The subject was one male rhesus macaque(Macacamulatta), Ebbinghaus, who was about nine years of age at the beginning of the experiment. The subject’s prior experimental
experience includes training on simultaneous
chaining (Terrace, 2005), numerical tasks (Brannon and Terrace, 1998) and pilot studies on metacognition (Son and Kornell, 2005; Son et al., 2004). The subject was housed individually in a cage among a colony of 20 rhesus macaques at the New York Psychiatric Institute,
New York, New York. The conditions of the colony followed the requirements set by NIH guidelines and the Institutional Animal Care and Use Committees at NYSPI and Columbia University. A second subject was also run but has not yet completed the tasks. Therefore, the preliminary data with one subject are presented in this paper.
The subject was trained and tested in a stainless steel experimental chamber (23” h x 28.5” l x 27” w), which was located in a sound attenuated booth. The experimental
chamber contained a 15” 3M touch-sensitive LCD monitor, which displayed the task and all stimuli. During the experiment, white noise was played in the chamber to wipe out outside noises. The touch-sensitive
monitor was connected to an iMac computer which recorded the subject’s responses.
To familiarize the subject with the recall task, the subject
was trained on the recall task with no risk judgment
involved (Figure 2). The number of samples and distractors presented were gradually increased as the subject’s accuracy on the task increased. Feedback was provided using a token economy, with which the subject already had experience from previous studies.
Finally, to re-familiarize the subject with the metacognition paradigm involving low and high-risk judgments, the subject was simultaneously given 30 trials per day of a match to successive sample memory task, identical to the one described by Kornell, Son and Terrace (2007).
Retrospective Recall Task
The retrospective recall task required the subject to reflect on how well he performed on the test trial.To initiate the task, the subject pressed the ‘start’ button displayed on the screen. A fixed number of three sample
photographs were presented on the screen simultaneously,
ensuring an equal level of familiarity to each photograph. To attract the subject’s attention to the target sample, a blinking border surrounded the target sample for the last 1.25 seconds of the total 2.5 seconds that the photographs were displayed. The test phase began 0.8 seconds after the three samples disappeared. During the test phase, the three samples and five distractors
were presented on the screen in random positions
(Figure 1). A correct response was when the subject
selected the previously highlighted target sample from the previous screen. Selecting any other sample or distractor was incorrect. After each trial, the metacognitive
paradigm appeared on the screen.
After the completion of each recall response, two confidence icons were displayed on the screen (
Figure2),one representing high confidence and the other representing
low confidence.The subject had been previously
trained to discriminate between the two icons and press the icon that reflected how well they completed
the memory task. A reward in the form of tokens
was dropped in a hopper on the right side of the screen, based on the relationship between the subject’s accuracy on the task and confidence judgment.The outcome contingencies were as follows: choosing high risk following a correct response earned three tokens; high risk following and incorrect response resulted in the loss of three tokens. Choosing low risk, whether correct or not, always earned one token. When the hopper reached eight tokens, the subject received two banana-flavored pellets as a reinforcement and the hopper reset to six.
Prospective Recall Task
The prospective task required the subject to assess how well he learned the study trial before taking the test. The study and test phases of this task (Figure3) were similar to the retrospective recall task with minor parameter
differences.After the rhesus monkey initiated the study trial, two sample photographs were simultaneously
presented on the screen. A blinking border surrounded the target sample for last 1.5 seconds of the total 2.5 seconds that the photographs were displayed. In this prospective task, the prompt for the metacognitive
judgment was presented before the test phase. Following
selection of either low or high risk, the subject entered the test phase in which the two samples and five distractors were presented on the screen in random positions. The subject was required to select the target sample (previously surrounded by a blinking border) in order to successfully complete the trial.