Spatio-temporal processing of tactile stimuli in autistic children

Abstract

Altered multisensory integration has been reported in autism; however, little is known concerning how the autistic brain processes spatio-temporal information concerning tactile stimuli. We report a study in which a crossed-hands illusion was investigated in autistic children. Neurotypical individuals often experience a subjective reversal of temporal order judgments when their hands are stimulated while crossed, and the illusion is known to be acquired in early childhood. However, under those conditions where the somatotopic representation is given priority over the actual spatial location of the hands, such reversals may not occur. Here, we showed that a significantly smaller illusory reversal was demonstrated in autistic children than in neurotypical children. Furthermore, in an additional experiment, the young boys who had higher Autism Spectrum Quotient (AQ) scores generally showed a smaller crossed hands deficit. These results suggest that rudimentary spatio-temporal processing of tactile stimuli exists in autistic children, and the altered processing may interfere with the development of an external frame of reference in real-life situations.

Figure 1. Tactile TOJs under the arms-uncrossed condition.

(a) Judgment probabilities of autistic (black solid symbols) and neurotypical (gray open symbols) children. The judgment probability (ordinate) that participants reported that their left hand was stimulated second was plotted against stimulus-onset asynchrony (abscissa). The black and gray solid lines highlight the results of model-fitting for the autistic and neurotypical children, respectively. Each symbol represents the average of the 60 judgments made by the 10 autistic participants and the 60 judgments made by the 10 neurotypical participants. (b) Distributions of the temporal resolution (σ_u) in autistic (black line) and neurotypical (gray line) children. (c) Reaction times (RTs) of autistic (black solid symbols) and neurotypical (gray open symbols) children under the arms-uncrossed condition. RTs (ordinate) are plotted as a function of the SOA (abscissa). The drawings of arms were drawn by W.M.

Figure 2. Representative data for the tactile TOJs of autistic children under the arms-uncrossed (black open squares) and arms-crossed (blue solid circles) conditions.

(a) Judgment probability. (b) RTs. Notice that there is no difference between arms-uncrossed and arms-crossed conditions in this participant. Each symbol represents the average of six judgments. The drawings of arms were drawn by W.M.

Figure 3. Tactile TOJs under the arms-crossed condition.

(a) Judgment probabilities for autistic (blue solid circles) and neurotypical (red open diamonds) children. Judgment probabilities under the arms-uncrossed condition are also displayed (same data as in Fig. 1). Each symbol represents the average of the 60 judgments made by the 10 autistic participants and the 60 judgments made by the 10 neurotypical participants. (b) Distribution of the sums of confusion (SC) in autistic (blue line) and neurotypical (red line) children. Notice that the SCs were smaller in autistic than in neurotypical children. (c) RTs of autistic and neurotypical children. RTs under the arms-uncrossed condition are also displayed (same data as in Fig. 1). The drawings of arms were drawn by W.M.

Figure 4. Difference between autistic (n = 10) and neurotypical (n = 10) children in the judgment probability at each SOA under the arms-crossed condition.

The P-value (ordinate) is plotted as a function of the SOA (abscissa).

Figure 5. Correct response rate of the unilateral stimulation trials in the arms-uncrossed condition (a) and arms-crossed condition (b).

Figure 6. Relationship between Japanese version of Autism Spectrum Quotient (AQ) scores and the degree of the crossed hand illusion (n = 12).

The fitting parameters (Ã_l (a) and Ã_r (b); ordinate) are plotted against the AQ score (abscissa) of individual participants.