software. Subjects sat at a viewing distance of approximately 60 cm from the computer screen. During each trial, subjects viewed a stream of 60 cue–outcome pairs. Each cue–outcome pair was presented in a frame (8.5 cm in height, 5.5 cm in width), displayed in the center of the screen in grey against a white background. There were four possible cue – outcome pairs, and examples of each of these pairs (e.g., A, B, C, D) are depicted in Figure 1A. Cues were always presented in a square (3.3 cm), centered at the bottom of the frame, and outcome were always presented in a square (3.3 cm), centered at the top of the frame. Each streamed trial used a unique cue randomly selected from a set of 17 pictures of food items, and a unique outcome randomly selected from a set of four cartoon depictions of allergic reactions.
Design & Procedure. The experiment used a 2x2x2 within-subjects design involving contingency (noncontingent: ∆P=0, vs. contingent: ∆P= .47), outcome density (low: P(O)=.27 vs. high: P(O)=.73), and stream speed (Duration and inter-frame interval 100 ms vs. 300 ms). There were four streamed-trials in each condition, for a total of 32 trials. The stream speed factor was manipulated between two blocks of 16 trials, with order counterbalanced across subjects.
Each streamed-trial involved the rapid-serial-visual-presentation (RSVP) of 60 frames of cue-outcome pairs. The order of frames within each stream was randomly generated from one of the four contingency structures listed in Table 1, which defines the frequency of each cue-outcome event for each condition. These cell frequencies were adapted from (4) and modified so that each level of contingency had the same two levels of outcome density (in prior work the difference between outcome density levels was larger for the noncontingent than contingent conditions).
Within a stream, each frame was displayed for 100 (or 300) ms with a 100 (or 300) ms inter-frame interval (blank screen). In total, each stream lasted approximately either 12 seconds or 36 seconds. Following each streamed-trial, subjects gave contingency ratings using a continuous scroll-bar that participants could vary between a maximum negative value (– 100) and a maximum positive value (+100).
We used the same general procedure and instructions described in (4). Subjects first received the following general instructions:
“On each trial you will watch a stream of frames depicting a food item and an allergic reaction. The food item always appears on the bottom, and the allergic reaction always appears on the top. The presence or absence of the item represents eating or not eating the food. The presence or absence of the allergic reaction represents the presence or absence of the symptom. After each trial your task will be to rate the association between eating the food and developing an allergic reaction.”
Next, subjects viewed example streams containing a medium positive contingency (∆P=.47), zero contingency (∆P=0), and medium negative contingency (∆P=-.467). Each example was accompanied with definition of positive, zero, and negative contingencies. For brevity, we describe the instructions and definition for the positive contingency example. This format was modified appropriately for the descriptions of zero and negative contingency examples.
“A positive contingency means that eating the food predicts the allergic reaction. In other words, most of the time when the food item appears, the allergic reaction also appears; and, most of the time when the food does not appear, the allergic reaction does not appear. When you press the mouse button, you will be given an example that demonstrates a positive association. You will notice that food usually appears with the allergic reaction. And, when the food is not presented, the allergic reaction will usually not occur.
You just viewed a positive association. In the real experiment, you will be asked to rate the strength of this association. You will be shown a rating bar, and you will need to click on the line to rate the strength of association. In the example that you just saw, the association was about +50, so you would want to click about here (the instructions display the rating scale, and an arrow points to the indicated position).”
Following the instruction phase, subjects viewed and gave contingency ratings for each of the streamed trials.
Participants. Twenty students from Brooklyn College took part. All subjects were compensated with course credit. All subjects had normal or corrected-to-normal vision, and provided written informed consent. All experimental protocols were approved by the Brooklyn College Institutional Review Board.
Apparatus & Stimuli. With the exception that the subjects completed the tasks on iMacs, the apparatus and stimuli were the same as Experiment 1.
Design & Procedure. The experiment used a 3x7 within-subjects design involving contingency (∆P=0, .13, .267), and outcome density (P(O)=.167, .267, .367, .467, .567, .667, and .767). Table 2 lists the cue-outcome event frequencies for each condition. Streamed trials from all 21 conditions were presented in each block, for a total of four blocks, and 84 total trials. Condition order was randomized within each block. Frame duration and inter-frame interval were both set to 100 ms. The same procedure and instructions from Experiment 1 were used for Experiment 2.