Moving the mind's eye depends upon an intact eye movement system

An important aspect of human vision is the ability to attend to objects or events appearing in our peripheral vision without shifting our gaze. This way of effectively looking out of the corner of the mind's eye is thought to be particularly important for alerting us to danger. Researchers have made the seemingly paradoxical discovery that even though eye movement itself is actually dispensable for such an attention shift, eye muscle function is nevertheless required for this ability to reflexively redirect one's attention. The new finding tests an important theory about brain function, and represents a remarkable example of the brain's complex relationship with movement.

The ability to attend to objects or events that are not at the current centre of gaze (e.g., rapid movements which might signal danger) is referred to as the covert orienting of attention. This mechanism can be contrasted with the overt orienting of attention which typically involves the execution of an eye movement (saccade) intended to bring the object of interest into central vision.

In their new work, researchers Daniel Smith, Chris Rorden and Stephen Jackson of the University of Nottingham, UK, aaddress an important question concerning the precise relationship between eye movements and the covert orienting of attention. While some have argued that covert orienting of attention and eye movements are independent of one another, other researchers have supported the so-called "premotor theory" of attention, which holds that covert attention is mediated by the same system that controls saccadic eye movements, and that a covert shift of attention is simply an unexecuted eye movement.

In a novel test of the premotor hypothesis, Smith and colleagues investigated the covert orienting of attention by a woman (AI) who, because of a congenital impairment in the development of her eye muscles (opthalmoplegia), had never been able to make an eye movement, but could read and scan the visual world by making saccadic head movements.

The researchers found that in contrast to individuals who possessed the ability to move their eyes, AI could not reflexively orient her attention in response to the appearance of a salient peripheral cue. Nevertheless she had no problem orienting her attention voluntarily in response to centrally presented direction cues (i.e., an arrow pointing left or right).

The results demonstrate that intact eye movements are necessary for the normal development of reflexive attention. They also show that, contrary to what one might expect, intact brain regions alone are not sufficient for the normal development of attention. Together the new findings provide strong support for the premotor theory of attention.

Daniel T. Smith, Chris Rorden, and Stephen R. Jackson : "Exogenous Orienting of Attention Depends upon the Ability to Execute Eye Movements"

Publishing in Current Biology, Volume 14, Number 9, May 4, 2004.

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