An afterimage is the illusory “photo negative” experienced immediately following exposure to a real stimulus. Afterimages used to be attributed exclusively to retinal adaptation, but a growing body of http://www.selleckchem.com/products/ABT-263.html work suggests that adaptation within cortical visual areas also contributes to afterimage formation (Brascamp et al., 2010; Ito, 2012; Shimojo et al., 2001; Tsuchiya and Koch, 2005). Of relevance for our purposes, a stimulus suppressed under rivalry causes weaker subsequent afterimages —a phenomenon believed to arise from

attenuated responses within phase-sensitive neural representations (Brascamp et al., 2010). We reasoned that if attention plays a critical role in modulating the shape of the contrast response under suppression, two key effects should emerge in the induction of afterimages under rivalry, depending

on whether attention is directed toward or away from the rival stimuli. Directing attention toward a small, high-contrast competitor viewed by one eye should elicit a response gain shift when the other eye’s competitor is small, but a contrast gain shift when that other eye’s competitor is large. For a high-contrast, suppressed stimulus, this should induce a weaker afterimage when the competitor stimulus viewed by the dominant eye is small compared to when that competitor is large. The model predicts that without attention the balance between excitation and inhibition will be preserved regardless of competitor size. Thus, diverting attention away from high-contrast, competing stimuli should transform the response Bortezomib cell line gain modulation associated with small stimuli into a contrast gain modulation. For a high-contrast stimulus, a contrast gain shift would be signified by an attenuation of the suppressive effects that rivalry has on afterimages, for all competitor sizes. To test afterimage strength, we implemented a psychophysical paradigm that quantitatively indexes the strength

of negative afterimages (Brascamp et al., 2010; Kelly and Martinez-Uriegas, 1993; Georgeson and Turner, 1985; Leguire and Blake, 1982). To induce heptaminol afterimages, observers were given brief, 2 s exposures to a sinusoidal grating (the inducer) presented to one eye while, at the same time, the other eye received one of three possible stimulus arrangements (Figure 7): (1) an uncontoured field that produced no suppression of the inducer, (2) a large (8°) competitor, or (3) small (1.5°) competitor, both of which suppress visibility of the inducer. Immediately following each brief induction period, the competitor grating, if present, was removed and the contrast of the inducer viewed by the other eye was ramped off and was replaced by a “nuller” stimulus, itself a sinusoidal grating presented to the same eye that received the inducer.