Mohinish Shukla

Near-infrared spectroscopy: A report from the McDonnell infant methodology consortium

Near-infrared spectroscopy (NIRS) is a new and increasingly widespread brain imaging technique, particularly suitable for young infants. The laboratories of the McDonnell Consortium have contributed to the technological development and research applications of this technique for nearly a decade. The present paper provides a general introduction to the technique as well as a detailed report of the methodological innovations developed by the Consortium. The basic principles of NIRS and some of the existing developmental studies are reviewed. Issues concerning technological improvements, parameter optimization, possible experimental designs and data analysis techniques are discussed and illustrated by novel empirical data.

Prosody guides the rapid mapping of auditory word forms onto visual objects in 6-mo-old infants

Human infants are predisposed to rapidly acquire their native language. The nature of these predispositions is poorly understood, but is crucial to our understanding of how infants unpack their speech input to recover the fundamental word-like units, assign them referential roles, and acquire the rules that govern their organization. Previous researchers have demonstrated the role of general distributional computations in prelinguistic infants’ parsing of continuous speech. We extend these findings to more naturalistic conditions, and find that 6-mo-old infants can simultaneously segment a nonce auditory word form from prosodically organized continuous speech and associate it to a visual referent. Crucially, however, this mapping occurs only when the word form is aligned with a prosodic phrase boundary. Our findings suggest that infants are predisposed very early in life to hypothesize that words are aligned with prosodic phrase boundaries, thus facilitating the word learning process. Further, and somewhat paradoxically, we observed successful learning in a more complex context than previously studied, suggesting that learning is enhanced when the language input is well matched to the learners expectations.

An interaction between prosody and statistics in the segmentation of fluent speech

Sensitivity to prosodic cues might be used to constrain lexical search. Indeed, the prosodic organization of speech is such that words are invariably aligned with phrasal prosodic edges, providing a cue to segmentation. In this paper we devise an experimental paradigm that allows us to investigate the interaction between statistical and prosodic cues to extract words from a speech stream. We provide evidence that statistics over the syllables are computed independently of prosody. However, we also show that trisyllabic sequences with high transition probabilities that straddle two prosodic constituents appear not to be recognized. Taken together, our findings suggest that prosody acts as a filter, suppressing possible word-like sequences that span prosodic constituents.

Hemodynamic Correlates of Cognition in Human Infants

Over the past 20 years, the field of cognitive neuroscience has relied heavily on hemodynamic measures of blood oxygenation in local regions of the brain to make inferences about underlying cognitive processes. These same functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) techniques have recently been adapted for use with human infants. We review the advantages and disadvantages of these two neuroimaging methods for studies of infant cognition, with a particular emphasis on their technical limitations and the linking hypotheses that are used to draw conclusions from correlational data. In addition to summarizing key findings in several domains of infant cognition, we highlight the prospects of improving the quality of fNIRS data from infants to address in a more sophisticated way how cognitive development is mediated by changes in underlying neural mechanisms.

The quest for generalizations over consonants: Asymmetries between consonants and vowels are not the by-product of acoustic differences

Consonants and vowels may play different roles during language processing, consonants being preferentially involved in lexical processing, and vowels tending to mark syntactic constituency through prosodic cues. In support of this view, artificial language learning studies have demonstrated that consonants (C) support statistical computations, whereas vowels (V) allow certain structural generalizations. Nevertheless, these asymmetries could be mere by-products of lower level acoustic differences between Cs and Vs, in particular the energy they carry, and thus their relative salience. Here we address this issue and show that vowels remain the preferred targets for generalizations, even when consonants are made highly salient or vowels barely audible. Participants listened to speech streams of nonsense CVCVCV words, in which consonants followed a simple ABA structure. Participants failed to generalize this structure over sonorant consonants (Experiment 1), even when vowel duration was reduced to one third of that of consonants (Experiment 2). When vowels were eliminated from the stream, participants showed only a marginal evidence of generalizations (Experiment 4). In contrast, participants readily generalized the structure over barely audible vowels (Experiment 3). These results show that different roles of consonants and vowels cannot be readily reduced to acoustical and perceptual differences between these phonetic categories.

SMART-T: A system for novel fully automated anticipatory eye-tracking paradigms

Anticipatory eye movements (AEMs) are a natural and implicit measure of cognitive processing and have been successfully used to document such important cognitive capacities as learning, categorization, and generalization, especially in infancy (McMurray & Aslin, Infancy, 6, 203–229, 2004). Here, we describe an improved AEM paradigm to automatically assess online learning on a trial-by-trial basis, by analyzing eye gaze data in each intertrial interval of a training phase. Different measures of learning can be evaluated simultaneously. We describe the implementation of a system for designing and running a variety of such AEM paradigms. Additionally, this system is capable of a wider variety of gaze-contingent paradigms, as well as implementations of standard noncontingent paradigms. Our system, Smart-T (System for Monitoring Anticipations in Real Time with the Tobii), is a set of MATLAB scripts with a graphical front end, written using the Psychophysics Toolbox. The system gathers eye gaze data using the commercially available Tobii eye-trackers via a MATLAB module, Talk2Tobii. We report a pilot study showing that Smart-T can detect 6-month-old infants’ learning of simple predictive patterns involving the disappearance and reappearance of multimodal stimuli.

Why is language unique to humans

Cognitive neuroscience has focused on language acquisition as one of the main domains to test the respective roles of statistical vs. rule-like computation. Recent studies have uncovered that the brain of human neconates displays a typical signature in response to speech sounds even a few hours after birth. This suggests that neuroscience and linguistics converge on the view that, to a large extent, language acquisition arises due to our genetic endowment. Our research has also shown how statistical dependencies and the ability to draw structural generalizations are basic processes that interact intimately. First, we explore how the rhythmic properties of language bias word segmentation. Second, we demonstrate that natural speech categories play specific roles during language acquisition: some categories are optimally suited to compute statistical dependencies while other categories are optimally suited for the extraction of structural generalizations.

Language from a biological perspective

The faculty of language is unique to the human species. This implies that there are human-specific biological changes that lie at the basis of human language. However, it is not clear what the nature of such changes are, and how they could be shaped by evolution. In this paper, emphasis is laid on describing language in a Chomskyan manner, as a mental object. This serves as a standpoint to speculate about the biological basis of the emergence and evolution of language.

Transfer of learning across the somatosensory cortex.

Barosi G 1994 Inadequate erythropoietin response to anemia: definition and clinical relevance; Ann. Hematol. 68 215–223 Bocci V 1981 Determinants of erythrocyte aging: A reappraisal; Br. J. Haematol. 48 515–522 Connor J, Pak C C and Schroit A J 1994 Exposure of phosphotidyl-serine in the outer leaflet of human red blood cells. Relationship to cell density, cell age and clearance by mononuclear phagocytes; J. Biol. Chem. 269 2399–2404 Galili U, Clark M R and Shohet S B 1986 Excessive binding of natural anti-alpha-galactosyl immunoglobin G to sickle erythrocytes may contribute to extravascular cell destruction; J. Clin. Invest. 77 27–33 Hensley K, Howard B J, Carney J M and Butterfield D A 1989 Membrane protein alterations in rodent erythrocytes and synaptosomes due to aging and hyperoxia; Biochim. Biophys. Acta 1270 203–206 Jacobsen S E 1995 IL12, a direct stimulator and indirect inhibitor of haematopoiesis; Res. Immunol. 146 506–514 Kay M M, Flowers N, Goodman J and Bosman G 1989 Alteration in membrane protein band 3 associated with accelerated erythrocyte aging; Proc. Natl. Acad. Sci. USA 86 5834–5838 Kosower N S 1993 Altered properties of erythrocytes in the aged; Am. J. Hematol. 42 241–247 Landaw S A 1988 Factors that accelerate or retard red blood cell senescence; Blood cells 14 47–67 Miller B A, Floros J, Cheung J Y, Wojchowski D M, Bell L, Begley C G, Elwood N J, Kreider J and Christian C 1994 Steel factor affects SCL expression during normal erythroid differentiation; Blood 84 2971–2976 Roeder I, de Haan G, Engel C, Nijhof W, Dontje B and Loeffler M 1998 Interactions of erythropoietin, granulocyte colony-stimulating factor, stem cell factor, and interleukin-11 on murine hematopoiesis during simultaneous administration; Blood 91 3222–3229 Saxena R K and Chandrasekhar B 2000 A novel non-phagocytic mechanism of erythrocyte destruction involving direct cell mediated cytotoxicity; Int. J. Hematol. (in press)