Monday, July 26, 2010

(Mis)understanding mirror neurons -- An alternative interpretation to "action understanding" and why they got it wrong in the first place

The idea that mirror neurons support action understanding is by far the dominant interpretation of the function of these cells in the monkey motor system. However, it is not the only interpretation. A "sensory-motor" hypothesis, such as that proposed by Cecelia Heyes and others, has been gaining steam in the last few years. In a just published piece in Current Biology, Marc Hauser and I propose a variant of the sensory-motor view, namely that mirror neurons function not for action understanding but for action selection, just like "canonical neurons" in the macaque motor system. We also outline why, in our view, mirror neurons were misunderstood from the beginning, namely that the more straightforward action selection interpretation was not supported by monkey behavioral data available at the time. We point out that the relevant behavioral data has now emerged from recent research and that the action understanding view requires serious re-evaluation. The outline of the argument is presented in the following summary from our paper:

It is hard to imagine a class of neurons that has generated more excitement than mirror neurons, cells discovered by Rizzolatti and colleagues in macaque area F5 that fire both during action execution and action observation. We suggest, however, that the interpretation of mirror neurons as supporting action understanding was a wrong turn at the start, and that a more appropriate interpretation was lying in wait with respect to sensorimotor learning. We make a number of arguments, as follows. Given their previous work, it would have been natural for Rizzolatti's group to interpret mirror neurons as involved in action selection rather than action understanding. They did not make this assumption because, at the time, the data suggested that monkey behavior did not support such an interpretation. Recent evidence shows that monkeys do, in fact, exhibit behaviors that support this alternative interpretation. Thus, the original basis for claiming that mirror neurons mediate action understanding is no longer compelling. There are independent arguments against the action understanding claim and in support of a sensorimotor learning origin for mirror neurons. Therefore, the action understanding theory of mirror neuron function requires serious reconsideration, if not abandonment. (p. 593).

Heyes, C. (2010). Where do mirror neurons come from? Neuroscience & Biobehavioral Reviews, 34 (4), 575-583 DOI: 10.1016/j.neubiorev.2009.11.007

Hickok G, & Hauser M (2010). (Mis)understanding mirror neurons. Current biology : CB, 20 (14) PMID: 20656198

Wednesday, July 21, 2010

The (non-)role of mirror neurons: Greg Hickok's new critical review

An important new paper by the tireless Greg (guess on which topic ... :-) has just appeared in the journal Language and Cognitive Processes -- Cognitive Neuroscience of Language (which, yes, I edit). The paper is called "The role of mirror neurons in speech perception and action word semantics" and has just been picked up by the very popular BPS Research Digest.

Here is the abstract:

The discovery of mirror neurons in the macaque monkey has ignited intense interest in motor theories of cognition, including speech and language. Here we examine two such claims, that the perception of speech sounds critically depends on motor representations of speech gestures (the motor theory of speech perception) and that the representation of action-related semantic knowledge critically depends on motor representations involved in performing actions. We conclude that there is strong evidence against the claim that speech perception critically depends on the motor system and that there is no conclusive evidence in support of the view that the motor system supports action semantics. We propose instead that motor-related activity during perceptual processes stem from spreading activation in sensory-motor networks that are critical for speech and language production.

The publisher of the journal has made this paper free to read until August 15. Run -- don't walk -- to your nearest computer and read this next installment (after Greg's "8 Problems" paper from 2009) of Greg's arguments for resisting the mirror neuron juggernaut.

Then write a brilliant paper on some aspect of the cognitive neuroscience of language (does not even have to be mirror neuron related, promise) and submit it to the journal.

Thursday, July 15, 2010



The Northwestern Bilingualism and Psycholinguistics Laboratory is accepting applications for a post-doctoral position to assist in implementing studies on bilingualism and its consequences for linguistic and cognitive processing.

We welcome individuals with psycholinguistic training from broad backgrounds including communication sciences and disorders, psychology, linguistics, neuroscience, and other related fields, with expertise in areas such as bilingualism, language learning, linguistic and cognitive processing, and computational modeling. The ideal candidate will have solid quantitative skills (e.g., multivariate statistics, MATLAB), eye-tracking experience, strong writing skills, ability to think critically and broadly, and ability to work well both independently and with others. Access to ERP and fMRI facilities is available for candidates interested in using those methodologies.

The Chicago area offers world-class metropolitan, suburban, and rural living possibilities within a 30-mile radius for individuals of diverse backgrounds and interests. Salary is competitive and dependent on qualifications and experience.

To apply, candidates should email a Curriculum Vitae, a brief research statement, two sample publications, and three letters of recommendation to Viorica Marian,, or mail them to Dr. Viorica Marian, Department of Communication Sciences and Disorders, Northwestern University, 2240 Campus Drive, Evanston, IL 60208-3570. Review of applications will start on September 15, 2010 and will continue until the position is filled.

Wednesday, July 14, 2010

Can individuals perceive and understand speech without the ability to produce it?

"Yes" is the correct answer. Here's the background to the question:

I finally mustered the courage (i.e., sufficient control over my blood pressure) to read Pulvermuller & Fadiga's recent (2010) review paper in Nature Reviews Neuroscience. But I don't want to talk about their paper -- yet. I want to discuss a paper they cite. Here is the context in which they cite it: P & F are, of course, arguing for the importance of the motor system in receptive language. After arguing correctly that sensory and motor aspects of speech must interact and proposing (controversially) that this interaction is important not only for production but for perception/understanding, they write:

We acknowledge that, apart from action-perception learning, the human brain also supports the purely perceptual learning of small vocabularies of word forms in the absence of articulation, but note that monkeys also exhibit this type of perceptual learning. Notably, children with severe neurological motor deficits that affected articulation had reduced auditory vocabularies -- that is, they understood fewer words than children with similar deficits that did not affect articulation [Bishop et al. 1990] -- a finding consistent with the importance of motor links for vocabulary learning. -Pulvermuller & Fadiga, 2010, pp. 352-353

I was not aware of the Bishop et al. paper (embarrassingly), so I had a look. I'm glad I did because it shows (i) that the ability to produce speech does not affect the ability to perceive speech sounds and (ii) let me say it again: TASK MATTERS.

Bishop, Brown, & Robson studied 48 10-18 year olds, all with cerebral palsy. 12 were congenitally anarthric (A) "never having been able to produce articulate speech", 12 were severely dysarthric (D) "with labored, and often unintelligible, speech", and 24 were control (C) subjects with cerebral palsy but with normal speech. The controls are critical because cerebral palsy is associated with a general lowering of intellectual ability. Thus, to a first approximation, group differences could be attributed to differences motor speech control. (This is not entirely true because the anarthric patients in general had more severe motor problems, e.g., there were nonambulatory unlike most control subjects which as the the authors point out could affect health and learning generally.)

In a first set of experiments subjects were tested on

1. a test of non-verbal intelligence, Raven's Matrices, to ensure good matching between groups
2. a phoneme discrimination task (yes-no, nonword syllable discrimination using minimal pair phonemic contrasts) -- Yes they used d'! Woohoo!
3. a receptive vocabulary task (British Picture Vocabulary Scale, similar to the Peabody scale)
4. a test for receptive grammar (TROG), a sentence-picture matching test.


1. Groups did not differ on the non-verbal test (they are reasonable matched)
2. Speech impaired groups (anarthric and dysarthric) performed worse than controls on the phoneme discrimination test (d' = 1.6, 1.5, ~2.5, for A, D, and C groups respectively -- there were actually two C groups that I've combined here). No difference between the speech impaired groups.
3. Vocabulary was reduced in the speech impaired groups relative to controls. Vocabulary age equivalents were: A, 8:0; D, 8:5; C, ~10. No diff between the speech impaired groups.
4. No differences between any of the groups on the receptive grammar test.

What does this mean? It suggests that the ability to speak indeed affects speech sound discrimination and is associated with vocabulary reduction (although 8 year old vocabularies are probably better than a monkeys, cf, P&V quote above), but lack of motor speech does not impair receptive grammar. The latter finding is relevant (i.e., contradictory) to another of P&V's claims, but won't be discussed here.

Before all you motor theory/mirror neuron enthusiasts start celebrating there are two important caveats regarding the discrimination test. One is the fact that despite the a complete lack of speech development, anarthric patients are nonetheless able to discriminate minimal pair phonemic contrasts better than chance (remember discrimination threshold for d' measures = 1.0), have receptive vocabularies that afford everyday communication, and have relatively good receptive grammar skills. Therefore, motor speech ability is not necessary for basic receptive speech competence.

The other caveat is Bishop et al.'s second experiment involving the same population. They worried that the nonword syllable discrimination task may unnecessarily tax phonological working memory, which is dependent on motor articulatory ability, so they used another task: subjects were presented with a picture (e.g., a boy) and then a spoken syllable (e.g., "boy" or "voy"); they were asked to decide whether the syllable correctly named the picture or whether the syllable was incorrectly pronounced and therefore did not match. The matches and mismatches represented minimal pairs. A standard syllable discrimination task (boy-voy, same or different?) was also administered for comparison.


1. The standard discrimination task replicated what was found in Experiment 1: speech impaired subjects performed worse than controls (d'=1.72 vs. 2.24, respectively; A & D were pooled in this study).
2. The picture-syllable judgment task, which involved the *same* phonemic contrasts, came out differently: no difference between speech impaired and control subjects (d'=2.52 vs. 2.59 respectively).

Bishop et al. summarize the findings nicely:

The lack of impairment on the word [picture-syllable] judgment task rules out the possibility that the speech-impaired persons are operating with a reduced system of phoneme contrasts. An alternative explanation in terms of short-term memory seems the most plausible.... It may be that if one has to retain novel, meaningless phonological information then the process is facilitated by overtly or covertly generating an articulatory representation. Indeed, some of the normal speakers in our study were observed repeating nonword pairs to themselves in the same-different task before making a judgment. This strategy would be difficult or impossible for those with dysarthria or anarthria.... p. 218.

So when measured properly the ability to perceive speech is unimpaired, relative to controls, in individuals who never developed the ability to speak. The motor speech system is not necessary for speech perception.

But what about vocabulary? Is motor speech necessary for vocabulary development? It depends on what you mean by necessary. The Bishop et al. study showed that a vocabulary of an 8 year old is achievable -- which is not bad considering that the control group achieved an average vocabulary of a 10 year old -- but still below par. Why might this be?

Drawing the work of Gathercole & Baddeley (1989) which showed a correlation between vocabulary development and phonological STM, Bishop et al. suggest that it has to do with phonological short-term memory. Learning new words requires the retention of sequences of novel phoneme strings that can be associated with meanings. If the ability to internally rehearse such strings is impaired, one might be consistently behind the curve in vocabulary development, having to rely more on external repeated exposure to new vocabulary items.

Thus, the influence of the motor speech system on receptive language ability all boils down to its role in phonological short-term memory. Basic perceptual abilities are largely unaffected by even severe disruption of the motor speech system.


Bishop DV, Brown BB, & Robson J (1990). The relationship between phoneme discrimination, speech production, and language comprehension in cerebral-palsied individuals. Journal of speech and hearing research, 33 (2), 210-9 PMID: 2359262

GATHERCOLE, S., & BADDELEY, A.D. (1989). Evaluation of the role of phonological STM in the development of vocabulary in children: A longitudinal study Journal of Memory and Language, 28 (2), 200-213 DOI: 10.1016/0749-596X(89)90044-2

Pulvermüller F, & Fadiga L (2010). Active perception: sensorimotor circuits as a cortical basis for language. Nature reviews. Neuroscience, 11 (5), 351-60 PMID: 20383203

Monday, July 12, 2010

Endowed Chair in Cognitive Neuroscience; MRI -- University of Missouri, Columbia

Title: Miller Family Chair in Cognitive Neuroscience
Department of Psychological Sciences, University of Missouri, Columbia
Location: Columbia, Missouri, US

The DEPARTMENT OF PSYCHOLOGICAL SCIENCES at the UNIVERSITY OF MISSOURI-COLUMBIA seeks applications for the MILLER FAMILY CHAIR IN COGNITIVE NEUROSCIENCE. We expect this endowed position to be filled by a tenured faculty member to provide intellectual leadership for a research-dedicated brain imaging center that has been in operation for about a year. The substantive area is open and includes such topics as understanding the neural basis of cognition, development, aging, social behavior, psychopathology, and addiction. The department has an excellent faculty, including several neuroimaging researchers (see the departmental web site,, who value collaborative, cross-disciplinary work. We have recently hired an MR physicist and have plans for several more neuroimaging hires. Priority for the Miller Chair will be given to individuals whose research programs are both well-established and synergistic with those of current faculty. The brain imaging center houses a research-dedicated, 3T Siemens MRI scanner well-equipped for research, supplementing other Siemens scanners in the medical school, and a mock scanner equipped with head movement apparatus. Send a vita, a brief introductory letter, and two reprints to the search committee chair, Nelson Cowan, preferably electronically (Email); or call with inquiries (573-882-4232) or send mail to Search Committee Chair, Department of Psychological Sciences, University of Missouri, McAlester Hall, University of Missouri, Columbia MO 65211, USA. We will begin screening applications immediately and will continue until the position has been filled. The University of Missouri does not discriminate on the basis of race, color, religion, national origin, ancestry, sex, age, and disability, status as a disabled veteran or veteran of Vietnam era and is an Equal Opportunity/Affirmative Action/ADA employer.

The Role of Broca's Area in Sentence Comprehension

After first being rejected as an invited paper at Frontiers and then suffering through a somewhat contentious second set of reviews, a critical review paper on the role of Broca's area in sentence comprehension by Corianne Rogalsky and yours truly will finally see the light of day in the Journal of Cognitive Neuroscience.

What makes the paper so controversial? Basically we argue, despite the claims of Grodzinsky, Friederici, and colleagues, that there is no evidence for Broca's area playing any specific role in syntactic and/or basic hierarchical processing during sentence comprehension. Rather, posterior sectors of Broca's area (pars opercularis) seems to support sentence comprehension indirectly via articulatory rehearsal and more anterior sectors appear to be playing some higher-order process (there are several proposals on the table).

Have a look at let us know what you think. Abstract below.

The role of Broca's area in sentence processing has been debated for the last 30 years. A central and still unresolved issue is whether Broca's area plays a specific role in some aspect of syntactic processing (e.g., syntactic movement, hierarchical structure building) or whether it serves a more general function on which sentence processing relies (e.g., working memory). This review examines the functional organization of Broca's area in regard to its contributions to sentence comprehension, verbal working memory, and other multimodal cognitive processes. We suggest that the data are consistent with the view that at least a portion of the contribution of Broca's area to sentence comprehension can be attributed to its role as a phonological short-term memory resource. Furthermore, our review leads us to conclude that there is no compelling evidence that there are sentence-specific processing regions within Broca's area.