Visual deficits in early and high level processing nodes have been documented in Parkinson’s disease (PD). Non-motor high level visual integration deficits in PD seem to have a cortical basis independently of a low level retinal contribution. It is however an open question whether sensory and visual attention deficits can be separated in PD. Here, we have explicitly separated visual and attentional disease related patterns of performance, by using bias free staircase procedures measuring psychophysical contrast sensitivity across visual space under covert attention conditions with distinct types of cues (valid, neutral and invalid). This further enabled the analysis of patterns of dorsal–ventral (up–down) and physiological inter-hemispheric asymmetries. We have found that under these carefully controlled covert attention conditions PD subjects show impaired psychophysical performance enhancement by valid attentional cues. Interestingly, PD patients also show paradoxically increased visual homogeneity of spatial per- formance profiles, suggesting flattening of high level modulation of spatial attention. Finally we have found impaired higher level attentional modulation of contrast sensitivity in the visual periphery, where mechanisms of covert attention are at higher demands. These findings demonstrate a specific loss of attentional mechanisms in PD and a pathological redistribution of spatial mechanisms of covert attention.

This research was funded by grants from the Portuguese Science and Technology Foundation (FCT): PTDC SAU NEU 68483 2006, PTDC PSI 67381 2006 and PIC IC 82986 2007, as well as by the National Brain Imaging Network of Portugal (BIN).

Visual impairment,covert attention,visual integration,Parkinson’s disease,Visual dorsal stream,parietal cortex,Inter-hemispheric asymmetries,Spatial processing

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