Monthly Archives: January 2016

Babies show the way

It is January and therefore we see the answers to the Edge Question. This year the question is “What do you consider the most interesting recent (scientific) news? What makes it important?” I have to say that I did not find this year’s crop of short essays as interesting as in previous years – but there were some gems.

For example N.J. Enfield’s ‘Pointing is a Prerequisite for Language’ fits so well with what I think and is expressed so well (here). I have a problem with the idea that language is not primarily about communication but rather is about a way of thinking. I cannot believe that language arose over a short space of time rather than a long evolution (both biological and cultural evolution). And it began as communication not as a proper-ish language. “Infants begin to communicate by pointing at about nine months of age, a year before they can produce even the simplest sentences. Careful experimentation has established that prelinguistic infants can use pointing gestures to ask for things, to help others by pointing things out to them, and to share experiences with others by drawing attention to things that they find interesting and exciting. … With pointing, we do not just look at the same thing, we look at it together. This is a particularly human trick, and it is arguably the thing that ultimately makes social and cultural institutions possible. Being able to point and to comprehend the pointing gestures of others is crucial for the achievement of “shared intentionality,” the ability to build relationships through the sharing of perceptions, beliefs, desires, and goals.”

So this is where to start to understand language – with communication and with gestures, and especially joint attention with another person as in pointing. EB Bolles has a lot of information on this, collected over quite a few years in his blog (here).

Get rid of the magic

I have difficulty with the reaction of many people to the idea that consciousness is a process of the brain. They say it is impossible, consciousness cannot be a physical process. How can that vivid subjective panorama be the product of a physical process? They tend to believe either some variety of dualism – consciousness is not physical but spiritual (or magical), or consciousness is a natural primitive – a sort of state of matter/energy that objects possess more of less of (another sort of magic). Or they fudge the issue by believing it is an emerging aspect of physical processes (kind of physical but arising by magic). I find explanations like these far more difficult than a plain and simple physical process in the brain (with no magic).

My question is really, “what would you expect awareness to be like?” “Have you a better idea of how to do awareness?” It would certainly not be numeric values. It would not be word descriptions. Why not a simulated model of ourselves in the world based on what our sensory organs can provide? Making a model seems a perfectly reasonable brain process with no reason to reject it as impossible. It sounds like what we have. But does it need to be a conscious model? (Chalmers’ idea of philosophical zombies assumes that consciousness is an added extra and not needed for thought.)

But it seems that consciousness is an important aspect of a shared simulation. It is reasonable to suppose that all our senses, our memory, our cognition, our motor plans, our emotional states, all contribute to create a simulation. And it is reasonable to assume that they all are responsive to the simulation, use it to coordinate and integrate all the various things going on in the brain so making our behaviour as appropriate as possible. If a model is going to be created and used by many very different parts and functions of the brain it has to be something like a conscious model - a common format, tokens and language.

There have been a number of good and interesting attempts to explain how consciousness might work as the physical process; and there have been a number of attempts to show that such an explanation is impossible. They pass one another like ships in the night. Agreement is not getting any closer. There is not even the start of a concensus and the reason is that one group will not accept something is a valid explanation if it include the magic and the other group will not accept an explanation that loses the magic. The hard question is all about the magic and not about anything else. The question boils down to how can consciousness be explained scientifically while including the magic? I hope that more and more science throws out the magic and the hard question and gets on with explaining consciousness.

Language in the left hemisphere

Here is the posting mentioned in the last post. A recent paper (Harvey M. Sussman; Why the Left Hemisphere Is Dominant for Speech Production: Connecting the Dots; Biolinguistics Vol 9 Dec 2020), deals with the nature of language processing in the left hemisphere and why it is that in right-handed people with split brains only the left cortex can talk although both sides can listen. There is a lot of interesting information in this paper (especially for someone like me who is left-handed and dyslexic). He has a number of ‘dots’ and he connects them.

Dot 1 is infant babbling. The first language-like sounds babies make are coos and these have a very vowel-like quality. Soon they babble consonant-vowel combinations in repetitions. By noting the asymmetry of the mouth it can be shown that babbling comes from the left hemisphere, non-babbling noises from both, and smiles from the right hemisphere. A speech sound map is being created by the baby and it is formed at the dorsal pathway’s projection in the frontal left articulatory network.

Dot 2 is the primacy of the syllable. Syllables are the unit of prosodic events. A person’s native language syllable constraints are the origin of the types of errors that happen in second language pronunciation. Also syllables are the units of transfer in language play. Early speech sound networks are organized in syllable units (vowel and associated consonants) in the left hemisphere of right-handers.

Dot 3 is the inability for the right hemisphere to talk in split brain people. When language tasks are directed at the right hemisphere the stimulus exposure must be longer (greater than 150 msec) than when directed to the left. The right hemisphere can comprehend language but does not evoke a sound image from seen objects and words although the meaning of the objects and words is understood by that hemisphere. The right hemisphere cannot recognize if two words rhyme from seeing illustations of the words. So the left hemisphere (in right-handers) has the only language neural network with sound images. This network serves as the neural source for generating speech, therefore in a split brain only the left side can speak.

Dot 4 deals with the problems of DAS, Development Apraxia of Speech. I am going to skip this.

Dot 5 is the understanding of speech errors. The ‘slot-segment’ hypothesis is based on analysis of speech errors. Two thirds of errors are the type where phonemes are substituted, omitted, transposed or added. The picture is of a two-tiered neural ‘map’ with syllable slots serially ordered as one tier, and an independent network of consonant sounds in the other tier. The tiers are connected together. The vowel is the heart of the syllable in the nucleus slot. Forms are built around it with consonants (CV, CVC, CCV etc.). Spoonerisms are restricted to consonants exchanging with consonants and vowels exchanging with vowels; and, exchanges occurring between the same syllable positions – first with first, last with last etc.

Dot 6 is Hawkin’s model, “the neo-cortex uses stored memories to produce behaviors.” Motor memories are used sequentially and operate in an auto-associative way. Each memory elicits the next in order (think how hard it is to do things backwards). Motor commands would be produced in a serial order, based on syllables - learned articulatory behaviors linked to sound equivalents.

Dot 7 is experiments that showed representations of sounds in human language at the neural level. For example there is a representation of a generic ‘b’ sound, as well as representations of various actual ‘b’s that differ from one another. This is why we can clearly hear a ‘b’ but have difficulty identifying a ‘b’ when the sound pattern is graphed.

Here is the abstract:

Evidence from seemingly disparate areas of speech/language research is reviewed to form a unified theoretical account for why the left hemisphere is specialized for speech production. Research findings from studies investigating hemispheric lateralization of infant babbling, the primacy of the syllable in phonological structure, rhyming performance in split-brain patients, rhyming ability and phonetic categorization in children diagnosed with developmental apraxia of speech, rules governing exchange errors in spoonerisms, organizational principles of neocortical control of learned motor behaviors, and multi-electrode recordings of human neuronal responses to speech sounds are described and common threads highlighted. It is suggested that the emergence, in developmental neurogenesis, of a hard-wired, syllabically-organized, neural substrate representing the phonemic sound elements of one’s language, particularly the vocalic nucleus, is the crucial factor underlying the left hemisphere’s dominance for speech production.

Language in the right hemisphere

Language in the right hemisphere

I am going to write two posts: this one on the right hemisphere and prosody in language, and a later one on the left hemisphere and motor control of language. Prosody is the fancy word for things like rhythm, tone of voice, stress patterns, speed and pitch. It is not things like individual phonemes, words or syntax. In order to properly understand language, we need both.

A recent paper (Sammler, Grosbras, Anwander, Bestelmeyer, and Belin; Dorsal and Ventral Pathways for Prosody; Current Biology, Volume 25, Issue 23, p3079–3085, 7 December 2020) gives evidence of the anatomy of the auditory system in the right hemisphere that is like that in the left. Of course the two hemispheres collaborate in understanding and producing language but the right side processes the emotional aspects while the left processes the literal meaning.

Here is the abstract:

Our vocal tone—the prosody—contributes a lot to the meaning of speech beyond the actual words. Indeed, the hesitant tone of a “yes” may be more telling than its affirmative lexical meaning. The human brain contains dorsal and ventral processing streams in the left hemisphere that underlie core linguistic abilities such as phonology, syntax, and semantics. Whether or not prosody—a reportedly right-hemispheric faculty—involves analogous processing streams is a matter of debate. Functional connectivity studies on prosody leave no doubt about the existence of such streams, but opinions diverge on whether information travels along dorsal or ventral pathways. Here we show, with a novel paradigm using audio morphing combined with multimodal neuroimaging and brain stimulation, that prosody perception takes dual routes along dorsal and ventral pathways in the right hemisphere. In experiment 1, categorization of speech stimuli that gradually varied in their prosodic pitch contour (between statement and question) involved (1) an auditory ventral pathway along the superior temporal lobe and (2) auditory-motor dorsal pathways connecting posterior temporal and inferior frontal/premotor areas. In experiment 2, inhibitory stimulation of right premotor cortex as a key node of the dorsal stream decreased participants’ performance in prosody categorization, arguing for a motor involvement in prosody perception. These data draw a dual-stream picture of prosodic processing that parallels the established left-hemispheric multi-stream architecture of language, but with relative rightward asymmetry.

The ventral and dorsal pathways are also found in both hemispheres in vision. The ventral is often called the ‘what’ pathway and identifies objects and conscious perception while the dorsal is called the ‘where’ pathway and is involved in spatial location for motor accuracy. The auditory pathways appear to also have the dorsal path going to motor centers and the ventral to perceptual centers. And although they deal with different processing functions the pair of auditory pathways appear in both hemispheres, like the visual ones.

 

Complexity of conversation

Language is about communication. It can be studied as written sentences, as production of spoken language, or as comprehension of spoken language, but these do not get to the heart of communicating. Language evolved as conversation, each baby learns it in conversation and most of our use of it each day is in conversations. Exchanges, taking turns, is the essence of language. A recent paper by S. Levinson in Trends in Cognitive Sciences, “Turn-taking in Human Communication – Origins and Implications for Language Processing”, looks at the complications of turn-taking.

The world’s languages vary in almost all levels of organization but there is a striking similarity in exchanges – rapid turns of short phrases or clauses within single sound envelopes. There are few long gaps or much overlapping speech during the changes of speaker. Not only is a standard turn-taking universal in human cultures but it is found in all types of primates and it is learned by babies before any language is acquired. It may be the oldest aspect of our language.

But it is paradoxical – for the gap between speakers is too short to produce a response to what has been said by the last speaker. In fact, the gap tends to be close to the minimum reflex time. A conversational speaking turn averages 2 seconds (2000ms) and the gap between speakers is about 200ms, but it takes 600ms to prepare the first word (1500ms for a short phrase). So it is clear that production and comprehension must go on at the same time in the same areas of the brain and that comprehension must include a good deal of prediction of how a phrase is going to end. Because comprehension and production have been studied separately, it is not clear how this multitasking, if that is what it is, is accomplished. First, the listener has to figure out what sort of utterance the speaker is making – statement, question, command or whatever. Without this the listener does not know what sort of reply is appropriate. The listener then must predict (guess) the rest of the utterance, decide what the response should be and formulate it. Finally the listener must recognize the signal/s of when the end of the utterance will be. The listener can immediately begin to talk as soon as the utterance ends. There is more to learn about how the brain does this and what the effect of turn-taking has on the nature of language.

There are cultural conventions that override turn-taking so that speakers can talk for some time without interruption, and even if they pause from time to time, no one jumps in. Of course, if someone speaks for too long without implicit permission, they will be forcibly interrupted fairly soon, people will drift away or some will start new conversations in sub-groups. That’s communication.

Here is the abstract of - Stephen C. Levinson. Turn-taking in Human Communication – Origins and Implications for Language Processing. Trends in Cognitive Sciences, 2015:

Most language usage is interactive, involving rapid turn-taking. The turn-taking system has a number of striking properties: turns are short and responses are remarkably rapid, but turns are of varying length and often of very complex construction such that the underlying cognitive processing is highly compressed. Although neglected in cognitive science, the system has deep implications for language processing and acquisition that are only now becoming clear. Appearing earlier in ontogeny than linguistic competence, it is also found across all the major primate clades. This suggests a possible phylogenetic continuity, which may provide key insights into language evolution.

Trends

The bulk of language usage is conversational, involving rapid exchange of turns. New information about the turn-taking system shows that this transition between speakers is generally more than threefold faster than language encoding. To maintain this pace of switching, participants must predict the content and timing of the incoming turn and begin language encoding as soon as possible, even while still processing the incoming turn. This intensive cognitive processing has been largely ignored by the language sciences because psycholinguistics has studied language production and comprehension separately from dialog.

This fast pace holds across languages, and across modalities as in sign language. It is also evident in early infancy in ‘proto-conversation’ before infants control language. Turn-taking or ‘duetting’ has been observed in many other species and is found across all the major clades of the primate order.