1,720,972 research outputs found
OLFACTION IN ACTION
Full text linkRecent evidence has contributed to change the view according to which action representation chiefly depends on visual information. In particular, research on hand grasping actions has emphasized that a multimodal interplay across vision, audition, the sense of touch, and proprioception occurs when performing and understanding an action (e.g., Castiello, 1996; Patchay, Castiello, & Haggard, 2003; Gazzola, Aziz-Zadeh, & Keysers, 2006; Zahariev & MacKenzie, 2007).
The experimental work included in the present thesis aimed at extending the multisensory aspects of action representation to the olfactory domain. I first addressed this issue from the perspective of action execution by asking participants to reach and grasp a target-object under different circumstances of visual and olfactory stimulation. The angular excursion at the level of individual digits, digits’ angular distance, and arm movement duration were recorded. Next, I focused on action understanding by asking participants to observe others’ grasping actions under different visual and olfactory conditions. Here, cerebral activity of the neural system responsible for action understanding, i.e., the Action Observation System (AOS) was recorded.
An overview of this experimentation is outlined in the following section.
OVERVIEW OF THE PRESENT RESEARCH
In the first two experiments (Thesis Chapters 3 and 4) participants were requested to reach towards and grasp either a small or a large visual target calling for different types of grasp, precision grip (PG) and whole hand grasp (WHG), respectively. This task was performed in the absence or in the presence of an odour associated with objects that, if grasped, would require a PG or a WHG. The aim of these experiments was twofold. First, to understand whether the central nervous system (CNS) can use olfactory information to select and execute a ‘grasp’ motor plan. Second, to shed light on how detailed the motor commands embedded within the ‘grasp’ plans elicited by an object’s olfactory representation are. The results showed that merely smelling the odour associated with a small and a large object activates the kinematic parameterization of the action appropriate for grasp that object, i.e., PG and WHG, respectively. Therefore, the CNS is able to convert the geometric features of an olfactory-encoded object (e.g., size) into the motor prototype for interacting with that object. In other words, the visuomotor mechanism underlying the control of action (e.g., Castiello, 1996) appears to be sensitive to olfactory information.
From a perceptual perspective, the representation evoked by the odour seems to contain highly detailed information regarding the object (i.e., volumetric features). This is because the effect of odour ‘size’ was played out on the hand posture at the level of individual digits’ motion. If olfaction had provided a blurred and holistic object’s representation (i.e., a low spatial-resolution of the object’s image), then the odour would have not affected would have not affected the hand in its entirety. From a motor perspective, the olfactory representation seems to be mapped into the action vocabulary with a certain degree of reliability. The elicited motor plan is not an incomplete primal sketch which only provides a preliminary descriptive in the terms of motor execution but it embodies specific and selective commands for handling the ‘smelled’ object.
In the experiments described above the odour associated with the object was always delivered before movement initiation and before the target became visually available. For the motor control system this entailed to prioritize the ‘olfactory’ non-target object with respect to the visual target. Specifically, planning and execution of action was first based on the sense of smell. In this respect, previous research on grasping actions revealed that visual nontarget-objects do not activate the corresponding ‘grasp’ plans when prior knowledge regarding the visual target is given to participants (e.g., Castiello, 1996). In order to investigate whether this caveat also applies for nontarget-objects signalled via olfaction, I performed an experiment (Thesis Chapters 5) similar to those reported above, but participants were given sufficient time to code for the visual target before movement initiation. The results showed that in such circumstances the odour ‘size’ did modulate the temporal organization of the arm movement. Therefore, even when olfactory information plays a secondary role with respect to visual information for action guidance, the olfactory-encoded object is represented within the motor system. And, traces of the ‘grasp’ motor plan associated with the olfactory object remain evident at the level of the arm movement.
Having demonstrated the influence that olfactory stimuli might have for the control of action I reasoned that such phenomenon might be relevant for investigating possible gender differences in the use of olfactory information within the action domain (e.g., Ecuyer-Dab & Robert, 2004). Therefore by using an experimental paradigm similar to that reported in Thesis Chapter 4, I investigated whether gender differences were evident when odours of objects had to be mapped into the corresponding ‘grasp’ motor plans (Thesis Chapter 6). The results showed that for men arm-movement duration increased when the ‘size’ of the odour did not match the size of the visual target. Whereas, for women such effect was not revealed. Remember that a lengthening in movement duration was taken as evidence for an odour-induced activation of the ‘grasp’ motor plans associated with the ‘smelled-objects’ (Thesis Chapter 4). Therefore, it appears that male sense of smell is action-oriented, i.e., tailored to elicit specific and selective motor commands for act upon olfactory-encoded objects. Whereas, in line with previous evidences stemming from research on human olfaction, the female sense of smell would be perception-oriented, i.e., optimised to detect, discriminate, identify, recognise, and categorise odours (e.g., Brand & Millot, 2001).
Once documented that the sense of smell provides useful information for planning and execute an action I investigated whether olfactory cues may also contribute to the understanding of others’ actions. The fMRI experiment reported in Thesis Chapter 7 was conceived to specifically address this issue. The results showed that the neural system devoted to action understanding (i.e., the ASO) represented both a hand grasping an ‘olfactory’ object and a mimed hand grasp. Importantly, evidence that the AOS was also able to differentiate between these two type of actions was also found. The discrimination process might solely be ascribed to the olfactory information which signalled the target-object. Therefore, the role played by olfactory information in action understanding was demonstrated.
With this in mind the central advance of the present work is twofold. First, I demonstrated that processes of selection for the control of actions may be based on olfactory information. This was done by linking current advances in the methodology for recording hand kinematics and paradigms considering the presence of nontarget-object. Second, I provided evidence for the contribution of olfactory information to the understanding of other’s actions. This was achieved by combining the fMRI technique with an action observation paradigm.
REFERENCES
Brand, G., & Millot, J. L. (2001). Sex differences in human olfaction: between evidence and enigma. Quarterly Journal of Experimental Psychology, 54, 259-270.
Castiello, U. (1996). Grasping a fruit: selection for action. Journal of Experimental Psychology: Human Perception and Performance, 22, 582-603.
Ecuyer-Dab, I., & Robert, M. (2004). Have sex differences in spatial ability evolved from male competition for mating and female concern for survival? Cognition, 91, 221-257.
Gazzola, V., Aziz-Zadeh, L., & Keysers, C. (2006). Empathy and the somatotopic auditory mirror system in humans. Current Biology, 16, 1824-1829.
Patchay, S., Castiello, U., & Haggard, P. (2003). A crossmodal interference effect in grasping objects. Psychological Bulletin Reviews, 10, 924-931.
Zahariev M. A., & MacKenzie, C. L. (2007) Grasping at thin air: multimodal contact cues for reaching and grasping. Experimental Brain Research, 180, 69-84.Evidenze ottenute da studi recenti hanno cambiato la concezione secondo cui la rappresentazione dell’azione si basa principalmente sulle informazioni di natura visiva. In particolare, la ricerca sulle azioni di prensione ha dimostrato che si verifica un’interazione tra la visione, l’udito, il tatto e la propriocezione sia quando una persona esegue un’azione sia quando cerca di capire l’azione di un altro individuo (Castiello, 1996; Patchay, Castiello, & Haggard, 2003; Gazzola, Aziz-Zadeh, & Keysers, 2006; Zahariev & MacKenzie, 2007).
Il lavoro sperimentale riportato nella presente tesi ha lo scopo di estendere gli aspetti multisensoriali della rappresentazione dell’azione al dominio olfattivo. Per prima cosa ho trattato questa questione dalla prospettiva dell’esecuzione dell’azione chiedendo ai partecipanti di raggiungere ed afferrare un oggetto target in diverse condizioni di stimolazione visiva ed olfattiva. Ho registrato l’escursione angolare a livello delle singole giunture delle dita della mano e delle distanze tra le dita. Inoltre ho misurato la durata del movimento del braccio. Poi mi sono concentrato sulla comprensione dell’azione chiedendo ai partecipanti di osservare le azioni di prensione compiute da altri individui in diverse condizioni di stimolazione visiva ed olfattiva. Qui, usando la risonanza magnetica funzionale (fMRI), ho registrato l’attività cerebrale dell’Action Observation System (AOS), la rete di aree responsabile della comprensione dell’azione.
Nella seguente sezione fornisco un riassunto di questa sperimentazione.
RIASSUNTO DELLA RICERCA
Nei primi due esperimenti (Capitoli 3 e 4 della Tesi) i partecipanti raggiungevano ed afferravano degli oggetti target grandi oppure piccoli che richiedevano rispettivamente un precision grip (PG) e un whole hand grasp (WHG). Questo compito era svolto in assenza o in presenza di un odore associato con un oggetto che, se afferrato, avrebbe richiesto un PG o un WHG. L’obiettivo di questi esperimenti era duplice. Innanzitutto volevo capire se il sistema nervoso centrale (SNC) può usare l’informazione olfattiva per selezionare ed eseguire un piano motorio di prensione. Poi volevo valutare quanto sono dettagliati i comandi motori inclusi nel piano di prensione eventualmente attivato dall’odore. I risultati mostrano che semplicemente annusare l’odore associato con un oggetto grande oppure piccolo attiva la parametrizzazione cinematica dell’azione di prensione appropriata per agire su quell’oggetto, i.e., rispettivamente un PG e un WHG. Quindi, il SNC è in grado di convertire le caratteristiche geometriche di un oggetto codificato attraverso l’olfatto nel piano motorio per interagire con quell’oggetto. In altre parole il meccanismo visuomotorio sottostante il controllo dell’azione (Castiello, 1996) è sensibile all’informazione olfattiva.
Da una prospettiva percettiva, la rappresentazione evocata dall’odore contiene informazioni altamente dettagliate circa l’oggetto (i.e., caratteristiche volumetriche). Questo perché l’effetto di ‘dimensione’ dell’odore è evidente a livello del movimento delle singole giunture delle singole dita della mano. Se l’olfatto avesse fornito una rappresentazione olistica e non dettagliata dell’oggetto (i.e., un’immagine dell’oggetto a bassa risoluzione spaziale), l’odore non avrebbe modulato la mano nella sua interezza. Da una prospettiva motoria, la rappresentazione olfattiva è mappata nel vocabolario delle azioni con un buon grado di affidabilità. Il piano motorio attivato dall’odore non è una bozza incompleta e primitiva che fornisce solo una descrizione preliminare in termini di esecuzione motoria ma incorpora comandi specifici e selettivi per manipolare l’oggetto ‘annusato’.
Negli esperimenti appena descritti l’odore associato con l’oggetto era sempre somministrato prima dell’inizio del movimento e prima che l’oggetto target diventasse visibile. Per il sistema di controllo motorio questo implica una priorità dell’oggetto ‘olfattivo’ nontareget rispetto al target visivo. Nello specifico, la pianificazione e l’esecuzione dell’azione è basata sull’informazione olfattiva. A tal proposito, la ricerca sulle azioni di prensione ha mostrato che gli oggetti visivi nontarget non attivano i corrispondenti piani motori di prensione quando i partecipanti conoscono in anticipo il target (Castiello, 1996). Al fine di investigare se ciò vale anche per gli oggetti ‘olfattivi’ nontarget, ho condotto un esperimento simile a quelli riportati sopra, tuttavia, qui i partecipanti avevano tempo di codificare il target visivo prima dell’inizio del movimento (Capitolo 5 della Tesi). I risultati mostrano che la ‘dimensione’ dell’odore modula l’organizzazione temporale del movimento del braccio. Quindi, anche quando l’informazione olfattiva gioca un ruolo secondario rispetto all’informazione visiva per la guida dell’azione, l’oggetto ‘olfattivo’ è rappresentato nel sistema motorio.
Dopo aver dimostrato l’influenza degli stimoli olfattivi sul controllo dell’azione, ho pensato che tale fenomeno poteva essere rilevante per investigare possibili differenze di genere nell’uso dell’informazione olfattiva entro il dominio dell’azione (Ecuyer-Dab & Robert, 2004). Quindi, usando un paradigma sperimentale simile a quello riportato nel Capitolo 4 della Tesi, ho valutato se la capacità di trasformare gli odori degli oggetti nei corrispondenti piani motori varia a seconda del genere (Capitolo 6 della Tesi). I risultati mostrano che per i maschi la durata del movimento del braccio aumenta quando la ‘dimensione’ dell’odore non corrisponde alla dimensione del target visivo. D’altra parte, per le femmine questo effetto non è evidente. Si ricordi che l’aumento della durata del movimento del braccio indica l’attivazione del piano motorio di prensione associato con l’oggetto ‘annusato’ (Capitolo 4 della Tesi). Quindi, sembra che l’olfatto dei maschi sia orientato all’azione, i.e., predisposto ad innescare comandi motori specifici e selettivi per agire sugli oggetti codificati a livello olfattivo. Invece, in linea con precedenti evidenze (Brand & Millot, 2001), l’olfatto femminile sarebbe orientato alla percezione, i.e., ottimizzato per rilevare, discriminare, identificare, riconoscere e categorizzare odori.
Una volta dimostrato che l’olfatto fornisce informazioni utili per la pianificazione e l’esecuzione dell’azione, ho indagato se gli indizi olfattivi possono contribuire anche alla comprensione dell’azione altrui. L’esperimento fMRI riportato nel Capitolo 7 della Tesi è stato disegnato per trattare questa questione. I risultati mostrano che l’AOS rappresenta sia una mano che afferra un oggetto di cui si sente l’odore che una prensione mimata. Inoltre l’AOS è in grado di differenziare tra questi due tipi di azione. Questo processo di discriminazione è imputabile solamente all’informazione olfattiva che segnala l’oggetto afferrato da un altro individuo. Quindi il ruolo giocato dall’informazione olfattiva nella comprensione dell’azione risulta dimostrato.
In conclusione le evidenze riportate nella mia tesi forniscono due contributi fondamentali all’idea di rappresentazione dell’azione multimodale. Primo, il processo di selezione dei piani motori per il controllo delle azioni può basarsi sull’informazione olfattiva. Questa nozione poggia sui dati ottenuti combinando le recenti tecniche di registrazione delle cinematiche della mano con i paradigmi che considerano la presenza di oggetti nontarget. Secondo, l’olfatto contribuisce alla comprensione dell’azione degli altri. Ciò è stato dimostrato usando il paradigma di osservazione dell’azione e l’fMRI.
RIFERIMENTI BIBLIOGRAFICI
Brand, G., & Millot, J. L. (2001). Sex differences in human olfaction: between evidence and enigma. Quarterly Journal of Experimental Psychology, 54, 259-270.
Castiello, U. (1996). Grasping a fruit: selection for action. Journal of Experimental Psychology: Human Perception and Performance, 22, 582-603.
Ecuyer-Dab, I., & Robert, M. (2004). Have sex differences in spatial ability evolved from male competition for mating and female concern for survival? Cognition, 91, 221-257.
Gazzola, V., Aziz-Zadeh, L., & Keysers, C. (2006). Empathy and the somatotopic auditory mirror system in humans. Current Biology, 16, 1824-1829.
Patchay, S., Castiello, U., & Haggard, P. (2003). A crossmodal interference effect in grasping objects. Psychological Bulletin Reviews, 10, 924-931.
Zahariev M. A., & MacKenzie, C. L. (2007) Grasping at thin air: multimodal contact cues for reaching and grasping. Experimental Brain Research, 180, 69-84
The Effects of Task Irrelevant Olfactory Information on the Planning and the Execution of Reach-to-Grasp Movements
No full textPrevious evidence indicates that, when reaching to grasp a target object, the presence of nontarget irrelevant information (i.e., distractor) presented either in the visual or olfactory modality determines significant interference effects on temporal parameters, such as reaction time and movement time, and on movement kinematics. While research on “visual” distractor has also revealed that such interference effects disappear when prior knowledge about the target is given to participants, this aspect for olfactory distractors has yet to be investigated. Therefore, here we asked participants to reach towards and grasp a small or a large visual target following the delivery of an odor evoking either a small or a large object. When the type of grasp evoked by the odor did not coincide with that for the visual target, interference effects were evident on reach duration and reaction time, but kinematics of hand shaping remained unaltered. This study demonstrates that, when participants knew in advance which object was the target, olfactory nontargets produced no interference effects on movement kinematics, but they did on key temporal measures, i.e., reaction time and reach duration. These findings are discussed in light of current theories put forward to explain the sensory processes underlying the control of action
Mirror neurons in humans: Consisting or confounding evidence?
No full textThe widely known discovery of mirror neurons in macaques shows that premotor and parietal cortical areas are not only involved in
executing one’s own movement, but are also active when observing the action of others. The goal of this essay is to critically evaluate the
substance of functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies whose aim has been to
reveal the presence of a parallel system in humans. An inspection of this literature suggests that there is relatively weak evidence for
the existence of a circuit with ‘mirror’ properties in humans, such as that described in monkeys
Odours grab his hand but not hers
No full textGender is important for the determination of olfactory abilities. Previous reports on
gender differences in human odour perception claimed that the sensitivity and discrimination
ability of females for odours is superior to that of males. Evolutionary theories, however, open
up the possibility of an interesting dissociation between females and males in terms of odour
processing: there is an advantage for women for the perceptual aspects of olfactory stimuli and
an advantage for men when translating perceptual olfactory information into action. In line
with this hypothesis our observations suggest that encoding odours has the ability to guide the
movement of males but not that of females
Control of hand shaping in response to object shape perturbation
No full textThis study assessed how hand shaping responds to a perturbation of object shape. In blocked trials (80% of total), subjects were instructed to reach, to grasp and lift a concave or a convex object. In perturbed trials (20% of total), a rotating device allowed for the rapid change from the concave to the convex object or vice versa. In this situation subjects grasped the last presented object. Flexion/extension at the metacarpal-phalangeal and proximal interphalangeal joints of all digits was measured by resistive sensors embedded in a glove. In the blocked condition we found that most joints of the fingers were modulated by the type of the to-be-grasped object during the reach. When object shape was perturbed, reach duration was longer and angular excursion of all fingers differed with respect to blocked trials. For the 'convex --> concave' perturbation, a greater degree of finger extension was found than during the blocked 'concave' trials. In contrast, for the 'concave --> convex' perturbation, fingers were more flexed than for the blocked 'convex' trials. The thumb reacted to the perturbation showing a similar pattern (i.e., over-flexion with respect to the blocked trials) regardless the 'direction' of the perturbation. The present results suggest that applying an object shape perturbation during a reach-to-grasp action determines a reorganization of all digits. This pattern is suggestive of a control strategy, which assigns to opposing digits different roles
Motor ontology in representing gaze–object relations
No full textEvent-related functional magnetic resonance imaging (fMRI) was used to explore how the human brain models gaze–object relations. During
scanning participants observed a human model gazing towards or away a target object presented either in isolation or flanked by a distractor
object. In two further conditions the model’s gaze was shifted and subsequently maintained away from the stimulus/i. These four conditions were
implemented within a factorial design in which the main factors were “type of observed behavior” (gaze vs. gaze-away) and “context” (target
alone vs. target flanked by a distractor). Results revealed that premotor, parietal and temporal areas, known to sub-serve the understanding of other
people actions, were significantly more activated by the observation of the model gazing towards rather than away from the stimulus/i. In addition,
a significant interaction indicated that, when the target was presented in isolation, neural activity within the inferior frontal gyrus, another key
area for action understanding, was influenced by gaze–object relations. Our findings suggest that this area is important for the establishment of
intentional gaze–object relations and indicate that the presence of a distractor interferes with the representation of such relations
- …
