Observation Of Human Actions Research Articles

Neural correlates of human action observation in hearing and deaf subjects

Accumulating evidence has suggested the existence of a human action recognition system involving inferior frontal, parietal, and superior temporal regions that may participate in both the perception and execution of actions. However, little is known about the specificity of this system in response to different forms of human action. Here we present data from PET neuroimaging studies from passive viewing of three distinct action types, intransitive self-oriented actions (e.g., stretching, rubbing one’s eyes, etc.), transitive object-oriented actions (e.g., opening a door, lifting a cup to the lips to drink), and the abstract, symbolic actions-signs used in American Sign Language. Our results show that these different classes of human actions engage a frontal/parietal/STS human action recognition system in a highly similar fashion. However, the results indicate that this neural consistency across motion classes is true primarily for hearing subjects. Data from deaf signers shows a non-uniform response to different classes of human actions. As expected, deaf signers engaged left-hemisphere perisylvian language areas during the perception of signed language signs. Surprisingly, these subjects did not engage the expected frontal/parietal/STS circuitry during passive viewing of non-linguistic actions, but rather reliably activated middle–occipital temporal–ventral regions which are known to participate in the detection of human bodies, faces, and movements. Comparisons with data from hearing subjects establish statistically significant contributions of middle–occipital temporal–ventral during the processing of non-linguistic actions in deaf signers. These results suggest that during human motion processing, deaf individuals may engage specialized neural systems that allow for rapid, online differentiation of meaningful linguistic actions from non-linguistic human movements.

Mirror neuron system

Byline: V. Rajmohan, E. Mohandas Mirror neuron system is a group of specialized neurons that mirrors the actions and behaviour of others. The involvement of mirror neuron system (MNS) is implicated in neurocognitive functions (social cognition, language, empathy, theory of mind) and neuropsychiatric disorders. MNS discovery is considered to be the most important landmark in neuroscience research during the last decade. Mirror neuron system - discovery The mirror neurons were discovered serendipitously by Giacomo Rizzolatti and colleagues while working on the grasp response of macaques. They observed that a group of neurons in the area F5 of the premotor cortex that fires when a macaque performs an action; also discharges when it observes the same action being performed by another animal.[sup] [1] Subsequent research has elucidated the diverse regions involved in the MNS of monkeys. Recently different cortical structures have been described as part of the MNS in humans. MNS in monkeys The area F5 of the premotor cortex (premotor area located.in the posterior bank of the inferior arcuate sulcus and the cortical convexity immediately caudal to it) in monkeys has two sets of visuomotor neurons namely the 'canonical' and the 'mirror neurons'. The 'canonical neurons' (in F5 bank region) respond to presentation of an object while mirror neurons (in F5 convexity) respond to performance of an action and observation of an object directed action.[sup] [2] The mirror neurons are triggered by any action that involves the interaction between a biological effector (mouth, hand etc.) and an object. They are stimulated by the observation of the exact same action involving the effector and object ('strictly congruent' neurons) and also by actions that are similar but not having exact effector-object interaction ('broadly congruent' neurons).[sup] [3] Other areas that form part of the MNS are the superior temporal sulcus (STS) and the area 7b (PF of Von Economo) in the inferior parietal lobule (IPL). The STS codes for a larger number of movements than the F5 neurons but lacks motor properties (i.e., does not discharge while performing the movement). The area 7b neurons in IPL are heterogeneous and have a role in coding sensory stimuli and respond to somatosensory, visual or bimodal stimuli. I in addition to this, they also have motor properties and discharge on action observation and performance. The IPL receives inputs from the STS and sends an important output to the ventral premotor cortex including area F5 [Figure 1].[sup] [3],[4] MNS in humans Brain imaging studies reveal that action observation in humans activates the inferior frontal gyrus (IFG), lower part of the precentral gyrus, the rostral part of the IPL and also the temporal, occipital and parietal visual areas.[sup] [3] The frontal and the parietal mirror neuron regions are somatotopically organized. The activation of pars opercularis of the IFG reflects the observation of distal hand and mouth actions, whereas the activation of the premotor cortex reflects proximal arm and neck movements [Figure 2]. The mirror neurons in humans, unlike those in monkeys fire even while observing meaningless (intransitive) movements. The observation of transitive actions causes the firing of the frontal and the temporal nodes of the MNS while that of intransitive actions result in the firing of the frontal node only.[sup] [5],[6] FUNCTIONS OF MNS Action understanding Action understanding is the fundamental function of the MNS. Each time the animal observes a certain action being performed by another animal, the mirror neurons representing the performance of that action are activated. The mirror neurons transform visual observation into knowledge.[sup] [3] Studies on humans during action observation have shown activation of the IFG, the IPL and a region within the STS. The precentral motor cortex though not activated by action observation is involved indirectly in action understanding as they have a role in motor imagery. …

Bottom‐up, not top‐down, modulation of imitation by human and robotic models

Visual observation of human actions provokes more motor activation than observation of robotic actions. We investigated the extent to which this visuomotor priming effect is mediated by bottom-up or top-down processing. The bottom-up hypothesis suggests that robotic movements are less effective in activating the 'mirror system' via pathways from visual areas via the superior temporal sulcus to parietal and premotor cortices. The top-down hypothesis postulates that beliefs about the animacy of a movement stimulus modulate mirror system activity via descending pathways from areas such as the temporal pole and prefrontal cortex. In an automatic imitation task, subjects performed a prespecified movement (e.g. hand opening) on presentation of a human or robotic hand making a compatible (opening) or incompatible (closing) movement. The speed of responding on compatible trials, compared with incompatible trials, indexed visuomotor priming. In the first experiment, robotic stimuli were constructed by adding a metal and wire 'wrist' to a human hand. Questionnaire data indicated that subjects believed these movements to be less animate than those of the human stimuli but the visuomotor priming effects of the human and robotic stimuli did not differ. In the second experiment, when the robotic stimuli were more angular and symmetrical than the human stimuli, human movements elicited more visuomotor priming than the robotic movements. However, the subjects' beliefs about the animacy of the stimuli did not affect their performance. These results suggest that bottom-up processing is primarily responsible for the visuomotor priming advantage of human stimuli.

Transfer of interfered motor patterns to self from others

Previous behavioural and neuroimaging data on humans demonstrated that kinematics and the level of brain activity vary according to whether participants reach towards and grasp a target object presented in isolation or flanked by a distractor object. Here we seek to explore whether a differential activation can be revealed by the mere observation of another person grasping an object in isolation or alongside a distractor. To this end we used event-related functional magnetic resonance imaging to localize neural activity related to action observation that was influenced by the presence of a distractor object. We found that observing a human model reaching-to-grasp a three-dimensional target alongside a distractor elicits a differential level of activation in a network of areas typically involved during action observation: the dorsal sectors of the premotor cortex and the inferior frontal gyrus. Whereas our previous understanding of the human action observation system has been restricted to actions directed to single objects, we provide compelling evidence that areas within this network modulate with respect to the context in which the observed action takes place. This may prove to be a fundamental process for our understanding of how others' actions can be represented at a neural level.

Sign Language Processing and the Mirror Neuron System

In this paper we review evidence for frontal and parietal lobe involvement in sign language comprehension and production, and evaluate the extent to which these data can be interpreted within the context of a mirror neuron system for human action observation and execution. We present data from three literatures — aphasia, cortical stimulation, and functional neuroimaging. Generally, we find support for the idea that sign language comprehension and production can be viewed in the context of a broadly-construed frontal-parietal human action observation/execution system. However, sign language data cannot be fully accounted for under a strict interpretation of the mirror neuron system. Additionally, we raise a number of issues concerning the lack of specificity in current accounts of the human action observation/execution system.

Robotic learning from distributed sensory sources

Recent work toward the development of low-complexity, sensor-based inferencing methods to serve as the initial links of incremental robotic learning systems is described. A multimodal learning approach is proposed in which distributed sensory sources are used to both trigger the observation of and perceive relevant learning instances in a human-robot synergistic framework. Three components of the incremental learning system for the CESARm advanced manipulator testbed are presented that encompass the learning of objects and work area characteristics through the triggering of attention and rote learning, the learning of elemental manipulation tasks by observation of human actions, and the self-assessment of acquired skills and learned knowledge through task performance evaluation. Feasibility experiments with each of these three learning methodologies are presented, and some results are discussed. >