Effects of Brain-stimulation on Metamemory Monitoring and Control

• semantic recognition as assessed by a general knowledge task[ Time Frame: Through study completion, an average of 3 weeks ]
  Differences in recognition are compared between each condition (each active HD-tDCS and sham).
• semantic recall as assessed by a general knowledge task[ Time Frame: Through study completion, an average of 3 weeks ]
  Differences in recall are compared between each condition (each active HD-tDCS and sham).
• Feeling-of-knowing ratings and their accuracy[ Time Frame: Through study completion, an average of 3 weeks ]
  Feeling of knowing ratings are given on a scale. To assess the accuracy of these ratings, the subjective ratings are compared to objective accuracy, using signal detection based measures. Differences in feeling-of-knowing ratings and their accuracy are compared between each condition (each active HD-tDCS and sham).

Sometimes when people fail to recall information, they nevertheless have a feeling-of-knowing that the sought after information resides in their memory. These subjective feelings often correlate with later memory, but sometimes feeling of knowing judgments are incorrect (i.e., people have a feeling-of-knowing but don't remember the information later or lave a low feeling-of-knowing and remember the information later. The investigators have previously shown that applying high definition transcranial direct current stimulation (HD-tDCS) over the dorsolateral prefrontal cortex leads to more accurate feeling-of-knowing judgments. Accurate feeling-of-knowing judgments are useful in that they may later subsequent behavior. For example, individuals who have a feeling-of-knowing about the answer to a general knowledge question will continue to search their memory, whereas individuals who do not have a feeling-of-knowing will stop searching their memory. In this experiment, the investigators test the hypothesis that improving memory awareness via HD-tDCS over the DLPFC leads to improved control of memory. The approach taken is to have participants visit the lab on 3 separate occasions where they receive 3 different HD-tDCS protocols while completing a feeling-of-knowing, metamemory control, and recognition tasks: HD-tDCS over the DLPFC during the feeling-of-knowing task, HD-tDCS over the DLPFC after the feeling-of-knowing task, and sham HD-tDCS during the feeling-of-knowing task. To test metamemory control, participants are asked to select a subset of general knowledge questions that they would like to receive a hint about the answer. The expectation is that if individuals make more accurate feeling-of-knowing judgments, then they will make better choices about which items they would like to receive a hint for, thereby improving their overall memory performance.

• Device: HD-tDCS
  Participants will complete a metamemory and memory task

• Experimental: Active DLPFC during task
  HD-tDCS will be applied over the DLPFC at 2mA in a single session for up to 30 min during the FOK task
• Active Comparator: Active DLPFC after task
  HD-tDCS will be applied over the DLPFC at 2mA in a single session for up to 30 min after the FOK task and during a filler task.
• Sham Comparator: Sham DLPFC during task
  Sham HD-tDCS will be applied over the DLPFC at 2mA in a single session for up to 30 min during the FOK task