Abstract
Previous literature suggests that visual regions of the brain such as the lateral occipital cortex and fusiform gyrus are involved in object recognition and may operate as perceptual evidence accumulators (James et al., 2000; Ploran et al., 2007). This work also suggests that these accumulators mimic the properties of cognitive models of evidence accumulation (or, more generally, diffusion models) that have been used to formally assess the cognitive mechanisms of decision making (James et al., 2006; Ratcliff & Smith, 2004). That is, changes to object characteristics have predictable effects on reaction time and neural accumulation slopes. An important characteristic of objects that may affect evidence accumulation is affective salience, which is known to affect object recognition. Here, we used a gradual reveal fMRI paradigm, which slows the presentation of visual information, to assess the influence of affective salience on the accumulation of evidence leading to recognition. Subjects (n=37) performed a 2-alternative forced-choice decision task on categories of body parts that had either high negative affective salience(body parts with mutilations, lacerations) or low affective salience. As expected, high salience produced longer reaction times (distractor effect) during object recognition and were accompanied by longer time to peak activation (evidence). More unexpected was the lack of significant difference between the accumulation slopes (drift rates) of the salient and non-salient conditions. Thus, affective salience did not affect the mechanism responsible for accumulation of evidence. Instead, high affective salience appeared to raise the threshold of neural evidence needed for a decision. The results suggest that highly salient, distracting attributes of objects may raise neural decision thresholds.