Abstract
The perception of objects does not rely only on visual brain areas, but also involves cortical motor regions. In particular, different parietal and premotor areas host neurons discharging during both object observation and grasping. Most of these cells often show similar visual and motor selectivity for a specific object (or set of objects), suggesting that they might play a crucial role in representing the “potential motor act” afforded by the object. The existence of such a mechanism for the visuomotor transformation of object physical properties in the most appropriate motor plan for interacting with them has been convincingly demonstrated in humans as well. Interestingly, human studies have shown that visually presented objects can automatically trigger the representation of an action provided that they are located within the observer's reaching space (peripersonal space). The “affordance effect” also occurs when the presented object is outside the observer's peripersonal space, but inside the peripersonal space of an observed agent. These findings recently received direct support by single neuron studies in monkey, indicating that space-constrained processing of objects in the ventral premotor cortex might be relevant to represent objects as potential targets for one's own or others' action.
Highlights
Perception and action have been considered for a long time as two serially organized steps of processing, with the former relying on sensory brain areas and the latter implemented by the motor cortex
Cognition would emerge as an intermediate step of information processing performed by associative cortical areas. This classical “sandwich model” (Hurley, 1998), in which perception and action do never directly interact one with the other, has been challenged by a growing body of evidence in the last three decades. These studies suggest that a crucial role in perception is played by cortical motor regions as well, especially when sensory information is required for acting
Costantini et al (2011b) replicated the finding that the affordance effect is evoked only when the object falls within the observer’s peripersonal space, not when it is located in the extrapersonal space. They added a further interesting condition in which another individual was sat close to the object presented in the extrapersonal space: in this condition, the affordance effect was restored, showing that objects can afford suitable motor acts to interact with them when they are ready for the subject’s hand, and for another agent’s hand. In line with this view, recent monkey (Ishida et al, 2010) and human (Brozzoli et al, 2013, 2014) studies showed that neuronal populations do exist in parietal and ventral premotor cortex encoding the spatial position of objects relative to both one’s own body and the corresponding body part of an observed subject, suggesting the existence of a shared representation of the space near oneself and others
Summary
Perception and action have been considered for a long time as two serially organized steps of processing, with the former relying on sensory brain areas and the latter implemented by the motor cortex. Cognition would emerge as an intermediate step of information processing performed by associative cortical areas This classical “sandwich model” (Hurley, 1998), in which perception and action do never directly interact one with the other, has been challenged by a growing body of evidence in the last three decades (see Goodale and Milner, 1992; Rizzolatti and Matelli, 2003). These studies suggest that a crucial role in perception is played by cortical motor regions as well, especially when sensory information is required for acting. Within the originally defined dorsal stream, there is a subsystem, the v-d stream, which might play a role in perceptual functions
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