Preliminary data from the Dyad-Adaptive PASAT

The Paced Auditory Serial Addition Test (PASAT) is a neuropsychological
assessment that is widely used to evaluate processing speed and executive
function in patients with multiple sclerosis, traumatic brain injury, and other
neuropsychiatric disorders. In the PASAT, subjects listen to sequences of
digits while continuously reporting the sum of the last two digits presented. Four
different stimulus onset asynchronies (SOAs) are usually tested, with
difficulty increasing as SOAs are reduced. Ceiling effects are common at long
SOAs. In contrast, the digit delivery rate often exceeds the subject’s
processing capacity at short SOAs, resulting in frustration and stress and causing
some subjects to stop performing altogether. In addition, subjects may adopt an
“alternate answer” strategy at short SOAs, which reduces the test’s demands on working-memory
and processing speed. Consequently, studies have shown that the number of dyads
(consecutive correct answers) is a more sensitive measure of PASAT performance than
the overall number of correct sums. Here, we describe a 2.5-minute computerized
test, the Dyad-Adaptive PASAT (DA-PASAT), where stimulus onset asynchronies
(SOAs) are adjusted based on dyad accuracy and processing capacity is reflected
in the minimum SOA (minSOA) achieved in 54 trials. Experiment 1 gathered
normative data in two large populations: 1617 subjects in New Zealand ranging
in age from 18 to 65 years, and 214 Californians ranging in age from 18 to 82
years. Minimum SOAs were influenced by age, education, and daily hours of
computer-use. Minimum SOA z-scores, calculated after factoring out the
influence of these factors, were virtually identical in the two control groups,
as were response times (RTs). The dyad ratio (the proportion of hits occurring
in dyads) averaged 0.93 in both experiments. Experiment 2 measured the test-retest
reliability of the DA-PASAT in 44 young subjects who underwent three test
sessions at weekly intervals. High intraclass correlation coefficients (ICCs) were
found for minSOAs (0.87), response times (0.76), and dyad ratios (0.87). Performance
improved across test sessions for all measures. Experiment 3 investigated the
effects of simulated malingering in 50 subjects: 42% of simulated malingerers
produced abnormal (p< 0.05) minSOA z-scores. Simulated malingerers with
abnormal scores were distinguished with 87% sensitivity and 69% specificity
from control subjects with abnormal scores by differences between performance during
training and during the actual test. Experiment 4 investigated patients with
traumatic brain injury (TBI): patients with mild TBI performed within the
normal range while patients with severe TBI showed deficits. The DA-PASAT reduces
the time and stress of PASAT assessment while gathering sensitive measures of
dyad processing that reveal the effects of aging, malingering, and traumatic
brain injury on performance.