Table 2.
Summary of cognitive tests and outcome measures.
| Cognitive Test | Domain Assessed | Description | Outcome Measures |
|---|---|---|---|
| Spatial Working Memory (SWM)* | Working memory | Three, four, six, and eight boxes are dispersed on the screen. Subjects search for blue tokens hidden inside one of the boxes. Only one blue token is hidden at a time, without replacement (subjects must remember which boxes have produced a token). |
Between Errors**—The number of times a box in which a token has previously been found is revisited. Strategy**—The number of times the subject begins a new search with a different box for six- and eight- box trials (note that this denotes an inefficient strategy). |
| Spatial Span (SSP) (forward and reverse modes)* | Working memory | White squares (boxes) are arranged in a variable sequence on screen. Subjects touch the boxes in the order in which they changed color. The length of the sequence begins at two and increases adaptively up to nine boxes. In reverse mode, subjects touch the boxes in the reverse order that they changed color. | The longest sequence successfully recalled by the subject, calculated for both the forward and reverse modes. |
| WAIS-IV Letter-Number Sequencing | Working memory | Subjects repeat back a string of letters and numbers in numerical order, followed by alphabetical order. The number of items in a string increases from 2 to 8 letters and digits. |
Total Score—Number of items correctly reported, up to a maximum of 30. Longest—Longest string completed by a subject. |
| Reading Span | Working memory (complex test) | Subjects read aloud a series of unconnected sentences. After each sentence, subjects indicate whether the sentence made sense or not (e.g., “the girl sang a song” vs. “the train sang a song”) to prevent rehearsal of items. At the end of a series, they recall the last word of each sentence. The span of the series begins at 3 and increases to 6. |
Number of Correct Responses—This is the sum of correct responses given for whether sentences were absurd or not. This score was used for validity purposes—a score of 85% correct or greater was deemed acceptable (which all subjects achieved). This score was not used in subsequent analyses. Reading Span (Total)—Total number of words correctly recalled. Longest—The longest series for which a subject was able to recall the last word of every item in the series. |
| Semantic/Category Fluency | Category fluency/processing speed | Subjects name as many animals, fruits, or vegetables as possible within 60 s. | Total number of correct items named. |
| Paired Associate Learning Test (PAL)* | Episodic memory | Subjects are presented with two, three, six, and eight boxes displayed on the screen that open one at a time in a randomized order to reveal a pattern. Respondents must select the box in which each pattern appeared. |
Errors Adj.**—Total number of errors made, adjusting for each stage not attempted due to previous failure (the test discontinues if 10 consecutive errors are made at a stage). Errors, 8 Shapes, Adj.*—Total number of errors made at 8 shapes stage, adjusted if this stage is not reached. |
| Stop Signal Task (SST)* | Inhibition | Subjects make a two-choice button response, but withhold their response of a beep is heard on a trial. The timing of the auditory stop signal is set such that the subject is able to stop successfully approximately 50% of the time. |
Direction Errors on Stop/Go Trials**—Number of trials in which the wrong button was pressed (left button when the right arrow was shown on screen and vice versa). Proportion of Successful Stops (Last Half)—The number of times the subject stopped successfully divided by the total number of stop signals during the last half of sub-blocks. Median Correct Reaction Time on Go Trials**—Median reaction time for Go trials (trials without a beep), in milliseconds. Stop Signal Delay (50%) (last half)**—Stop signal delay at which subject was able to stop 50% of the time. Stop-Signal Reaction Time—Time taken to respond. |
| Reaction Time (RTI)* | Motor/processing speed | Subjects respond to a yellow dot appearing on the screen. In simple reaction time, the dot appears in a circle in the center of the screen, and in five-choice reaction time, the spot appears in any one of five circles located concentrically to the center of the screen. |
Five-choice Reaction Time**—Speed at which subject releases the press pad button in response to the appearance of the yellow dot during the five-choice reaction time task (speed of cognitive function). Five-choice Movement Time**—Time taken to touch the screen after the press pad button has been released during the five-choice reaction time task (speed of motor functions). |
| Rapid Visual Information Processing (RVP)* | Sustained visual attention | Digits from 2 to 9 appear in a box in the center of the screen in a pseudo-random order, at the rate of 100 digits per minute. Subjects are required to make a button press response to all of three target sequences (2-4-6, 3-5-7, or 4-6-8). | A'—A prime is the signal detection measure of sensitivity to the target, accounting for response bias. |
This table lists cognitive tests repeated across the three time points, with a brief description of each test and outcome measures used. Bolded tests assess near-transfer (i.e., working memory ability), whereas the remainder of tests assess far-transfer to other cognitive domains. Tests with
*
are taken from the Cambridge Neuropsychological Test Automated battery (CANTAB).
Outcome measures with
**
are reverse coded (such that a lower value reflects a higher score).