Reading point-light walkers and amorphous—A TMS study.

Abstract

Objective: (a) Evaluate if human actions with and without pictorial information result in comparable motor facilitation; and (b) verify if the isolated features of movement and human shape increase motor excitability. Method: Motor evoked potentials (MEPs) of M1 were recorded from 18 healthy subjects using transcranial magnetic stimulation (TMS) during presentation of full-body video clips of everyday human actions either with (real movement, RM) or without (biological point-light, PLbio) pictorial information, non-biological/scrambled moving point-lights (PLnb), and static point-lights arranged in a human shape (PLs). All videos were approximately 1,000 ms long. Peak-to-peak MEP amplitude was individually averaged for each condition. Results: repeated measures analysis of variance (rmANOVA) considering MEP as dependent variable and stimuli as within-subject factor revealed an effect for Stimuli (F 1,17 = 6.53; p < .001; η 2 p = .227). Such effect was due to lower MEP amplitude in PLs when compared to RM ( p = .002), PLbio ( p = .002) and PLnb ( p = .005). Conclusion: The similar corticospinal excitability (CE) increase during PLbio and RM observation corroborates the use of human PL in motor resonance/action observation studies. Noteworthy, PLnb also engaged the motor network, which could be due to kinematic aspects of human velocity profile or anthropomorphism of non-biological agents. Observation of PLs resulted in significantly smaller MEPs. Therefore, M1 activation seems restrict to movement perception but might not be strictly dependent on human form. Thus, planning the control stimuli and task context is crucial when using PL displays in the study of human action perception and the action observation network (AON). Public Significance StatementOur study demonstrated that observing real and point-light human actions activates motor brain areas in a similar fashion. Furthermore, observing moving point-light deprived of human shape also increased motor activation whereas static human shaped point-lights didn't. Thus, either movement feature suffice to engage motor areas or most likely, humans anthropomorphized the scrambled dots in an attempt to attribute meaning to the observed movement.

TMS-induced inhibition of the left premotor cortex modulates illusory social perception

“…Previous TMS literature reported effect sizes of d = 0.9 - 1.2. 20 , 21 , 23 , 79 , 80 Yet we suggest such effect sizes may be overestimated due to rather small sample sizes tested in these studies. As a conservative estimation, an effect size of d = 0.7 (f = 0.35) was used to find differences between sham and real TMS, and resulted in a minimal sample size of 19 participants.…”

TMS-induced inhibition of the left premotor cortex modulates illusory social perception

“…An a-priori power analysis was performed with G*Power 3.1 (Faul et al, 2009) to determine the sample size for a repeated-measures ANOVA with α=0.05 and a power of 1-ß=0.8. Previous TMS literature reported effect sizes of d = 0.9 - 1.2 (Basil et al, 2017; Lapenta et al, 2022; Michael et al, 2014; Stadler et al, 2012; van Kemenade et al, 2012). Yet we suggest such effect sizes may be overestimated due to rather small sample sizes tested in these studies.…”

“…Previous TMS literature reported effect sizes of d = 0.9 -1.2 (Basil et al, 2017;Lapenta et al, 2022;Michael et al, 2014;Stadler et al, 2012;van Kemenade et al, 2012). Yet we suggest such effect sizes may be overestimated due to rather small sample sizes tested in these studies.…”