Category: Science

Broca's Area and Hierarchical Structure Building

Considering I devoted two blog posts (pt.1 & pt.2) to Broca’s area and its role in processing hierarchically organised sequences, I’m happy report the following from a Talking Brains post on Disentangling syntax and intelligibility:

Hierarchical structure building can be achieved without Broca’s area involvement.

I’ve only just finished reading the post and, despite having some thoughts on the topic, I’m going to read the actual paper in question (Disentangling syntax and intelligibility in auditory language comprehension) before commenting. Especially since the authors, Friederici et al, don’t seem to arrive at the same conclusions as the bloggers over at Talking Brains. Still, as far as I can tell, this is only looking at syntactic information within speech, and doesn’t really tell us anything about the processing of hierarchically organised sequences in other linguistic (e.g. written language) and non-linguistic (e.g. tool manufacturing) domains.

Here’s the abstract for the paper in question:

Studies of the neural basis of spoken language comprehension typically focus on aspects of auditory processing by varying signal intelligibility, or on higher-level aspects of language processing such as syntax. Most studies in either of these threads of language research report brain activation including peaks in the superior temporal gyrus (STG) and/or the superior temporal sulcus (STS), but it is not clear why these areas are recruited in functionally different studies. The current fMRI study aims to disentangle the functional neuroanatomy of intelligibility and syntax in an orthogonal design. The data substantiate functional dissociations between STS and STG in the left and right hemispheres: first, manipulations of speech intelligibility yield bilateral mid-anterior STS peak activation, whereas syntactic phrase structure violations elicit strongly left-lateralized mid STG and posterior STS activation. Second, ROI analyses indicate all interactions of speech intelligibility and syntactic correctness to be located in the left frontal and temporal cortex, while the observed right-hemispheric activations reflect less specific responses to intelligibility and syntax. Our data demonstrate that the mid-to-anterior STS activation is associated with increasing speech intelligibility, while the mid-to-posterior STG/STS is more sensitive to syntactic information within the speech.

Some links #1

Having now returned, I feel a long list of links is needed to kick start things:

Right, that’s all I’ve got time for at the moment. Laptop battery is dying and my bladder is urging me towards the toilet.

What conclusions can we draw from Neanderthal DNA pt.2

ResearchBlogging.org4. Nuclear DNA: Forays into 3 billion base pairs

4.1 Before Vi-80

The Vindija-80 (Vi-80) specimen is an important find for geneticists: it yielded a minimally contaminated sample and provided those first steps into Neanderthal genomics.

Previously, attempts at retrieving ancient nuclear DNA sequences proved to be a notoriously difficult process, plagued with problems of degradation, contamination and chemical damage (Hofreiter et al., 2001). Researchers also need to contend with quantities of nuclear genome available: for every nuclear genome there are approximately several hundred mtDNAs (Green et al., 2008). The severity of these problems, especially contamination, is magnified through Neanderthal genetic similarity with humans (Green et al., 2006). This is troubling because nuclear DNA presents far less variability than mtDNA (Russell, 2002). As a result, huge stretches of nuclear sequences are required to find a significant number of polymorphisms (ibid). Such implications meant that discovering endogenous DNA sequences requires sifting through a large corpus of “[…] more than 70 Neanderthal bone and tooth samples from different sites in Europe and western Asia” (Green et al., 2006, pg. 331).

Continue reading “What conclusions can we draw from Neanderthal DNA pt.2”

What conclusions can we draw from Neanderthal DNA pt.1

ResearchBlogging.orgIn recent times, genetic technology has progressed sufficiently to elucidate upon some of the questions normally preserved for archaeologists. One such question concerns the fate of a group of hominins that roamed Europe and East Asia for at least 250,000 years. During this time, this species adapted and endured some of the harshest environments on offer, all while showing signs of a unique culture. Only for them to suddenly disappear from the fossil record approximately 30,000 years before present (BP) (cf. Barton et al. 2007). So, what happened to our closest evolutionary relatives, the Neanderthals?

Continue reading “What conclusions can we draw from Neanderthal DNA pt.1”

The arcuate fasciculus within the dual stream model pt.2

ResearchBlogging.org3.1 What is the dual stream model?

Given these separate anatomical accounts, attributing a function(s) to the arcuate is not clear cut, and any current account is far from the authoritative statement on the matter. Nonetheless, a vast majority of literature does place the arcuate as part of the dual stream model[1] of speech processing, although its exact role within these neural networks is still being disputed – and largely depends on which anatomical account you prescribe to.

The basic assumption of dual stream accounts is that phonological networks interact with both conceptual-semantic and motor-articulatory systems, leading to a distinction between the neural networks that process this speech information. These separate interactions are summarised under two processing streams: the dorsal stream and the ventral stream (Hickok and Poeppel, 2007). Connecting phonological networks with conceptual-semantic systems, using structures in the superior and middle portions of the temporal lobe, is the ventral stream. Meanwhile, the dorsal stream is linked via structures in the posterior frontal lobe to the posterior temporal lobe and parietal operculum, which connects phonological networks with motor-articulatory systems (ibid).

Continue reading “The arcuate fasciculus within the dual stream model pt.2”

Some changes

Now I’ve had a month-long break from blogging you may, or may not, have noticed a few changes to the blog, notably the inclusion of three additional features: Dissertation, Minifeed and Basic Concepts. So from now on in, I will definitely be adding a post every day, and hopefully a research-related post every week or so. But before all this happens, I really suggest you go over and visit Babel’s Dawn, as Mr Bolles is putting much of us slightly less prolific bloggers to shame with his coverage of the ways to protolanguage conference.

As for my own opinion of protolanguage: yes, it probably existed, but I really haven’t got any more to add at the moment. It is a topic I plan on returning to in another post, although I’m not really sure I can add anything extra to the current debate. There is one thing, though: I do find debates on concerning the transition of protolanguage into a fully fledged language a bit tiresome. I mean we’re not even fully sure as to the impact that writing systems have had on how we speak. Take Chomsky’s favourite topic of recursion. As far as I know, there is no evidence of complex recursion being present in languages prior to the emergence of writing systems. It may be the case that writing allowed for languages with no, or very circumscribed, recursion in their syntax to develop into a system that allows for embedding of indefinite complexity.

In truth, you can argue many features of language didn’t appear until the development of writing, as there is no solid record of languages existing prior to this invention. This is a problem all linguists face, and it does require a lot of assumptions to be made beforehand — some of which are reasonable (languages did exist before writing) and some of which may be construed as not reasonable (literate societies process language in the same way as non-literate societies).

Discerning the role of the arcuate fasciculus in speech processing pt.1

ResearchBlogging.orgOriginally identified by Reil (1809) and subsequently named by Burdach (1819), the arcuate fasciculus is a white-matter, neural pathway that intersects with both the lateral temporal cortex and frontal cortex via a “dorsal projection that arches around the Sylvain fissure.” (Rilling et al., 2008, pg. 426). Classical hypotheses saw this pathway as a critical component in connecting two centres of language: Broca’s area (speech production) and Wernicke’s area (speech comprehension) (Catani and Mesulam, 2008).

Much of these assumptions were based on a tentative relationship between language-impairment and damaged portions of the brain. Notably, damage to the arcuate fasciculus is implicated in a syndrome known as conduction aphasia, where an individual has difficulty in speech repetition. Often characterised by errors in spontaneous speech, an individual with conduction aphasia will be fully aware of their mistake, retaining well-preserved auditory comprehension and speech production while also being syntactically and grammatically correct (ibid).

Continue reading “Discerning the role of the arcuate fasciculus in speech processing pt.1”

Broca's area and the processing of hierarchically organised sequences pt.2

ResearchBlogging.org3. Neurological processing of hierarchically organised sequences in non-linguistic domains

A broader perspective sees grammar as just one of many hierarchically organised behaviours being processed in similar, prefrontal neurological regions (Greenfield, 1991; Givon, 1998). As Broca’s area is found to be functionally salient in grammatical processing, it is logical to assume that this is the place to search for activity in analogous hierarchical sequences. Such is the basis for studies into music (Maess et al., 2001), action planning (Koechlin and Jubault, 2006) and tool-production (Stout et al., 2008).

Continue reading “Broca's area and the processing of hierarchically organised sequences pt.2”

Broca's area and the processing of hierarchically organised sequences pt.1

ResearchBlogging.orgEver since its discovery in 1861, Broca’s area (named after its discoverer, Paul Broca) has been inextricably linked with language (Grodzinsky and Santi, 2008). Found in the left hemisphere of the Pre-Frontal Cortex (PFC), Broca’s region traditionally[1] comprises of Broadmann’s areas (BA) 44 and 45 (Hagoort, 2005). Despite being relegated in its status as the centre of language, this region is still believed to play a vital role in certain linguistic aspects.

Of particular emphasis is syntax. However, syntactic processing is not unequivocally confined to Broca’s area, with a vast body of evidence from “Studies investigating lesion deficit correlations point to a more distributed representation of syntactic processes in the left perisylvian region.” (Fiebach, 2005, pg. 80). A more constrained approach places Broca’s area as processing an important functional component of grammar (Grodzinsky and Santi, 2007). One of these suggestions points specifically to how humans are able to organise phrases in hierarchical structures[2].

In natural languages, “[…] the noun phrases and the verb phrase within a clause typically receive their grammatical role (e.g., subject or object) by means of hierarchical relations rather than through the bare linear order of the words in a string. [my emphasis]” (Musso et al., 2003, pg. 774). Furthermore, these phrases can be broken down into smaller segments, with noun phrases, for example, consisting of a determiner preceding a noun (Chomsky, 1957). According to Chomsky (1957) these rules exist without the need for interaction in other linguistic domains. Take for example his now famous phrase of “Colourless green ideas sleep furiously.” (ibid, pg. 15). Despite being syntactically correct, it is argued the sentence as a whole is semantically meaningless.

The relevant point to take away is a sentence is considered hierarchical if phrases are embedded within other phrases. Yet, examples of hierarchical organisation are found in many domains besides syntax. This includes other language phenomena, such as prosody. Also, non-linguistic behaviours – such as music (Givon, 1998), action sequences (Koechlin and Jubault, 2006), tool-use (cf. Scott-Frey, 2004) and tool-production (Stout et al., 2008) – are all cognitively demanding tasks, comparable with that of language. We can even see instances of non-human hierarchical representations: from the songs of humpback whales (Suzuki, Buck and Tyack, 2006) to various accounts of great apes (McGrew, 1992; Nakamichi, 2003) and crows (Hunt, 2000) using and manufacturing their own tools[3].

With this in mind, we can ask ourselves two questions corresponding to Broca’s area and hierarchical organisation: Does Broca’s area process hierarchically organised sequences in language? And if so, is this processing language-specific? The logic behind this two-part approach is to help focus in on the problem. For instance, it may be found hierarchical structures in sentences are processed by Broca’s area. But this belies the notion of other hierarchically organised behaviours also utilising the same cognitive abilities.

Continue reading “Broca's area and the processing of hierarchically organised sequences pt.1”

Lady Liberty's Awful Health

Readers from either Britain or the US will know about the relatively recent furore over comparisons between private and NHS-style healthcare. I was hoping to post an old article I wrote about the topic, but sadly it’s disappeared from my hard drive. Instead, here is a very good video from the New Scientist website that takes a scientific, rather than a political approach to the problem:

Hat tip to Evolving Thoughts.