The Visual Scanning Test: a Neuropsychological Tool to Assess Extrapersonal Visual Unilateral Spatial Neglect

Unilateral spatial neglect (USN) represents one of the most frequent and disabling neuropsychological consequences of acute brain damage. Patients with USN show an impaired ability to perceive sensory events and to perform actions in the contralesional side of the space, in absence of a lower-level sensory or motor deficit. Several studies found that controlesional USN is more frequent and more severe in right than left parietal damage and due to its prominent impairment, USN has broadly been studied in the visual modality (VUSN). VUSN can affect patient's own contralesional body (personal neglect), into the near space within reaching distance (peripersonal) or space beyond reaching distance (far extrapersonal space). Those portions of space may dissociate and patient may show extrapersonal VUSN without alterations on the other portions of space (i.e. personal and peripersonal). Traditional paper-and-pencil neuropsychological tests are useful and widely used to evaluate VUSN, even if several of them can provide an assessment of peripersonal VUSN. In fact, this portion of space can be assessed through line bisection, cancellation, or copy tasks which are normally completed within reaching distance. Instead, personal and extrapersonal neglect are less easily evaluated: this lack of assessment tools may lead to lower detection rates for USN in patients in clinical setting and lead to relevant clinical implications. Finally, paper-and-pencil tests can detect only a moderate or even severe deficit due to VUSN but not a mild impairment and they are not informative about patients' disability in natural setting. According to this limitations of traditional paper-and-pencil tests, several studies have shown that computerized reaction time tasks are more sensitive in the detection of lateralized spatial attention deficits in patients with mild or remitted VUSN. The primary aim of this study was to present and standardize a new neuropsychological tool to provide a quantitative assessment of VUSN in the extrapersonal portion of space.

The Visual Scanning Test (VST) involved a visual search for a target between similar visual distractors, projected in the far space, so as to simulate the search within a visual field. It is overall composed by four trials, each trial contained 20 cases and made up by 20 stimuli. On about the 80% of cases, the test provided the presence of target in the left, center or in right hemispace. In the remaining 20% of cases, the test provided the presence of a catch trial (absence of the target), to assess the presence of frontal disturbances or malingering. The test is constructed according to an increasing attentional load for the target on the left-hemispace. Participants, sitting in front a blank wall, were required to actively and free explore the projected visual field to search for the visual target, naming its identification (saying YES or NO). During the task, the examiner annotated the reaction times and the errors. From these data it was possible to get some informative indexes regarding the reaction times, the accuracy and the implicit learning of the progressive shift to the left of the target and the possible presence of asymmetry in the visual exploration.