Neuropsychology of 3D space

Spatial behaviour refers to all interactions humans can have with objects in
space. Space, however is not a unitary entity. A division has been suggested
between near space (within reaching distance) and far space (beyond reaching
distance). Specific impairments in neurological patients (with temporal or
parietal brain lesions) related to the representation of either far or near
space have been suggested recently, yet most research and rehabilitation
focuses on near space only, thus missing and failing to ameliorate impairments
in far space. The aim of the current proposal is therefore to specifically
investigate spatial behaviour in near as well as far space in the
abovementioned patients.

* Far space is argued to be important in orienting and navigating, has a
gaze-centered frame of reference and uses mainly visual and auditory input, and
has been linked to processing in the superior temporal region.

* Near space, on the other hand, is important in reaching, grasping and
manipulating objects, has an egocentric frame of reference, employs mainly
visual and somatosensory input, and has been associated with processing in the
inferior portion of the posterior parietal lobe.

This distinction would suggest that lesions in either the temporal or parietal
region would lead to impairments in processing of information in one of both
regions of space. Impairments in behaviour after stroke, however, are usually
only (neurologically, neuropsychologically) screened and investigated in near
space, thereby systematically missing possible impairments in far space
processing.

The aim of the current proposal is therefore to specifically investigate
spatial behaviour in near as well as far space in the abovementioned patients;
first, a neuropsychological screening will be performed, both in near and far
space; second, patients will be invited to participate in experimental trials.
Dissociations and interactions between near and far space will thus be
investigated.

The first line of research encompasses the frequency, severity, and
(dis)similarities of perceptual and attentional impairments in near and far
space. Differential impairments of near and far space processing are more
likely to be found when spatial performance of a large group of neurological
patients is tested at different distances in space. Neuropsychological
screening of all cognitive domains (but particularly visuo-spatial attention
and neglect) will be performed. Neuropsychological screening usually focuses on
near space only, thus will be expanded to include (visual) stimuli presented in
far space as well. Stimuli for the screening (and all experiments) will be
presented at multiple distances to measure processing information in near and
far space.

Patient will additionally be invited for scientific experiments, such as visual
search and cross-modal cueing and integration (see below). All experiments will
be performed in near and far space. Based on their performance in the near
versus far space conditions, patients will be grouped. Lesion overlap analyses
will be performed to look into the neural mechanisms underlying processing in
the different regions of space. Common lesion locations in patients with
specific impairments in near space or far space will be observed.

Last, plasticity of near and far space will be investigated. It has been found
that the use of tools can enlarge near space, as it enlarges reaching distance.
Here, tools (e.g. pointing and griping devices) will be used to investigate the
possibility of extending near space in neurological patients. It is expected
(for instance) that when patients with specific impairments in far space use a
pointing device, impairments in far space may be ameliorated.

All patients with parietal and temporal lesions will start with a
neuropsychological screening in which all cognitive domains will be
investigated. Standard neuropsychological test will be digitalised and adapted
for far space presentations, such that the visual angle of all stimuli will
remain the same for near and far space presentations. Special attention is
given to hemispatial neglect, a disorder in which patients systematically
ignore information in the contralesional side of space. Neglect has been
associated with parietal or temporal lesions.

Patient will additionally be invited for scientific experiments to investigate
specificity of information processing in near and far space. One of the
experiments will be visual search, in which patients have to search for a
target among distractors. Presentation of the stimuli will be in near as well
as far space and dissociations in search behaviour will as such be obtained.

For the added multisensory integration paradigm, the general idea of our
stimulation is that we use a multisensory-defined (visual and audible) object
that moves from the unaffected visual hemifield into the neglected hemifield.
We will present a multisensory object in the intact field which moves towards
the neglect field. Once the object enters the neglected visual field it either
goes upwards or downwards. The task of the patient is to say whether the object
goes up or down. To be able to induce a multisensory aspect of the object we
use a looming object. The size of the object grows and shrinks with a frequency
of * Hz (once every four seconds). The magnitude variation of the sound must be
synchronous (also once every four seconds). When the variation in sound and the
size of the object are congruent, patients will be better in detecting the
direction of the moving object, compared to no sound or an incongruent sound.

Based on their performance in the near versus far space conditions, patients
will be grouped. Lesion overlap analyses will be performed to look into the
neural mechanisms underlying processing in the different regions of space.
Common lesion locations in patients with specific impairments in near space or
far space will be observed.

Burden and risks are very limited.