” One goal of the current study was to develop a more objective definition of ambiguity in perceptual processing. Definitions of perceptual ambiguity have been offered in the literature in other contexts. In fact, Olivers and Meeter are not the first to develop an ‘ambiguity resolution hypothesis’; Luck et al. (1997a) also used this name for a model of visual attention. According to Luck et al., ambiguity

occurs when visual objects share a neural receptive field (RF). This is based on the observation that visual neurons are preferentially selective for stimuli that fall in their RFs. At low-level visual areas RFs are small and the information encoded by any given neuron is quite simple. High-level visual areas consolidate information such that the encoded information becomes more complex, and RFs associated with these higher-level neurons become correspondingly larger learn more (Desimone and Ungerleider, 1989). This eventually creates

a problem: stimuli come to share receptive fields and cellular output can no longer be attributed to discrete stimuli. Luck et al. propose that the core responsibility of visual attention is the resolution of this problem, and that this takes place through the suppression of 3-MA distractor representations. This makes Luck et al.’s ambiguity resolution hypothesis similar in nature to other competition-based theories of attention like the biased competition model of Desimone and Duncan (1995) and the spatial tuning model of Tsotsos et al. (1995). A central premise of the Luck et al., 1997a and Luck et al., 1997b hypothesis

is that ambiguity resolution can be indexed in the N2pc component of the visual event-related potential (ERP). The N2pc is a lateralized component that is evident as an increased negativity in the ERP elicited over visual cortex contralateral to an attended item (Luck and Hillyard, 1994a and Luck and Hillyard, 1994b). Early work suggested that the N2pc reflects distractor suppression, for example Astemizole showing that the component is absent when visual search displays do not contain distractor stimuli or when distractors cannot be suppressed because they contain relevant information or somehow define the target (Luck and Hillyard, 1994b). There also appears to be a close correspondence between the N2pc and electrophysiological evidence of attentional suppression in monkey visual cortex: both become evident at approximately 175 ms post-stimulus and are more pronounced for difficult discrimination tasks and when distractors are near the target rather than far away (Luck et al., 1997a and Luck et al., 1997b). Other results have been difficult to reconcile with the distractor suppression hypothesis.