Do you see what I see? Joint tasks modulate the expression of visual pathway biases

Magnocellular and parvocellular visual pathways are thought to be differentially employed on the basis of hand proximity to stimuli. Consequently, visual biases associated with the increased relative contributions of each are observed. We extend this to joint tasks showing that the presence of another’s hands also influences visual pathway biases. BACKGROUND The ability to successfully engage in a task with another person is thought to be supported by the mechanisms of simulation and co-representation. We covertly run through (simulate) another person’s actions and co-represent their mental states which allows us to predict and respond in a dynamic interactive environment (Bekkering et al., 2009; Sebanz & Knoblich, 2009). The purpose of the present study was to determine if the co-representation of another’s bodily state leads to similar biases in visual processing that result from an individual context. One manipulation that alters visual processing biases is hand-to-target proximity. Specifically, when stimuli are presented in near-hand space, the influence of the magnocellular pathway on perceptual processing is increased relative to the parvocellular pathway (Gozli et al., 2012). Object feature integration is one such phenomena that is influenced by promoting magnocellular activity and thereby inhibiting parvocellular activity (Gozli et al., 2014). We sought to use this finding in the context of a joint task to determine if individuals adopt another’s perceptual space as their own. Gozli and colleagues (2014) had participants perform a task investigating feature integration while hand posture was manipulated (hands close vs. hands far). Two symbols appeared briefly in two horizontally aligned placeholders. The placeholders then shifted until they were vertically aligned and one symbol appeared in one of the placeholders. Participants were asked to indicate if the symbol was new or a repeat of one of the initial symbols. When participants completed the task with their hands far from the stimuli, they were faster to respond on repeat trials where the symbol remained in the same place holder as compared to when it changed placeholders. This finding is likely due to the formation of an ‘object file’ (i.e. a unified multi-featured percept) that contains not only the symbol but the original placeholder (Kahneman, Triesman &Gibbs,1992). When the symbol changes placeholders, the representation no longer matches the original ‘object file’ resulting in a switch cost. This object-related benefit was interrupted in the hands close condition, which Gozil et al. (2014) attributed to a visual bias away from parvocellular activity which is involved in detailed feature processing. To determine if biases in pathways can be co-represented, the present study had two participants (P1, P2) complete an adapted version of the paradigm described above. They were seated across from each other with a monitor between them and asked to do the task with different hand postures: P1 hands close and P2 hands far, P1 hands far and P2 hands close, and both participants’ hands far. One participant responded to new trials, the other to repeat trials. Contrary to the notion that partners engage in active co-representation of their partner’s task and simulation of their bodily state in all joint tasks, we found an object related benefit across all postures. We conclude that the presence of a co-actors hands influences the way in which perceptual space is segmented in relation to both bodies in a flexible manner that is biased towards parvocellular processing.