Visual extinction: the effect of temporal and spatial bias.

Unlike patients with neglect, neurological patients with extinction can detect a single event presented at any location. However, when shown two brief near-simultaneous stimuli they only report the ipsilesional item. The question of what inter-stimulus delay leads to maximal extinction has clear clinical and theoretical implications. di Pellegrino et al. [di Pellegrino, G., Basso, G., & Frassinetti, F. (1997). Spatial extinction on double asynchronous stimulation. Neuropsychologia, 35, 1215-1223] report that extinction is maximal when the two stimuli are presented simultaneously, with less extinction when either item has a slight temporal lead. This finding supports traditional clinical diagnosis (which only presents simultaneous events), and is in accord with theories of extinction that entail individuation of objects (e.g. "token" accounts). In contrast, Cate and Behrmann [Cate, A., & Behrmann, M. (2002). Spatial and temporal influences of extinction. Neuropsychologia, 40, 2206-2225] report that extinction is maximal when the ipsilesional item is presented slightly prior to the contralesional item. This finding appears to support disengage models of attention. Our aim was to reveal whether the difference between these studies reflects different patients, or different methods. Specifically, we note that the stimuli used by Cate and Behrmann were biased both temporally (more ipsilesional first trials) and spatially (more items presented in ipsilesional field). We examined the performance of nine individuals with extinction, and found that maximal extinction was not influenced by temporal biases, but extinction was modulated by the spatial location of stimuli. This finding reconciles previous studies and offers new insight into this syndrome.