Superior Temporal Summation Performance to Detect Near Threshold Tactile Stimulus in Individuals with Autism Spectrum Disorder

Background: Several studies reported lower detection threshold to vibro-tactile stimuli in individuals with autism spectrum disorder (ASD) than typically developing (TD) individuals as a candidate for underlying basis of the symptom of sensory hyper-responsivity. We previously demonstrated that higher temporal resolution discriminating two successive vibro-tactile stimuli associated severity of sensory hyper-responsivity. This indicates that the high temporal resolution of sensory stimuli may result in superior number of temporal summation of sensory inputs. Therefore, we assumed that the individuals with ASD would perceive strong subjective intensity of the stimuli even if the stimulus is delivered in short time duration.

Objectives: Our purpose in the current study is to elucidate underlying mechanisms of the association between the high temporal resolution and the sensory hyper-responsivity. We hypothesized that the individuals with ASD can detect the near threshold stimuli despite short temporal duration by summarizing sensory inputs in high temporal frequency.

Methods: 8 individuals with ASD (16-24 years old) and 10 TD individuals (16-21 years old) were participated. We first conducted a detection task of single vibro-tactile stimulus delivered for 50 ms. Using the near threshold stimulus intensity in each participant identified in the prior task, we applied 7 duration condition (50 – 1000 ms) of vibro-tactile stimuli in the main experiment. One of vibro-tactile stimuli from the duration condition was delivered to the left index finger in a randomized-order, and they were asked to judge whether the stimulus was presented or not. We calculated detection thresholds representing the stimulus duration that each participant can detect it (defined as Threshold of stimulus duration). Low threshold indicates that the participants could detect the stimulus regardless of short duration (Fig.1). We also evaluated the symptomatic severity of hypersensitivity using the adolescent / adult sensory profile (AASP).

Results: The mean degree of Threshold of stimulus duration were 96.77 (SE = 48.24) in ASD and 229.03 ms (SE =44.32) in TD groups. The ASD group showed lower Threshold of stimulus duration than TD group (t (16) = 2.01, p = 0.03). Although we also conducted correlation analysis between the Threshold of stimulus duration and the severity of hyper-responsivity across both groups’ data (N = 18) (Fig.2), no significant correlation was found in any sub-scales of AASP (Low Registration, r = −0.30, p = 0.22; Sensation Seeking, r = 0.30, p = 0.23; Sensory Sensitivity, r = 0.12, p = 0.64; Sensation Avoiding, r = −0.06, p = 0.82).

Conclusions: Our data demonstrated that the individuals with ASD can detect the near threshold vibro-tactile stimuli which is delivered in shorter time duration relative to TD controls. This finding is partly congruent with our assumption that the individuals with ASD having high temporal resolution result in more frequent summarizing of sensory inputs. However, association between the Threshold of stimulus duration and the severity of sensory hyper-responsivity was not obvious. We need to add more samples in order to make our data robust.