“…Extinction is typically defined as a failure to respond to a contralesional target during simultaneous presentations of stimuli to both the left and right hemifields, known as double simultaneous stimulation or DSS (Marzi et al, 1996), and is not considered to be due to a sensory deficit (Baylis et al, 2001;Shisler et al, 2004). For example, during DSS, individuals with RH lesions with extinction have shown decreased contralesional performance when asked to respond to two simultaneous targets (left and right) (Baylis et al, 2001;Shisler et al, 2004); however, participants are typically able to correctly identify a single stimulus presented in the contralesional hemifield (single left presentation). Due to the fact that individuals are able to identify a single stimulus on the contralesional side, many researchers have argued that extinction is caused by a deficit in attention and not due to sensory difficulties per se (Baylis et al, 1993;Volpe, LeDoux, & Gazzaniga, 1979).…”