Experiment Design

In this experiment, a feature delayed response task was used. The description of the tasks is given in the following paragraphs.

Design of Task 1

In the first task (illustrated in Fig. 14.1), for the first objective, the participant must remember the position of the red cubes relative to each other. The only cubes to be remembered were the red color cubes. The color/ number of distracting cubes might change. The cubes could be positioned in 18 different places in each visual field (VF). We limited the number of

Design of experimental task 1

Figure 14.1 Design of experimental task 1.

red cubes to six, since it is believed that WM can hold items in the range of 7 ± 2,1 depending on the content.

The number of red cubes was not altered throughout the experiment; only their position was changed. The attention of the participant was altered by adding different color cubes. As mentioned, each side can accommodate 18 cubes, since 6 spaces were filled with red cubes, there were 12 empty places left that could contain the distracting cubes with different colors. The colors of the distracting cubes varied between 7 colors (black, blue, lime, aqua, magenta, yellow, and white). The steps of the experiment can thus be described as follows:

Stimuli with no distraction. Six cubes in different positions were placed in each VF (12 in total image). The result of this experiment was used as the baseline/reference to compare the changes when distraction was introduced.

Stimuli with low distraction—4 (<6). In this step, the distracting cubes were added to the stimuli. The reason for choosing 4 was because we wanted to examine the brain activity when there were distracting cubes, but the number of distracting cubes was less than the red cubes. In other words, the intensity of distraction was low.

Stimuli with high distraction—8 (>6). In this step, we introduced more distraction as compared to the previous step, i.e., the number of nonred cubes was greater than the number of red cubes.

Please note that the number of red cubes was the same throughout the experiment. Only their position (relative to each other) was changed.

The participants were supposed to remember the position of the red cubes relative to each other as a whole pattern. In the testing array, the distractions would not appear, the reason being that the participants were asked to remember the position of red cubes and that is what they were going to be tested for. The point of introducing distraction was to alter the attention while encoding new information, and not to alter attention during retrieval.

The timing information of a single trial of task 1 is explained in Fig. 14.2. There were a total of 50 trials in task 1. Each trial started with a cue, presented for 200 ms, informing the participants to focus on a visual hemifield, either left or right. After the cue, the stimulus was presented for 300 ms (memory array) followed by a delayed period of duration of 1000 ms. Finally, the test array was displayed and the participants were required to respond by pressing a button if the test array matched with the memory array. There was a 2000-ms intertrial interval (ITI) between two consecutive trials.

In the second task (illustrated in Fig. 14.3), which was to achieve the second objective, there was no distraction or alteration of attention in the encoding stage; rather, we altered the attention during the maintenance stage through a combination of distraction and interruption (secondary task). Pictures were presented to participants containing red cubes; in case of distraction they must ignore, and in case of interruption they must perform a secondary task (explained below). In this task, as well as task 1, we had three (3) different levels. With respect to this explanation, the tasks were:

No distraction, no-interruption. In this case there was no distraction throughout the experiment; the result of this was used as a baseline/ reference to enable comparison with and analysis of the results of the other situations.

Explanation of timeline of tas

Figure 14.2 Explanation of timeline of task 1.Total time for one trial = 3800 ms Intertrial interval (ITI) = 2000 ms, Total time for one level (50 trials) = 3800 x 50 + 2000 x 49 = almost 5 min, Total time for task 1 = 5 x 3= 15 min (exclusive of breaks between levels).

Design of experimental task 2

Figure 14.3 Design of experimental task 2.

Explanation of timeline of task 2

Figure 14.4 Explanation of timeline of task 2. Total time for one trial = 4800 ms Intertrial interval (ITI) = 2000 ms, Total time for one level (50 trials) = 4800 x 50 + 2000 x 49 = almost 6 min, Total time for task 2 = 6 x 3 = 18 min (exclusive of breaks between levels).

With distraction only. In this case, the stimulus containing cubes (same color with the cubes presented earlier in encoding stage) was presented to participants, and they were supposed to ignore it.

With interruption only. In this case, the stimulus containing cubes (same color) was presented to participants, and they were asked to distinguish whether the number of cubes (in the VF cued at the beginning of experiment) was more or less than 6. We chose 6 because that was the number of cubes presented in the encoding stage and it is a critical number in this case (at least more critical than other numbers).

The timing information of a single trial of task 2 is explained in Fig. 14.4. There were also a total of 50 trials in task 2. Each trial started with a cue, presented for 200 ms, informing the participants to focus on a visual hemifield, either left or right. After the cue, the stimulus was presented for 300 ms (memory array) followed by a delayed period of duration of 1000 ms. In this task, the delayed period was divided into two and in the middle a distraction or interruption image was displayed for 1000 ms. Finally, the test array was displayed and the participants were required to respond by pressing a button if the test array matched with the memory array. There was a 2000-ms ITI between two consecutive trials.

Experiment Procedure

All the participants were informed of the schedule of the data collection and as per their ease, experiments were arranged individually. Each participant was seated in a partially sound-attenuated experiment room and briefed about the experimental task before performing the actual experiment. The EEG cap was set and the participant was asked to perform the actual experimental task. The cap setting required 10-15 minutes.

 
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