Quantifying the Use of Space in the Clock Drawing Test: Validity in Hemispatial Neglect.

Objective: The Clock Drawing Test (CDT) is a widely used test for cognitive screening as its execution taps into a large number of cognitive functions. Because of the involvement of visuospatial abilities, the CDT is also commonly used to assess hemispatial neglect. In the present study, we introduce a new quantitative scoring method for the CDT that aims to measure the use of space for each half of the clock face and asymmetries of space use.

Method: Two measures are introduced: the explored space (ES) and used space (US) for each half of the clock, as well as two derived asymmetry indices. Such new measures were applied to CDTs of four groups of participants: right brain-damaged patients without visuospatial neglect, two groups of right brain-damaged patients with varying degrees of visuospatial neglect, and a group of neurologically healthy participants.

Results: Analyses showed that only neglect patients explored and used the left clock half significantly less than the right one. This result was also confirmed by the asymmetry indices, where neglect patients showed a stronger rightward bias. For neglect patients, the US asymmetry index correlated with the patients' scores on the neuropsychological tests. The analyses of receiver operating characteristic curves showed that left US and left ES scores had good accuracy in categorizing neglect patients.

Conclusions: The present work provides new quantitative indices of CDT space usage in hemispatial neglect. Cutoffs are provided for clinical practice.