Impairments in top down attentional processes in right parietal patients: paradoxical functional facilitation in visual search.

It is well known that the right posterior parietal cortex (PPC) is involved in attentional processes, including binding features. It remains unclear whether PPC is implicated in top-down and/or bottom-up components of attention. We aim to clarify this by comparing performance of seven PPC patients and healthy controls (HC) in a visual search task involving a conflict between top-down and bottom-up processes. This task requires essentially a bottom-up feature search. However, top-down attention triggers feature binding for object recognition, designed to be irrelevant but interfering to the task. This results in top-down interference, prolonging the search reaction time. This interference was indeed found in our HCs but not in our PPC patients. In contrast to HC, the PPC patients showed no evidence of prolonged reactions times, even though they were slower than the HCs in search tasks without the conflict. This finding is an example of paradoxical functional facilitation (PFF) by brain damage. The PFF effect enhanced our patients' performance by reducing the top down interference. Our finding supports the idea that right PPC plays a crucial role in top-down attentional processes. In our search tasks, right PPC induces top-down interference either by directing spatial attention to achieve viewpoint invariance in shape recognition or by feature binding.