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    • br Study chasing versus inanimate motion br

    2018-10-29


    Study 1: chasing versus inanimate motion
    Study 2: chasing versus random
    General discussion Both studies postulate evidence of a strong positive amplitude for the chasing agent in the low occipital and post temporal areas 400ms post hydroxylase inhibitor onset. Given that prior research examining early perception to social information in infancy found a similar P400 component (Bakker et al., 2015, 2016; Gredebäck et al., 2010; Melinder et al., 2015; Senju et al., 2006), present findings are compatible with the notion that the chasing geometrical shape is processed as a social agent compared to an inanimate object or a randomly moving object. This highlights that animacy alone may not fully explain the effect but rather the socialness of the chasing event that drives the effect. Furthermore, given that the P400 component has been found to be an index for adult pSTS activity which in turn has been shown in response to interacting animated interactions of which chasing may be considered the hallmark (Gao et al., 2009), it is likely that the infant P400 found here has its main sources in the pSTS. In both studies, we find a main effect of hemisphere with higher P400 amplitude in the right than left channels. This finding corroborates with previous adult research that has found higher engagement of the right pSTS when observing correlated motion such as chasing (Schultz et al., 2005). In other studies, the engagement of the right pSTS has been especially sensitive to goals and intentions behind motion (Gao et al., 2012) as well as in response to unsuccessful compared to successful outcomes of goal-directed actions (Shultz et al., 2011). In addition to the P400 component, here we find a negative deflection around 290ms. For both the random and the inanimate agent, the N290 was larger (more negative) followed by a lower (less positive) P400 amplitude in comparison to the chasing agent. Previous research suggests that this amplitude pattern may appear for novel rather than familiar stimuli in 9-month-olds (Key et al., 2009 but see also Key and Stone, 2012; Scott et al., 2006), suggesting it to be involved in longer processing and greater visual attention. It is thus possible that the inanimate agent and the random animate agent required more visual processing, while the chasing agent was more easily recognized as such. Increased visual attention to randomly moving shapes has also been previously found in 5-month-old infants when presented with a display showing discs chase next to a displays with inanimately moving discs (Rochat et al., 1997). The infant N290/P400 complex has been suggested to be the precursor to the adult N170 (de Haan et al., 2003, 2002; Halit et al., 2003), which in adults has been localized to the fusiform gyrus and the superior temporal sulcus (Itier and Taylor, 2002, 2004) activated during perception of social stimuli, biological motion and animate motion. Here we find similar components, suggesting that the amplitude difference during chasing perception may be related to the social aspects of interactions rather than the presence of motion cues pertaining to animacy as defined by the violation of the Newtonian laws of mechanics. However, which aspects of the chasing interactions may be responsible for the emergence of the N290/P400 complex is an important question for future research and one that is beyond the scope of the present paper. Good candidates for further assessment may be correlated motion between the chaser and the target, such as the goal-directedness of the chaser and the contingent reaction of the target. Since the processing responses are so rapid, visual pop-out paradigms could possibly be used in parallel with neurophysiological measures. Study 1 did not find any differences in the Nc component between animate and inanimate objects, as Kaduk et al. (2013) did. The different findings might have to do with the way animacy was measured in both studies. In Kaduk et al. (2013) a single object was moving through an obstacle course continuously either violating or abiding by the Newtonian laws of physics from a side view. In contrast, in the present study, infants were presented with two objects from a top view, and they had to process not only how the objects move in their environment but also how they move in relation to each other. Given the finding that inanimate motion engages increased attention (Kaduk et al., 2013), lactose intolerance is possible that motion cues pertaining to a socially contingent interaction between agents required similar attentional effort as the inanimate motion, rendering the effect null. It could also be that we have a “ceiling effect” since the infants had to track multiple objects. In all cases, it seems like all conditions in our studies were equally engaging for the infants.