The touch in action: exploring sensorimotor interactions with motor imagery.

The current research investigates the role of tactile information and its associated neural substrates in controlling the action. We employ a combination of motor and sensory components by asking participants to imagine exerting force with the index finger while either touching or not touching a surface. Assuming action imagination and action performance present similar patterns of activation along the motor system, we applied single-pulse transcranial magnetic stimulation over the primary motor cortex (M1) during action imagination. We observed increased amplitude of motor-evoked potentials (MEPs) of the relevant muscle when imagined actions were performed concurrently with tactile stimulation, suggesting a facilitatory effect of touch on the motor system. The motor system activity was scaled-based on the different amounts of force required, and crucially, this effect was specific to the body part involved in the action imagined. An intriguing positive correlation was observed between participants' ratings of their imagery level of vividness and the activation of the motor system, indicating that those participants exhibiting MEPs scaled correctly also had strong visualization abilities, as reflected by their capacity to accurately distinguish between varying levels of force.

Transcranial direct current stimulation (tDCS) modulates motor execution in a limb reaching task.

The majority of human activities show a trade-off between movement speed and accuracy. Here we tested 16 participants in a quick pointing action after 20 minutes (2 mA) of transcranial direct current stimulation (tDCS) delivered at the supplementary motor area in a single-blind crossover design study for testing the feedforward components in the control of action. tDCS stimuli were delivered in three randomized sessions of stimulations as anodal, cathodal and sham as a control. The task performed pre- and post-tDCS stimulation, was to point as fast and as precise as possible with the big toe to targets having different sizes (2 and 8 cm; Width) and positioned at different distances (20 and 60 cm; Distance). An optoelectronic motion capture system was used to collect the kinematics of movement. The result indicates that individuals after receiving anodal stimulation decreased their movement time and increased their movement speed, while the opposite happened after receiving a cathodal stimulation. The scarcity of studies in this area invites us to plan a research that aims at the trade-off especially in the clinical settings.

Neural underpinnings of the interplay between actual touch and action imagination in social contexts.

While there is established evidence supporting the involvement of the sense of touch in various actions, the neural underpinnings of touch and action interplay in a social context remain poorly understood. To prospectively investigate this phenomenon and offer further insights, we employed a combination of motor and sensory components by asking participants to imagine exerting force with the index finger while experiencing their own touch, the touch of one another individual, the touch of a surface, and no touch. Based on the assumption that the patterns of activation in the motor system are similar when action is imagined or actually performed, we proceeded to apply a single-pulse transcranial magnetic stimulation over the primary motor cortex (M1) while participants engaged in the act of imagination. Touch experience was associated with higher M1 excitability in the presence and in the absence of force production imagination, but only during force production imagination M1 excitability differed among the types of touch: both biological sources, the self-touch and the touch of one other individual, elicited a significant increase in motor system activity when compared to touching a non-living surface or in the absence of touch. A strong correlation between individual touch avoidance questionnaire values and facilitation in the motor system was present while touching another person, indicating a social aspect for touch in action. The present study unveils the motor system correlates when the sensory/motor components of touch are considered in social contexts.

The dynamics of reading complex words: evidence from steady-state visual evoked potentials.

The present study used steady-state visual evoked potentials (SSVEPs) to examine the spatio-temporal dynamics of reading morphologically complex words and test the neurophysiological activation pattern elicited by stems and suffixes. Three different types of target words were presented to proficient readers in a delayed naming task: truly suffixed words (e.g., farmer), pseudo-suffixed words (e.g., corner), and non-suffixed words (e.g., cashew). Embedded stems and affixes were flickered at two different frequencies (18.75 Hz and 12.50 Hz, respectively). The stem data revealed an earlier SSVEP peak in the truly suffixed and pseudo-suffixed conditions compared to the non-suffixed condition, thus providing evidence for the form-based activation of embedded stems during reading. The suffix data also showed a dissociation in the SSVEP response between suffixes and non-suffixes with an additional activation boost for truly suffixed words. The observed differences are discussed in the context of current models of complex word recognition.

Frequency-tagged visual evoked responses track syllable effects in visual word recognition.

The processing of syllables in visual word recognition was investigated using a novel paradigm based on steady-state visual evoked potentials (SSVEPs). French words were presented to proficient readers in a delayed naming task. Words were split into two segments, the first of which was flickered at 18.75 Hz and the second at 25 Hz. The first segment either matched (congruent condition) or did not match (incongruent condition) the first syllable. The SSVEP responses in the congruent condition showed increased power compared to the responses in the incongruent condition, providing new evidence that syllables are important sublexical units in visual word recognition and reading aloud. With respect to the neural correlates of the effect, syllables elicited an early activation of a right hemisphere network. This network is typically associated with the programming of complex motor sequences, cognitive control and timing. Subsequently, responses were obtained in left hemisphere areas related to phonological processing.

Steady state visual evoked potentials in reading aloud: Effects of lexicality, frequency and orthographic familiarity.

The present study explored the possibility to use Steady-State Visual Evoked Potentials (SSVEPs) as a tool to investigate the core mechanisms in visual word recognition. In particular, we investigated three benchmark effects of reading aloud: lexicality (words vs. pseudowords), frequency (high-frequency vs. low-frequency words), and orthographic familiarity ('familiar' versus 'unfamiliar' pseudowords). We found that words and pseudowords elicited robust SSVEPs. Words showed larger SSVEPs than pseudowords and high-frequency words showed larger SSVEPs than low-frequency words. SSVEPs were not sensitive to orthographic familiarity. We further localized the neural generators of the SSVEP effects. The lexicality effect was located in areas associated with early level of visual processing, i.e. in the right occipital lobe and in the right precuneus. Pseudowords produced more activation than words in left sensorimotor areas, rolandic operculum, insula, supramarginal gyrus and in the right temporal gyrus. These areas are devoted to speech processing and/or spelling-to-sound conversion. The frequency effect involved the left temporal pole and orbitofrontal cortex, areas previously implicated in semantic processing and stimulus-response associations respectively, and the right postcentral and parietal inferior gyri, possibly indicating the involvement of the right attentional network.

The effect of decreased interletter spacing on orthographic processing.

There is growing interest in how perceptual factors such as the spacing between letters within words modulate performance in visual word recognition and reading aloud. Extra-large letter spacing can strongly improve the reading performance of dyslexic children, and a small increase with respect to the standard spacing seems beneficial even for skilled word recognition in adult readers. In the present study we examined the effect of decreased letter spacing on perceptual identification and lexical decision tasks. Identification in the decreased spacing condition was slower than identification of normally spaced strings, thereby confirming that the reciprocal interference among letters located in close proximity (crowding) poses critical constraints on visual word processing. Importantly, the effect of spacing was not modulated by string length, suggesting that the locus of the spacing effect is at the level of letter detectors. Moreover, the processing of crowded letters was facilitated by top-down support from orthographic lexical representation as indicated by the fact that decreased spacing affected pseudowords significantly more than words. Conversely, in the lexical decision task only word responses were affected by the spacing manipulation. Overall, our findings support the hypothesis that increased crowding is particularly harmful for phonological decoding, thereby adversely affecting reading development in dyslexic children.

Spatial attention in written word perception.

The role of attention in visual word recognition and reading aloud is a long debated issue. Studies of both developmental and acquired reading disorders provide growing evidence that spatial attention is critically involved in word reading, in particular for the phonological decoding of unfamiliar letter strings. However, studies on healthy participants have produced contrasting results. The aim of this study was to investigate how the allocation of spatial attention may influence the perception of letter strings in skilled readers. High frequency words (HFWs), low frequency words and pseudowords were briefly and parafoveally presented either in the left or the right visual field. Attentional allocation was modulated by the presentation of a spatial cue before the target string. Accuracy in reporting the target string was modulated by the spatial cue but this effect varied with the type of string. For unfamiliar strings, processing was facilitated when attention was focused on the string location and hindered when it was diverted from the target. This finding is consistent the assumptions of the CDP+ model of reading aloud, as well as with familiarity sensitivity models that argue for a flexible use of attention according with the specific requirements of the string. Moreover, we found that processing of HFWs was facilitated by an extra-large focus of attention. The latter result is consistent with the hypothesis that a broad distribution of attention is the default mode during reading of familiar words because it might optimally engage the broad receptive fields of the highest detectors in the hierarchical system for visual word recognition.

A new adaptive videogame for training attention and executive functions: design principles and initial validation.

A growing body of evidence suggests that action videogames could enhance a variety of cognitive skills and more specifically attention skills. The aim of this study was to develop a novel adaptive videogame to support the rehabilitation of the most common consequences of traumatic brain injury (TBI), that is the impairment of attention and executive functions. TBI patients can be affected by psychomotor slowness and by difficulties in dealing with distraction, maintain a cognitive set for a long time, processing different simultaneously presented stimuli, and planning purposeful behavior. Accordingly, we designed a videogame that was specifically conceived to activate those functions. Playing involves visuospatial planning and selective attention, active maintenance of the cognitive set representing the goal, and error monitoring. Moreover, different game trials require to alternate between two tasks (i.e., task switching) or to perform the two tasks simultaneously (i.e., divided attention/dual-tasking). The videogame is controlled by a multidimensional adaptive algorithm that calibrates task difficulty on-line based on a model of user performance that is updated on a trial-by-trial basis. We report simulations of user performance designed to test the adaptive game as well as a validation study with healthy participants engaged in a training protocol. The results confirmed the involvement of the cognitive abilities that the game is supposed to enhance and suggested that training improved attentional control during play.