Jacques Luauté, Annabelle Blangero, Heiner Deubel, N. Laverdure, Yves Rossetti, Romeo Salemme, Werner X. Schneider, Aarlenne Z. Khan, Dominique Boisson, Laure Pisella, Gilles Rode, Centre de recherche en neurosciences de Lyon (CRNL), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Université Jean Monnet [Saint-Étienne] (UJM)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Université de Lyon, Hôpital Henry Gabrielle [CHU - HCL], and Hospices Civils de Lyon (HCL)
Neuro-CognitivePsychology, Bielefeld University, Bielefeld 33501, GermanyA well-known theory in the field of attention today is the premotortheory of attention which suggests that the mechanisms involved ineye movements are the same as those for spatial attention shifts.We tested a parietal damaged patient with unilateral optic ataxiaand 4 controls on a dual saccade/attentional task and showa dissociation between saccadic eye movements and presaccadicperceptual enhancement at the saccade goal. Remarkably, thoughthe patient was able to make the appropriate saccades to the left,impaired visual field (undistinguishable from saccades to his right,intact visual field), he was unable to discriminate the letter at thesaccade goal (whereas his performance was like controls for letterdiscrimination in his right visual field). This suggests that saccadeplanning and presaccadic perceptual facilitation are separable—planning a saccade to a location does not necessitate that theprocessing of this location is enhanced. Based on these results, wesuggest that the parietal cortex is necessary for the couplingbetween saccade planning and presaccadic perceptual facilitation.Keywords: attention, optic ataxia, parietal cortex, saccadesIntroductionEye movements and attention are very closely related.Normally, when we want to pay attention to an object, wemove our eyes so as to foveate on it (i.e., we shift our gaze) andthis is known as overt attention. However, it is also possible toshift attention without moving the eyes. This process is knownas covert attention. Both overt and covert attention have thesame objective: to enhance a location in space for furtherprocessing, either by bringing the object into higher-precisionprocessing pathways associated with central vision (Anstis1998), or by enhancing the efficiency of the processing inperipheral vision selectively at this specific location (Bushnellet al. 1981).According to the premotor theory of attention (Rizzolatti1983; Rizzolatti et al. 1987, 1994), a command to shift attentionis the same as a command to shift gaze. In both cases, attentionis shifted (covertly or overtly). This theory suggests thatpreparing a saccade to a peripheral target location involves thesame process as orienting selective attention to this peripherallocation, except that this process is then followed by the motorexecution. Inversely, any saccade will be associated witha spatially specific enhancement of processing at the locationof the saccade goal, i.e. saccades to a spatial location cannotoccur without a previous shift of attention to the location(Hoffman and Subramaniam 1995; Kowler et al. 1995; Goldberget al. 2006). In a behavioral study, Deubel and Schneider (1996)tested subjects’ ability to discriminate letter symbols atlocations around or at the saccade target location, beforesaccadic execution. They found that letter discrimination wasbest when it was in the same position as the saccade goal. Theability to discriminate a letter at any location other than thegoal of the saccade decreased to chance level. By showing thatwhen a saccade is executed toward a peripheral target, it ispreceded by a phenomenon of ‘‘presaccadic facilitation’’ ofletter discrimination specifically at this precise peripherallocation, this paradigm confirmed the spatial and temporalrelationship between saccades and attention: attention isoriented before saccadic execution toward the specific locationof the saccade goal, and may thus share common mechanismswith saccadic preparation (Schneider and Deubel 2002).Central to this theory is the finding that the same areas in thebrain that are involved in gaze or eye movements are alsoinvolved in attention shifts (Ignashchenkova et al. 2004; Mooreand Fallah 2004; Goldberg et al. 2006). One of the key areasshown to be involved in both attention and saccadic eyemovements is the lateral intraparietal area (LIP) in the monkeyposterior parietal cortex (Goldberg et al. 2006). We thereforetested involvement of the parietal cortex in the couplingbetween presaccadic attentional shifts and eye movements byobserving the performance of a patient with unilateral opticataxia due to damage to the right posterior parietal cortex. Ifsaccade planning and attentional shifts involve the samemechanisms, we should find a similar pattern of performancein target discrimination and saccade execution to the damagedvisual field. On the other hand, a dissociation between saccadicperformance and target discrimination performance couldsuggest that separate neural substrates govern attention andsaccade planning, but those processes could be coupled andoccur simultaneously. A second possibility could be that theparietal cortex mediates the coupling between a network ofareas involved in saccade planning and presaccadic facilitation,such as frontal and temporal areas. In normal behavior, it isimpossible to distinguish between a coupling and a commonsubstrate, however the impaired region/pathways in thispatient may provide valuable insight into these mechanisms.We tested the patient and 4 control subjects on a simplifiedversion of the task used by Deubel and Schneider (1996). In ourtask the saccade was always directed to the same location (at10 visual degrees of eccentricity) leftward or rightward.Subjects were then required to discriminate letters presentedbriefly during the saccade latency either at the saccade goal orat nonsaccade goal locations 3 closer or further away in thesame visual field. This task allowed us to test the presence ofpresaccadic facilitation, 1) at the location of the saccade goaland 2) at surrounding locations, testing for potential spatialdistortions in attentional shifts. Spatial distortions have been