The overall goal of this protocol is to examine the relationship between working memory processes and anxiety by combining the Sternberg working memory and threat of shock paradigms. This method can help answer key questions about the relationship between anxiety and cognition. The main advantage of this technique is that it can be adapted to a variety of other cognitive tasks.
Begin by escorting the participant to the testing room. Prior to placing electrodes on the participant, clean the skin area. Place two disposable 11 millimeter silver, silver chloride electrodes on the palm of the left hand, about two centimeters apart, to monitor skin conductance.
Next, place two disposable 11 millimeter silver, silver chloride electrodes on the inner wrist of the left hand, about three centimeters apart, to administer the electrical stimulation. Then, place one disposable 11 millimeter silver, silver chloride electrode on the inside of the left arm, just above the elbow, and one disposable electrode just under the right clavicle, to monitor the heart rate. Attach two four millimeter silver, silver chloride cup electrodes to the lower side of the left orbicularis oculi muscle, to measure the startle response.
Then, secure all electrodes with biomedical tape. Next, attach leads to the electrodes on the palm, and plug them in to the EDA channel of the psychophysiology monitoring hardware. Attach leads to the electrodes on the wrist, and plug them in to the shock device.
Then, attach leads to the electrodes on the arm and clavicle, and plug them in to the ECG channel of the psychophysiology monitoring hardware. Plug the cup electrodes, attached to the orbicularis oculi muscle, into the electromyography, or EMG channel, of the psychophysiology monitoring hardware. Check the impedance of the EMG electrodes, and ensure that it is below 10 kilohms.
Finally, administer nine unsignaled white noise probes through the headphones, to allow for an habituation of the startle response. Begin the shock calibration procedure by asking the participant to rate a series of 100 millisecond sample electrical stimulations to identify andintensity level that is unpleasant and uncomfortable, but not painful. Then use the experimental software to administer a series of presentations of the 100 millisecond shock stimulation to the wrist.
After each presentation, ask the participant to verbally rate each presentation on a scale from one, not uncomfortable at all, to ten, uncomfortable, but not painful. Next, use the milliamp scale on the shock device to gradually increase the intensity of the shock, and continue the series of stimulations, until the subject rates the stimulation as a 10. Lastly, record this intensity value to use during the experimental procedure.
Next, within the experimental software, enter the participant ID number, counterbalance condition, and run number into the run box. Then, click start on the psychophysiology monitoring recording. Then, position the monitor so that it is in front of the participant.
Press enter on the experimental software prompt box to start the experiment. Have the participant complete four runs of the experiment, during which they should select the right or left arrow key if the letter and position number match or mismatch the trial sequence respectively. After each run, have the participant verbally rate their anxiety level on a scale from zero, meaning not anxious, to 10, meaning extremely anxious, during the safe and threat blocks of the run they just completed.
Finally, ask the participant to verbally rate the intensity of the shocks presented during the previous run on the same zero to 10 scale use in the initial calibration procedure. Begin by opening the psychophsiology analysis software, and preparing the raw EMG data for analysis. Select transform, digital filters, FIR, then band pass to apply digital band pass of 30 to 300 hertz, and smooth the raw EMG channel.
Next, select analysis, electromyography, and derived average rectified EMG to rectify the smoothed EMG signal, using a time windowed mean of 20 milliseconds. Then, select analysis, Stim-Response, and Digital Input to Stim events to label the stimulus events that correspond to the digital inputs for each trial type. To extract the blink magnitude around each stimulus event, select analysis, Stim-Response, Stim-Response Analysis, and specify the mean of channel to extract the mean baseline activity in a fixed window of minus 50 to zero milliseconds preceding the onset of the white noise.
Then, select analysis, Stim-Response, Stim-Response Analysis, and specify the maxive channel to identify the blink onset and peak in a fixed window of 20 to 100 milliseconds, following the onset of the white noise. Finally, inspect EMG trace for artifacts that occur around stimulus events, and reject trials with artifacts. This protocol yields three primary data types, accuracy, reaction time, or RT, and anxiety-potentiated startle, or APS.
For accuracy, participants are typically more accurate on the low load than the high load trials. However, performance does not tend to vary as a function of threat of shock. For RT, participants typically show faster RTs during low load trials than during high load trials, and faster RTs during threat blocks than during safe blocks.
Lastly, there are two experimental manipulations for APS, load and startle timing. Participants typically show significantly larger APS during low load versus high load trials, but only when the startle probe is delivered during the maintenance interval. However, this effect does not hold when startle is probed during the ITI.
Once mastered, this experiment can be done in two hours, if it is performed properly. While attempting this procedure, it's important to remember to properly clean and secure the electrodes. Following this procedure, other cognitive tasks can be adapted in order to answer additional questions like how to start a shock effect sustained attention, or memory and coding.
