Marieke Longcamp

What differs in visual recognition of handwritten vs. printed letters? An fMRI study.

In models of letter recognition, handwritten letters are considered as a particular font exemplar, not qualitatively different in their processing from printed letters. Yet, some data suggest that recognizing handwritten letters might rely on distinct processes, possibly related to motor knowledge. We applied functional magnetic resonance imaging to compare the neural correlates of perceiving handwritten letters vs. standard printed letters. Statistical analysis circumscribed to frontal brain regions involved in hand‐movement triggering and execution showed that processing of handwritten letters is supported by a stronger activation of the left primary motor cortex and the supplementary motor area. At the whole‐brain level, additional differences between handwritten and printed letters were observed in the right superior frontal, middle occipital, and parahippocampal gyri, and in the left inferior precentral and the fusiform gyri. The results are suggested to indicate embodiment of the visual perception of handwritten letters. Hum Brain Mapp, 2011.

A new statistical test based on the wavelet cross-spectrum to detect time–frequency dependence between non-stationary signals: Application to the analysis of cortico-muscular interactions

The study of the correlations that may exist between neurophysiological signals is at the heart of modern techniques for data analysis in neuroscience. Wavelet coherence is a popular method to construct a time-frequency map that can be used to analyze the time-frequency correlations between two time series. Coherence is a normalized measure of dependence, for which it is possible to construct confidence intervals, and that is commonly considered as being more interpretable than the wavelet cross-spectrum (WCS). In this paper, we provide empirical and theoretical arguments to show that a significant level of wavelet coherence does not necessarily correspond to a significant level of dependence between random signals, especially when the number of trials is small. In such cases, we demonstrate that the WCS is a much better measure of statistical dependence, and a new statistical test to detect significant values of the cross-spectrum is proposed. This test clearly outperforms the limitations of coherence analysis while still allowing a consistent estimation of the time-frequency correlations between two non-stationary stochastic processes. Simulated data are used to investigate the advantages of this new approach over coherence analysis. The method is also applied to experimental data sets to analyze the time-frequency correlations that may exist between electroencephalogram (EEG) and surface electromyogram (EMG).

Functional Specificity in the Motor System: Evidence From Coupled fMRI and Kinematic Recordings During Letter and Digit Writing

A few intriguing neuropsychologial studies report dissociations where agraphic patients are severely impaired for writing letters whereas they write digits nearly normally. Here, using functional magnetic resonance imaging (fMRI) together with graphic tablet recordings, we tested the hypothesis that the motor patterns for writing letters are coded in specific regions of the cortex. We found a set of three regions that were more strongly activated when participants wrote letters than when they wrote digits and whose response was not explained by low‐level kinematic features of the graphic movements. Two of these regions (left dorsal premotor cortex and supplementary motor complex) are part of a motor control network. The left premotor activation belongs to what is considered in the literature a key area for handwriting. Another significant activation, likely related to phoneme‐to‐grapheme conversion, was found in the right anterior insula. This constitutes the first neuroimaging evidence of functional specificity derived from experience in the cortical motor system. Hum Brain Mapp 35:6077–6087, 2014.

Response planning in word typing: evidence for inhibition.

Typing is a pervasive phenomenon, yet the underlying neural processes have hardly been studied. Here, the mechanisms of keystroke preparation were studied with a typed picture-naming task performed by expert typists. Electroencephalographic activities recorded over sensorimotor areas prior to first-keystroke onset were examined with time-frequency and event-related potential (ERP) analyses. In the time-frequency domain, a beta event-related desynchronization was present bilaterally. In the ERP analyses, the activity was asymmetric, with negativity and positivity patterns developing over, respectively, contra- and ipsilateral recording sites. This pattern is similar to that observed in choice reaction time tasks, and thus can be interpreted as evidence of contralateral motor cortex activation accompanied by inhibition of the ipsilateral motor cortex. These data constitute the first electrophysiological demonstration of inhibitory activity in typing and pave the way to a thorough study of typing.

Motor control of handwriting in the developing brain: A review

ABSTRACT This review focuses on the acquisition of writing motor aspects in adults, and in 5-to 12-year-old children without learning disabilities. We first describe the behavioural aspects of adult writing and dominant models based on the notion of motor programs. We show that handwriting acquisition is characterized by the transition from reactive movements programmed stroke-by-stroke in younger children, to an automatic control of the whole trajectory when the motor programs are memorized at about 10 years old. Then, we describe the neural correlates of adult writing, and the changes that could occur with learning during childhood. The acquisition of a new skill is characterized by the involvement of a network more restricted in space and where neural specificity is increased in key regions. The cerebellum and the left dorsal premotor cortex are of fundamental importance in motor learning, and could be at the core of the acquisition of handwriting.

Motor expertise for typing impacts lexical decision performance

Abstract The massive shift in writing habits calls for a better understanding of the possible consequences of typing practice on language processing, including reading. To assess a possible impact of typing knowledge on word recognition, we built a set of words and pseudowords differing by their ratio of bimanual transitions between letters, an index of typing difficulty for experts. An effect of typing difficulty was observed in expert participants who were actually typing the items and not in a control group of hunt-and-peck typists. We then tested whether word recognition, measured with the task of lexical decision, was impacted by the typing difficulty of words. We found that lexical decision latencies varied as a function of typing difficulty, but differently for experts and non-experts. The effect was mostly driven by pseudowords. This suggests that motor representations built during the practice of typing have a collateral effect on visual recognition processes. The implications for education are discussed.

Biological geometry perception: visual discrimination of eccentricity is related to individual motor preferences.

Background In the continuum between a stroke and a circle including all possible ellipses, some eccentricities seem more “biologically preferred” than others by the motor system, probably because they imply less demanding coordination patterns. Based on the idea that biological motion perception relies on knowledge of the laws that govern the motor system, we investigated whether motorically preferential and non-preferential eccentricities are visually discriminated differently. In contrast with previous studies that were interested in the effect of kinematic/time features of movements on their visual perception, we focused on geometric/spatial features, and therefore used a static visual display. Methodology/Principal Findings In a dual-task paradigm, participants visually discriminated 13 static ellipses of various eccentricities while performing a finger-thumb opposition sequence with either the dominant or the non-dominant hand. Our assumption was that because the movements used to trace ellipses are strongly lateralized, a motor task performed with the dominant hand should affect the simultaneous visual discrimination more strongly. We found that visual discrimination was not affected when the motor task was performed by the non-dominant hand. Conversely, it was impaired when the motor task was performed with the dominant hand, but only for the ellipses that we defined as preferred by the motor system, based on an assessment of individual preferences during an independent graphomotor task. Conclusions/Significance Visual discrimination of ellipses depends on the state of the motor neural networks controlling the dominant hand, but only when their eccentricity is “biologically preferred”. Importantly, this effect emerges on the basis of a static display, suggesting that what we call “biological geometry”, i.e., geometric features resulting from preferential movements is relevant information for the visual processing of bidimensional shapes.

On the functional relationship between language and motor processing in typewriting: an EEG study

ABSTRACT The functional relationship between language and motor processing was investigated to elucidate whether it is better described in terms of a discrete or a continuous account of information flow. To this end, we recorded event-related potentials during a typewriting task that combined a semantic priming paradigm with a manipulation of response side (response initiated with right vs. left hand), and focused on the lateralised potentials indexing motor-response activation and inhibition. The critical issue was to assess whether, in the semantically related condition, the increased evidence for the target representation at the conceptual-lexical levels percolates into motor-response preparation, thus triggering an enhanced activation of the corresponding response hand, or whether lexical-semantic and motor-preparation processes unfold independently. Despite effective priming on response times, no selective influence of semantic relatedness was observed on motor-preparation potentials. These results are more compatible with a discrete account.

Testing the physiological plausibility of conflicting psychological models of response inhibition: A forward inference fMRI study

HighlightsWe used forward inference on BOLD patterns of competing models of go/nogo inhibition.No evidence was found for processes operating selectively in reaction to nogo stimuli.Evidence was found for non‐selective but context‐dependent control mechanisms.Proactive and reactive control support global action restraint in uncertain context. Abstract The neural mechanisms underlying response inhibition and related disorders are unclear and controversial for several reasons. First, it is a major challenge to assess the psychological bases of behaviour, and ultimately brain–behaviour relationships, of a function which is precisely intended to suppress overt measurable behaviours. Second, response inhibition is difficult to disentangle from other parallel processes involved in more general aspects of cognitive control. Consequently, different psychological and anatomo‐functional models coexist, which often appear in conflict with each other even though they are not necessarily mutually exclusive. The standard model of response inhibition in go/no‐go tasks assumes that inhibitory processes are reactively and selectively triggered by the stimulus that participants must refrain from reacting to. Recent alternative models suggest that action restraint could instead rely on reactive but non‐selective mechanisms (all automatic responses are automatically inhibited in uncertain contexts) or on proactive and non‐selective mechanisms (a gating function by which reaction to any stimulus is prevented in anticipation of stimulation when the situation is unpredictable). Here, we assessed the physiological plausibility of these different models by testing their respective predictions regarding event‐related BOLD modulations (forward inference using fMRI). We set up a single fMRI design which allowed for us to record simultaneously the different possible forms of inhibition while limiting confounds between response inhibition and parallel cognitive processes. We found BOLD dynamics consistent with non‐selective models. These results provide new theoretical and methodological lines of inquiry for the study of basic functions involved in behavioural control and related disorders.

The Serial Order of Response Units in Word Production: The Case of Typing.

The selection and ordering of response units (phonemes, letters, keystrokes) represents a transversal issue across different modalities of language production. Here, the issue of serial order was investigated with respect to typewriting. Following seminal investigations in the spoken modality, we conducted an experiment where participants typed as many times as possible a pair of words during a fixed time-window. The 2 words shared either their first 2 keystrokes, the last 2 ones, all the keystrokes, or were unrelated. Fine-grained performance measures were recorded at the level of individual keystrokes. In contrast with previous results from the spoken modality, we observed an overall facilitation for words sharing the initial keystrokes. In addition, the initial overlap briefly delayed the execution of the following keystroke. The results are discussed with reference to different theoretical perspectives on serial order, with a particular attention to the competing accounts offered by position coding models and chaining models. Our findings point to potential major differences between the speaking and typing modalities in terms of interactive activation between lexical and response units processing levels.