Does thumb posture influence the mental rotation of hands?

Abstract

The function of thumb posture in mental rotation has not yet been studied intensely, despite its special role in manual action. To investigate if thumb posture modifies relative visual and proprioceptive contributions, we conducted two experiments comprising hand laterality judgement tasks with identical stimuli (left and right hands in palmar and dorsal views presented at four orientations). In half of the stimuli, all digits were extended, whereas in the other half the thumb was flexed into the palm of the hand. In the second experiment, participants' thumbs were taped in the same flexed posture that was displayed in half of the stimuli one hour previous to and throughout the experiment. Results of both experiments revealed effects of orientation, side and view on reaction time, but an effect of stimulus thumb posture occurred only in the second experiment in which participants' thumbs were fixed. In palmar view, stimuli rotated by 90°with fingers pointing toward the participant's midline had shorter reaction times than stimuli rotated (evidentially less comfortably) in the opposite direction. This finding suggests that participants applied motor imagery strategies for palmar but not for dorsal views of the hand, indicating a difference in visual and sensorimotor familiarity. AbstractThe function of thumb posture in mental rotation has not yet been regarded intensely, despite of the specific role of the thumb in manual action. To investigate whether thumb posture would modify the relative visual and proprioceptive contributions, we conducted two experiments with identical stimuli (left and right hands in palmar and dorsal views presented at four orientations) in which participants were asked to give handedness judgements. In half of the stimuli, the thumb was extended like the other digits, in the other half the thumb was flexed into the palm of the hand. In the second experiment, the participant's thumbs were fixed in the same posture as displayed in half of the stimulus pictures; thumbs were taped to the palm of the hands one hour previous to and throughout the experiment. Results of both experiments revealed effects of orientation, side and view on reaction time, but an effect of stimulus thumb posture occurred only in the second experiment in which the participants' thumbs were fixed. Medial-over-lateral advantage as indicator of motor imagery was found only for palmar stimuli, suggesting that participants applied different strategies for the different views of the hand, probably based on different visual and sensorimotor familiarity. IntroductionMental rotation of human body parts, especially hands, has been found to differ essentially from mental rotation of abstract objects [13,17]. Using a handedness paradigm in which participants had to decide if a displayed hand was a right or left one, Parsons [13,14] showed that RTs were not only influenced by the rotation angle of the hand stimulus but also by the implicit awkwardness of the displayed hand position. He concluded that movements performed...

Phantom limb perception interferes with motor imagery after unilateral upper-limb amputation

“…Paired t-test revealed that the symmetric angles (60 o vs. 300 o , 120 o vs. 240 o ) did not show significant differences of RTs for any participant (P ≥ 0.261), which was in line with previous findings in healthy people that angular disparity patterns of back-view hands remain symmetric for medially and laterally rotated stimuli 59 60 . Therefore, symmetric orientations (60 o and 300 o , 120 o and 240 o ) were collapsed to obtain four categories of orientations (i.e., 0 o , (±)60 o , (±)120 o and 180 o ) in the statistical analysis.…”

Implicit Motor Imagery and the Lateral Occipitotemporal Cortex: Hints for Tailoring Non-Invasive Brain Stimulation

“…The present findings on healthy individuals, showing a specific interference of rTMS on judgments of right-hand images, are strikingly consistent with Helmich et al's [7] data on Parkinson's disease, while the lack of rTMS on the biomechanical effect is consistent with van Nuenen et al's data [8]. It is worth noting here that posture manipulation during hand laterality judgment can alter the classical way in which the participants deal with the task, even producing unexpected interference of posture manipulation upon task performance in the congruent conditions, rather than the congruence effect [36,43,44]. Moreover, manipulating body posture, as in both Helmich et al's [7] and Nuenen et al's [8] studies, elicits proprioceptive and tactile information, also affecting the activity of the lateral occipitotemporal cortex independently from the requirement to concurrently perform the hand laterality task [45][46][47].…”

“…Following available literature (e.g., [36,37]), trails outside the range of 500-3500 msec were discarded from the analysis. On both accuracy and RTs (msec) data, two separate ANOVAs were performed.…”

Cortical Asymmetries during Hand Laterality Task Vary with Hand Laterality: A fMRI Study in 295 Participants

“…Moreover, in the present work, and similar to the study by Michelon et al (2006) not only the hand primary motor area showed a difference in asymmetry with hand presentation in the present experiment, but the whole brain approach also evidenced a significant difference in the cerebellar area ipsilateral to the presented hand confirming the involvement of motor system during HLT (see Figure S1). Thus, although some behavioral studies concluded that identifying the laterality of hands from their back views rely on a visuo-spatial strategy rather than a motor strategy (ter Horst et al, 2010; Bläsing et al, 2013), and despite the absence of medial over lateral effect in three different sets of behavioral data collected here, the brain imaging results of the present study support that some motoric processes are actually involved in the laterality judgment of hands viewed from their back. It has been proposed that motor imagery is only confirmatory and was preceded by an automatic visual analysis allowing the identification of handedness (Parsons, 1994; Gentilucci et al, 1998b).…”

“…At the behavioral level, the motoric nature of the involved processes is supported by the fact that reaction times (RT) for identifying the laterality of the presented hand are longer when the hand is in an awkward position (typically away from the body midline) than when it is presented in a more familiar position, thus reproducing the biomechanical constraints of actual movements (Parsons, 1987a, 1994). Based on this behavioral signature, it has been shown that the perspective of the presented hands influences the strategy: palm views favor a motor imagery strategy while back views promote a visuo-spatial strategy (ter Horst et al, 2010; Bläsing et al, 2013). A recent meta-analysis has shown that strategies can be distinguished at the brain level (Tomasino and Gremese, 2015): the direct comparison between the motor and visual strategy evidenced activations in the postcentral gyrus while the reverse contrast revealed more important activations in occipito-temporo-parietal cortex.…”