Within extrastriate areas in the ventral visual pathway, populations of neurons would tend to strengthen their connections when co-activated by groups of objects that tend to appear simultaneously. In performing our task that requires to respond only to an animal target, top-down preparation of the visual system is presumably maximal and this preparation would extend to contextual scenes in which animals are commonly seen. Through parallel processing, an animal in a natural scene would be the expected optimal stimulus and would co-activate multiple populations of neurons (
Figure 6A) that are usually co-activated. On the other hand, when the animal appears in an urban scene, a conflict would arise between populations of neurons that respond to elements of the scene that are not usually co-activated (animal and urban man-made features). Such conflict might range from moderate (when some expected natural features are present in an urban background, e.g.,
Figure 6B) to extreme (
Figure 6C). The more incongruent features in the background of the scene, the greater the competition between the neuronal responses to the background and the neuronal responses to the animal target. Facilitation would arise between populations of neurons that have reinforced mutual connections because they tend to fire simultaneously (Hebb,
1949); such learning of visual covariations has been shown to be implicit (Chun & Jiang,
1999; Jiang & Chun,
2001). Otherwise, interference would take place. Hence, with strong interference, the conflict between go and no-go responses would take longer to resolve or might lead to an incorrect motor decision at the level of the prefrontal cortex (Rousselet et al.,
2002; Rousselet, Thorpe, & Fabre-Thorpe,
2004). It has recently been postulated that the parahippocampal cortex (PHC) could mediate the representation of familiar object associations (Aminoff, Gronau, & Bar,
2007; Bar,
2004; Bar & Aminoff,
2003). Thus, the conflict might be present all along the visual stream; it might be maximal in the PHC that receives information directly from the ventral visual stream (Suzuki,
1996; Suzuki & Amaral,
1994) and would encode recurrent regularities or associations in our surrounding world. The conflict could thus arise in the first feed-forward sweep of the earliest available visual information and might explain why the interaction between object and background can be observed even on the earliest behavioral responses that have been suggested to depend mostly on feed-forward processing (Fabre-Thorpe et al.,
2001; Macé et al.,
2005; VanRullen & Thorpe,
2002).