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It has been suggested that actions can provide a fruitful conceptual context for sound symbolism phenomena, and that tight interaction between manual and articulatory processes might cause that hand actions, in particular, are sound-symbolically associated with specific speech sounds. Experiment 1 investigated whether novel words, built from speech sounds that have been previously linked to precision or power grasp responses, are implicitly associated with perceived actions that present precision manipulation or whole-hand grasp tool-use or the corresponding utilisation pantomimes. In the two-alternative forced-choice task, the participants were more likely to match novel words to tool-use actions and corresponding pantomimes that were sound-symbolically congruent with the words. Experiment 2 showed that the same or even larger sound-action symbolism effect can be observed when the pantomimes present unfamiliar utilisation actions. Based on this we propose that the sound-action symbolism might originate from the same sensorimotor mechanisms that process the meaning of iconic gestural signs. The study presents a novel sound-action phenomenon and supports the view that hand-mouth interaction might manifest itself by associating specific speech sounds with grasp-related utilisations.

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The aim of the present study was to investigate the role of mental representation processes during the planning, reaching, and use phases of actions with tools commonly used toward the body (TB, e.g., toothbrush) or away from the body (AB, e.g., pencil). In the first session, healthy participants were asked to perform TB (i.e., making circular movements with the toothbrush near the mouth) and AB (i.e., making circular movements with the pencil near the desk) actions both with (i.e., actual use) and without the tool in hand (i.e., the pantomime of tool use). In the second session, the same participants performed a series of mental rotation tasks involving body- (i.e., face and hands) and object-related (i.e., abstract lines) stimuli. The temporal and kinematic analysis of the motor actions showed that the time required to start the pantomimes (i.e., the planning phase) was shorter for the AB action than for the TB action. In contrast, the reaching phase lasted longer for the AB action than for the TB action. Furthermore, the TB pantomime was associated with the performance in the mental rotation of body-related stimuli, especially during the planning and reaching phases, whereas the AB pantomime was more related to the performance in the mental rotation of object-related stimuli, especially during the tool use phase. Thus, the results revealed that the direction of a goal-directed motor action influences the dynamics of the different phases of the motor action and can determine the type of mental images involved in the planning and execution of the action.

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The middle temporal gyrus (MTG) has been shown to be recruited during the processing of words, but also during the observation of actions. Here we investigated how information related to words and gestures is organized along the MTG. To this aim, we measured the BOLD response in the MTG to video clips of gestures and spoken words in 17 healthy human adults (male and female). Gestures consisted of videos of an actress performing object-use pantomimes (iconic representations of object-directed actions; e.g., playing guitar), emblems (conventional gestures, e.g., thumb up), and meaningless gestures. Word stimuli (verbs, nouns) consisted of video clips of the same actress pronouncing words. We found a stronger response to meaningful compared with meaningless gestures along the whole left and large portions of the right MTG. Importantly, we observed a gradient, with posterior regions responding more strongly to gestures (pantomimes and emblems) than words and anterior regions showing a stronger response to words than gestures. In an intermediate region in the left hemisphere, the response was significantly higher to words and emblems (i.e., items with a greater arbitrariness of the sign-to-meaning mapping) than to pantomimes. These results show that the large-scale organization of information in the MTG is driven by the input modality and may also reflect the arbitrariness of the relationship between sign and meaning.SIGNIFICANCE STATEMENT Here we investigated the organizing principle of information in the middle temporal gyrus, taking into consideration the input-modality and the arbitrariness of the relationship between a sign and its meaning. We compared the middle temporal gyrus response during the processing of pantomimes, emblems, and spoken words. We found that posterior regions responded more strongly to pantomimes and emblems than to words, whereas anterior regions responded more strongly to words than to pantomimes and emblems. In an intermediate region, only in the left hemisphere, words and emblems evoked a stronger response than pantomimes. Our results identify two organizing principles of neural representation: the modality of communication (gestural or verbal) and the (arbitrariness of the) relationship between sign and meanings.

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Recent years have witnessed a growing interest in behavioral and neuroimaging studies on the processing of symbolic communicative gestures, such as pantomimes and emblems, but well-controlled stimuli have been scarce. This study describes a dataset of more than 200 video clips of an actress performing pantomimes (gestures that mimic object-directed/object-use actions; e.g., playing guitar), emblems (conventional gestures; e.g., thumbs up), and meaningless gestures. Gestures were divided into four lists. For each of these four lists, 50 Italian and 50 American raters judged the meaningfulness of the gestures and provided names and descriptions for them. The results of these rating and norming measures are reported separately for the Italian and American raters, offering the first normed set of meaningful and meaningless gestures for experimental studies. The stimuli are available for download via the Figshare database.

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Since the first studies on limb apraxia carried out by Hugo Liepmann more than a century ago, research interests focused on the way humans process manual gestures by assessing gesture production after patients suffered neurologic deficits. Recent reviews centered their attention on deficits in gesture imitation or processing object-related gestures, namely pantomimes and transitive gestures, thereby neglecting communicative/intransitive gestures. This review will attempt to reconcile limb apraxia in its entirety. To this end, the existing cognitive models of praxis processing that have been designed to account for the complexity of this disorder will be taken into account, with an attempt to integrate in these models the latest findings in the studies of limb apraxia, in particular on meaningful gestures. Finally, this overview questions the very nature of limb apraxia when other cognitive deficits are observed.

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An important debate exists in contemporary cognitive neuroscience about the innate or experience-dependent origin of the brain representation of conceptual categories. The 'domains of knowledge' hypothesis maintains that innate factors subsume the categorical organization at the brain level of animals, plant life and artefacts. On the other hand, the 'sensory-motor model of conceptual knowledge' and the embodied cognition theory attribute this categorical organization to experience-dependent factors. I tried to clarify this issue by surveying the influence that handedness could have on the lateralization of tools representation in the inferior fronto-parietal and posterior middle temporal cortices of the left hemisphere. The underlying assumption was that, if this lateralization results from innate mechanisms, then handedness should not influence this hemispheric asymmetry. If, on the other hand, this lateralization is due to the motor and somatosensory experiences made with the right dominant hand during the manipulation of tools and other artefacts, then this asymmetry should be inverted or strongly attenuated in left-handers. Results of the review strongly suggest that manual experience acquired during tool manipulation can influence the hemispheric representation of tools and other artefacts. They also suggest, however, that handedness-related embodiment is not fixed, but influenced by personal motor experiences (such as those made by left-handers who have been forced to use their right hand) and by social visual experiences (such as the fact that, living in a right-handed world, left-handers see more people in their environment who use the right rather than the left hand) during tool manipulation.

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Although the control of meaningful gestures is one of the most left-lateralized functions, the relative contribution of the two hemispheres to their processing is still debated. We tested the effects of primes appearing in the left or right visual field in the form of pictures (Experiment 1), and words (Experiment 2) on categorization of movies showing intransitive ("communicative") gestures, tool use (transitive) pantomimes, and meaningless movements. Fifteen participants (eight women) watched 36 movies (12 from each category) primed for 150 ms with either a congruent or incongruent stimulus followed by a 50-ms mask. On congruent trials, a picture or word was directly related to the presented gesture, including nonsense pictures or non-words for meaningless actions. On incongruent trials, a picture or word belonged to a different category. In Experiment 1, intransitive gestures were categorized significantly faster than the other two types of hand movements. Moreover, whereas the categorization of transitive gestures was significantly facilitated by congruent pictures on the right, the effect was weaker for intransitive, and reversed for meaningless movements. In Experiment 2, intransitive gestures were again categorized significantly faster, but transitive significantly slower than the other two gesture categories. Yet, there was now a significant facilitation of intransitive, and inhibition of transitive gesture categorization following congruent prime words in the right visual field, and significantly faster categorization of intransitive gestures following incongruent words in the left visual field. These outcomes lend support to the complexity account of differences in left-hemisphere representations of meaningful gestures reported in the neuropsychological, behavioral, and neuroimaging literature. Nevertheless, they also indicate that the representations of intransitive gestures show some differential, and sometimes counterintuitive sensitivity to right hemisphere processing.