Is the hemispatial deficit produced by right parietal lobe damage associated with retinal or gravitational coordinates?

The hypothesis that right posterior parietal lesions cause two attentional deficits, namely, a reduced reactivity to stimuli in the left visual field (LVF), and a reduced reactivity to any stimulus which occupies a relative left position, was tested in 8 patients with an extinction syndrome. In Experiments 1 and 2 the first hypothesis was tested by measuring reaction times (RTs) to visual stimuli presented in the LVF and in the RVF, whereas the second hypothesis was tested by measuring RTs to stimuli totally positioned in the LVF, and in the RVF. The results showed that RTs to stimuli which occupied a relative left position were longer than RTs to stimuli which occupied a relative right position independent of the visual field stimulated and RTs to LVF stimuli were longer than RTs to RVF stimuli. Experiment 3 was designed to examine whether the attentional deficit associated with right parietal damage was mostly related to the use of gravitational rather than to retinal coordinates. In this experiment the patients tilted the head either to the left or the right by 90 deg and they responded to two stimuli displayed above and on either side of a fixation mark. The results showed that the difficulty in attending to the left was related both to the gravitational and the retinal frames of reference.