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Most animals appear to possess motion-sensitive circuitry for interpreting action patterns generated by other animals. The specificity of action perception is evident in humans: we can interpret human action under extremely impoverished stimulus conditions, for example when conveyed by a dozen moving dots.
Figure 1 We have identified and experimentally characterized a 4-stage framework for action perception: motion detection (1), skeleton retrieval (2), action interpretation (3), and multi-agent interaction (4). Fighting action (left) is from Muybridge’s ‘Animal locomotion’ (1887).
Our work has demonstrated that local motion signals are integrated into action patterns by a highly nonlinear process (Neri et al, 1998) involving separate identifiable stages (Fig. 1), such as limb reconstruction (Neri 2009) and the interpretation of inter-agent interaction (Neri et al 2006). These different stages operate within an integrated process, so that perturbations of inter-agent information may impact lower-level modules.
Figure 2 Sensitivity for discriminating motion signals associated with action patterns (fighting, dancing) is slightly poorer in the autistic population (A) when non-specific effects (e.g. due to attentional engagement) are included. When those effects are factored out and only effects specific to action interpretation are retained (B), no difference is evident between autistic and typically-developing samples.
We have also demonstrated that these mechanisms are intact in some atypical neural perceptual systems, such as amplyopia (Neri et al 2007) and autism spectrum disorder (ASD). With relation to ASD, we have demonstrated that potential deficits in action interpretation (as posited for example by mirror-neuron or theory-of-mind accounts) are not specific to action processing, but rather result from aspecific factors such as reduced attention and/or engagement with the stimulus (Cusack et al 2015). When measured against these factors, action sensitivity is slightly poorer in ASD (Fig. 2A); however, when measured against factors specific to action processing, performance in the ASD population is equivalent to the typically-developing (control) sample (Fig. 2B), indicating that the autistic brain contains intact perceptual machinery for interpreting other people's actions. Any potential deficit may derive from accessing the signals generated by this machinery, not from the nature of the signals per se.
Relevant publications:
• Cusack J, Williams JHG, Neri P Action perception is intact in autism spectrum disorder 2015 Journal of Neuroscience 35 1849-1857
• Neri P Wholes and subparts in visual processing of human agency 2009 Proc. R. Soc. London B 276 861-869
• Neri P, Luu JY, Levi DM Sensitivity to biological motion drops by ~½ log-unit with inversion, and is unaffected by amblyopia 2007 Vision Research 47 1209-1214
• Neri P, Luu JY, Levi DM Meaningful interactions can enhance visual discrimination of human agents 2006 Nature Neuroscience 9 1186-92
• Neri P, Morrone MC, Burr DC Seeing biological motion 1998 Nature 395 894-6
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