Directional Bias in Line Orientation Test Errors in Parkinson's Disease

Value in evaluating error subtypes on visuospatial line orientation tests has been reported. Directional bias metrics for line orientation test errors represent easily quantifiable data that have not previously been studied. We evaluated whether patients with a clinical condition known to affect visuospatial functioning (Parkinson's disease [PD]) exhibited unique directional error patterns on the RBANS Line Orientation test relative to other neuropsychology-referred patients.

We compared overall directional bias in errors, directional bias by line location (left or right line and visual field), and absolute error rates (regardless of direction) by line location in a retrospective sample of patients with PD and a sample of neuropsychology-referred patients without PD. Groups were roughly matched on age, education, gender, and overall level of cognitive impairment.

Patients with PD exhibited higher rates of leftward bias in errors, both overall and for the left stimulus line in each pair. Directional bias error scores better predicted PD versus non-PD group status than RBANS Line Orientation raw scores. Classification accuracy data for these variables were modest in the entire sample but stronger in a subsample of patients with mild levels of overall cognitive impairment.

Directional bias metrics for line orientation tests represent easily quantifiable data with potential theoretical and clinical value. In our sample, patients with PD made more left-biased line orientation errors than other neuropsychology-referred patients. By themselves, directional bias scores may have limited diagnostic potential, but they may be useful in diagnostic classification models and may have implications for clinical care.