Visuospatial attention in cerebral palsy: an eye movement study

The tight link between visuospatial attention and eye movements has been well-established from behavioral and neurophysiological studies. Moreover, neuroimaging evidence strongly supports the hypothesis that oculomotor areas provide signals for overt and covert shifts of attention. However, albeit in a more complex way, visuospatial attention interacts also with other goal-directed motor systems, such as those controlling limbs for common visually-guided tasks (e.g., ambulation or pointing, reaching and manipulating salient objects). Furthermore, early motor deficits might affect the development of the attentional system. In the present study we tested visuospatial attention abilities in 7 children (5 males, mean age: 11.6 years) with cerebral palsy (CP), which is one of the most common cause of physical disability in childhood. All CP subjects suffered from spastic hemiplegia or diplegia. Visuospatial attention was investigated by recording eye movements while subjects executed visually-guided saccades randomly towards one of 4 possible positions marked by placeholders equally distributed around a central fixation cross. A cueing paradigm was also administered: a placeholder flashed for 50 ms (cue) at the same spatial position of the target (valid condition), or at a different location (invalid condition). The visual cue did not predict the position of the target, whose onset occurred 150 ms later. Saccade latency and accuracy of CP subjects were compared with those of a typically developing (TD) reference group of 13 participants (mean age: 12.3 years). On average, CP and TD subjects showed a similar performance in the saccadic task, being both groups quick to react to the onset of the visual target. Moreover, in the spatial cueing task, a coupling between the task-irrelevant location of the cue and the direction of a following overt shift of attention emerged, being saccadic latencies of CP and TD subjects faster to valid targets. However, PC children were more frequently (on mean, in 30% of trials) attracted by the onset of the cue, suggesting the tendency to execute ocular movements towards the target of the exogenous attention. Furthermore, during the fixation of the central cross, the CP group often performed saccadic intrusions, which were always aimed at orienting the gaze to one of the placeholder. This occurred irrespectively of whether CP children executed the saccadic or the cueing task and clearly shows a difficulty of patients to suppress overt ocular movements towards the target of the endogenous attention. From a clinical perspective, the present work encourages efforts to design reliable procedures, using eyetracking techniques combined with cognitive protocols, aimed at improving the assessment of people suffering from motor impairments, in the field of neuropsychological, neurological and psychiatric aspects. Indeed, motor deficits make often difficult to apply procedures typically employed by clinicians and cognitive neuropsychologists, like paper-and-pencil tests or manual reaction time paradigms. This represents a crucial limitation in the diagnostic and rehabilitative fields considering that the brain damage that leads to CP, as well as to other neurological disorders affecting muscle tone, movement and motor skills, is usually accompanied by other deficits including visuospatial attention abilities.