The positive dimension of schizotypy is associated with a reduced attenuation and precision of self-generated touch

Abstract

The brain predicts the sensory consequences of our movements and uses these predictions to attenuate the perception of self-generated sensations. Accordingly, self-generated touch feels weaker than an externally generated touch of identical intensity. In schizophrenia, this somatosensory attenuation is substantially reduced, suggesting that patients with positive symptoms fail to accurately predict and process self-generated touch. If an impaired prediction underlies the positive symptoms of schizophrenia, then a similar impairment should exist in healthy nonclinical individuals with high positive schizotypal traits. One hundred healthy participants (53 female), assessed for schizotypal traits, underwent a well-established psychophysics force discrimination task to quantify how they perceived self-generated and externally generated touch. The perceived intensity of tactile stimuli delivered to their left index finger (magnitude) and the ability to discriminate the stimuli (precision) was measured. We observed that higher positive schizotypal traits were associated with reduced somatosensory attenuation and poorer somatosensory precision of self-generated touch, both when treating schizotypy as a continuous or categorical variable. These effects were specific to positive schizotypy and were not observed for the negative or disorganized dimensions of schizotypy. The results suggest that positive schizotypal traits are associated with a reduced ability to predict and process self-generated touch. Given that the positive dimension of schizotypy represents the analogue of positive psychotic symptoms of schizophrenia, deficits in processing self-generated tactile information could indicate increased liability to schizophrenia.

Fig. 1. Experimental methods and results.

a, b The two experimental conditions. c The boxplots show the median and interquartile ranges for the PSEs, the jittered points denote the raw data, and the violin plots display the full distribution of the data in each condition. A lower PSE value indicates a lower perceived magnitude. d Line plots illustrate the decreases in PSEs when experiencing self-generated tactile stimuli compared to externally generated stimuli. The PSEs were significantly decreased in the self-generated touch condition compared to the externally generated touch condition. e Density plot for somatosensory attenuation (difference in the PSEs between the two conditions). f A lower JND value indicates a higher somatosensory precision. g Line plots illustrate the changes in JNDs when experiencing self-generated tactile stimuli compared to externally generated stimuli. The JNDs did not significantly differ between the self-generated touch and externally generated touch conditions. h Density plot for the difference in the sensory precision between the two conditions.

Fig. 2. Schizotypal traits and somatosensory attenuation and precision.

a–d Density plots of the Schizotypal Personality Questionnaire (SPQ) scores (possible score ranges: total, 0–74; cognitive-perceptual, 0–33; interpersonal, 0–33; disorganized, 0–16). e–h Correlations between the Schizotypal Personality Questionnaire (SPQ) scores and somatosensory attenuation. i–l Correlations between the Schizotypal Personality Questionnaire (SPQ) scores and the inverse somatosensory precision of self-generated touch (JND). Note that the y-axis displays the JNDs (i.e., the inverse somatosensory precision). e–l Regression lines are shown for illustrative purposes only, since we used the Spearman correlation coefficient to calculate the correlation between the variables. The positive schizotypy was the only dimension that significantly correlated with somatosensory attenuation and the precision of self-generated touch.

Fig. 3. Somatosensory attenuation and precision in individuals with low, medium, and high positive schizotypal traits.

a Density plots for the three positive schizotypy subgroups of our sample. Vertical dotted lines indicate the mean of each subgroup. b The high positive schizotypy group showed significantly less somatosensory attenuation than the low positive schizotypy group. c The high positive schizotypy group showed significantly less somatosensory precision (significantly higher JND) in the self-generated touch condition than the low schizotypy group. d Group psychometric fits using the total sample. The fits for each condition were generated using the mean PSE and the mean JND across participants. e, f Group psychometric fits for the low (e) and the high (f) positive schizotypy groups. The high positive schizotypy group shows a substantially smaller shift in the curves between the self-generated and externally generated touch conditions (i.e., less attenuation) and a flatter slope for the self-generated touch condition (i.e., higher JND).