Adults with autism overestimate the volatility of the sensory environment

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Abstract

Insistence on sameness and intolerance of change are among the diagnostic criteria for autism spectrum disorder (ASD), but little research has addressed how people with ASD represent and respond to environmental change. Here, behavioral and pupillometric measurements indicated that adults with ASD are less surprised than neurotypical adults when their expectations are violated, and decreased surprise is predictive of greater symptom severity. A hierarchical Bayesian model of learning suggested that in ASD, a tendency to overlearn about volatility in the face of environmental change drives a corresponding reduction in learning about probabilistically aberrant events, thus putatively rendering these events less surprising. Participant-specific modeled estimates of surprise about environmental conditions were linked to pupil size in the ASD group, thus suggesting heightened noradrenergic responsivity in line with compromised neural gain. This study offers insights into the behavioral, algorithmic and physiological mechanisms underlying responses to environmental volatility in ASD.

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Figure 1: Task structure.
Figure 2: Behavioral results based on the ground truth.
Figure 3: Relationship between behavioral surprise and symptoms.
Figure 4: Computational-model details and results.
Figure 5: Pupillometry results.

Change history

  • 07 August 2017

    In the version of this article initially published online, the first sentence of the Online Methods referred to “29 adults with ASD and 26 healthy NT volunteers.” To avoid any implication that those with ASD are not healthy, this has been changed to “29 adults with ASD and 26 NT volunteers.” Similarly, in the first paragraph of the “Learning-rate data” section, “healthy volunteers” has been changed to “NT volunteers.” In the Life Sciences Reporting Summary, “healthy” has been changed to “NT” in the first sentences of items 3 and 12. In the supplementary information originally posted online, the legend to Supplementary Figure 4 read “non-clinical healthy volunteers.” This has been changed to “non-clinical volunteers.” The errors have been corrected in the PDF and HTML versions of this article.

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Acknowledgements

This work was supported by a Wellcome Trust Senior Clinical Research Fellowship (100227: G.R.). We thank all the participants who gave their time to take part in this research and M. Browning for helpful comments on an earlier poster presentation of these data.

Author information

R.P.L. conceived the study and collected and analyzed the data. R.P.L. and C.M. modeled the data. R.P.L., C.M. and G.R. wrote the manuscript.

Correspondence to Rebecca P Lawson.

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Competing interests

The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 Reaction time as a function of stimulus noise.

Collapsing across the three levels of expectedness, the non-significant stimulus noise*group interaction indicates that the linear relationship between noise and RT was equivalent in both groups (ASD, n=24; NT, n=25). See main text for supporting statistics. ASD, autism spectrum disorder. NT, neurotypical. RT, reaction time. Data points represent individual participants, red lines indicate the mean, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean for each condition and group. H=high noise, M=medium noise and N=no noise

Supplementary Figure 2 Inverse efficiency scores.

To ensure that the attenuated UE-E RT difference in the ASD participants was robust to correction accuracy, we calculated inverse efficiency scores (IES) as RT/(1-accuracy) for each condition. As for the analysis of RT and error rates alone, see main manuscript, there was a significant main effect of expectedness (F(1.8,83.11)=34.24, P<0.001) and noise (F(2,94)=6.87, P=0.002) and again only the expectedness*group interaction was significant in this analysis (F(2,94)=9.98, P<0.001). The noise*group (F(2,94)=0.24, P=0.79) and expectedness*noise*group interactions were not significant (F(4,188)=2.2, P=0.07). Thus, our primary reaction time finding is robust to correction condition-specific accuracy (ASD, n=24; NT, n=25). ASD, autism spectrum disorder. NT, neurotypical. RT, reaction time. Data points represent individual participants, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean for each condition and group. E=expected, N=neutral and UE=unexpected.

Supplementary Figure 3 Caution of responding control analysis.

To exclude the possibility that our group difference in UE-E RT (i.e. reduced behavioural surprise in ASD) is explainable by increased response caution in the ASD participants we compared the 12 fastest responders from the ASD group (mean RT 418 ms) against the 12 slowest responders in the NT group (mean RT 540 ms) on the primary UE-E RT difference measure. Here the 12 fastest overall responding ASD participants are those who are most impulsive/least cautious in general responding (i.e. have the lowest response thresholds) whereas the 12 slowest overall NTs are the least impulsive/most cautious (i.e. have the highest response thresholds). Indeed, mean reaction time is significantly faster in this subgroup of ASD participants than in the subgroup of NTs (t(22)=3.38, P=0.03). Nonetheless, independent-samples t-tests revealed that the ASD participants (in this subset of fast general responders) still show significantly diminished behavioural surprise (t(22)=2.39, P=0.026) relative to NTs (in this subset of slow responders). ASD, autism spectrum disorder. NT, neurotypical. RT, reaction time. Data points represent individual participants, red lines indicate the mean, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean. Star indicates significance at P<0.05.

Supplementary Figure 4 Replication of behavioral results in a nonclinical sample.

(a) The same task conducted in a sample of non-clinical volunteers characterised according to high or low autistic traits (AQ) replicates the interaction between expectedness (E=expected, N=neutral, UE=unexpected) and autistic tendency (high AQ, n=26; low AQ, n=31). There was a significant main effect of expectedness (F(2,110)=69.46, P<0.001) and, crucially, a significant expectedness*AQ group interaction (F(2,110)=13.29, P<0.001); suggesting that participants with high AQ scores show a reduced modulation of RT as a function of expectedness (e.g. reduced slope), relative to participants with low AQ scores. There was a main effect of noise (F(2,110)=16.96, P<0.001), and noise*group interaction (F(2,110)=5.07, P=0.008). No other linear interactions or main effects were significant (P’s>0.2). (b) An independent samples t-test demonstrated that behavioural surprise was significantly attenuated in the high AQ group (t(55)=4.32, P<0.001). (c, d) Error rates were subject to the same analysis as above. There was a significant main effect of expectedness (F(2,110)=19.89, P<0.001) but the expectedness*AQ group interaction did not reach significance (F(2,110)=.85, P=0.42); suggesting that the main effect of expectedness on accuracy did not vary as a function of autistic traits. The main effect of noise narrowly missed significance (F(2,110)=2.36, p=0.09), but there was no noise*group interaction (F(2,110)=1.67, P=0.1). One low AQ participant showed relatively high % errors in the UE condition, but their overall errors were within reasonable limits and results are not changed if they are excluded. Compare with Figure 2a-d in the main text. Data points represent individual participants, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean. Star indicates significance at P<0.05

Supplementary Figure 5 Responses to face and house stimuli.

To confirm that there were no group differences in RTs or error rates in responding to the different outcome image types (faces, houses) we examined these responses in two separate repeated-measures ANOVAs with group (ASD, n=24; NT, n=25) as a between participants factor in each case. For reaction times there was a significant main effect of stimulus type, reflecting the fact that participants were in general slower to respond to house images over face images (F(1,47)=16.52, P<0.001). Additionally there was a main effect of group indicating that the ASD participants were generally slower to respond than the NT participants (F(1,47)=5.54, P=0.023) but crucially there was no interaction between stimulus type and group (F(1,47)=1.23, P=0.2). For error rates, participants generally made more errors on house trials (main effect of stimulus type: F(1,47)=13.37, P=0.001), but there was no group difference in errors overall (non-significant main effect of group: F(1,47)=0.8, P=0.37) and there was no stimulus type x group interaction (F(1,47)=0.02, P=0.9). ASD, autism spectrum disorder. NT, neurotypical. Data points represent individual participants, red lines indicate the mean, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean.

Supplementary Figure 6 Results of Bayesian-model selection.

The protected exceedance probability from the Bayesian Model Selection (BMS) of log model evidences shows that the 3-level HGF (HGF-3) describes subject’s behaviour better than alternative learning models (RW; Rescorla Wagner, SK1; Sutton K1, HGF-2; 2-level Hierarchical Gaussian Filter). See main text for details.

Supplementary Figure 7 Model-simulated reaction times.

As an additional validation of the HGF model performance we simulated trial-wise RTs using the fitted perceptual and response model parameters from each of our 24 ASD and 25 NT participants. These simulations can recover the group differences in the main behavioural effect of expectation (compare to Figure 2a&b in the main manuscript). Statistical analysis of these model simulated RTs indicates a significant expectedness * group interaction (F(1,94)=4.44, P=0.014), and the simulated UE-E RT difference was significantly lower when simulated from the ASD parameters, relative to the NT parameters(t(47)=2.57, P=0.013). ASD, autism spectrum disorder. NT, neurotypical. UE, unexpected. N, non-predictive. E, expected. Data points represent the mean of 32 simulations for each individual participant, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the group mean, red lines indicate the group mean. Star indicates significance at P<0.05

Supplementary Figure 8 Average HGF-parameter estimates across groups.

Individual participant parameter estimates for each of the free parameters estimated from the HGF, for both the ASD (n=24) and NT (n=25) groups. A statistically significant MANOVA effect indicated that the groups would differ on one or more of the estimated model parameters, Pillai’s’ Trace =.43, F(8, 40) = 3.81, P=0.002). Independent samples t-tests indicate a significant group difference in baseline log RT (β0; t(47) = 2.33, P=0.024), phasic volatility (β4; t(47) = 2.15, P=0.037) and tonic volatility at the third level (ω3; t(47)=2.10, P=0.045). Outcome surprise (β1; t(47) = -1.73, P=0.09) and outcome uncertainty (β2; t(47) = -1.87, P=0.06) narrowly missed significance. There were no group differences in probability uncertainty (β3; t(47) = -.51, P=0.61), decision noise (ζ; t(47) = -.55, P=0.59) or tonic volatility at the second level (ω2; -.21, P=0.84). See the main text and Figure 4b for a multiple linear regression analysis predicting group status from these same parameters. ASD, autism spectrum disorder. NT, neurotypical. Data points represent individual participants, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean, red lines indicate the group mean. Star indicates significance at P<0.05

Supplementary Figure 9 Pupil size and dynamic learning rates.

The analysis reported in the main text indicates a sustained positive relationship between pupil size and precision-weighted prediction errors (ɛ3) in the ASD participants (Figure 5b). The precision weight (on the prediction error) is proportional to the update of environmental volatility and is formally related to dynamic trial-wise learning rate (α3) This additional analysis indicates that the learning rates themselves (α2 and α3) do not have a significant influence on pupil dilation in either group. As for the results reported in the main text (see Online Methods) this regression analysis included, trial type (face, house), fixation compliance, mean RT and UE-E ground truth contrasts, as control regressors. Shaded regions represent standard error of the mean.

Supplementary Figure 10 Pupil size and precision-weighted PEs in stable and volatile task periods.

The pupil regression reported in the main text (Figure 5b) examined the relationship between precision-weighted prediction errors (ɛ3; PE’s) and pupil size across all trials in the experiment. A strength of this analysis is that it represents the pupil response when each participant was actually surprised, and does not impose knowledge of the task structure. Nonetheless, to examine the relationship between precision-weighted PE and pupil size in the volatile and stable periods of the task we conducted the same regression analysis (see main text and online methods) but separately for the 72 ‘stable’ trials and ‘72’ volatile trials (see Figure 1) towards the end of the experiment. (left) In the stable period there is no relationship between precision-weighted prediction errors and pupil size in either group or no differences between the groups. (right) The relationship between precision-weighted PE’s and pupil size in the ASD participants (blue) is apparent 1000ms after the outcome appears in the volatile period of the task. Blue solid line shows where the ASD participants differ from zero and black dotted line shows where the ASD participants differed from the NT participants. Shaded region represents standard error of the mean. Consistent with the analysis of learning rates in the volatile and stable task periods (Figure 3c), this suggests that the ASD participants tend to show aberrant noradrenergic surprise about volatility, in response to volatility (e.g. over-updating learning about volatility and over-engaging noradrenergic responses to surprise about volatility, in the face of environmental volatility). However, we caution against the low trial numbers included in this analysis (72, vs a maximum of 456 in the analysis reported in the main text) and the fact that one control participant did not have enough good trials in the volatile period to be included in this analysis, so participant numbers are also reduced (ASD=11, NT=13).

Supplementary Figure 11 Fixation compliance across trial types.

Mean absolute deviation (MAD) from fixation (in degrees of visual angle) across groups and conditions. Generally fixation compliance was very good, <1° of visual angle in both the vertical and horizontal axes. Stimulus duration was purposefully short to eliminate saccades. Crucially there is no systematic difference in fixation compliance that would impact on the pupillometry results, either across groups or conditions. One participant showed systematically larger deviation from fixation in the horizontal plane, though fixation was still good (below 2° visual angle) and not beyond the physical limits of the stimulus being presented. Importantly, trial-wise absolute deviation from fixation was included as a regressor of no interest in all pupillometry analyses reported in the main text and supplemental results, and thus our pupillometry analyses are corrected for eye movements. ASD, autism spectrum disorder. NT, neurotypical. UE, unexpected. N, non-predictive. E, expected. Data points represent individual participants, shaded regions and error bars show 95% confidence intervals and 1 standard deviation of the mean, red lines indicate the group mean.

Supplementary Figure 12 Pupil size and reaction time.

The relationship between precision-weighted prediction errors and pupil size reported in the main text (Figure 5b), links pupil size to behaviour indirectly via the HGF model, since the precision-weighted prediction errors are estimated for each participant on the basis of their trial-wise RT. However, we conducted an additional regression analysis to investigate the relationship between basic behaviour (trial-wise RT) and pupil size directly. As RT increases, post-outcome pupil size shows an initial decrease from baseline followed by an increase towards the end of the trial. Crucially, there are no time points in which the relationship between RT and pupil size is significantly different between the ASD and NT groups. Notably, trial-wise RT is included as a control regressor in the results reported in the main text (Figure 5), and in the analyses reported above (Figure S9 & S10), so where there is a significant relationship between pupil size and the trial-wise model parameters this exists over and above any effect of RT on pupil size. Blue and yellow bars indicates where the relationship between RT and pupil size significantly differed from zero in the ASD and NT participants, respectively. As for the results reported in the main text (see online methods) this regression analysis included, trial type (face, house), fixation compliance and UE-E ground truth contrasts, as control regressors. Shaded region represents standard error of the mean.

Supplementary Figure 13 Raw pupil traces.

(a) Raw mean pupil dilation in ASD participants (blue) and NT participants (yellow) separated into trials in which the outcome was unexpected (UE: dotted line) and trials where the outcome was expected (E: solid line) (a) The UE-E difference (i.e. ground truth ‘surprise’) in the ASD participants (blue) and NT participants (yellow). Equivalent to the UE-E contrast from the regression model presented in Figure 5a. Shaded region shows standard error of the mean.

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Lawson, R., Mathys, C. & Rees, G. Adults with autism overestimate the volatility of the sensory environment. Nat Neurosci 20, 1293–1299 (2017) doi:10.1038/nn.4615

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