Objections against the view of visual extinction as an attentional disengagement deficit: the interaction between spatial position and temporal modulation

Visual extinction is a common consequence of brain injury where individuals fail to detect a contralesional target when it is presented with a competing ipsilesional target. This disorder is often seen as either a consequence of biased competitive interactions or as a consequence of an attentional disengagement deficit. A study of neurological patients by Rorden et al. (2008) found that extinction is maximal at stimulus simultaneity when the target stimuli straddle the central gaze fixation location, while it is maximal when the ipsilesional stimulus has a temporal lead on the contralesional stimulus when both target stimuli are presented in the ipsilesional visual field. The authors argued that these results are most parsimoniously explained as a consequence of low-level biased competitive interactions due to cortical magnification, but acknowledged that an attentional disengagement deficit could also accommodate the results. The present study set out to adjudicate between these models by examining the performance of neurologically healthy subjects who exhibit normal cortical magnification but do not have pathological attentional biases. We presented (a)synchronous double stimulation trials where both targets to be identified could straddle the central gaze fixation location or be presented in either the left or the right visual field. We found that in both the left and the right visual field target performance accuracy was poorest when the more peripheral stimulus led. This suggests that the findings from Rorden et al. can indeed be explained by a low-level physiological bias due to cortical magnification and argues against the notion that neurological extinction represents an attentional disengagement deficit.