The overall goal of this procedure is to evaluate cognitive performance under exposure to emotional content. This method can help answer key questions about cognitive processing, such as how do we perform on a focal task when irrelevant emotional stimuli are present, and particularly, when words match the tested pathology or anxiety of the patient. The main advantage of this technique is that it is objective, not intrusive, and is not based on participant self-reports.
At the present moment, this procedure was robustly established only at the group level. In the future, it may possibly extend toward individual patient diagnosis of anxiety disorders. Demonstrating the procedure will be my lab manager, Elia Avikasis.
Begin by creating two lists. One of emotional, and the other of neutral words. Use generally emotional words such as hate, or pox, and neutral words that are preferably orthographic neighbors to the emotionally relevant words, such as gate, or box.
For each word on the list write its length in characters, as well as its estimated frequency in the appropriate language, in order to match the word lists on lexical factors. Select words for each list by adding pairs that match in length and frequency, and that are orthographic neighbors of one another. If a complete match is not possible, add a pair of words with a small gap in frequency to balance the bias of frequency from the incomplete match.
Ensure that each final list contains 20 to 50 words in each word category in order, to have a minimum of 20 trials in a block, thus avoiding repetition of words and thereby, habituation. Begin by selecting one of two designs. Choose a blocked design where the stimuli are presented in separate blocks of trials, defined by word valence if seeking to test global effects at the level of the word category.
On the other hand, choose a mixed design where the stimuli are presented in one block with intermixed emotional and neutral words in the same list if seeking to analyze the Emotional Stroop Effect, or ESE, at the individual word level and determine short carryover effects. In the blocked experimental design, select either a counterbalanced or fixed order of blocks. For the counterbalanced order, present the two possible block orders to two different groups of participants.
For a fixed order present the neutral block first followed by the emotional block. If desired, present an additional new neutral block following the emotional block in order to examine sustained effects. Finally, to test the effects of fatigue, design an auxiliary experiment, with three blocks of neutral words, and perform on a different set of participants.
Begin by sitting the participant down in front of the testing computer. Open the stimulus presentation software that will measure the participant's responses and reaction times. Instruct the participant to respond with a keyboard press.
Administer 20 to 40 training trials in order for the participant to master the mapping of the colors onto the keys. Following training instruct the participant to respond to the ink color of the word as quickly and accurately as possible. Avoid mentioning word reading, or that the word should be ignored, as this request may artificially augment reading the words.
Finally, present the three experimental blocks which will show each word randomly assigned to a single color, one at a time, at the center of the computer screen. Allow short breaks of 30 to 60 seconds between successive blocks of trials. As an alternative mixed design, present emotional words and neutral words randomly intermixed in a single block.
To analyze the reaction time data, adhere to the following parameters:first, only use data from correct responses, and second, exclude extreme responses which are faster or smaller than 2.5 standard deviations around the mean. Use statistical software to perform planned comparisons of data from the fixed presentation order. To do this, choose statistics, advanced linear non-linear models, general linear models, more results, and planed comps.
To analyze counter-balanced blocks across participants, perform an ANOVA by selecting statistics, advanced linear non-linear models, and general linear models. Enter block valence as a within-subjects factor, and order of blocks as a between-subject factor. Finally, to test the ESE, compare the reaction times of the emotional block with the first neutral block, for sustained effects, compare the second neutral block with the first neutral block.
When blocks follow the neutral-emotion-neutral sequence as shown here, a large ESE of 34 milliseconds is observed via slower responses in the emotion block than in the first neutral block. Furthermore, the 21 milliseconds'difference in performance between the two blocks with neutral items, indicates the presence of a sustained effect. In order to verify that there was no flagging of attention, or fatigue an auxiliary experiment, using only three blocks of neutral items was performed with a different group of participants.
Here, no significant differences in performance across the successive blocks indicate that the effect of fatigue was minimal. Furthermore, when there are only two blocks of trials, an ESE is only expected to emerge when participants are given the neutral block first. No ESE is present when the emotion block is given first, due to sustained effects.
While preparing for this procedure, it's important to remember to avoid repetition of words as much as possible, in order to avoid habituation. Following this procedure other paradigms, like the dot-probe, can be performed in order to answer additional questions. Like testing attentional bias and cognitive performance in the context of emotional stimuli.
After watching this video you should have a good understanding of how to design and perform an Emotional Stroop Experiment that highlights the interference effect of emotional content.
