Eighteen individuals meeting DSM-IV criteria for schizophrenia spectrum disorders (schizophrenia, schizoaffective disorder) (SC) were recruited at the University of Illinois at Chicago, and via ads in the community and special-interest websites (NAMI, NIH) and physician referral. Twenty-four healthy individuals (HC) were recruited via ads in the community. Potential participants were excluded if they reported histories of head trauma with loss of consciousness greater than 15 minutes, current substance abuse, or neurological abnormalities that might influence cognitive functioning. Diagnoses for all participants were established using the Structured Clinical Interview for DSM-IV diagnosis (20
). Severity of symptoms was rated by clinicians blind to individuals' task performance using the Positive and Negative Syndrome Scale (PANSS: 21
) and the Hamilton Depression Rating Scale (HDRS; 22
). Premorbid IQ was estimated using the Wide Range Achievement Scale (WRAT: 23
All SC participants were clinically stable outpatients. Fourteen of the SC participants were taking second generation antipsychotic medications, one was taking a first-generation antipsychotic medication, and four were not taking any antipsychotic medications. Medicated subjects were tested after a minimum of 4 weeks on a stable medication regimen. Subject characteristics are shown in . The study protocol was approved by the Institutional Review Board of the University of Illinois at Chicago. All participants had to demonstrate the ability to describe the study demands, and articulate how they could terminate participation, as part of the consent process. Written informed consent was obtained from all participants.
This task is a slight modification of a preference conditioning task that has been successfully used in studies of human subjects with brain disorders (cf. 24
). It is designed to assess incidental preference conditioning, which is believed to be dependent on the amygdala, and closely replicates conditioned place preference tasks used in animal studies. The first two phases of the task were directly based on Johnsrude and colleagues' task (25
), and included a preference formation phase and a preference testing phase completed immediately after learning. A third phase was added to the task to assess retention of conditioned preferences following a 24 hour delay. The task is illustrated in . As a check on subject awareness of the conditioning, we included a final phase (based on the original Johnsrude et al paper), which required that subjects report the rationale for their preferences. Given our focus on indirect conditioning, if subjects were aware that their preferences were influenced by their reward history, their data was not included in statistical analyses. Data for one SC subject was excluded for this reason.
Description of Task. Top Row shows typical presentation during the Conditioning Task. Bottom row shows typical stimulus presentation during the immediate and delayed Preference Testing.
In the initial conditioning phase, subjects were presented with three boxes on a computer screen in each trial, and told to select a box to “open” (See ). Subjects were instructed that their goal was to accurately guess which box contained a red ball on each trial, and that they would receive reward points for every occasion on which they found the red ball. Subjects were also instructed that they should try to remember how often they found the red ball in the three different boxes, as they would be tested on this information. Subjects completed a total of 180 trials in the learning phase, and there was no time limit for responding.
Each time a box was selected and “opened” either a red or black ball would be shown in front of an un-namable symmetric black-and-white background for three seconds, and then the box closed and a new trial began. When a red ball was revealed, subjects heard a musical flourish and received feedback that they had “won 10 points”; when a black ball was revealed a buzzer would sound and the feedback was given “you did not win any points”.
Unbeknownst to subjects, the specific order of pattern and ball color presentations was pre-determined, such that a specific pattern and ball would appear regardless of what box was selected. The 180 learning trials were presented in three blocks of 60, and within each block of 60, the red ball was presented with pattern A 18 times, pattern B 10 times, and pattern C 2 times. The same pattern was never presented with the same color ball more than two times in succession. After every 60 trials, subjects were asked to indicate how many times they had found the red ball in each of the three box locations.
The red ball was differentially associated with the three different background patterns, such that 90% of the time that pattern 1 was shown it was associated with the red ball, 50% of the trials using pattern 2 paired it with the red ball, and 10% of the trials using pattern 3 paired it with the red ball. Subjects were distracted from conscious attention to the relationship between the red ball and the different patterns by being asked to focus on the number of times that they found the red ball in the three different locations.
At the end of the full 180 learning trials, preferences for the background patterns were assessed. In this immediate testing phase, the three patterns used in the study as well as three new patterns with similar physical characteristics were presented in pairs. Each pattern was presented with every other pattern two times in order to balance presentation on the left and right sides of the screen, resulting in a total of 30 preference trials. Subjects were instructed to indicate, for each pair of patterns, the pattern that they preferred, and to not think too much about it but go with their first impression.
On the second day of testing, subjects completed an additional preference test. This task again included the same six patterns used in the immediate preference test, but stimuli were presented in groups of three. Each pattern was presented with all other patterns on three occasions, in order to balance for presentation in each of the three visual positions, resulting in a total of 60 trials. Again, subjects were instructed to simply indicate the pattern that they preferred, and not to think about it too much but to go with their first impression. The delayed preference task was designed to differ from the immediate preference task in order to decrease the potential for subjects to attempt to use their memories from the immediate preference task to influence their responses to the delayed memory task. At the end of the task, subjects were shown the six different patterns and how often they had indicated they had preferred each. They were then asked to state why they preferred their top three selections. This information was used to assess whether subjects were aware of the relationship between patterns and reward histories. Notably, we found that pattern 2 was disliked by all subjects, and thus removed that background pattern from further analyses.
Preference rankings of background designs 1 and 3 at both the immediate and 24 hour delayed preference assessments were used in statistical analyses.