CONTRIBUTIONS OF THE PARIETAL AND FRONTAL LOBES TO SUSTAINED ATTENTION AND HABITUATION

The parietal cortex may be important in sustaining attention toward vi sual stimuli in peripheral space whereas the frontal cortex map mediat e selective attention through habituation to peripheral stimuli. To te st this hypothesis, patients with focal lesions of either the parietal or frontal cortex or both and normal controls were studied using a pa radigm known as Troxler fading. Accordingly, if one fixates on a centr ally located stimulus and attends to a stationary stimulus in peripher al vision, the peripheral stimulus quickly fades from awareness (i.e. Troxler fading: TROXLER [Verschwinden, unseres, Opthal, Vol. 2, pp. 51 -53. Fromann, Jena, 1804]). Movement of the peripheral stimulus on the retina normally prevents Troxler fading. Results indicated that patie nts with parietal lesions not only reported accelerated Troxler fading but also reported fading of moving peripheral stimuli contralateral t o their brain lesion. In contrast, patients with frontal lesions rarel y reported Troxler fading. In one patient with a left parietal and a r ight frontal lobe lesion fading was hemi-spatially dissociated, being accelerated in right hemispace but absent in left hemispace. These obs ervations suggest that the parietal and frontal cortices play compleme ntary roles in attentional processing.