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Asymmetric effects of graspable distractor disks on motor preparation of successive grasps: A behavioural and event-related potential (ERP) study
No full textAuthors: Stefano Uccelli, Letizia Palumbo, Neil Harrison, Nicola Bruno.
University of Parma
Liverpool Hope Universit
Asymmetric effects of graspable distractor disks on motor preparation of successive grasps: A behavioural and event-related potential (ERP) study
No full textAuthors: Stefano Uccelli, Letizia Palumbo, Neil Harrison, Nicola Bruno.
University of Parma
Liverpool Hope Universit
Il ruolo del contesto temporale in percezione e azione
No full textLa visione è fondamentale per interagire con gli oggetti. Il sistema visivo codifica le informazioni visive per creare rappresentazioni interne che sono usate per guidare azioni come l’afferramento, un’azione che eseguiamo con efficienza molte volte ogni giorno. Tuttavia è poco chiaro come il sistema motorio codifichi le caratteristiche degli oggetti per afferrarli. Nello specifico, un vecchio dibattito nelle neuroscienze cognitive riguarda la natura della rappresentazione della grandezza per afferrare oggetti. Secondo la più influente interpretazione funzionale del sistema visivo dei primati, i flussi dorsale e ventrale codificano la grandezza in modi diversi. Queste differenze hanno diverse conseguenze comportamentali, inclusa una certa immunità delle rappresentazioni dorsali a effetti stimolo-contestuali come quelli osservati nella percezione conscia. Lo scopo di questa tesi è di contribuire alla comprensione delle rappresentazioni per l’azione raccogliendo dati in paradigmi di psicofisica, cinematica, ed elettroencefalografia.
Ho condotto quattro esperimenti misurando risposte motorie e percettive all’illusione di Uznadze. In questa illusione, lo stesso oggetto ‘test’ appare più grande (o più piccolo) dopo aver visto un oggetto ‘inducente’ più piccolo (o più grande). Gli Studi 1 e 2 hanno indagato se le rappresentazioni della grandezza in azione e percezione sono influenzate da questa illusione. Nello Studio 1 i partecipanti afferravano il test o ne giudicavano la grandezza (eseguendo un confronto cross-modale chiamato ‘stima manuale’) dopo aver visto un inducente che poteva essere identico, più piccolo, o più grande. I risultati hanno rivelato che in entrambe le risposte motorie e percettive le aperture delle dita mostravano il contrasto di grandezza, cioè erano influenzate dalla grandezza dell’inducente. Lo Studio 2 ha esaminato due ulteriori manipolazioni dell’illusione di Uznadze. Gli inducenti erano presentati apticamente o visivamente, nella stessa posizione del test o in una diversa. I risultati hanno rivelato che le riposte motorie mostrano contrasto di grandezza (l’illusione di Uznadze), assimilazione di grandezza (l’illusione di Uznadze inversa), o nessuna illusione. Questo sembra dipendere da fattori legati all’integrazione multisensoriale e allo schema corporeo, piuttosto che a una distinzione fra azione e percezione. Complessivamente, gli Studi 1 e 2 provano che la codifica della grandezza per l’azione è influenzata da informazioni contestuali.
Gli Studi 3 e 4 indagavano il decorso temporale delle rappresentazioni motorie nel flusso dorsale. Abbiamo valutato se il tempo necessario per preparare una presa fosse influenzato dalla vista di un precedente oggetto distrattore di uguale o diversa grandezza. Lo Studio 3 ha mostrato che i partecipanti erano più lenti nel preparare la presa quando i distrattori erano più grandi del test, ma non quando erano più piccoli. Lo Studio 4 estende questo risultato a registrazioni di potenziali evento-reati (ERPs). Abbiamo esaminato indici corticali della preparazione motoria per afferrare il test dopo la presentazione di distrattori di uguale o diversa grandezza. I risultati hanno rivelato che componenti dei potenziali di preparazione lateralizzati (LRPs) erano spostati nel tempo in linea con i tempi di preparazione. Questi studi assieme mostrano che l’afferramento non è programmato solo online ma può essere influenzato da informazioni precedenti.
Concludo che il contrasto di grandezza temporale di Uznadze rivela che la preparazione visuomotoria si basa su informazioni spazio-temporali contestuali confrontabili a quelle usate per i giudizi percettivi. Questa conclusione contraddice i modelli attuali sulle proprietà funzionali del flusso dorsale, suggerendo una visione più sfumata dei fattori che influenzano l’afferramento e delle apparenti dissociazioni fra percezione-azione.Visual information is fundamental to interact with objects. For instance, information is coded by the visual system to create internal representations used to guide actions such as grasping, an action we perform efficiently daily many times. However, how the motor system codes object features for grasping remains poorly understood. In particular, a long-standing debate in the cognitive neurosciences concerns the nature of internal representations of object size during motor preparation, a key aspect of grasping. According to the most influential functional interpretation of the primate visual system, size representations are coded in critically different ways in the dorsal and ventral streams. These key differences in turn have several behavioural consequences, including a relative immunity of the dorsal representations of size from stimulus-contextual effects such as those observed for consciously perceived size. Accordingly, the goal of this thesis is to contribute to the understanding of representations for visually-guided actions by collecting data from psychophysical, kinematics, and EEG paradigms.
I conducted four experiments assessing motor and perceptual responses to the Uznadze illusion. In this illusion, the same ‘test’ object appears larger (or smaller) after having seen a smaller (or larger) ‘inducing’ object. Studies 1 and 2 investigated whether size representations in action and perception are affected by this form of size contrast. In Study 1, participants either grasped a test or provided a perceptual judgment of its size (by performing a cross-modal match called a “manual estimation”) after the presentation of an inducer that could be identical, smaller, or larger. Results revealed that finger apertures in both motor and perceptual responses showed a size contrast effect, that is, were affected by the inducer size. In Study 2, two further manipulations of the Uznadze illusion were investigated. Inducers were presented either haptically or visually, and either in the same or in a different position relative to the test. Surprisingly, results revealed that motor responses show size contrast (the Uznadze illusion), or size assimilation (the inverse Uznadze illusion), or even no illusion, depending on factors that seem related to multisensory integration and the body schema rather than a perception-action distinction. Overall, Studies 1 and 2 provide evidence that size representations for action are affected by contextual information.
Studies 3 and 4 investigated the time course of motor representations in the dorsal stream. We focussed on the time needed to prepare a grasp, testing whether motor preparation is affected by viewing a previous distractor object equal or different in size. Study 3 showed that participants were slower in preparing the grasp when distractors were larger than the test, but not when they were smaller. Study 4 extended this finding to event-related potentials (ERPs) recordings. Here, cortical indices of motor preparation to grasp the test were investigated after presenting distractors equal or different in size. Results revealed that components of lateralized readiness potentials (LRPs) were displaced in time consistent with the pattern of preparation times observed in Study 3 and 4. Taken together, Studies 3 and 4 show that grasping is not programmed solely from online information, but can be affected by information experienced recently.
I conclude that the Uznadze temporal size contrast reveals that visuomotor preparation relies on relative spatiotemporal information comparable to that used to produce perceptual judgments. This conclusion challenges current theoretical models of the functional properties of the dorsal stream, suggesting a more nuanced view of factors affecting grasping and seeming behavioural perception-action dissociations
Perception—Action dissociations depend on factors that affect multisensory processing.
No full textBehavioral perception-action dissociations are widely used to test models of high-level vision, but debates concerning their interpretation have underestimated the role of multisen- sory mechanisms in such tests. Sensorimotor tasks engage multisensory processing in fun- damentally different ways than perceptual tasks, and these differences can modulate dissociations in different ways based on task features. To test this idea, we compared per- ception and action using a well-understood size-contrast effect, the Uznadze illusion, and manipulated both unimodal and crossmodal stimulation as well as conditions that are known to favor or hinder multisensory integration. Results demonstrated that similar or dissociable effects on perception and action can be observed depending on factors that are known to affect multisensory processing. Specifically, such factors can cause a visual task to be affected by the illusion or remain fully unaffected, whereas a visuomotor task can be affected by the illusion, remain immune from the illusion, or, unexpectedly, even show a clear reverse effect. These findings provide a novel perspective on a long standing debate in behavioral cognitive neuroscience
Precision in grasping: Consistent with Weber's law, but constrained by “safety margins”
No full textWhether the visuomotor coding of size in grasping obeys Weber's law is currently debated. Following up on previous work from our laboratory, here we investigated the precision associated with the maximum in-flight index-thumb aperture (MGA) in grasping small-to-medium sized objects. We report three main findings. First, grasp preparation was longer with 5 mm objects and became increasingly faster as object size increased from 10 to 20–40 mm. Second, MGA variable errors increased as sizes increased from 5 to 10–20 mm, whereas they decreased as size reached 40 mm. Third, MGA distributions were symmetrical with 5 mm objects, but became increasingly right-skewed as size increased. These results, as well as a re-analysis of previous findings, suggest that the precision of visuomotor representations varies as a function of size, consistent with the key principle underlying Weber's law. However, a fundamental constraint on precision grips (the MGA must always exceed physical size) changes the skew of the distribution and reduces the variability of MGAs as size increases from very small to medium.</p
Emergent and planned interpersonal synchronization are both sensitive to 'tempo aftereffect contagion'.
No full textInterpersonal synchronization is fundamental for motor coordination during social interactions. Discerning emergent (entrainment) from planned synchronization represents a non-trivial issue in visually bonded in- dividuals acting together, as well as assessing whether inter-individual differences, e.g., in autistic traits, modulate both types of synchronization. In a visuomotor finger-tapping task, two participants replicated a target tempo either synchronizing (‘joint’ condition) or not (‘non-interactive’ condition, ‘non-int’) with each other. One participant was exposed (‘induced’) to tempo aftereffect (a medium tempo seems faster or slower after exposure to slower or faster inducing tempi), but not the other participant (‘not induced’); thus they had different timing perceptions of the same target. We assessed to what degree emergent and/or planned synchronization affected dyads by analyzing inter-tap-intervals, synchronization indexes, and cross-correlation coefficients. Results revealed a ‘tempo aftereffect contagion’: inter-tap-intervals of both induced and not-induced participants showed aftereffect in both the joint and non-int conditions. Moreover, aftereffects did not correlate across conditions suggesting they might be due to (at least in part) different processes, but the propensity for tempo aftereffect contagion correlated with individuals’ autistic traits only in the non-int condition. Finally, participants co- adjusted their tapping more in the joint condition than in the non-int one, as confirmed by higher synchroni- zation indexes and the mutual adaptation pattern of cross-correlation coefficients. Altogether, these results show the subtle interplay between emergent and planned interpersonal synchronization mechanisms that act on a millisecond timescale independently from synching or not with the partner
The Uznadze illusion reveals similar effects of relative size on perception and action
No full textMilner and Goodale (the visual brain in action, Oxford University Press Inc., Oxford, 1995) proposed a functional dissociation between vision-for-action and vision-for-perception (i.e., the “two-visual system hypothesis”, TVSH). Supporting the TVSH, it has been claimed that visual illusions affect perception but not actions. However, at least for the Ebbinghaus illusion, numerous studies have revealed consistent illusion effects on grasping. Thus, whether illusions affect actions remains controversial. To further investigate the dissociation predicted by the TVSH, we used a visual version of the Uznadze illusion (the same stimulus will feel smaller after feeling a larger stimulus and larger after feeling a smaller stimulus). Based on kinematic recordings of finger aperture in a motor (precision grip) and a perceptual task (manual estimation), we report two main findings. First, both action and perception are strongly affected by the Uznadze illusion. Second, the illusion decreases similarly in both tasks when inducing-induced pairs had different shape and color, in comparison to the equivalent condition where these features are the same. These results are inconsistent with a perception–action dissociation as predicted by the TVSH and suggest that, at least in the present conditions, vision-for-perception and vision-for-action are similarly affected by contextual cues
Who is the author of the 1876 Stefano manuscript?
No full textFor over one hundred years the Stefano manuscript was a private document in the possession of the Baccich family and descendants. It told a story of the 1875 Stefano shipwreck as narrated by the shipwreck survivor and the founding family patriarch Miho Baccich. In these circumstances the question of authorship of the manuscript was immaterial and did not arise as an issue. However, with the publication of the manuscript the author‟s name, or names, need to be formally attributed to it. It turns out that this is not such a clear-cut matter.
As we shall see, all informed sources attributed the authorship, and the ownership, of the manuscript to Miho Baccich. But the manuscript itself was written by Canon Stjepan Skurla – a priest from Miho‟s hometown of Dubrovnik. The question then arises: should Skurla also be considered as an author of the manuscript, or, even as the sole author (as some would have it)
EXPRESS: The effect of the Uznadze illusion is temporally dynamic in closed-loop but temporally constant in open-loop grasping
No full textAlthough it is known that the availability of visual feedback modulates grasping kinematics, it is unclear whether this extends to both the early and late stages of the movement. We tackled this issue by exposing participants to the Uznadze illusion (a medium stimulus appears larger or smaller after exposure to smaller or larger inducers). After seeing smaller or larger discs, participants grasped a medium disc with (closed-loop [CL]) or without (open-loop [OL]) visual feedback. Our main aim was to assess whether the time course of the illusion from the movement onset up to the grasp differed between OL and CL. Moreover, we compared OL and CL illusory effects on maximum grip aperture (MGA) and tested whether preparation time, movement time, and time to MGA predicted illusion magnitude. Results revealed that CL illusory effects decreased over movement time, whereas OL ones remained constant. At the time of MGA, OL, and CL effects were, however, of similar size. Although OL grasps were longer to prepare and showed earlier and larger MGAs, such differences had little impact on modulating the illusion. These results suggest that the early stage of grasping is sensitive to the Uznadze illusion both under CL and OL conditions, whereas the late phase is sensitive to it only under OL conditions. We discuss these findings within the framework of theoretical models on the functional properties of the dorsal stream for visually guided actions
Analisi dei movimenti spazio-temporali di uccelli acquatici svernati nelle zone umide dell'alto Adriatico
No full text2007/2008Le zone umide costiere dell’Alto Adriatico sono siti di grande importanza per lo svernamento di molte specie di uccelli acquatici. Gli uccelli acquatici possono essere considerati dei validi bioindicatori ambientali di queste aree, da cui essi dipendono in tutte le fasi del loro ciclo biologico. La conoscenza dei movimenti spazio-temporali dell’avifauna acquatica è un elemento essenziale per una corretta gestione delle zone umide e per lo sviluppo di adeguate politiche di conservazione. A tale scopo, è stato studiato il comportamento spazio-temporale degli uccelli acquatici a scala globale (variabilità intra- ed inter-annuale), a scala regionale (distribuzione nelle zone umide dell’alto Adriatico) ed scala locale (uso dello spazio e dell’habitat). In considerazione della notevole variabilità comportamentale che gli uccelli dimostrano ad ogni scala spazio-temporale, sono stati studiati i limiti e le dimensioni di queste variazioni in alcune specie di uccelli acquatici svernanti nell’Alto Adriatico, cercando di comprendere quale parte di questa variabilità è casuale e quale origina da risposte adattative a fattori ecologici. Come specie target è stato scelto il Piovanello pancianera Calidris alpina. Si è cercato, inoltre, di fornire alcune indicazioni per la gestione di queste zone umide e per una corretta metodologia di rilevamento e utilizzo dei dati di censimento.XXI Ciclo197
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