The letter memory test (LMT) is a computerized forced-choice test of malingering detection including two face valid difficulty manipulations: increase in target stimulus length and increase of response foils. Prior research suggests the LMT shows promise as a malingering detection measure. In the present study, the utility of the LMT in the identification of malingering was further explored, using a counterbalanced design in a simulated malingering sample. Prior work was extended by assessing the robustness of the LMT to coaching and assessing the effectiveness of an additional scoring method, utilizing the face valid difficulty manipulations. Results were consistent with prior research on the LMT, with the standard cutoff score yielding high indices of accuracy. The LMT showed no order effects and was superior to the 15-item test in accuracy indices. Both the standard LMT score and the proposed score based on difficulty manipulations were relatively robust to coaching. Overall, findings indicate the LMT is a viable contender among measures of memory malingering.
Malingering of cognitive impairment remains a significant problem in neuropsychological practice. The most popular malingering detection method in clinical practice is the forced-choice paradigm, in which a respondent with no exposure to the target stimulus has a 50% chance of accurately selecting it. However, as performance significantly below chance has poor sensitivity to malingering and multiple studies have demonstrated very high scores on forced-choice tasks, even in patients with severe memory impairment, most forced-choice measures have identified cutoff scores that are more sensitive to malingering, but still adequately specific. A number of forced-choice tests are available for use and vary slightly in terms of type of target stimulus presented, number of items, interval between stimulus and response choices and number of foils presented; generally these tests have yielded good indices of accuracy when comparing a variety of different groups (Inman & Berry, 2002; Orey, Cragar, & Berry, 2000; Strauss et al., 2002; Tan, Slick, Strauss, & Hultsch, 2002; Vickery, Berry, Inman, Harris, & Orey, 2001). A recent addition to malingering detection research is the letter memory test (LMT: Inman et al., 1998). The LMT presents stimuli synthesized from the first 10 consonants of the alphabet. Each target stimulus is presented for 5 s, followed by a 5 s delay. The examinee is then presented with the target stimulus and one or more foils. Stimulus length varies from 3, 4 or 5 letters and response foils vary from 1, 2 or 3 options in addition to the target stimulus. The increase in target stimuli length and number of foils were meant to counteract subject identification of the difficulty level for each item, which may lead examinees to perform more poorly on items that superficially appear more difficult. Inman and Berry (2002) found that an LMT cutoff score of cutoff score of <93% correct resulted in 100% specificity, 73% sensitivity and 87% overall hit rate; in comparison to the digit memory test, the LMT provided a higher sensitivity rate. Using the same cutoff, Orey et al. (2000) yielded a sensitivity of 58% and a specificity of 100%; in comparison to the digit memory test, Portland digit recognition test and LMT, the researchers found the LMT to have the highest sensitivity. To our knowledge, the LMT has only been examined by its authors. Given this, the LMT warrants further study by an independent research laboratory. One major purpose of the present study was to provide further information on the effectiveness of the LMT in malingering detection.
