|
|
 |
|
| Marcello Costantini |
 |
Dip. di Psicologia, Via dei marsi 78 - 00185 Roma
e-mail: marcello.costantini@inwind.it |
Poster Presentation: |
|
| Temporal dynamics of visuo-tactile extinction within and between hemispaces. |
|
|
| The capability to detect left sided stimuli (visual or tactile) in condition of single and double simultaneous and sequential stimulation delivered in the two hemispaces (one stimulus on the right and one on the left, across the corporeal midline) or within one hemispace (either the right or the left) was studied in a group of right brain damaged patients (RBD) selected for the presence of visual and tactile extinction and in a group of healthy subjects (C). Visual stimuli were delivered through two LEDs positioned 7° left or right of a central fixation point. Tactile stimuli consisted of non-noxious electric shock delivered to the left and right index finger. Double stimuli, were always cross-modal (one visual and one tactile), and could be released across the two hemispace (bilateral stimulation) or within the same hemispace (unilateral stimulation) and could be simultaneous or sequential (at one of three possible SOAs -105, 505 and 905 msec). In sequential bilateral trials, the left sided stimulus preceded or followed the right-sided one. In sequential unilateral trials, the visual stimulus preceded or followed the tactile one. Subjects were asked to verbally report the number (1 o 2), spatial localisation (left or right) and modality (tactile, visual). In trials in which both stimuli were detected, subjects were also asked to report whether the stimuli were simultaneous or sequential and, in the latter case, which stimulus in the pair occurred first. No constraints on the response order were given. C subjects were nearly perfect in detecting single and double stimuli in all conditions and SOAs. In contrast, RBD detected single tactile and visual stimuli with high accuracy but omitted the contralesional stimulus in bilateral trials (across space, classical extinction). Moreover the contralesional tactile stimulus was omitted also in unilateral left trials ( within hemispace extinction). Both effects showed the same temporal modulation, extinction being maximal at the shortest SOAs, minimal at 505 ms and intermediate at 900 ms regardless which stimulus appeared first. These results confirm that extinction may be due to attentional imbalances which bias the competition in favour of the ipsilesional stimulus. Moreover, results suggest that attentional processing of the visual stimulus inhibits processing of the tactile one even within the same, contralesional hemispace thus indicating that vision predominates over touch in tasks requiring bimodal integration in the space around the body. |
|
|
 |
|
|
|
