Fig. 1.

The percentage of subjects passing each stage of the IDED. All 29 patients (•) and 33 healthy volunteers (□) managed the test up to the ED stage, i.e. no difficulties were present at the intradimensional shift stages. There was a trend (ξ² = 3.3, p < 0.07) that fewer patients (55.1%) completed the whole test when compared to the controls (78.7%). Thus, most participants failed at the ED stage – except 1 patient who failed only at stage 8. The stages are simple discrimination (SD), simple discrimination reversal (SR), compound discrimination stages (C/D and CD), compound discrimination reversal (CDR), intradimensional shift (IDS), intradimensional shift reversal (IDR), extradimensional shift (EDS), and extradimensional shift reversal (EDR).