Abstract
Previous literature has shown that the involvement of the lateral occipital complex (LOC) in object recognition may operate via a mechanism of evidence accumulation. This work also has shown that these accumulators mimic cognitive diffusion models, specifically in that object characteristics which affect recognition time also affect accumulation slopes (James et al., 2006; Ploran et. al., 2007; Ratcliff et. al., 2016). Perceptual experience with an object (via priming/adaptation) also influenced accumulation slope (James et al., 2000). Another prominent attribute of objects that may affect accumulation is the visual salience. Visual salience affects sensory processing typically by orienting attention more efficiently, but how this affects visual evidence accumulators in the brain has not been investigated (Itti 2007). Here, we used a gradual reveal paradigm, which slowed visual information presentation, paired with fMRI to measure the BOLD response to color-saturated (salient) and non-saturated (non-salient) images while participants completed a 2-alternative-forced-choice image recognition task (n=17). Consistent with our hypothesis, salient objects were recognized faster and peak BOLD activation occurred sooner. However, the slower peak for non-salient objects was not due to a steeper accumulation slope or higher threshold. Instead, non-salient objects showed a delayed onset of accumulation, after which accumulation proceeded with the same slope and to the same threshold as the salient objects. The results add to our knowledge of how accumulation of evidence contributes to object recognition in the brain, specifically in areas considered visual evidence accumulators, such as the LOC. The results suggest that the speed advantage conveyed by higher salience involves the initiation of evidence accumulation, rather than changes to the accumulation mechanism itself. This suggests that the neural mechanism underlying orienting responses may be a more rapid accumulation onset.