Physiological Correlates of Emotion Recognition

1. Recruit 40 participants.

1. Participants should have normal or corrected-to-normal vision to ensure they will be able to see the stimuli properly.
2. Participants should not consume alcohol, caffeine, or other drugs for at least 6 hrs prior to the experiment.
3. Participants should have no history of neurological, psychiatric, or cardiac disorders.

2. Pre-experiment procedures

Figure 1: Electrode placement. Place the positive electrode below the heart, near the rib cage on the right side of the body. Place the negative above the heart, just below the left collarbone. Place the ground electrode below the heart, near the rib cage on the left side.

1. Attach three electrodes to the chest to record the heart rate (Figure 1). The electrodes should be pre-gelled. Check to make sure that the gel is not dried.
   1. Fix the positive electrode below the rib cage on the right side.
   2. Fix the negative electrode below the left collarbone forming a diagonal across the heart with the positive electrode.
   3. Fix the ground electrode below the rib cage on the left side.
2. Record a resting baseline of heart rate variability (HRV) for 5 min.
   1. The electrodes are connected to equipment that amplifies the signal and sends it to a computer for monitoring and recording.
   2. Verify the quality of the measured cardiac signal.
   3. Record the cardiac signal at sample rate of 1000 Hz.

3. Provide instructions for the participant.

1. Tell the participant that a series of faces will appear on the screen. Their task is to decide if the face is a fearful face or not. They should press the F key on the keyboard if the face is fearful, or the J key if it is not.
2. Instruct participants to respond as quickly and as accurately as they can.

4. Perform the facial emotion recognition task.

1. Each trial begins with a fixation cross that remains on the screen for 500 ms.
2. A face then appears and remains on the screen for 200 ms.
3. Half of the faces display a fearful expression, and half display a neutral expression. The order of faces is randomized for each participant.
4. The face is replaced by a fixation cross which remains on the screen for 2 s.
5. Present 120 trials.

5. Analyze the data.

1. Calculate the HRV measure from the recorded cardiac signal.
   1. Use automated software to identify the peak of each cardiac cycle known as the R wave.
   2. Visually inspect the data to ensure that each R wave is properly identified and make any adjustments that are necessary.
   3. Calculate the time from each identified R wave to the next, and record these values.
   4. Use specialized software to calculate high-frequency HRV power, which corresponds to the degree of HRV within the 0.15 to 0.4 Hz range.
2. Analyze behavioral performance on the facial emotion recognition task.
   1. Calculate accuracy separately for fearful and neutral faces.
3. Analyze the relationship between HRV and emotion recognition.
   1. Compute the correlation between HRV and accuracy at identifying fearful and neutral faces, separately.