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.

Beyond threat: amygdala reactivity across multiple expressions of facial affect.

The amygdala has been consistently isolated as a key neural substrate for processing facial displays of affect. Recent evidence from human lesion and functional neuroimaging studies have begun to challenge the notion that the amygdala is reserved for signals of threat (fear/anger). We performed a 4 T fMRI study in which 20 subjects viewed a contemporary set of photographs displaying 6 different facial expressions (fearful, disgusted, angry, sad, neutral, happy) while performing a task with minimal cognitive demand. Across subjects, the left amygdala was activated by each face condition separately, and its response was not selective for any particular emotion category. These results challenge the notion that the amygdala has a specialized role in processing certain emotions and suggest that the amygdala may have a more general-purpose function in processing salient information from faces.

The effect of ipsilesional cues on line-bisection errors: the importance of predictive value.

Patients with unilateral neglect were tested on a line-bisection task in which vertical lines were added to the ipsilesional or contralesional end. During some blocks, these vertical lines accurately predicted the horizontal length of the line, while on other blocks the vertical lines had little predictive value. We found that much of the improvement for ipsilesional vertical bars can be explained by their ability to predict the extent of the horizontal line. These results suggest that the predictive value of a ipsilesional cue is responsible for the reduction in line-bisection errors noted by Halligan and Marshall [Neuropsychologia 32 (1994) 13]. This effect of the predictive ipsilesional cue may work in combination with the expanded attentional effects posited by the ipsilesional contraction model that they proposed.