Touch-screen system for assessing visuo-motor exploratory skills in neuropsychological disorders of spatial cognition

A new computerised test adopting touch-screen technology has been developed to assess the visuo-motor exploration of extra-personal space. The test was derived from well-known paper-and-pencil cancellation tasks used widely in the diagnosis and quantitative assessment of unilateral spatial neglect (USN), a neuropsychological syndrome that is more frequent and severe after damage to the right cerebral hemisphere. A main component deficit of USN is the defective visuo-motor exploration of the side of space contralateral to the side of the lesion (contralesional), namely, in right-sided brain-damaged patients it occurs on the left side and vice versa. The computer-based paradigm consisted of a visuo-motor spatial exploratory task: the subjects were instructed to touch, in any order they wished, all the targets they detected on a computer touch-screen. This measured the time of occurrence and the spatial co-ordinates of each touch event and forwarded the data to the computer for storage; the computer provided feedback to the subject by 'tagging' the touched target. The paradigm allowed the calculation of accuracy and latency indexes and recorded the exploratory pathway taken by each subject. A pilot study was performed in ten normal subjects and 15 brain-damaged patients, with and without psychometric evidence of USN; the results showed that the equipment was able to provide quantitative indexes related to the spatial-temporal aspects of exploratory ability, which are useful for diagnostic purposes, and revealed significant differences between the controls and patients with USN: the overall average values of latency and crossing indexes increased in patients with USN, compared with the controls (latency from 0.77 to 1.90s; path crossing index from 7.0% to 59.5%), and the significantly negative USN patient latency gradient (-2.79 against a null control value) evidenced a worsening of performance towards the left side.