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Neurotypical individuals fail to understand action vitality form in children with autism spectrum disorder

Significance Action vitality forms are highly pervasive aspects of daily life and have been widely assumed to be critical for basic social interactions. Previous evidence indicates that ASD children express their own vitality forms in a way that is motorically dissimilar to TD children. Here we demonstrate that this motor dissimilarity prevents neurotypical adults from recognizing vitality forms, when observing ASD children acting gently or rudely. Although ASD children differentiate these vitality forms, neurotypical adults were remarkably inaccurate in identifying them. This indicates that difficulty in social interaction for ASD individuals should not be entirely ascribed to their lack of understanding others, as standardly assumed. The failure of neurotypical individuals to understand them plays a critical role too.


Supporting Information Appendix Control Experiment
To rule out the possibility that participants' performance in the Vitality Form (VF) task could have been merely driven by considering how fast or slow the observed actions were, instead of evaluating their rudeness or gentleness, we carried out a control experiment in which an independent group of participants were presented with the same stimuli as in the Experiment 1, but were asked to judge about their velocities rather than their vitality forms (Velocity task).

Participants
An independent sample of 20 neurotypical adult participants (mean age ± SD = 25.40 ± 4.59 y; all males) was recruited. No participants of the control experiment took part to the Experiment 1, and the two groups of participants were matched for chronological age (t = -0.02, P = 0.99). All participants had normal or corrected-to-normal vision, and reported no history of neurological or psychiatric disorders. All participants were university students or had at least one previous university degree. Left-handed individuals, as indicated by a questionnaire adapted from the Edinburgh Handedness Inventory (61) for Italian native speakers, were excluded. All participants provided informed consent approved by the local Ethics Committee (Scientific Institute IRCCSE. Medea, Bosisio Parini -Lecco). The entire study protocol was approved by the Scientific Institute IRCCSE. Medea, Bosisio Parini -Lecco Ethics Committee, and conformed to the principles elucidated in the Declaration of Helsinki.

Stimuli
The stimuli were the same as in the Experiment 1.

Procedure
The experimental procedure was the same as in the VF task (Experiment 1), but instead of judging whether the vitality form between the first and the second video was the same, participants were requested to judge whether the velocity of the observed actions was the same. The term velocity could appear ambiguous, referring to distinct kinematic parameter (e.g., mean velocity, peak of velocity, etc.). Nevertheless, it was functional to our aims given that we were interested in ruling out the possibility that VF task results could have been driven by simplistic assumptions (e.g., gentle » slow, rude » rapid).

Statistical Data Analysis
Sensitivity index (d') We computed the sensitivity (d') of each participant in judging the "velocity" in ASD actors' trials and in TD actors' trials (Velocity task). Noteworthy, the accuracy in the Velocity task was scored on the base of the vitality form accuracy: when one participant judged the "velocity" to be the same in a trial in which the two videos showed a same vitality form, this trial was considered as "hit". At first glance this might appear counterintuitive, but it is comprehensible considering that our aim was to rule out www.pnas.org/cgi/doi/10.1073/pnas.2011311117 the possibility that statements about "vitality forms" in Experiment 1 could have been driven by simplistic assumptions (e.g., gentle » slow, rude » rapid). This was tested performing two independent sample t-tests on d' between the VF task (Experiment 1) and the Velocity task, both within ASD actors' trials and within TD actors' trials. A statistical significant difference between performances in VF and Velocity task would demonstrate that participants did not simply assume that "rude corresponds to fast" and "gentle corresponds to slow", that is the notion of vitality form does not coincide with the notion of "velocity". As five blocks were available for both tasks, d' was computed on all the five blocks to maximize statistical power.
Reaction times A Mann-Whitney U test was performed on RTs between the VF task (Experiment 1) and the Velocity task, both within ASD actors' trials and within TD actors' trials. A statistically significant difference between tasks would suggest that vitality form and velocity are not comparable in terms of "directness"; in other words, the comparison between questions could not be considered reliable.
RTs: The two Mann-Whitney U tests carried out on RTs between the VF task (Experiment 1) and the Velocity task showed no significant differences neither within ASD actors' trials nor within TD actors' trials (all p>0.36) (Supplementary FigureS1b).

Graphs illustrating control Velocity task results on the sensitivity index (d') (panel [a]) and reaction times (RTs) (panel [b]).
Panel [a]. Two independent sample t-tests on d' between the VF task (Experiment 1) and the Velocity task, both within ASD actors' trials and within TD actors' trials were computed. The results showed significant differences both within ASD actors' trials (P < 0.001) and within TD actors' trials (P=0.04).
Panel [b]. Two Mann-Whitney U tests carried out on RTs between the VF task and the Velocity task showed no significant differences neither within ASD actors' trials nor within TD actors' trials (all P > 0.36). This suggests that neurotypical adults have similar access in terms of intelligibility to the "vitality form" and "velocity" notions.
Legend: * = statistical significance Velocity = Velocity task VF = VF task (Experiment 1) Graphical illustration of the experimental design.
All experiments (Experiment 1, Experiment 2, control experiment) had the same initial procedure. Each trial starts with a fixation cross at the center of the screen (1 sec duration), and a further "waiting window" for smoothly loading the stimulus (0.25 sec) was added. After that, the stimulus composed by the couple of videos was presented. To increase the readiness and to minimize potential perceptual confounds due to time duration variability of each video (mean duration ± SD = 1.60 ± 0.60 sec), we provided variable black windows at the beginning (mean duration ± SD = 2.50 ± 0.50 sec). Please, note that also "still frame window" at the beginning (mean duration ± SD = 0.98 ± 0.12) and at the end (0.20 sec) of the videos were added. All these expedients permitted to control perceptual confounds and, crucially, to preserve the intrinsic kinematic properties of each actor. Following this common part (upper panel), the response window was presented. The figure also illustrates the specificity of each experiment (bottom panel). In Experiment 1, we asked "Do the videos have the same style?" (VF task).
In Experiment 2, we asked "Do the videos have the same style?" (VF task with feedback) butdifferently from the previous experiment -we also asked to evaluate their confidence with a Likert scale and, critically, we provided the feedback about accuracy. In the control experiment, we asked "Do the videos have the same velocity?" (Velocity task).
Legend: Video = the illustration of a single action (e.g., placing-the-bottle with a rude vitality form), highlighted by an ochre parallelogram in the figure. Stimulus = the couple of videos with black windows, highlighted by light grey parallelogram in the figure.