Executive Function in Autism Spectrum Disorder

1. Participant recruitment

1. Autistic population recruitment
   1. Recruit 40 participants, aged 6-18 years, with autism spectrum disorder. Diagnosis of autism can be verified using the Autism Diagnostic Interview-Revised³ and the Autism Diagnostic Observation Schedule.⁴
2. Control population recruitment
   1. Recruit 40 participants aged 6-18 years, who are matched in age and intellect with the autistic participant population.
3. Make sure that the participants have been fully informed of the research procedures and have signed all the appropriate consent forms.

2. Data collection

Figure 1. Four stimulus cards presented on the computer screen. These cards are used as the categories to match each of the 64 cards from the deck. Cards can match based on three rules: number, color, and/or shape.

1. Wisconsin Card Sorting Test (WCST)
   1. Have the participant sit at a table in front of a computer.
   2. Tell the participant that the game requires the matching of a single card to one of four cards displayed at the top of the screen (Figure 1).
      1. After matching each card, the participant is informed if the correct or incorrect decision was made, based on if they guessed the rule correctly or not (the rules are predetermined for each card match).
      2. The rule is applied for a run of trials (10 correct card placements) and then changed without warning.
   3. Tell the participant:
      1. You have four cards placed face up and a pack of 64 cards to match to them.
      2. There is a rule for matching the cards and you will need to guess what it is.
      3. Your task is to choose which card matches your card, based on the rule in place.
      4. You will be told "correct" or "incorrect."
      5. You can take as long as you like for each decision, but may not change your mind.
      6. You should attempt to get as many right as possible.
      7. From time to time, the rule will change without you being told. You will then need to discover the new rule.
   4. End the task when rules have been followed for 10-card turns six times, or when all 64 cards have been placed.
2. Tower of London (ToL)
   1. The participant sits at a table in front of a computer.
   2. The computer screen shows a starting configuration of three colored balls that are arranged in a pattern on three different pegs. The screen also shows a goal configuration in which the balls have been re-arranged into a new configuration on the pegs.
   3. Tell the participant:
      1. Preplan a series of moves to reconfigure the start set of balls to the goal set (Figure 2).
      2. Execute the moves one by one, using the computer mouse, using as few moves as possible.
      3. There is no time limit, but once a ball is moved, the move cannot be undone.
   4. End the task when the participant has completed 20 trials.

Figure 2. Tower of London: Starting and final position of the colored balls on the three pegs. Participants are instructed to move balls from a prearranged sequence on three different pegs to match a goal state in as few moves as possible.

3. Stroop task
   1. The participant sits at a table in front of a computer.
   2. Tell the participant:
      1. A word will appear on the screen. Please say the color that the word is written in (Figure 3).
   3. Present 120 trials, consisting of equal numbers of congruent and incongruent trials.
   4. On each trial, present one of four color words (red, blue, green, or yellow) on the screen for 4.0 s or until a response is made. On half of the trials the ink color matches the word (congruent trials), while on the other half of the trials the ink color does not match the word (incongruent trials).
   5. Wait 1.5 s between each stimulus, and do not repeat the color name or presentation color from one trial to the next.
   6. The experimenter records if each response is correct or incorrect. Incorrect responses will be excluded from the reaction time analysis.

Figure 3. Stroop Test: Examples of a congruent and incongruent stimulus, with correct responses. Participants are instructed to verbally say the color of the word presented.

3. Data analysis

1. The WCST is scored by the computer according to the WCST manual.⁵
   1. For this study, the primary index of executive dysfunction used is the number of perseverative responses in which the participant continued to sort based on the previously correct rule despite feedback that it was incorrect.
2. The computerized version of the ToL is scored automatically based on: time spent preplanning, mean move times, number of moves made, and number of trials solved in the minimum number of moves possible.
   1. For this study, the primary index of executive dysfunction used is number of excess moves, which counts the number of moves made beyond the minimum required to solve the puzzle.
3. The computerized version of the Stroop test is scored automatically by recording the time of onset of the spoken color name.
   1. The average reaction time for congruent trials is subtracted from the average reaction time for incongruent trials for each participant, excluding incorrect responses.
4. A t-test can be used to test differences in these scores between autistic and control participants.