Inter-limb coupling of proximal and distal hand actions.

Past studies have revealed connections in directional programming between hands. The present study investigated whether there could also be interaction in programming proximal and distal components of a prehensile hand action. In Experiment 1, the participants performed simultaneously either a push or pull response with the left hand and the grip closure or opening with the right hand. In Experiment 2, the push and pull responses of the left hand were performed together with the precision or power grip responses of the right hand. The participants showed preference, measured in reaction times, to couple the push response with the grip opening and the precision grip, whereas the pull response was associated with the grip closure and the power grip. The study shows for the first time a systematic interaction in proximal and distal prehensile components between two hands. We propose that these effects reflect inter- and intra-limb connections between the representations that prepare the arm extension for the outward reaching, the finger extension for the grip opening, and the motor processes that prepare the precision grip. Conversely, there appear to be connections between the representations that prepare the arm flexion for the inward directed hand movements, the flexion of the thumb and the fingers for the grip closure, and flexion of four fingers for the power grip.

Interaction in planning movement direction for articulatory gestures and manual actions.

Some theories concerning speech mechanisms assume that overlapping representations are involved in programming certain articulatory gestures and hand actions. The present study investigated whether planning of movement direction for articulatory gestures and manual actions could interact. The participants were presented with written vowels (Experiment 1) or syllables (Experiment 2) that were associated with forward or backward movement of tongue (e.g., [i] vs. [ɑ] or [te] vs. [ke], respectively). They were required to pronounce the speech unit and simultaneously move the joystick forward or backward according to the color of the stimulus. Manual and vocal responses were performed relatively rapidly when the articulation and the hand action required movement into the same direction. The study suggests that planning horizontal tongue movements for articulation shares overlapping neural mechanisms with planning horizontal movement direction of hand actions.

Connecting directional limb movements to vowel fronting and backing.

It has been shown recently that when participants are required to pronounce a vowel at the same time with the hand movement, the vocal and manual responses are facilitated when a front vowel is produced with forward-directed hand movements and a back vowel is produced with backward-directed hand movements. This finding suggests a coupling between spatial programing of articulatory tongue movements and hand movements. The present study revealed that the same effect can be also observed in relation to directional leg movements. The study suggests that the effect operates within the common directional processes of movement planning including at least tongue, hand and leg movements, and these processes might contribute sound-to-meaning mappings to the semantic concepts of 'forward' and 'backward'.

Reaching and grasping with the tongue: Shared motor planning between hand actions and articulatory gestures.

Research has shown connections between articulatory mouth actions and manual actions. This study investigates whether forward-backward hand movements could be associated with vowel production processes that programme tongue fronting/backing, lip rounding/spreading (Experiment 1), and/or consonant production processes that programme tongue tip and tongue dorsum actions (Experiment 2). The participants had to perform either forward or backward hand movement and simultaneously pronounce different vowels or consonants. The results revealed a response benefit, measured in vocal and manual reaction times, when the responses consisted of front vowels and forward hand movements. Conversely, back vowels were associated with backward hand movements. Articulation of rounded versus unrounded vowels or coronal versus dorsal consonants did not produce the effect. In contrast, when the manual responses of forward-backward hand movements were replaced by precision and power grip responses, the coronal consonants [t] and [r] were associated with the precision grip, whereas the dorsal consonant [k] was associated with the power grip. We propose that the movements of the tongue body, operating mainly for vowel production, share the directional action planning processes with the hand movements. Conversely, the tongue articulators related to tongue tip and dorsum movements, operating mainly for consonant production, share the action planning processes with the precision and power grip, respectively.

Interaction in planning vocalizations and grasping.

Previous studies have shown a congruency effect between manual grasping and syllable articulation. For instance, a power grip is associated with syllables whose articulation involves the tongue body and/or large mouth aperture ([kɑ]) whereas a precision grip is associated with articulations that involve the tongue tip and/or small mouth aperture ([ti]). Previously, this effect has been observed in manual reaction times. The primary aim of the current study was to investigate whether this congruency effect also takes place in vocal responses and to investigate involvement of action selection processes in the effect. The congruency effect was found in vocal and manual responses regardless of whether or not the syllable or grip was known a priori, suggesting that the effect operates with minimal or absent action selection processes. In addition, the effect was observed in vocal responses even when the grip was only prepared but not performed, suggesting that merely planning a grip response primes the corresponding articulatory response. These results support the view that articulation and grasping are processed in a partially overlapping network.

Mismatch negativity (MMN) to speech sounds is modulated systematically by manual grip execution.

Manual actions and speech are connected: for example, grip execution can influence simultaneous vocalizations and vice versa. Our previous studies show that the consonant [k] is associated with the power grip and the consonant [t] with the precision grip. Here we studied whether the interaction between speech sounds and grips could operate already at a pre-attentive stage of auditory processing, reflected by the mismatch-negativity (MMN) component of the event-related potential (ERP). Participants executed power and precision grips according to visual cues while listening to syllable sequences consisting of [ke] and [te] utterances. The grips modulated the MMN amplitudes to these syllables in a systematic manner so that when the deviant was [ke], the MMN response was larger with a precision grip than with a power grip. There was a converse trend when the deviant was [te]. These results suggest that manual gestures and speech can interact already at a pre-attentive processing level of auditory perception, and show, for the first time that manual actions can systematically modulate the MMN.

Systematic Influence of Perceived Grasp Shape on Speech Production.

Previous research has shown that precision and power grip performance is consistently influenced by simultaneous articulation. For example, power grip responses are performed relatively fast with the open-back vowel [a], whereas precision grip responses are performed relatively fast with the close-front vowel [i]. In the present study, the participants were presented with a picture of a hand shaped to the precision or power grip. They were required to pronounce speech sounds according to the front/above perspective of the hand. The results showed that not only the grip performance is affected by simultaneously pronouncing the speech sound but also the production of speech sound can be affected by viewing an image of a grip. The precision grip stimulus triggered relatively rapid production of the front-close vowel [i]. In contrast, the effect related to the power grip stimulus was mostly linked to the vertical dimension of the pronounced vowel since this stimulus triggered relatively rapid production of the back-open vowel [a] and back-mid-open vowel [o] while production of the back-close vowel [u] was not influenced by it. The fact that production of the dorsal consonant [k] or coronal consonant [t] were not influenced by these stimuli suggests that the effect was not associated with a relative front-back tongue shape of the articulation in the absence of changes in any vertical articulatory components. These findings provide evidence for an intimate interaction between certain articulatory gestures and grip types, suggesting that an overlapping visuomotor network operates for planning articulatory gestures and grasp actions.

Connections of Grasping and Horizontal Hand Movements with Articulation in Czech Speakers.

We have recently shown in Finnish speakers that articulation of certain vowels and consonants has a systematic influence on simultaneous grasp actions as well as on forward and backward hand movements. Here we studied whether these effects generalize to another language, namely Czech. We reasoned that if the results generalized to another language environment, it would suggest that the effects arise through other processes than language-dependent semantic associations. Rather, the effects would be likely to arise through language-independent interactions between processes that plan articulatory gestures and hand movements. Participants were presented with visual stimuli specifying articulations to be uttered (e.g., A or I), and they were required to produce a manual response concurrently with the articulation. In Experiment 1 they responded with a precision or a power grip, whereas in Experiment 2 they responded with a forward or a backward hand movement. The grip congruency effect was fully replicated: the consonant [k] and the vowel [α] were associated with power grip responses, while the consonant [t] and the vowel [i] were associated with precision grip responses. The forward/backward congruency effect was replicated with vowels [α], [o], which were associated with backward movement and with [i], which was associated with forward movement, but not with consonants [k] and [t]. These findings suggest that the congruency effects mostly reflect interaction between processes that plan articulatory gestures and hand movements with an exception that the forward/backward congruency effect might only work with vowel articulation.

Preparation and execution of teeth clenching and foot muscle contraction influence on corticospinal hand-muscle excitability.

Contraction of a muscle modulates not only the corticospinal excitability (CSE) of the contracting muscle but also that of different muscles. We investigated to what extent the CSE of a hand muscle is modulated during preparation and execution of teeth clenching and ipsilateral foot dorsiflexion either separately or in combination. Hand-muscle CSE was estimated based on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) and recorded from the first dorsal interosseous (FDI) muscle. We found higher excitability during both preparation and execution of all the motor tasks than during mere observation of a fixation cross. As expected, the excitability was greater during the execution phase than the preparation one. Furthermore, both execution and preparation of combined motor tasks led to higher excitability than individual tasks. These results extend our current understanding of the neural interactions underlying simultaneous contraction of muscles in different body parts.

Selective Influences of Precision and Power Grips on Speech Categorization.

Recent studies have shown that articulatory gestures are systematically associated with specific manual grip actions. Here we show that executing such actions can influence performance on a speech-categorization task. Participants watched and/or listened to speech stimuli while executing either a power or a precision grip. Grip performance influenced the syllable categorization by increasing the proportion of responses of the syllable congruent with the executed grip (power grip-[ke] and precision grip-[te]). Two follow-up experiments indicated that the effect was based on action-induced bias in selecting the syllable.

Excitability of hand motor areas during articulation of syllables.

It is known that articulating different syllables is linked to different grasp actions, e.g. [ti] is linked to precision grip, and [kɑ] to power grip. The aim of the present study was to test whether articulating or hearing these syllables would result in an increased activity in the representation of hand muscles involved in these two actions in a muscle-specific manner. To this end, we used transcranial magnetic stimulation (TMS) to investigate changes in the excitability of the left primary motor cortex (M1) innervating hand muscles while participants articulated or listened to meaningless syllables, listened to a metronome, or observed a fixation cross. The motor-evoked potentials of two hand muscles associated with either a precision or power grip exhibited significantly greater amplitudes during articulation than in passive listening, metronome, and fixation cross conditions. Moreover, these muscles exhibited similar patterns of excitability during articulation regardless of which syllable was articulated. The increased excitability of the left M1 hand area during articulation, but not during perception of the syllables, might be due to the cortico-cortical interaction between the motor representations of oral organs with the hand area.

Computational methods for estimation of cell cycle phase distributions of yeast cells.

Two computational methods for estimating the cell cycle phase distribution of a budding yeast (Saccharomyces cerevisiae) cell population are presented. The first one is a nonparametric method that is based on the analysis of DNA content in the individual cells of the population. The DNA content is measured with a fluorescence-activated cell sorter (FACS). The second method is based on budding index analysis. An automated image analysis method is presented for the task of detecting the cells and buds. The proposed methods can be used to obtain quantitative information on the cell cycle phase distribution of a budding yeast S. cerevisiae population. They therefore provide a solid basis for obtaining the complementary information needed in deconvolution of gene expression data. As a case study, both methods are tested with data that were obtained in a time series experiment with S. cerevisiae. The details of the time series experiment as well as the image and FACS data obtained in the experiment can be found in the online additional material at http://www.cs.tut.fi/sgn/csb/yeastdistrib/http://www.cs.tut.fi/sgn/csb/yeastdistrib/.