Immediate and delayed reaching in hemispatial neglect

Milner and Goodale (The visual brain in action, Oxford: Oxford University Press, 1995; The visual brain in action, 2nd ed., Oxford: Oxford University Press, 2006) propose a model of vision that makes a distinction between vision for perception and vision for action. One strong claim of the model is that the dorsal stream's control of action is designed for dealing with target stimuli in the ‘here and now’, yet when time is allowed to pass and a reaction has to be made on the basis of a visual memory, the ventral stream is required for successful performance. Regarding the syndrome of hemispatial neglect, Milner and Goodale further claim that the visual dorsal stream is relatively spared in these patients. In the current study we tested whether neglect patients would indeed be unimpaired in immediate pointing, yet show inaccurate pointing in a condition where a delay is interposed between the presentation of the stimulus and the response signal (in particular in left space). We tested the ability of nine neglect patients (and healthy and right hemisphere no neglect control groups) to perform reaches towards immediate and delayed targets, placed in left, central and right locations. Neglect patients showed no accuracy impairments when asked to perform an immediate action. Conversely, when pointing towards remembered leftward locations, they markedly overshoot the target or failed to initiate a reach altogether. These results confirm that patients with neglect are not specifically impaired when performing ‘here and now’ actions, but rather present deficits when the visuomotor task taps into more perceptual ‘off-line’ representations thought to depend on ventral visual stream activation