Spatial and temporal influences on extinction.

This study investigated the spatial and temporal characteristics of the attentional deficit in patients exhibiting extinction to determine the extent to which these characteristics can be explained by a theory of an underlying gradient resulting from the differential contribution of interacting cell populations. The paradigm required the identification of two letters whose spatial location was varied both within and across hemifields. Additionally, the interval between the appearances of the two stimuli was manipulated by changing the stimulus onset asynchrony (SOA). A final variable, that of expectancy, was introduced by making the stimulus location more or less predictable and examining the effect of this top-down contingency on performance. The findings were consistent across two patients and indicated the joint contribution of both spatial and temporal factors: the contralesional stimulus was maximally extinguished when it was preceded by the ipsilesional stimulus by 300-900 ms, but this extinction was reduced when the stimuli appeared further ipsilesionally. Interestingly, there was increased extinction of the contralesional stimulus when location was predictable. These findings support the hypothesis that the attentional deficit in extinction patients arises from a contralesional-to-ipsilesional gradient of cell populations that interact in a mutually inhibitory manner.