Added: Beryl Bernardino - Date: 04.12.2021 13:51 - Views: 39462 - Clicks: 9555
A strong male prevalence has been observed in autism spectrum disorder ASD since its definition, but the behavioral manifestations of sex disparity have yet to be clarified. Here, we investigate sex differences in the perception of the Numbness Illusion NI , a procedure based on a tactile conflict, in adults with ASD and with typical development. We aim to assess if women and men with ASD perceive NI-dependent body ownership differently and whether sex differences emerge in individuals with typical development. In particular, women with ASD report a stronger illusion than men with ASD, that is more evident in the asynchronous conditions.
In the typical sample, the NI emerges only in the synchronous condition and no sex difference is observed. We discuss our in terms of potential advantage of women in sociality and sensory information processing that might lead women with ASD to use different modalities to solve the illusion compared to men with ASD. In sum, these outcomes describe sex differences in individuals with ASD in the domain of illusory perception. This may be used in the future to support the characterization of the female phenotype of autism.
Autism spectrum disorder ASD is defined as a heterogeneous disorder characterized by impairments in social interactions, communication, and repetitive and stereotyped behaviors, which is more commonly diagnosed in male than in female individuals 4M: 1F; Werling and Geschwind, a , b ; Halladay et al. The male prevalence in ASD is known from the origin of the disorder.
Indeed, both Kanner and Asperger reported that the children with autism that they examined were exclusively boys. Consequently, the majority of the research on ASD has chiefly focused on male participants. As a consequence, the female phenotype of ASD is still poorly understood and research in that area are highly inconsistent Head et al.
To date, these s have been used to explain the mechanisms underlying sex disparity in ASD with some studies suggesting that the female phenotype of ASD may be the result of innate characteristics that protect girls and women from ASD and make them less vulnerable to develop the core symptoms of the disorder female protective effect or FPE; Robinson et al.
Moreover, it has been proposed that sex differences in the development of the cognitive profile may lead to different manifestations of ASD in women and men Carter et al. From the studies that have addressed sex disparity in ASD, it becomes evident that intellectual abilities play a role in facilitating the diagnosis of ASD in female individuals. In this view, it has been supposed that high IQ scores may represent a confounding factor that le to a missed diagnosis or a misdiagnosis in girls and women with ASD Van Wijngaarden-Cremers et al.
In this connection, several studies based on clinical observations have suggested that high-functioning girls and women with ASD show different and less severe social and communication impairments compared to boys and men with ASD Rivet and Matson, ; Werling and Geschwind, a. In particular, girls and women with ASD tend to have better expressive behavior e. These greater social and communication abilities attributed as a feature of the female phenotype of ASD may help them to cope with social situations, masking some of the symptoms recognized as core symptoms of the male phenotype of ASD and causing misdiagnoses or late identification of ASD in girls and women Wing, ; Attwood, ; Dworzynski et al.
In other words, the ASD profile may represent an extreme form of the typical male profile, which is characterized by enhanced systemizing and reduced empathizing skills. Agency refers to the experience of generating and controlling actions and the events caused by them in the environment Gallagher, ; David et al.
The sense of body ownership, which origins from the integration of different sensory information i. Successful perturbation of body ownership has been achieved by presenting incongruent sensory stimulation able to shift the belonging of one body part to either external objects e. The multisensory foundations of body ownership and its underpinnings have been usually investigated by means of the rubber hand illusion RHI; Botvinick and Cohen, The RHI is an experimental paradigm that modulates the sense of body ownership by presenting incongruent sensory stimulations i.
Several variants of RHI were developed to investigate the sense of body ownership: the virtual body illusion Slater et al. The latter is an experimental paradigm that allows for the manipulation of the experience of the body-ownership of fingers Dieguez et al. In this paradigm, two individuals i. Then, both the participant and the confederate stroke with the thumb and the index finger of their respective free hand two t index fingers in a synchronous i. This illusion only emerges when the stroking occurs simultaneously. When the stimulation is asynchronous or performed by another person, the illusion is not perceived or its illusory effects are reduced.
Such illusory experience has been replicated in individuals with typical development Dieguez et al. However, whether body ownership illusory experiences are comparable among women and men with ASD is still unknown. Considering that women with ASD reportedly show less impairment in social information processing e. In other words, we expect women with ASD to be more subjected to the NI, in virtue of a greater disruption of the sense of body ownership. If this were true, outcomes may point out for the first time to the existence of sex differences in the domain of sensory and illusory experiences in ASD and they may contribute to further support the characterization of the female phenotype of ASD.
To delineate whether the ASD diagnosis modulates the expression of body ownership and whether sex differences in the NI are evident irrespective of the ASD diagnosis, we additionally tested a Control sample of typical individuals. Indeed, evidence has suggested that sex influences many aspects of typical development Kimura, ; Baron-Cohen et al. In particular, men score higher in spatial abilities e. Thus, considering the potential female advantage in the social domain and given that the development of adaptive social functioning requires an efficient sense of body ownership, we would expect a stronger disruption of the sense of body ownership during synchronous stroking in women with typical development compared to men.
The sample for the two experiments also ly included in Guerra et al. Individuals with ASD were age-, gender- and full scale IQ-matched with the individuals with typical development see Table 1. Participants with typical development had no history of ASD and they did not have any first or second-degree relatives with a diagnosis of ASD. The project was approved by the local ethical committee and the experimental procedures were in accordance with the Declaration of Helsinki Williams, All participants ed a written informed consent prior to the beginning of their experimental session.
The procedures were the same as in Guerra et al. Each participant and the experimenter sat facing each other. Figure 1. The stroking was performed synchronously i. In this posture, the participant stroked the dorsal side of the distal phalanges of the ed index fingers with the thumb and the index finger of the other hand, either in a synchronous or in an asynchronous way.
Instead, in asynchronous conditions the index finger of the agent started from the first phalanx, whereas the thumb started from the third phalanx of the index finger of the receiver and they moved in opposite directions stroking one finger at a time, alternatively. Before the beginning of the experimental phase, participants were trained to achieve a consistent stroking frequency and pressure. The frequency in stroking i. The factor Synchrony — how the t index fingers were stroked — had two levels, namely synchronous i.
The factor Agent — who performed the stroking of the t index fingers —had two levels, namely self i. Given that the NI emerges only when the stimulation is self-administered and it primarily depends on the synchrony of the stimulation i. Indeed, the stroking performed by other people is not effective in inducing changes in the experience of the NI, irrespective of the type of synchrony of the stimulation.
By removing this condition, we were able to gain power to evaluate the sex effects on the NI. This led to two experimental conditions, namely self-synchronous and self-asynchronous. Each condition was repeated four times in a pseudo-randomized order for a total of 8 trials. Each trial lasted 10 s. At the end of each trial, participants rated the strength of the illusion experienced during the task by means of a questionnaire composed by 5 questions presented on 5-point Likert scale Dieguez et al.
The scale ranged from 1 completely disagree to 5 completely agree. In line with studies e. Questions were repeated in a pseudo-randomized order across all trials, to reduce contextual influences on responses. All statistical analyses were carried out with the R software R package version 3. For each participant, the mean of the responses across all conditions were computed to produce an individual index of the illusion experienced by the participant during the task as in Dieguez et al. At first, the data from the ASD group were analyzed by means of fitting a linear mixed-effect model with Synchrony synchronous and asynchronous as within factor, Sex women and men as between factors.
Then, data from the two groups ASD and Control were analyzed by means of fitting a linear mixed-effect model with Synchrony synchronous and asynchronous as within factor, while Sex women and men and Group ASD and Control as between factors. When ificant interactions were retrieved, we conducted pairwise comparisons. Figure 2. Error bars indicate the standard error of the mean SEM. To test whether this sex difference is characteristic of the ASD experience of the NI or it is also experienced by individuals with typical development, we fitted a linear mixed-effect model including the variable Group as a between factor.
Indeed, the strength of the NI changed depending on the type of stroking synchronous or asynchronous; Figure 3. More specifically, the synchronous self-stroking produces the illusory effect of the NI in individuals of both the ASD and the Control groups. Figure 3. The horizontal line with intercept 3 refers to the level of which the illusion was experienced by participants. Figure 4. Strength of the NI for women F and men M in the Control group in the synchronous and asynchronous conditions. Error bars refer to the standard error of the mean SEM. Researchers and clinicians are devoting more and more effort to understanding whether and how the differences between the female and male phenotypes of ASD can emerge.
So far, the influence of sex differences in sensory experiences in ASD has only been marginally addressed. This study aimed to explore whether the experience of sensory-induced body ownership — measured behaviorally by means of the NI - differs between women and men with ASD. Our findings showed a clear sex difference in the strength of the NI experienced by individuals with ASD.
Despite both women and men with ASD reported to experience the disruption of the body ownership over their own finger in the synchronous and in the asynchronous conditions, women reported to experience the illusion ificantly more strongly than men. To evaluate whether such sex difference in the experience of the NI is specific to ASD or it is a more general phenomenon, we also tested the effect of sex on the NI in a group of women and men with typical development.
Comparing the performance of individuals with ASD with that of a group of matched controls, it emerges that women with ASD were more susceptible to the NI than women and men with typical development, especially when considering the asynchronous condition. This result acquires even more relevance when considering that no sex differences appeared when analyzing the Control group alone, showing that the NI manifests in a similar manner in both typically developing women and men.
When focusing on the performance of men in both groups it is evident that both men in the ASD and Control groups were less susceptible to the NI compared to the women in both groups. Two explanations, one focused on social skills and the other on sensory abilities, can be advanced to interpret these data.
First, this finding may be interpreted as a reflection of the ability of women with ASD to better deal with socialization and empathy e. Indeed, the sense of body ownership has been deemed crucial in the development of adaptive social skills, particularly imitation and empathy Gallese, The literature exploring the link between body ownership and empathy reveals that both participants with ASD Cascio et al. Although not tested directly, we may speculate that the women with ASD in the present sample may present better empathic skills than their male counterparts.
A second explanation, not in contrast with the one, may suggest that the increased susceptibility to the NI in women is the result of the ability of women to differentially focus on the sensory input received. Women seem to be more focused on the sensory information to solve the mismatch produced by the tactile conflict in the NI, whereas men rely less on such sensory information. Furthermore, increased sensory issues e. When directly comparing women with ASD and with typical development, self-reports suggest that they are both more sensitive to sensory stimulation than men Tavassoli et al.
Indeed, showed that the NI emerged in both groups when the stroking was synchronous, while, when the movement was performed asynchronously, only the participants in the ASD group experienced the illusion. An interesting observation, that was not part of our initial set of hypotheses, is related to the range of the responses given by the ASD group. Both women and men with ASD were highly reliable in providing the same rating of the strength of the NI. In other words, at the group level, the responses are locked around a limited range of options, as the inspection of the error bars suggests.
This finding might be taken as evidence that the participants with ASD had difficulties in the understanding of the questions posed in the self-report. However, all participants with ASD presented a full-scale IQ comparable to that of controls, and this seems to be sufficient reason to believe that the instructions were understood and complied to the same extent as in the Control group.
A more likely explanation for the reduced range of responses in the ASD sample can be found when interpreting this outcome in the context of the aberrant precision theory Bolis et al. Such theory posits that individuals with ASD use abnormal strategies i. Such strategies, rather than maximizing the confidence in the sensory evidence estimated based on a priori beliefs i.
In other words, and compatibly with the neural instantiation of Bayesian inference from which this principle is extracted e. In the context of the NI, the expectation of the participant is to feel their own index finger pressed against the hand of the experimenter as part of their own body. However, the sensory inputs visual and tactile produce an experience compatible with the reduction of body ownership for such finger self and attributing the ownership of that finger to the experimenter other.
Put in these words, it appears evident how the precision ascribed to the sensory evidence retrieved is imbalanced with respect to the a priori belief hold about the experience. Although our data are not directly able to test this issue, we contend that this may be unlikely for at least two reasons.
First, sensory suggestibility does not seem to be impaired in ASD. Specifically, when looking at sensory suggestibility in the RHI, it has been reported that the temperature of the hand subjected to the RHI similarly does not drop in participants with ASD and controls, calling for similar levels of sensory suggestibility across groups. Furthermore, studies on unusual tactile sensitivity in autism reported no differences in the domain of tactile perception across different tactile stimuli e. However, these findings reflect a non-social aspect of sensory suggestibility and may not be impaired in ASD.
In lack of other evidence directly linking socially relevant sensory suggestibility to the tactile domain, we turn to the evidence gathered from eye-witnesses. Second, if sensory suggestibility in the tactile domain is key to the perception of the NI, we should expect that the variability in sensory suggestibility would also be reflected at the level of the Control group.
However, this is not the case, since a difference between the synchronous and asynchronous conditions is reported in the Control group, as expected when also looking at other illusory paradigms Stone et al. In line with the call from the ASD and the scientific community for research into the female autistic phenotype Halladay et al. As for most innovative studies, some limitations in data interpretation exist and future studies will be needed to address them. First, although proportional to what found in the ASD population, the sample of women with ASD included in the present study is rather limited.
Therefore, to confirm the present set of we call for the replication of this study in a larger sample of individuals with ASD. Second, to better characterize the female phenotype of ASD a developmental perspective is needed. Indeed, testing our hypotheses from childhood to adulthood will allow to understand more deeply how sex differences in body ownership emerge over development.
Third, to confirm the specificity of these to ASD, it would be important to investigate sex differences in the NI in a group of individuals with non-ASD atypical development. Fourth, the administration of standardized self-reports on sensory perception e.Adult in Padova sex
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