Working memory
cognitive impairment
We measured the working memory through the digit span test (DST) with forward digit span (DS-forward) and backward digit span (DS-backward). A string of numbers starting with two digits and then gradually increasing in length are read to the participants. The test was performed twice. The participants listened carefully to one string of random numbers per second. The DS-forward assessment required the participants to repeat the numerical strings in the exact order, and the DS-backward required the participants to repeat the number strings in reverse order. These types of tests are commonly used to assess defects in short-term memory capacity. DST forward and backwards tests can quickly and easily measure performance in short-term memory capacity, providing a basis for diagnosis, and are a widely accepted, research-proven method to measure mild cognitive impairment. The test had no time limit and exhibited favourable internal consistency (0.85-0.99) and test-retest reliability (0.75-0.99) [