Web-based language production experiments: Semantic interference assessment is robust for spoken and typed response modalities.

For experimental research on language production, temporal precision and high quality of the recorded audio files are imperative. These requirements are a considerable challenge if language production is to be investigated online. However, online research has huge potential in terms of efficiency, ecological validity and diversity of study populations in psycholinguistic and related research, also beyond the current situation. Here, we supply confirmatory evidence that language production can be investigated online and that reaction time (RT) distributions and error rates are similar in written naming responses (using the keyboard) and typical overt spoken responses. To assess semantic interference effects in both modalities, we performed two pre-registered experiments (n = 30 each) in online settings using the participants' web browsers. A cumulative semantic interference (CSI) paradigm was employed that required naming several exemplars of semantic categories within a seemingly unrelated sequence of objects. RT is expected to increase linearly for each additional exemplar of a category. In Experiment 1, CSI effects in naming times described in lab-based studies were replicated. In Experiment 2, the responses were typed on participants' computer keyboards, and the first correct key press was used for RT analysis. This novel response assessment yielded a qualitatively similar, very robust CSI effect. Besides technical ease of application, collecting typewritten responses and automatic data preprocessing substantially reduce the work load for language production research. Results of both experiments open new perspectives for research on RT effects in language experiments across a wide range of contexts. JavaScript- and R-based implementations for data collection and processing are available for download.

Lesion correlates of patholinguistic profiles in chronic aphasia: comparisons of syndrome-, modality- and symptom-level assessment.

One way to investigate the neuronal underpinnings of language competence is to correlate patholinguistic profiles of aphasic patients to corresponding lesion sites. Constituting the beginnings of aphasiology and neurolinguistics over a century ago, this approach has been revived and refined in the past decade by statistical approaches mapping continuous variables (providing metrics that are not simply categorical) on voxel-wise lesion information (voxel-based lesion-symptom mapping). Here we investigate whether and how voxel-based lesion-symptom mapping allows us to delineate specific lesion patterns for differentially fine-grained clinical classifications. The latter encompass 'classical' syndrome-based approaches (e.g. Broca's aphasia), more symptom-oriented descriptions (e.g. agrammatism) and further refinement to linguistic sub-functions (e.g. lexico-semantic deficits for inanimate versus animate items). From a large database of patients treated for aphasia of different aetiologies (n = 1167) a carefully selected group of 102 first ever ischaemic stroke patients with chronic aphasia (∅ 12 months) were included in a VLSM analysis. Specifically, we investigated how performance in the Aachen Aphasia Test-the standard clinical test battery for chronic aphasia in German-relates to distinct brain lesions. The Aachen Aphasia Test evaluates aphasia on different levels: a non-parametric discriminant procedure yields probabilities for the allocation to one of the four 'standard' syndromes (Broca, Wernicke, global and amnestic aphasia), whereas standardized subtests target linguistic modalities (e.g. repetition), or even more specific symptoms (e.g. phoneme repetition). Because some subtests of the Aachen Aphasia Test (e.g. for the linguistic level of lexico-semantics) rely on rather coarse and heterogeneous test items we complemented the analysis with a number of more detailed clinically used tests in selected mostly mildly affected subgroups of patients. Our results indicate that: (i) Aachen Aphasia Test-based syndrome allocation allows for an unexpectedly concise differentiation between 'Broca's' and 'Wernicke's' aphasia corresponding to non-overlapping anterior and posterior lesion sites; whereas (ii) analyses for modalities and specific symptoms yielded more circumscribed but partially overlapping lesion foci, often cutting across the above syndrome territories; and (iii) especially for lexico-semantic capacities more specialized clinical test-batteries are required to delineate precise lesion patterns at this linguistic level. In sum this is the first report on a successful lesion-delineation of syndrome-based aphasia classification highlighting the relevance of vascular distribution for the syndrome level while confirming and extending a number of more linguistically motivated differentiations, based on clinically used tests. We consider such a comprehensive view reaching from the syndrome to a fine-grained symptom-oriented assessment mandatory to converge neurolinguistic, patholinguistic and clinical-therapeutic knowledge on language-competence and impairment.

Separability and cross talk: optimizing dual wavelength combinations for near-infrared spectroscopy of the adult head.

By means of noninvasive near-infrared spectroscopy (NIRS), cerebral concentration changes in oxygenated and deoxygenated hemoglobin ([oxy-Hb] and [deoxy-Hb]) can be determined. The quality of the concentration changes' assessment critically depends on the wavelength combination used. Trying to optimize this combination, two spectroscopic effects must be taken into account: cross talk and separability. Cross talk between [oxy-Hb] and [deoxy-Hb] occurs because the assumption made in the analysis-that there is a homogeneous concentration change-does not hold true for the adult human head. Separability-to be introduced in this paper-is a measure for the degree of physical noise of the measurement that will influence the noise of the concentration changes' assessment. In other words, high separability corresponds to a low noise with respect to the concentration changes assessed. Here, we present analytical expressions for both measures and provide model-based estimates of cross talk and separability for any combination of two wavelengths between 610 and 920 nm. These theoretical considerations allow for two predictions: (a) if both wavelengths used are greater than approximately 780 nm, cross talk is high and separability is low resulting in erroneous and noisy concentration data. (b) If one wavelength is chosen below 720 nm while the other is greater than 730 nm, cross talk is low and separability is high resulting in accurate concentration changes. We show the relevance of these theoretical results for noninvasive NIRS by testing the predictions on experimental data obtained in adults undergoing visual stimulation.

Functional assessment of Broca's area using near infrared spectroscopy in humans.

We used near-infrared spectroscopy (NIRS) to compare functional hemoglobin concentration changes (delta[oxy-Hb] and delta[deoxy-Hb]) over human language and motor cortices. Eight subjects performed finger opposition, tongue movement, and covert visual object naming in an interleaved block paradigm design. NIRS revealed paradigm specific patterns of delta[oxy-Hb] and delta[deoxy-Hb] providing cortical localization of each function. During each task, significant response overlap was observed when comparing the [oxy-Hb] signals, whereas delta[deoxy-Hb] seemed more localized. Furthermore, by applying magnitude and time to significance measures to the delta[deoxy-Hb] response profile, Broca's area was easily distinguished from neighboring tongue (and hand) motor representation. Delta[oxy-Hb] did not provide this level of specificity. These findings suggest delta[deoxy-Hb] as the preferential NIRS parameter to map language cortices.