Abstract
Others' observed actions cause continuously changing retinal images, making it challenging to build neural representations of action identity. The monkey anterior intraparietal area (AIP) and its putative human homologue (phAIP) host neurons selective for observed manipulative actions (OMAs). The neuronal activity of both AIP and phAIP allows a stable readout of OMA identity across visual formats, but human neurons exhibit greater invariance and generalize from observed actions to action verbs. These properties stem from the convergence in AIP of superior temporal signals concerning: (i) observed body movements; and (ii) the changes in the body-object relationship. We propose that evolutionarily preserved mechanisms underlie the specification of observed-actions identity and the selection of motor responses afforded by them, thereby promoting social behavior.
Highlights
A substantial fraction of neurons in the monkey anterior intraparietal area (AIP) and its human homologue phAIP are selective for observed manipulative actions (OMAs)
OMA identity may result from the combination of two visual signals originating in the superior temporal sulcus (STS) and concerning: (i) observed body movements: and (ii) the changes in the hand/ object relationship
We first review evidence of neuronal signatures of OMA-identity coding in the primate brain, which point to area AIP as a critical node for this function
Summary
Others’ observed actions cause continuously changing retinal images, making it challenging to build neural representations of action identity. As compared with other complex static visual stimuli, such as objects [8], faces [9,10], others’ gaze direction [11], and body posture [12], observed actions of others are inherently dynamic stimuli, and their dynamics are essential for an observer’s brain to compute their identity, despite the rapid changes in their retinal image. The changes an agent’s action causes in the target object constitute an element that is almost as important as the body movement itself, because its dynamics make the OMA predictable in terms of its motor goal [15,16,17] These two types of signal, specifying: (i) how the dynamics of body movement unfold; and (ii) how it will change the position or shape of an object, naturally coexist in everyday manipulative actions, and characterize the action identity.
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