The critical concept is below-chance performance. On a two-alternative forced-choice task a patient with genuinely absent memory would guess and score approximately 50 percent; scoring 6 of 30 and 2 of 10 is significantly below chance, which can only be achieved by knowing the correct answer and avoiding it. The coin-in-the-hand test was designed as a simple bedside test of this principle for patients with claimed memory disorder, and even patients with severe genuine amnesia score close to ceiling on it because the task is extremely easy.
The approximate answers, giving "five" for the number of legs of a horse and "5" for 2 plus 2, are Vorbeireden, the near-miss answers of Ganser syndrome. Answers that are close to but not the correct answer require intact knowledge of the correct answer, and this phenomenon is regarded as a marker of factitious behaviour rather than as a manifestation of a functional or organic amnesia. Both findings therefore point away from a genuine memory disorder and toward invalid effort in a medicolegal context.
Performance validity testing and Ganser phenomena are fellowship-level neuropsychiatry and neuropsychology, placing this item at the Subspecialty level of RITE content. Note that failure of effort testing does not establish conscious motive, and that invalid effort can coexist with genuine impairment.
Incorrect Answers
- B. Diffuse axonal injury severe enough to cause profound amnesia would follow a major trauma with prolonged loss of consciousness and abnormal imaging, and would not produce below-chance performance.
- C. Transient global amnesia lasts under 24 hours, spares personal identity, and is characterized by repetitive questioning rather than by failed forced-choice tasks.
- D. Semantic dementia degrades knowledge symmetrically and progressively with anomia and surface dyslexia; patients do not systematically choose the wrong forced-choice option.
- E. Korsakoff syndrome produces anterograde amnesia with confabulation and a history of chronic alcohol use or malnutrition, and performance on forced-choice tasks remains at or above chance.
Testing Pearls
- Below-chance forced-choice performance requires knowledge of the correct answer.
- The coin-in-the-hand test is a simple bedside performance validity measure.
- Patients with severe genuine amnesia perform near ceiling on the coin-in-the-hand test.
- Ganser approximate answers are considered a marker of factitious behaviour.
- Failed effort testing does not prove motive and can coexist with genuine impairment.
References
- Jankovic J, Mazziotta JC, Newman NJ, Pomeroy SL, editors. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022. p. 2086.
- Kapur N. The coin-in-the-hand test: a new "bed-side" test for the detection of malingering in patients with suspected memory disorder. J Neurol Neurosurg Psychiatry. 1994;57(3):385-386.
- Bass C, Halligan P. Factitious disorders and malingering: challenges for clinical assessment and management. Lancet. 2014;383(9926):1422-1432.
