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The present study aimed at determining whether the observation of two functionally compatible artefacts, that is which potentially concur in achieving a specific function, automatically activates a motor programme of interaction between the two objects. To this purpose, an interference paradigm was used during which an artefact (a bottle filled with orange juice), target of a reaching-grasping and lifting sequence, was presented alone or with a non-target object (distractor) of the same or different semantic category and functionally compatible or not. In experiment 1, the bottle was presented alone or with an artefact (a sphere), or a natural (an apple) distractor. In experiment 2, the bottle was presented with either the apple or a glass (an artefact) filled with orange juice, whereas in experiment 3, either an empty or a filled glass was presented. In the control experiment 4, we compared the kinematics of reaching-grasping and pouring with those of reaching-grasping and lifting. The kinematics of reach, grasp and lift was affected by distractor presentation. However, no difference was observed between two distractors that belonged to different semantic categories. In contrast, the presence of the empty rather filled glass affected the kinematics of the actual grasp. This suggests that an actually functional compatibility between target (the bottle) and distractor (the empty glass) was necessary to activate automatically a programme of interaction (i.e. pouring) between the two artefacts. This programme affected the programme actually executed (i.e. lifting). The results of the present study indicate that, in addition to affordances related to intrinsic object properties, "working affordances" related to a specific use of an artefact with another object can be activated on the basis of functional compatibility.

An experiment investigated the ability by human observers to detect temporal reversals in dynamic displays of human locomotion. We video-taped the lower portion of the body of actors walking at their preferred speed either in the normal, forward direction (FW) or in the backward direction (BW). The videos were presented in a random order either as recorded (N) or in reverse (R). In one session, we presented both normal and time-reversed stimuli in the original upright orientation. In a second session, the stimuli were rotated by 180° around the horizontal axis. Observers were informed that the real recorded movement was either forward or backward and were asked to decide whether or not the movement had been time-reversed prior to the presentation. Although the kinematics of forward and backward human locomotion is quite similar, the detection of temporal reversals followed a consistent pattern showing a good accuracy in condition FW-N and a reduced but still above-chance performance in condition BW-R (by design, in both conditions actors appeared to walk forward). Performance was instead at chance level in the other two conditions where the apparent direction of the movement was backward. Inverting the spatial orientation of the stimuli reduced but did not suppress the ability to detect temporal reversals in the two conditions with apparent forward direction of movement. It is argued that implicit motor competence is at least in part instrumental for extracting the subtle discriminal information from the stimuli.

The present study aimed at determining whether, and in what conditions, covert imitation of different manual grasps of the same object influences estimation of those object properties whose variations afford those different grasp interactions. Participants matched the size of spheres after observation of the same spheres being grasped using both a power and a precision grasp: these actions are used preferentially to grasp large and small objects, respectively. The type of matching varied across four experiments. In experiment 1, participants matched the object size by opening their thumb and index finger; in experiment 2, they abducted their index and middle fingers as in a finger opening of a cutting pantomime, and in experiment 3, they opened their mouth. In experiment 4, the sphere size was reproduced on a PC monitor by moving the mouse forward/backward. Grasp observation affected matching in experiments 1 and 3. Kinematics analysis showed overestimation after observation of a power grasp as compared to a precision grasp. The data are interpreted as a consequence of covert imitation of the observed hand kinematics, which varied congruently with the object sizes potentially activating that type-of-grasp. This affected estimation of object size. Covert imitation was favored by the types of matching requiring motor patterns related to grasp movements independently of the effector used. This finding supports the existence of motor commands to the hand as well as to the mouth, activated when the same potential goal guides the movements of both these effectors.

The present study aimed at determining whether or not the comprehension of symbolic gestures, and corresponding-in-meaning words, makes use of cortical circuits involved in movement execution control. Participants were presented with videos of an actress producing meaningful or meaningless gestures, pronouncing corresponding-in-meaning words or pseudo-words; they were required to judge whether the signal was meaningful or meaningless. Single pulse TMS was applied to forearm primary motor cortex area 150–200 ms after the point when the stimulus meaning could be understood. MEPs were significantly greater when processing meaningless signals as compared to a baseline condition presenting a still-and-silent actress. In contrast, this was not the case for meaningful signals whose motor activation did not differ from that for the baseline stimulus. MEPs were significantly greater for meaningless than meaningful signals and no significant difference was found between gesture and speech. On the basis of these results, we hypothesized that the observation-of/listening-to meaningless signals recruits motor areas. In contrast, this did not occur when the signals were meaningful. Overall, the data suggest that the processes related to comprehension of symbolic gestures and communicative words do not involve primary motor area and probably use brain areas involved in semantics.

Using transcranial magnetic stimulation (TMS), motor evoked potentials (MEPs) were recorded from two antagonistic muscles, the first dorsal interosseus (FDI) of the hand and the extensor communis digitorum (EC) of the forearm. FDI is involved in grasping actions and EC in releasing. TMS pulses were delivered while participants were reading adjectives expressing either negative or positive pragmatic properties, at 150 ms after presentation of language material. Overall findings showed an interaction of adjective type (positive, negative) and muscle (FDI, EC), the effect being driven by a significant difference for negative adjectives. Further analysis aimed at investigating the effectiveness of positive adjectives showed a similar, but opposite, pattern of effects for the positive words in the initial two blocks. The present results indicate that, as for verbs and nouns, adjectives recruit the sensorimotor system, and their processing is best explained by an embodiment rather than an amodal approach to language.

We tested whether a system coupling hand postures related to gestures to the control of internal mouth articulators during production of vowels exists and it can be precursor of a system relating hand/arm gestures to words. Participants produced unimanual and bimanual representational gestures expressing the meaning of LARGE or SMALL. Once the gesture was produced, in experiment 1 they pronounced the vowels “A” or “I”, in experiment 2 the word “GRANDE” (large) or “PICCOLO” (small), and in experiment 3 the pseudo-words “SCRANTA” or “SBICCARA”. Mouth, hand kinematics and voice spectra were recorded and analyzed. Unimanual gestures affected voice spectra of the two vowels pronounced alone (experiment 1). Bimanual and both unimanual and bimanual gestures affected voice spectra of /a/ and /i/ included in the words (experiment 2) and pseudo-words (experiment 3), respectively. The results support the hypothesis that a system coupling hand gestures to vowel production exists. Moreover, they suggest the existence of a more general system relating gestures to words.

One of the most important faculties of humans is to understand the behaviour of other conspecifics. The present study aimed at determining whether, in a social context, request gesture and gaze direction of an individual are enough to infer his/her intention to communicate, by searching for their effects on the kinematics of another individual's arm action. In four experiments participants reached, grasped and lifted a bottle filled of orange juice in presence of an empty glass. In experiment 1, the further presence of a conspecific not producing any request with a hand and gaze did not modify the kinematics of the sequence. Conversely, experiments 2 and 3 showed that the presence of a conspecific producing only a request of pouring by holding the glass with his/her right hand, or only a request of comunicating with the conspecific, by using his/her gaze, affected lifting and grasping of the sequence, respectively. Experiment 4 showed that hand gesture and eye contact simultaneously produced affected the entire sequence. The results suggest that the presence of both request gesture and direct gaze produced by an individual changes the control of a motor sequence executed by another individual. We propose that a social request activates a social affordance that interferes with the control of whatever sequence and that the gaze of the potential receiver who held the glass with her hand modulates the effectiveness of the manual gesture. This paradigm if applied to individuals affected by autism disorder can give new insight on the nature of their impairment in social interaction and communication.

Is the human kinematics automatically imitated when an individual observes transitive actions (i.e. directed upon an object) executed with different effectors and then executes either the same or a different action? In three experiments participants executed actions of reaching-grasping after observation of reaching-grasping, bringing-to-the-mouth, foot-touching, and arrow-touching. Both power and precision interactions were presented. The kinematics of all movements was those typical of humans. The observed variations in velocity due to the type of interaction were imitated when an interacting biological effector (i.e. arm, mouth and foot) was presented. In contrast, no imitation was observed when a non-biological effector (i.e. the arrow) was presented. The results of the present study suggest that there exists a kinematic representation of the rules governing the types of interaction of biological effectors with objects. It is automatically activated by action observation and affects kinematic landmarks of the successive action, i.e. the peak velocities and accelerations. This representation is common to different biological effectors probably because it shares the aim of those actions.

The present study aimed at determining whether and what factors affect the control of motor sequences related to interactions between conspecifics. Experiment 1 demonstrated that during interactions between conspecifics guided by the social intention of feeding, a social affordance was activated, which modified the kinematics of sequences constituted by reaching-grasping and placing. This was relative to the same sequence directed to an inanimate target. Experiments 2 and 4 suggested that the related-to-feeding social request emitted by the receiver (i.e. the request gesture of mouth opening) is prerequisite in order to activate a social affordance. Specifically, the two experiments showed that the social request to be fed activated a social affordance even when the sequences directed towards a conspecific were not finalized to feed. Experiment 3 showed that moving inside the peripersonal space of a conspecific, who did not produce any social request, marginally affected the sequence. Finally, experiments 5 and 6 indicated that the gaze of a conspecific is necessary to make a social request effective at activating a social affordance. Summing up, the results of the present study suggest that the control of motor sequences can be changed by the interaction between giver and receiver: the interaction is characterized by a social affordance that the giver activates on the basis of social requests produced by the receiver. The gaze of the receiver is a prerequisite to make a social request effective.

The present study aimed at determining whether, in healthy humans, postures assumed by distal effectors affect the control of the successive grasp executed with other distal effectors. In experiments 1 and 2, participants reached different objects with their head and grasped them with their mouth, after assuming different hand postures. The postures could be implicitly associated with interactions with large or small objects. The kinematics of lip shaping during grasp varied congruently with the hand posture, i.e. it was larger or smaller when it could be associated with the grasping of large or small objects, respectively. In experiments 3 and 4, participants reached and grasped different objects with their hand, after assuming the postures of mouth aperture or closure (experiment 3) and the postures of toe extension or flexion (experiment 4). The mouth postures affected the kinematics of finger shaping during grasp, that is larger finger shaping corresponded with opened mouth and smaller finger shaping with closed mouth. In contrast, the foot postures did not influence the hand grasp kinematics. Finally, in experiment 5 participants reached-grasped different objects with their hand while pronouncing opened and closed vowels, as verified by the analysis of their vocal spectra. Open and closed vowels induced larger and smaller finger shaping, respectively. In all experiments postures of the distal effectors induced no effect, or only unspecific effects on the kinematics of the reach proximal/axial component. The data from the present study support the hypothesis that there exists a system involved in establishing interactions between movements and postures of hand and mouth. This system might have been used to transfer a repertoire of hand gestures to mouth articulation postures during language evolution and, in modern humans, it may have evolved a system controlling the interactions existing between speech and gestures.

The present study aimed at verifying whether and why sequences of actions directed to oneself are facilitated when compared to action sequences directed to conspecifics. In experiment 1, participants reached to grasp and brought a piece of food either to their own mouth for self-feeding or to the mouth of a conspecific for feeding. In control conditions, they executed the same sequence to place the piece of food into a mouth-like aperture in a flat container placed upon either their own mouth or the mouth of a conspecific. Kinematic analysis showed that the actions of reaching and bringing were faster when directed to the participant's own body, especially for self-feeding. The data support the hypothesis that reaching to grasp and bringing to one's own body and, in particular, one's own mouth for self-feeding, form an automatic sequence, because this is the result of more frequent execution and coordination between different effectors of one's own body, such as arm and mouth. In contrast, the same sequence directed toward a conspecific is not automatic and requires more accuracy probably because it is guided by social intentions. This hypothesis was supported by the results of control experiment 2 in which we compared the kinematics of reaching to grasp and placing the piece of food into the mouth of a conspecific (i.e. feeding) with those of reaching to grasp and placing the same piece of food into a mouth-like aperture in a human body shape (i.e. placing). Indeed, the entire sequence was slowed down during feeding when compared to placing.

Both intersubjectivity and embodied cognitive processes are based on mechanisms for sharing actions, common to the species. The evolution of spoken language and of communication systems in general are good examples of this. In the present review, we propose that, by a process of observation and imitation, the sharing of object-directed actions (i.e., transitive arm/hand actions) and their pantomimes could have been used to progressively construct communication systems capable of representing action meaning (i.e., their goals). Starting from this process of observation and imitation, humans may have constructed progressively more complex communication systems based on iconic and symbolic arm gestures. These communication systems may have gradually been translated into more specific, buccal, gesture-based systems that gave rise to spoken language. In support of these hypotheses, we report evidence showing that the execution and observation of transitive actions and their pantomimes affects the production of phonological units. We describe the effects of the production and observation of symbolic gestures on word pronunciation. Finally, we report evidence that these systems relating gesture to speech have neural correlates in neural circuits located in the frontal cortex, understood to be involved in spoken language..

Is the motor system involved in language processing? In order to clarify this issue, we carried out three behavioral experiments, using go-no-go and choice paradigms. In all the experiments, we used a semantic decision task with an early delivery of the go signal (during processing language material). Italian verbs expressing hand actions, foot actions or an abstract content served as stimuli. Participants executed intransitive (Experiment 1) or transitive (Experiment 2) actions with their right hand in response to the acoustic presentation of action-related verbs and refrained from responding to abstract verbs. The kinematics of the actions was slowed down by hand action-related verbs when compared with foot action-related verbs. In Experiment 3, hand-related and foot-related verbs were presented. Participants responded to hand-related and foot-related verbs with their hand and their foot (compatible condition) and in another block of trials they responded to hand-related and foot-related verbs with their foot and their hand (incompatible condition), respectively. In the compatible condition, the beginning of the action was faster, whereas the kinematics of the action was slower. The present findings suggest complete activation of verb-related motor programs during language processing. The data are discussed in support of the hypothesis that this complete activation is necessary requisite to understand the exact meaning of action words because goal and consequence of the actions are represented.

Does the mirror system affect the control of speech? This issue was addressed in behavioral and Transcra- nial Magnetic Stimulation (TMS) experiments. In behavioral experiment 1, participants pronounced the syllable /da/ while observing (1) a hand grasping large and small objects with power and precision grasps, respectively, (2) a foot interacting with large and small objects and (3) differently sized objects presented alone. Voice formant 1 was higher when observing power as compared to precision grasp, whereas it remained unaffected by observation of the different types of foot interaction and objects alone. In TMS experiment 2, we stimulated hand motor cortex, while participants observed the two types of grasp. Motor Evoked Potentials (MEPs) of hand muscles active during the two types of grasp were greater when observing power than precision grasp. In experiments 3–5, TMS was applied to tongue motor cortex of participants silently pronouncing the syllable /da/ and simultaneously observing power and precision grasps, pantomimes of the two types of grasps, and differently sized objects presented alone. Tongue MEPs were greater when observing power than precision grasp either executed or pantomimed. Finally, in TMS experiment 6, the observation of foot interaction with large and small objects did not modulate tongue MEPs. We hypothesized that grasp observation activated motor commands to the mouth as well as to the hand that were congruent with the hand kinematics implemented in the observed type of grasp. The commands to the mouth selectively affected postures of phonation organs and consequently basic features of phonological units.