FEATURE INTEGRATION IN CHILDREN WITH EARLY BRAIN DAMAGE : MEDICAL PSYCHOPHYSICS AND BRAIN IMAGING

We psychophysically examine feature integration in patients with brain damage of very early origin. Paticipants were patients (aged 14-16 yrs) with mild and severe periventricular leikomalacia (PVL) over the parieto-occipital area born at 27-33 weeks of gestation and two groups of healthy controls (preterms without PVL and fullterms) matched for age, gender and parental occupational status. They were shown point-light biological motion. Half the stimuli represented an 11-dot point-light walker embedded in a 44-dot simultaneous mask, while the other half were 55-dot masks. In a confidencerating procedure, participants judged the presence of a walker. ROC-analysis indicates higher susceptibility of patient’s visual system to camouflage of a point-light figure. Sensitivity in fullterm controls as well as in preterms without PVL was equally high, and significantly better than detection by patients. The findings indicate that specific visuoperceptual deficits for preterms with bilateral parieto-occipital PVL can be revealed in middle childhood. This points to some restrictions in the spontaneous compensatory potential of the brain with early bilateral periventricular lesions. Although recent theoretical framework and experimental findings help to recognize a great compensatory potential of the human developing brain, the mechanisms of the spontaneous compensatory plasticity and, in particular, limitations on it are still largely unknown. This is especially true for the case when damage of the functionally relevant brain regions are prenatal or of very early origin, and symmetrical, i.e. equally involve both brain hemispheres (Kr geloh-Mann, Toft, Lunding, et al., 1999). Here we tested (i) whether patients born preterm with bilateral periventricular lesions, namely, with periventricular leukomalacia (PVL) over the parieto-occipital area, exhibit specific pattern of visuo-perceptual deficits, and (ii) whether these deficiencies can be revealed in middle childhood. Clinical diagnostic procedures routinely applied to detect the visuo-perceptual deficits are confined to either low-level visual tasks (e.g., visual acuity measurements) or standard psychometric tests. The disadvantage of such approaches is that both low-level visual performance and the results of cognitive tests fail to account for difficulties on "intermediate" visual-perceptual tasks. Apparently, preterm children have difficulties in building coherent Gestalt-like representations, although they demonstrate unimpaired ability to detect even very small details (Jacobson, Lundin, Flodmark, & Ellstr m, 1998). For testing Gestalt-formation in preterm children, we suggest using impoverished point-light biological motion stimuli. Although in such a display only a few moving dots are visible, by the age of 5 years children without a history of neurological disorders reach a ceiling level for recognition of a noncamouflaged point-light figures (Pavlova, Kr geloh-Mann, Sokolov, & Birbaumer, 2001). On the other hand, deficits in higher cognitive functions affects interpretation of point-light displays very little: Adolescents with impairments in high-level symbolic processing need only very brief exposure to recognize human figures in point-light displays (Moore, Hobson, & Anderson, 1995). In the present study, by using a simultaneous masking paradigm, we psychophysically examined the susceptibility of the visual system to distortions caused by camouflaging biological motion. The mature visual system robustly tolerate such distortions (e.g., Neri, Morrone, & Burr, 1998; Pavlova & Sokolov, 2000). We hypothesize that if preterms with parieto-occipital PVL have specific perceptual deficits, their sensitivity to a point-light walker embedded in a moving-dot mask would be lower than in fullterm controls. Moreover, if these deficits relate to the brain damage, the detection by preterms with PVL would be significantly worse than by preterms without brain lesions. We also examined whether even mild periventricular bilateral damage of the functionally relevant brain regions (mild parietooccipital PVL) lead to a reduction of sensitivity.