Eye Position Affects Orienting of Visuospatial Attention

Laila Craighero, Mauro Nascimben, Luciano Fadiga
2004 Current Biology  
Section of Human Physiology keep the eyes still appears at first glance quite bizarre. Cognitive theories of attention interpret the oculomotor University of Ferrara 44100 Ferrara activation as an epiphenomenon due to the inhibition of motor programs automatically generated to move the Italy eyes toward the appearing stimulus [11]. An alternative interpretation considers orienting of attention as the result of the preparation of a saccadic eye movement Summary toward the location to be attended
more » ... [12]. Here we investigated the role of oculomotion in orient-The ability to detect an incoming visual stimulus is ing of attention by dissociating perceptual from motor enhanced by knowledge of stimulus location (orienting capabilities. If causal relationships link oculomotion and of visuospatial attention [1]). Although the brain mechorienting of attention, any constraint limiting eye moveanisms at the basis of this enhancement are not yet ments should abolish, or at least reduce, attentional fully clarified, there is evidence that orienting of attenbenefits in the region of the spatial field barely reachable tion is accompanied by the activation of oculomotor by the eye. On the contrary, if attention is a purely cognicircuits [2-6]. It remains unclear, however, whether tive process, then no effects are expected to arise from this oculomotor activity is an epiphenomenon or is oculomotor constraints. We decided to evaluate attenfunctionally related to the attentional process. Attentional benefits by using a classical Posner paradigm [7]. tional benefits are usually measured by the classical Although this method does not represent the only way Posner paradigm [7]. When subjects fixate centrally to investigate visuospatial attention, it is one of the most and are requested to detect a visual stimulus that diffused in this kind of literature. Fourteen naive univercould appear in an attended or unattended location, sity students participated in the experiment. In order to they react faster to stimuli appearing in the attended exclude possible influences of eye dominance on spatial one. Here, we demonstrate that in monocular vision attention [13], we included equal numbers of right and visuospatial attention was significantly modulated by left ocular dominants in the sample. Subjects fixated the position of the eye in the orbit. When the screen the center of a computer screen in monocular vision. was placed 40؇ to the right or to the left of subjects' According to a central cue (see Figure 1 ), they oriented sagittal plane, attentional benefits for stimuli aptheir attention toward one of two locations (5Њ to the pearing in subjects' temporal spatial hemifield dramatright and 5Њ to the left of the fixation box) to detect a ically decayed, even if the retinal stimulation was exstimulus that could appear either in the attended or actly the same as in the classical paradigm. The finding in the unattended location. The probability of stimulus that eyes and attention show a common limit stop appearance in the cued location (valid trials) was 70% point supports their close functional coupling. and in the uncued location (invalid trials), 30%. While maintaining fixation, subjects had to signify detection Results and Discussion of the stimulus as quickly as possible by pressing a switch. In 1867, von Helmholtz [8] first reported that, while keep- Each eye was involved in two experimental conditions ing the eyes at the center of a picture, an observer can (see Figure 1 ). In the first condition, the screen was perceptually enhance the details of any part of the scene "canonically" placed in front of the subject (frontal conif he "concentrates his attention ... simply by a condition). In the second condition, the screen was located scious and voluntary effort." More recently, several at the same distance but was rotated 40Њ to the right of brain-imaging studies aiming to describe the brain netsubjects' sagittal plane when the right eye was open work underlying orienting of attention showed that, alor 40Њ to the left when the left eye was open (rotated though subjects were required to keep their eyes still, condition). We selected the degree of screen rotation orienting of attention determined a brain activation patin order to keep the entire experimental display centered tern largely coincident with that specific for eye moveon the fovea and within the effective oculomotor range ments [2-6]. This functional overlap between attention [14]. No perceptual differences were present between and eye movements has been further suggested by frontal and rotated conditions, as we assessed by testmonkey electrophysiological experiments both during ing subjects' visual acuity with an eye chart. Particithe recording of visual neurons in the superficial layers pants' reaction times (RTs) were calculated from stimuof the superior colliculus (enhancement effect [9]) and lus appearance to the pressing of the switch. For both during the electrical microstimulation of oculomotor the frontal and the rotated conditions, RTs obtained centers [10]. This last study shows an improvement in from the left and right eye conditions were grouped the perception of visual stimuli appearing in that portion according to the spatial hemifield in which the stimulus was presented (nasal and temporal). Data were standardized within subjects and submitted to two separate whereas it allowed saccadic execution toward the nasal hemifield. This motor limitation appears to be the only References plausible explanation of the present findings; attention cannot be directed toward spatial locations that are
doi:10.1016/j.cub.2004.01.054 pmid:14972685 fatcat:nhmdhxfghvdz5p4xgb6qcozvye