Seeing out of the corner of the eye
A new study by LMU psychologists reveals that stimuli located beyond the range of saccadic eye movements can nevertheless attract our visual attention. This result effectively refutes previous reports to the contrary.
Humans receive a vast amount of sensory information about their environment via the visual system – indeed, far more than the brain can process at any one time. The brain must therefore be capable of filtering out the most salient features from this ceaseless deluge of information, while ignoring the less relevant and irrelevant aspects of the visual scene. Neurobiologists refer to this capacity as visual attention, and it enables us to selectively focus on specific locations or particular elements of our surroundings. Neurophysiological investigations have shown that the regions of the brain involved in mediating visual attention also participate in controlling the eye movements (saccades) that monitor the passing scene and redirect the eyes to new targets. Recent reports suggested that the range of visual attention is confined to the field that can be scanned by saccadic eye movements. Using a novel experimental design, LMU psychologists led by Professor Heiner Deubel have now shown that this assumption is in fact false. As they report in the journal PNAS, the range of visual attention extends to points that lie beyond of the eye’s field of view.
Eye movements are highly variable from one individual to another. Indeed, depending on the conditions, they can differ widely in the same subject. To account for this variability, Deubel and his colleagues began by characterizing the extent of the oculomotor area (i.e., the area that is covered by ocular saccades) in each of their experimental subjects. Objects that lie on the visual periphery beyond the limits of this area can still be seen, but cannot be directly brought into focus. “According to the generally accepted theory, the capacity for visual attentiveness should be drastically restricted in the periphery of the visual field,” says Nina Hanning, first author of the study. “We have now experimentally tested the validity of this assumption.” In the experiments, the participants were seated with their heads rotated to the left and confronted with four patterns, which were displayed on a monitor that was placed such the right edge of the screen lay outside the range of the individual’s oculomotor region. The subjects were then presented with a cue and the researchers recorded whether this stimulus caused the subject to shift her attention to a specific pattern on the screen.
The results showed that these cues indeed induced subjects to redirect their attention, irrespective of whether they were presented within or beyond the limits of the oculomotor area. The study therefore reveals, for the first time, that the visual system is in a position to target its attention to locations that lie outside the range that is covered by saccadic eye movements. “This implies that the coupling between attention and the control of eye movements is not as tight as is suggested, for example, by the premotor theory proposed in 1987 by the neurophysiologist Giacomo Rizzolatti. Clearly, we are able to shift our attention freely across the whole of the visual field, independently of any pathological or physiological limitations of the oculomotor system,” says Deubel.
Visual attention is not limited to the oculomotor range
Nina M. Hanning, Martin Szinte and Heiner Deubel