Sensory and response interference by ipsilesional stimuli in tactile extinction

Extinction is thought to be due to a pathologically limited attentional cap acity in which multiple stimuli cannot be processed simultaneously to consc ious awareness. Patients with tactile extinction are aware of being touched on a contralesional limb, but seem unaware of similar contralesional touch if touched simultaneously on their ipsilesional limb. The ipsilesional sti mulus interferes and competes with the processing of the contralesional sti mulus. Most theorists assume that the ipsilesional stimulus affects the sen sory processing of the contralesional stimulus, although the precise functi onal level at which this interference occurs is not clear. We report a seri es of experiments using signal detection analyses to investigate tactile ex tinction in one patient (DC). These analyses revealed that ipsilesional sti muli, in addition to interfering with processing of contralateral sensation s, also interfere with verbal reports of those sensations. This influence o n responses suggests that interference in tactile extinction can occur at a post-perceptual level, further 'downstream' than previously thought.