Post 2: Emotional Priming Studies

For the latter portion of my research period, I have begun work on a new study to be conducted in the fall. The study is comprised of six experiments that I am programming, test running, and analyzing before testing on subjects in the fall. The experiments are programmed and run using Neurobehavioral System’s Presentation software. Upon become proficient using the software, I programmed the six experiments and below is an outline of the various conditions and constraints of that programming.

Target-Decoy Search Task

These experiments use either a target-decoy search task, or a context singleton search task. In the target-decoy task, 12 items are presented in a circular array with one item being the target item, one being the decoy item, and the remaining 10 being filler items. The items are arranged in positions corresponding to the hour positions on an analog clock face. Items are presented as unfilled circles with a gray-colored carat at the center. Target items have a unique color and a left or right facing carat. Decoy items have a different unique color with an upward or downward facing carat. Filler items are gray and have a carat facing left or right.

Context Singleton Search Task

In a context singleton search task, 3 items are presented in a triangular arrangement with one item on the vertical meridian and remaining two items on lateral positions in the left and right hemisphere. The target item is never on the vertical meridian and can only be on one of the two lateral positions. The remaining two positions are filled by a decoy and filler item. In both search tasks, target and decoy arrangements are randomized but the likelihood of a target and decoy occupying a certain position but be equal for each position.

Trial Arrangement

Each trial consists of the following sequence of events: a fixation event, a context event, a blank event, a stimulus event, and a fixation event. The fixation event involves a blank, black screen with a gray point at the center. For the context event, a picture of a certain context is selected and presented. The blank event is a blank, black screen. For the stimulus event, the search task is presented. The interval between the context event and the stimulus event is known as the inter-stimulus interval (ISI). The duration from the onset of context event to the onset of the stimulus event is known as the stimulus onset asynchrony (SOA).

Context Stimuli

Context-event pictures are selected from the International Affective Picture System (IAPS, Lang et al., 2008). The IAPS contains 956 pictures, with each picture normed on valence, arousal, and dominance. Neutral pictures are selected for their neutral valence and low arousal and threatening pictures are selected for their low valence and high arousal. Each context will contain pictures with people represented. Using a Matlab script, the average contrast intensity of the selected pictures is measured and each picture’s contrast is readjusted to avoid bias.

Experiments 1 and 2

The first two experiments use a target-decoy task to examine the effects of arousal on priming by manipulating the SOA. In both experiments, 5 SOAs (150, 250, 500, 1000, 1500ms) are used. The duration of the first fixation event is selected from a random set of values ranging from 100ms to 1500ms. The stimulus event lasts for 200ms and the second-fixation event lasts until a response is made. In Experiment 1, the ISI is kept constant at 50ms while the context event duration varies with respect to each SOA. In Experiment 2, the context event duration is kept constant at 150ms while the ISI varies with respect to each SOA.

In both experiments, target and decoy colors are selected from two values: orange and green, for a total of 2 unique target-decoy color combinations. A repeat trial occurs when the target-decoy color combination in trial N is the same as that of N-1. A switch trial occurs when these two are different. A precursor trial is added to ensure that repeat and switch trials occur in all experimental trials.

The target positions are selected from 8 positions corresponding to the following analog clock positions: 1, 2, 4, 5, 7, 8, 10 and 11 o’clock. Distractor positions are chosen from the following 3 sets of positions with respect to a selected target position: the same quadrant, the same hemisphere, and the opposite hemisphere. Neither the target nor the decoy can lay on the vertical and horizontal meridian positions corresponding to clock positions 12, 3, 6, and 9 o’clock. The same hemisphere and opposite hemisphere decoy positions both correspond to 3 clock positions away from the selected target. This allows for 24 unique target-decoy maps.

A set of 24 context pictures, 12 neutral and 12 threatening are selected from IAPS for the context event.

This allows for a total of 960 unique SOA by target-decoy color combination by target-decoy map by context configurations. Subjects will be presented with a practice set of 24 trials followed by one precursor trial and 48 blocks of 20 trials for a total of 960 experimental trials. Each SOA is represented in 192 trials, each target-decoy map by target-decoy color combination is represented in 20 trials, both contexts are represented in 480 trials, and repeat and switch trials occur in 480 of the trials each.

Experiments 3 and 4

These two experiments use the target-decoy task mentioned above to examine the effects of rarity of arousing context stimuli on priming. The same 5 SOAs as above are used. In Experiment 3, the ISI is kept constant at 50ms while the context event duration varies with respect to each SOA. In Experiment 4, the context event is kept constant at 150ms while the ISI varies with respect to each SOA.

Target, decoy, and filler items, colors, and positions are selected in the same fashion as above resulting in 24 target-decoy maps and 2 target-decoy color combinations. Repeat and switch trials occur in the same fashion as above.

A set of 160 pictures, 80 neutral and 80 threatening are selected from IAPS for the context event. There are three contexts: neutral context, inverted-neutral context, and threatening context. The inverted-neutral context contains the same set of pictures as the neutral context but they are inverted 180 degrees. In Experiments 1 and 2, the two context, neutral and threatening, are represented equally, both occurring in half the total number of trials. In Experiments 3 and 4, the threatening context and inverted-neutral context are represented, on average, in 1/7 of the total trials each. The neutral context is represented, on average, in 5/7 of the total trials.

This allows for a total of 80 unique SOA by target-decoy color by target position configurations. Subjects will be presented with a practice set of 24 trials followed by a precursor trial and 20 blocks of 28 trials for a total of 560 experimental trials. Each SOA is represented in 112 trials, each target location by color is represented in 35 trials, the threatening context and inverted-neutral context are represented in 80 trials each, the neutral context is represented in 400 trials and repeat and switch trials are represented in 280 trials each.

Experiments 5

Experiment 5 seeks to determine whether arousal influences facilitory and/or inhibitory processes in intertrial priming using both reaction time and event-related potentials (ERPs) to address this issue. 2 SOAs, a short SOA and a long SOA, are chosen based on the results of the above experiments. The ISI will be kept constant while the context event duration varies with respect to each SOA.

In Experiment 5, a compound singleton search task is used. Target and decoy colors will be selected from a set of four values (green, orange, blue, and yellow) allowing for 12 unique target-decoy color combinations. Expanding the color value set allows for target-color repeat trials, distractor-color repeat trials, target-decoy color repeat trials, and target-decoy color switch trials.

The target position can only be one of two lateral positions and the decoy position can be one of the two remaining positions allowing for 4 unique target-decoy maps.

Context pictures will be selected in the same fashion as Experiments 1 and 2 with 12 neutral pictures and 12 threatening pictures.

This allows for a total of 192 unique SOA by target-decoy color by target-decoy map by context configurations. Subjects will be presented with a practice set of 24 trials followed by a precursor trial and 48 blocks of 20 trials for a total of 960 experimental trials. Each SOA is represented in 192 trials, each target-decoy map by target-decoy color combination is represented in 20 trials, and both contexts are represented in 480 trials.

Experiment 6

Experiment 6 seeks to determine whether arousal influences facilitory and/or inhibitory processes in intertrial priming using both reaction time and event-related potentials (ERPs) to address this issue. . 2 SOAs, a short SOA and a long SOA, are chosen based on the results of the above experiments. The ISI will be kept constant while the context event duration varies with respect to each SOA.

In experiment 6, a modified target-decoy task is used. Target positions are selected from two sets of positions. The first set is the same 8 values as Experiments 1-4 and corresponds to analog clock positions: 1, 2, 4, 5, 7, 8, 10 and 11 o’clock. Unlike Experiments 1-4, target and decoy items can lie on the vertical meridian. The second set is two positions corresponding to analog clock positions: 12 and 6 o’clock. When a target position is selected from the first set, the decoy positions can be in the same quadrant, the same hemisphere, the opposite hemisphere, (as in Experiments 1 and 2) or on the near vertical meridian position. When a target position is selected from the second set, the decoy position can be one of the four positions on either side of the selected vertical meridian position. This allows for 32 unique target-decoy maps.

Target and decoy colors are selected from a set of four values (green, orange, blue, and yellow) allowing for 12 unique target-decoy color combinations. Repeat and Switch trials operate in the same fashion as Experiment 5.

Context pictures are selected in the same fashion as Experiments 1 and 2 with 12 neutral pictures and 12 threatening pictures.  This allows for a total of 128 unique SOA by target-decoy map by context configurations. Subjects will be presented with a practice set of 24 trials followed a precursor trial and by 48 blocks of 24 trials for a total of 1152 experimental trials. Each SOA is represented in 576 trials, each target-decoy map is represented in 36 trials, and both contexts are represented in 576 trials each.

Response and Codes

Responses are made following the stimulus event using the num-pad keys ‘1’ or ‘2’ for a target with a left or right facing carat, respectively. Responses are categorized as correct or incorrect. Trial configurations are composed of information for the SOA, target-decoy color combination, target-decoy map, arousal context, and priming type (repeat, switch, etc.) for a specific trial. For each trial, response type and the trial configuration are coded to a numeric number that is used as a marker in the EEG data. It can be referenced to later to determine the trial configuration and response corresponding to an elicited ERP.