WAIS Processing Speed Index (PSI) 3 — Questions and Answers
Question 1: Which of the following BEST describes what the Coding subtest measures within the PSI?
- Verbal fluency under time pressure
- Psychomotor speed and visual-symbol association learning (Correct answer)
- Spatial rotation ability
- Auditory working memory
Correct answer: Psychomotor speed and visual-symbol association learning
Coding measures how quickly and accurately a person can copy symbols paired with numbers, tapping psychomotor speed and associative learning.
Question 2: When interpreting a low PSI in a child transitioning to adult norms, the clinician should FIRST consider:
- Whether the subtest scores within the PSI are consistent with each other (Correct answer)
- Replacing the PSI with the Processing Speed Quotient
- Disregarding the index because it is unreliable
- Administering only verbal subtests
Correct answer: Whether the subtest scores within the PSI are consistent with each other
Checking subtest scatter within the PSI determines whether the composite is a valid summary of the domain.
Question 3: A clinician suspects ADHD in an adult. Which PSI pattern would be MOST consistent with inattention rather than motor slowing?
- Low Coding but average Symbol Search
- Low Symbol Search but average Coding (Correct answer)
- Both subtests equally depressed
- Both subtests above average
Correct answer: Low Symbol Search but average Coding
Selectively low Symbol Search with preserved Coding suggests attentional scanning difficulties rather than generalized motor slowing.
Question 4: The PSI composite is computed by summing scaled scores and converting to a standard score with mean 100 and SD of:
Correct answer: 15
Like all WAIS index scores, the PSI has a mean of 100 and a standard deviation of 15.
Question 5: Traumatic brain injury (TBI) most consistently impairs which WAIS index first and most severely?
- Verbal Comprehension Index
- Perceptual Reasoning Index
- Working Memory Index
- Processing Speed Index (Correct answer)
Correct answer: Processing Speed Index
TBI reliably and disproportionately reduces processing speed, making PSI the index most sensitive to acquired brain injury.
Question 6: Which statistical concept explains why a very low PSI can lower the Full Scale IQ even when other indexes are average?
- Regression to the mean
- Composite averaging across indexes (Correct answer)
- Floor effects
- Practice effects
Correct answer: Composite averaging across indexes
The FSIQ averages contributions from all four indexes, so a depressed PSI pulls the overall composite downward.
Question 7: On the Coding subtest, what is the primary reason examinees are given a sample practice row before the timed portion?
- To allow the examiner to score the practice items
- To ensure the examinee understands the symbol-digit key before timing begins (Correct answer)
- To provide a baseline for regression analysis
- To screen for color blindness
Correct answer: To ensure the examinee understands the symbol-digit key before timing begins
The practice row ensures comprehension of the task so that the timed score reflects processing speed, not confusion about instructions.
