Dominic J. Mort

We are very interested in the letter from Karnath and colleagues and welcome the opportunity to continue this stimulating debate about the anatomy of neglect. Although the arguments advanced by Karnath and his colleagues are interesting, we disagree with them. We hope they will reconsider their interpretation of our findings (Mort et al., 2003), as well as those of Binder et al. (1992), in the light of our responses. In addition, we draw attention to the fact that the limited new data provided in their letter does not actually support well the controversial claim that neglect is associated with superior temporal gyrus (STG) damage (Karnath et al., 2001).

A greater understanding of the underlying component mechanisms of normal visual search provides explanations for disturbances seen in certain neurological conditions. This review focuses on recent advances in this field which bear on the neurology of visual search in health and disease. Foremost, visual search requires a normal apparatus for the application of attentional resources to the visual environment and, with that facility lost in hemispatial neglect, search becomes uselessly stuck within one portion of the field. New evidence suggests that loss of normal registration of where the eyes have been compounds the problem. Even if attention can be deployed flexibly, its parameters must be chosen strategically, in terms of saccade amplitude, size of attentional window at each fixation and search path taken. Evidence is growing that the prefrontal cortex plays a complex role in this strategic control. Rehabilitation strategies of the future may be tailored according to which component functions have been lost in different patient groups. Visual search is a dominant human activity and provides not only a window into how brain function is deranged after structural damage, but also offers the prospect of an ideal modality through which to deliver future behavioural therapies. New techniques have advanced our understanding of the physiology of visual search enormously in the past few decades. The time is now ripe in which to begin to integrate these findings into our understanding of the pathophysiology and treatment prospects of neurological disorders like hemispatial neglect, hemianopia and other deficits after stroke.

Purpose of review A greater understanding of the underlying component mechanisms of normal visual search provides explanations for disturbances seen in certain neurological conditions. This review focuses on recent advances in this field which bear on the neurology of visual search in health and disease. Recent findings Foremost, visual search requires a normal apparatus for the application of attentional resources to the visual environment and, with that facility lost in hemispatial neglect, search becomes uselessly stuck within one portion of the field. New evidence suggests that loss of normal registration of where the eyes have been compounds the problem. Even if attention can be deployed flexibly, its parameters must be chosen strategically, in terms of saccade amplitude, size of attentional window at each fixation and search path taken. Evidence is growing that the prefrontal cortex plays a complex role in this strategic control. Rehabilitation strategies of the future may be tailored according to which component functions have been lost in different patient groups. Summary Visual search is a dominant human activity and provides not only a window into how brain function is deranged after structural damage, but also offers the prospect of an ideal modality through which to deliver future behavioural therapies. New techniques have advanced our understanding of the physiology of visual search enormously in the past few decades. The time is now ripe in which to begin to integrate these findings into our understanding of the pathophysiology and treatment prospects of neurological disorders like hemispatial neglect, hemianopia and other deficits after stroke.