1,720,977 research outputs found
"The neural correlates of grasping actions:observation and execution"
Full text linkSummary
The aim of the present thesis was to shed further light on the properties characterizing the neural system underlying action understanding in humans. This was done in terms of both pure action observation and “mirror” type of activity by means of functional resonance imaging (fMRI). In first instance, I conducted a series of studies in which participants were simply asked to observe a model’s grasping action while their brain was scanned. Here the targeted neural system was the action observation system (AOS), a network of regions automatically recruited during the observation of action performed by others (Buccino et al., 2001). In second instance, the performed experimentation involved the recording of the participants’ neural activity during both the observation and the execution of grasping actions. Here the targeted neural system was the so called “mirror” system (Rizzolatti & Craighero, 2004).
To start with, I considered the investigation of the AOS in a population affected by a severe neurological disorder, i.e. early relapsing remitting multiple sclerosis (RRMS) patients (Chapter 3). During scanning, participants simply observed images depicting a human hand either grasping an object or resting alongside an object. Although previous evidence indicates a selective impairment of the AOS in MS patients, the present findings are not suggestive of any specific deficit at the level of this system in these patients. Rather, they showed a general, but unspecific, effect of BOLD over-activation which was probably determined by the extensive demyelination caused by the disease and by the consequent repairing process carried out by our organism. Such unspecific over-activation has been discussed in terms of the spared ability of the AOS to re-enact stored motor representations which might be used for rehabilitating motor control in RRMS (action observation therapy; Ertelt et al., 2007; Buccino, Solodkin, & Small, 2006).
In the second experimental chapter (Chapter 4), I focused on a more basic feature of the human AOS, the coding of not-object-related (intransitive) actions. This is a unique feature of the human AOS, because in non-human primates the AOS seems not to code for such types of actions. The central advance of this study is the demonstration that transitivity conveyed by previous knowledge regarding the presence/absence of a target-object modulates activity within the AOS. By manipulating this type of information we revealed that the AOS is able to generate a representation of an observed action on the basis of the action goal, even when the most crucial part of the action (i.e., hand-object interaction) is not visible. A number of studies put forward the proposal that the human AOS responds to intransitive actions (Buccino et al., 2001; Wheaton, Thompson, Syngeniotis, Abbott, & Puce, 2004; Dinstein, Hasson, Rubin, & Heeger, 2007; Dinstein, Gardner, Jazayeri, & Heeger, 2008; Lui, et al., 2008) suggesting that when a target-object is not present the AOS is still recruited. The present study add to this literature revealing that the AOS has the ability to discriminate and understand observed actions on the basis of the properties characterizing their goal (i.e. transitivity) rather than their perceived physical features. In this sense, we were able to find a modulation within the AOS with respect to the transitivity, suggesting that at least part of the system can be extremely selective in terms of processing the abstract properties of the goal characterizing the observed action.
The two final experimental Chapters (Chapters 5 and 6) of the present thesis were concerned with the definition/identification of the human “mirror” regions and (if any) of what they code for. In general, the present results support the notion that in humans “mirror” activity spreads across a number of areas which exceeds those classically thought to be part of the ‘mirror’ system (e.g., Raos, Evangeliou, & Savaki, 2007; Gazzola, Rizzolatti, Wicker, & Keysers, 2007; Gazzola & Keysers, 2009; Evangeliou, Raos, Galletti, & Savaki, 2009). Further, a region of interest analysis (ROI) on the putative human mirror region within the premotor cortex indicate that, in contrast to monkeys (Nelissen, Luppino, Vanduffel, Rizzolatti, & Orban, 2005), this region is activated in a similar fashion irrespective of whether the agent's entire body, or only the grasping hand, is seen.
Altogether these results are discussed in terms of the possibility that the AOS and the ‘mirror’ systems chiefly represent actions in terms of goals independently by contextual information (Ferrari, Rozzi, & Fogassi, 2005; Gazzola et al., 2007). The idea is that what is represented in the premotor cortex is not bounded to the physical appearance of the agent, but it is a rather abstract representation centred on the goal of the action, independently of what is acting, a human, a robot, or even a tool. The present findings confirm and extend this notion by broadening the several dimensions within which action goals affect the response of the AOS and how such dimensions may vary across species. Indeed on the basis of monkeys fMRI findings using a paradigm similar to ours (Nelissen et al., 2005) differences in action observation activity depending on type of view were expected, at least within premotor and other prefrontal areas. However, in the present study the type of view had little impact at the level of action observation. I suspect that this might be ascribed to the fact that the processing of particular stimulus properties, which in principle should occur in homologue areas, might not be common to both species (Sereno & Tootell, 2005; Orban, Van Essen, & Vanduffel, 2004; Nakahara, Adachi, Osada, & Miyashita, 2007). In this perspective the conclusion would be that in humans the observation of a grasping hand alone (and an object) is sufficient to trigger significant differential activity. This aspect is particularly important because most of the human studies on the mirror neuron system have been conducted with movies zooming into the hand-part of the stimulus. If, as monkeys’ fMRI indicated (Nelissen et al., 2005), this were to cancel out key mirror areas, much of the human literature would have been challenged. The present data, however, show convincingly that this is not the case, at least in humans, and therefore enhance the validity of a large number of studies providing important and novel evidence within this flourishing field of research.
References
Buccino, G., Binkofski, F., Fink, G.R., Fadiga, L., Fogassi, L., Gallese, V., et al., (2001). Action observation activates premotor and parietal areas in a somatotopic manner: an fMRI study. European Journal of Neuroscience, 13, 400–404.
Buccino, G., Solodkin, A., & Small, S. (2006). Functions of the mirror neuron system: implications for neurorehabilitation. Cognitive and behavioral neurology, 19, 55-63.
Dinstein, I., Hasson, U., Rubin, N., & Heeger, D.J. (2007). Brain areas selective for both observed and executed movements. Journal of Neurophysiology, 98, 1415–1427.
Dinstein, I., Gardner, J.L., Jazayeri, M. & Heeger, D.J. (2008). Executed and observed movements have different distributed representations in human aIPS. Journal of Neuroscience, 28, 11231–11239.
Ertelt, D., Small, S., Solodkin, A., Dettmers, C., McNamara, A., & Buccino, G. (2007). Action observation has a positive impact on rehabilitation of motor deficits after stroke. NeuroImage, 36, T164-173.
Evangeliou, M.N., Raos, V., Galletti, C., & Savaki, H.E. (2009). Functional imaging of the parietal cortex during action execution and observation. Cerebral Cortex, 19, 624–639.
Ferrari, P.F., Rozzi, S. & Fogassi, L. (2005). Mirror neurons responding to observation of actions made with tools in monkey ventral premotor cortex. Journal of Cognitive Neuroscience, 17, 212-226.
Gazzola, V., Rizzolatti, G., Wicker, B. & Keysers, C. (2007). The anthropomorphic brain: The mirror neuron system responds to human and robotic actions. NeuroImage, 35, 1674-1684.
Gazzola, V., & Keysers, C. (2009). The observation and execution of actions share motor and somatosensory voxels in all tested subjects: single-subject analyses of unsmoothed fMRI data. Cerebral Cortex, 19, 1239-55.
Lui, F., Buccino, G., Duzzi, D., Benuzzi, F., Crisi, G., Baraldi, P., et al. (2008). Neural substrates for observing and imagining non-object-directed actions. Social Neuroscience, 3, 261-75.
Nakahara, K., Adachi, Y., Osada, T., & Miyashita, Y. (2007). Exploring the neural basis of cognition: multi-modal links between human fMRI and macaque neurophysiology. Trends in Cognitive Sciences, 11, 84–92.
Nelissen, K., Luppino, G., Vanduffel, W., Rizzolatti, G., & Orban, G. A. (2005). Observing others: multiple action representation in the frontal lobe. Science, 310, 332-336.
Orban, G.A., Van Essen, D., & Vanduffel, W. (2004). Comparative mapping of higher visual areas in monkeys and humans. Trends in Cognitive Sciences, 8, 315–324.
Raos, V., Evangeliou, M.N., & Savaki, H.E. (2007). Mental simulation of action in the service of action perception. Journal of Neuroscience, 27, 12675-12683.
Rizzolatti, G., Fogassi, L., & Gallese, V. (2001). Neurophysiological mechanisms underlying the understanding and imitation of action. Nature Reviews Neuroscience, 2, 661–670.
Sereno, M.I. & Tootell, R.B. (2005). From monkeys to humans: what do we now know about brain homologies? Current Opinion in Neurobiology, 15, 135-144.
Wheaton, K.J., Thompson, J.C., Syngeniotis, A., Abbott, D.F., & Puce, A. (2004). Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex. NeuroImage, 22, 277-88.Riassunto
L’obiettivo della presente tesi è quello di investigare le proprietà del sistema neurale sottostante la comprensione delle azioni nell’uomo. I miei studi si sono concentrati sull’attività cerebrale sottostante l’osservazione dell’azione e in relazione al cosiddetto sistema “mirror”, attraverso l’uso della tecnica della risonanza magnetica funzionale (fMRI).
Nella prima parte sperimentale della tesi (capitoli 3-4) sono descritti alcuni studi in cui ai soggetti sperimentali veniva richiesto di osservare una persona che afferrava degli oggetti, mentre l’attività del loro cervello era registrata. Questo tipo di compito permette di studiare il cosiddetto sistema di osservazione dell’azione (AOS), un network di regioni cerebrali attivato automaticamente durante l’osservazione di azioni compiute da altre persone (Buccino et al., 2001).
Nella seconda parte sperimentale della tesi (capitoli 5-6), gli studi si sono focalizzati sulla raccolta di dati di attivazione cerebrale in soggetti che dovevano portare a termine compiti sia di osservazione sia di esecuzione di movimenti di raggiungimento e prensione. In questi esperimenti, il substrato neurale investigato è il cosiddetto sistema “mirror” (Rizzolatti & Craighero, 2004).
Nel primo capitolo sperimentale (capitolo 3) ho studiato l’AOS in una popolazione di pazienti affetti da Sclerosi Multipla (SM) del tipo Recidivante-Remittente. Durante l’acquisizione dei dati fMRI, i soggetti dovevano semplicemente osservare immagini statiche di mani che afferravano oggetti comuni o che erano posizionate a fianco di tali oggetti.
Studi precedenti sembrano indicare un danno selettivo dell’AOS nei pazienti con SM, ma i risultati di questo studio non suggeriscono tale deterioramento in questo tipo di soggetti. Essi sembrano indicare invece un generale effetto di iperattivazione cerebrale, che potrebbe essere determinata dalla estesa demielinizzazione causata dalla SM e dai processi di riparazione messi in atto dall’organismo. Questa iperattivazione cerebrale non specifica è stata discussa nei termini di capacità residua dell’AOS per riattivare nuovamente le rappresentazioni motorie e quindi della possibilità di usare l’osservazione dell’azione come strumento di riabilitazione per tali pazienti (terapia basata sull’osservazione dell’azione, Buccino, Solodkin, & Small, 2006; Ertelt, Small, Solodkin, Dettmers, McNamara, & Buccino, 2007).
Nel secondo capitolo sperimentale (capitolo 4), mi sono concentrato sullo studio di una proprietà basica dell’AOS, cioè l’elaborazione di azioni intransitive (non dirette verso oggetti). L’elaborazione di questo tipo di azioni, sembra essere una caratteristica peculiare dell’AOS umano, in quanto nelle scimmie questo tipo di azione non sembra attivare l’AOS. Il punto centrale di questo studio è la dimostrazione che la transitività fornita dalla conoscenza della presenza o assenza dietro una partizione di un oggetto, che deve essere afferrato, modula l’attività dell’AOS.
Manipolando questo tipo di informazione siamo stati in grado di dimostrare che l’AOS è in grado di generare una rappresentazione dell’azione osservata basata sullo scopo di tale azione, anche nel caso in cui la parte più cruciale di tale movimento, l’interazione tra la mano e l’oggetto, era nascosta da una partizione.
Precedenti studi di neuroimmagine hanno dimostrato che l’AOS umano codifica azioni di tipo intransitivo (Buccino et al., 2001; Wheaton, Thompson, Syngeniotis, Abbott, & Puce, 2004; Dinstein, Hasson, Rubin, & Heeger, 2007; Dinstein, Gardner, Jazayeri, & Heeger, 2008; Lui, Buccino, Duzzi, Benuzzi, Crisi, Baraldi, et al., 2008), suggerendo che anche quando l’oggetto, scopo dell’azione, non è presente, l’AOS è comunque attivato.
Questo studio dimostra come l’AOS discrimini, e quindi possa permettere di comprendere le azioni osservate sulla base delle caratteristiche dello scopo dell’azione (in questo caso la transitività) piuttosto che da caratteristiche percettive. In questo senso, la modulazione prodotta dalla transitività nell’AOS suggerisce che almeno una sua parte sia estremamente sensibile alle proprietà astratte dello scopo di tale azione.
Negli ultimi due capitoli sperimentali della tesi (capitoli 5 e 6) mi sono concentrato sull’identificazione delle possibili regioni “mirror” nel cervello umano e, se presenti, sulle caratteristiche dei processi che avvengono in tali aree. In generale, i risultati qui riportati supportano la presenza di un sistema “mirror” nell’uomo, che comprende un numero di aree maggiore rispetto a quelle che classicamente vengono considerate “mirror” (Raos, Evangeliou, & Savaki, 2007; Gazzola, Rizzolatti, Wicker, & Keysers, 2007; Gazzola & Keysers, 2009; Evangeliou, Raos, Galletti, & Savaki, 2009). I dati del presente esperimento sembrano supportare l’idea che è lo scopo dell’azione ad essere il determinante principale dell’attivazione relativa all’osservazione dell’azione.
Inoltre, l’analisi dei dati di una singola area, la possibile omologa umana della regione mirror F5 nelle scimmie, sembra indicare che al contrario di questa specie (Nelissen, Luppino, Vanduffel, Rizzolatti, & Orban, 2005), nell’uomo quest’area è attivata in un modo simile indipendentemente dall’agente che compie l’azione. La stessa attivazione cerebrale è presente sia che l’agente sia un modello intero, sia che l’agente sia una mano isolata.
I miei risultati sono stati discussi considerando che l’AOS e il sistema “mirror” rappresentano l’azione rispetto al suo scopo e indipendentemente dall’informazione in cui l’azione viene eseguita (Ferrari, Rozzi, & Fogassi, 2005; Gazzola et al., 2007). In particolare, la rappresentazione dell’azione osservata nella corteccia premotoria non sembra essere legata all’apparenza percettiva dell’agente, ma essa sembra essere di tipo astratto, centrata sullo scopo dell’azione e non influenzata da cosa stia compiendo l’azione, sia esso un essere umano, un robot o un attrezzo. Sulla base dei risultati di uno studio fMRI nelle scimmie simile al mio (Nelissen et al., 2005) mi aspettavo di trovare delle differenze nell’attività relativa all’osservazione dell’azione almeno in aree premotorie e prefrontali. Ma nel mio studio il tipo di agente non ha avuto nessun impatto sull’attivazione cerebrale. Questo probabilmente può essere dovuto al fatto che l’elaborazione delle proprietà di uno stimolo, che dovrebbe avvenire in aree omologhe, può essere differente in specie diverse (Sereno & Tootell, 2005; Orban, Van Essen, & Vanduffel, 2004; Nakahara, Adachi, Osada, & Miyashita, 2007). Considerando questa prospettiva, la conclusione sarebbe che nell’uomo anche l’osservazione di una mano da sola è sufficiente ad attivare la corteccia premotoria. Questo aspetto è particolarmente importante considerando che quasi tutti gli studi sull’AOS e il sistema “mirror” nell’uomo sono stati condotti con stimoli che comprendevano solo una mano che agiva. Se, come è stato dimostrato nelle scimmie (Nelissen et al., 2005), l’utilizzo di uno stimolo che comprende solamente una mano non determinasse un’attivazione delle aree “mirror”, allora la letteratura che si riferisce ad attivazione mirror nell’uomo sarebbe da considerare errata. I miei risultati dimostrano, che nell’uomo, questo non è vero, confermando la validità di molti studi riguardanti l’AOS e il sistema mirror e contribuendo alla letteratura su questo campo con nuovi e importanti dati.
Referenze
Buccino, G., Binkofski, F., Fink, G.R., Fadiga, L., Fogassi, L., Gallese, V., et al., (2001). Action observation activates premotor and parietal areas in a somatotopic manner: an fMRI study. European Journal of Neuroscience, 13, 400–404.
Buccino, G., Solodkin, A., & Small, S. (2006). Functions of the mirror neuron system: implications for neurorehabilitation. Cognitive and behavioral neurology, 19, 55-63.
Dinstein, I., Hasson, U., Rubin, N., & Heeger, D.J. (2007). Brain areas selective for both observed and executed movements. Journal of Neurophysiology, 98, 1415–1427.
Dinstein, I., Gardner, J.L., Jazayeri, M., & Heeger, D.J. (2008). Executed and observed movements have different distributed representations in human aIPS. Journal of Neuroscience, 28, 11231–11239.
Ertelt, D., Small, S., Solodkin, A., Dettmers, C., McNamara, A., & Buccino, G. (2007). Action observation has a positive impact on rehabilitation of motor deficits after stroke. NeuroImage, 36, T164-173.
Evangeliou, M.N., Raos, V., Galletti, C., & Savaki, H.E. (2009). Functional imaging of the parietal cortex during action execution and observation. Cerebral Cortex, 19, 624–639.
Ferrari, P.F., Rozzi, S., & Fogassi, L. (2005). Mirror neurons responding to observation of actions made with tools in monkey ventral premotor cortex. Journal of Cognitive Neuroscience, 17, 212-226.
Gazzola, V., Rizzolatti, G., Wicker, B., & Keysers, C. (2007). The anthropomorphic brain: The mirror neuron system responds to human and robotic actions. NeuroImage, 35, 1674-1684.
Gazzola, V., & Keysers, C. (2009). The observation and execution of actions share motor and somatosensory voxels in all tested subjects: single-subject analyses of unsmoothed fMRI data. Cerebral Cortex, 19, 1239-55.
Lui, F., Buccino, G., Duzzi, D., Benuzzi, F., Crisi, G., Baraldi, P., et al. (2008). Neural substrates for observing and imagining non-object-directed actions. Social Neuroscience, 3, 261-75.
Nakahara, K., Adachi, Y., Osada, T., & Miyashita, Y. (2007). Exploring the neural basis of cognition: multi-modal links between human fMRI and macaque neurophysiology. Trends in Cognitive Sciences, 11, 84–92.
Nelissen, K., Luppino, G., Vanduffel, W., Rizzolatti, G., & Orban, G. A. (2005). Observing others: multiple action representation in the frontal lobe. Science, 310, 332-336.
Orban, G.A., Van Essen, D., & Vanduffel, W. (2004). Comparative mapping of higher visual areas in monkeys and humans. Trends in Cognitive Sciences, 8, 315–324.
Raos, V., Evangeliou, M.N., & Savaki, H.E. (2007). Mental simulation of action in the service of action perception. Journal of Neuroscience, 27, 12675-12683.
Rizzolatti, G., Fogassi, L., & Gallese, V. (2001). Neurophysiological mechanisms underlying the understanding and imitation of action. Nature Reviews Neuroscience, 2, 661–670.
Sereno, M.I. & Tootell, R.B. (2005). From monkeys to humans: what do we now know about brain homologies? Current Opinion in Neurobiology, 15, 135-144.
Wheaton, K.J., Thompson, J.C., Syngeniotis, A., Abbott, D.F., & Puce, A. (2004). Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex. NeuroImage, 22, 277-88
Hierarchical action encoding within the human brain.
No full textHumans are able to interact with objects with extreme f lexibility. To achieve this ability, the brain does not only control specific muscular patterns, but it also needs to represent the abstract goal of an action, irrespective of its implementation. It is debated, however, how abstract action goals are implemented in the brain. To address this question, we used multivariate pattern analysis of functional magnetic resonance imaging data. Human participants performed grasping actions (precision grip, whole hand grip) with two different wrist orientations (canonical, rotated), using either the left or right hand. This design permitted to investigate a hierarchical organization consisting of three levels of abstraction: 1) “concrete action” encoding; 2) “effector-dependent goal” encoding (invariant to wrist orientation); and 3) “effector-independent goal” encoding (invariant to effector and wrist orientation). We found that motor cortices hosted joint encoding of concrete actions and of effector-dependent goals, while the parietal lobe housed a convergence of all three representations, comprising action goals within and across effectors. The left lateral occipito-temporal cortex showed effector-independent goal encoding, but no convergence across the three levels of representation. Our results support a hierarchical organization of action encoding, shedding light on the neural substrates supporting the extraordinary flexibility of human hand behavior
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
When gaze turns into grasp
No full textPrevious research has provided evidence for a neural system
underlying the observation of another person’s hand
actions. Is the neural system involved in this capacity also
important in inferring another person’s motor intentions toward
an object from their eye gaze? In real-life situations,
humans use eye movements to catch and direct the attention
of others, often without any accompanying hand movements
or speech. In an event-related functional magnetic resonance
imaging study, subjects observed videos showing a human
model either grasping a target object (grasping condition) or
simply gazing (gaze condition) at the same object. These
two conditions were contrasted with each other and against
a control condition in which the human model was standing
behind the object without performing any gazing or grasping
action. The results revealed activations within the dorsal
premotor cortex, the inferior frontal gyrus, the inferior parietal
lobule, and the superior temporal sulcus in both ‘‘grasping’’
and ‘‘gaze’’ conditions. These findings suggest that
signaling the presence of an object through gaze elicits in an
observer a similar neural response to that elicited by the
observation of a reach-to-grasp action performed on the same
object
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Neurofunctional modulation of brain regions by the observation of pointing and grasping actions
No full textPrevious neuroimaging research on healthy humans has provided evidence for a neural system underlying the observation of another person's hand actions. However, whether the neural processes involved in this capacity are activated by the observation of other transitive hand actions such as pointing remains unknown. Therefore, using functional magnetic resonance imaging we investigated the neural mechanisms underlying the observation of static images representing the hand of a human model pointing to an object (pointing condition), grasping an object (grasping condition), or resting in proximity of an object (control condition). The results indicated that activity within portions of the lateral occipitotemporal and the somatosensory cortices modulates according to the type of observed transitive actions. Specifically, these regions were more activated for the grasping than for the pointing condition. In contrast, the premotor cortex, a neural marker of action observation, did not show any differential activity when contrasting the considered experimental conditions. Our findings may provide novel insights regarding a possible role of extrastriate and somatosensory brain areas for the perception of distinct types of human hand–object interactions
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
