A kinematic examination of dual-route processing for action imitation

Abstract

The dual-route model of imitation suggests that meaningful and meaningless actions are processed through either an indirect or a direct route, respectively. Evidence indicates that the direct route is more cognitively demanding since it relies on mapping visuospatial properties of the observed action on to a performed one. These cognitive demands might negatively influence reaction time and accuracy for actions performed following a meaningless action under time constraints. However, how meaningful and meaningless action imitation processing is reflected in movement kinematics is not yet clear. We wanted to confirm whether meaningless action performance incurs a reaction time cost, whether the cost is reflected in kinematics, and, more generally, to examine kinematic markers of emblematic meaningful and meaningless action imitation. We examined participants' reaction time and wrist movements when they imitated emblematic meaningful or matched meaningless gestures in either blocks of the same action type or mixed blocks. Meaningless actions were associated with a greater correction period at the end of the movement, possibly reflecting a strategy designed to ensure accurate completion for less familiar actions under time constraints. Furthermore, in mixed blocks, trials following meaningless actions had a significantly increased reaction time, supporting previous claims that route selection for action imitation may be stimulus-driven. However, there was only convincing evidence for this effect with an interval of~2,948ms, but not~3,573ms or~2,553ms, between movements. Future work motion-tracking the entire hand to assess imitation accuracy, and more closely examining the influence of duration between movements, may help to explain these effects.

The left ventral premotor cortex is involved in hand shaping for intransitive gestures: evidence from a two-person imitation experiment

“…Within each session, a single brain region was stimulated, and participants took part in both meaningful and meaningless action imitation tasks. Since there is evidence to suggest that performing novel and known actions in a sequence could recruit a single processing route, while presenting them separately recruits separate routes ([ 61 ], but see [ 62 ], and [ 63 ]), meaningful and meaningless action trials were split into separate blocks. Task order was counterbalanced across stimulation sites.…”

Repetitive Transcranial Magnetic Stimulation Over the Left Posterior Middle Temporal Gyrus Reduces Wrist Velocity During Emblematic Hand Gesture Imitation

“…In a previous experiment (Reader et al 2018a ), in which we motion-tracked participants’ wrist movements during meaningless and emblematic meaningful gesture imitation, we observed that the imitation of meaningless gestures was associated with a longer correction period than the imitation of meaningful gestures. That is, the deceleration phase of their wrist movements was longer, as reflected by a relatively earlier time to peak velocity (TPV/MT) and time to peak deceleration (TPD/MT), despite a longer overall movement time (MT).…”

“…The block order was counterbalanced across sessions and participants. Meaningless and meaningful actions were presented in separate blocks, since there is some evidence to suggest that performing novel and known actions in a sequence recruits a single processing route, whilst presenting them separately recruits separate routes (Tessari and Cubelli 2014 ; Tessari and Rumiati 2004 , but see; Press and Heyes 2008 ; Reader et al 2018a ). Hand and finger gestures were pseudorandomly interleaved within each separate block of action meaning.…”

“…In keeping with Reader et al ( 2018a ), four imitator wrist kinematic variables were extracted: MT, PV, TPV/MT, and TPD/MT. The mean values of these variables across every trial for each condition were analysed using repeated-measures ANOVAs with three levels: stimulation site (pMTG, vertex), action meaning (meaningful, meaningless), and action effector (hand, finger).…”

Repetitive transcranial magnetic stimulation over the left posterior middle temporal gyrus reduces wrist velocity during emblematic hand gesture imitation

“…In a previous experiment (Reader et al, 2018a), in which we motion-tracked participants' wrist 52 movements during meaningless and emblematic meaningful gesture imitation, we observed that the imitation 53 of meaningless gestures was associated with a longer correction period than the imitation of meaningful 54 gestures. That is, the deceleration phase of their wrist movements was longer, as reflected by a relatively …”