“Recent findings indicate that pupil dilation may track important changes in the causal statistics of the environment, including changes in environmental volatility…”


Recent findings indicate that pupil dilation may track important changes in the causal statistics of the environment, including changes in environmental volatilitytrait anxiety–related deficits in differential learning between volatile and stable task blocks would be accompanied by a reduced pupil dilatory response to environmental volatility.

This is consistent with a specific deficit in the use of environmental volatility to adjust action-outcome updating and, through this, to guide decision-making…high trait-anxious participants show a reduced pupil dilatory response to environmental volatility alone…Elevated trait anxiety was associated with a decreased mean pupil response to volatility…

We further addressed the possibility that high anxious individuals’ pupillary response does in fact track environmental volatility, but in a manner less like the Bayesian learner… an inverse relationship between trait anxiety and the effect of volatility, but not surprise, on the post outcome pupil response.

Non-luminance–related changes in pupil size are argued to reflect, among other influences, the activity of central arousal systems…Activity of this system is held to be closely linked to the processing of environmental volatility and the use of this to guide learning. Consistent with this, we observed that:

  • participants showed a significantly greater increase in pupil dilation following trial outcomes in which environmental volatility was high.
  • Furthermore, the degree to which participants’ post-outcome pupil dilatory response tracked environmental volatility was significantly correlated with the degree to which they adjusted their learning rate between stable and volatile blocks.
  • Of greatest pertinence to our study, trait anxiety modulated this pupil response to volatility, with high trait-anxious participants showing a smaller effect of volatility on post-outcome pupil dilatio

In conclusion, our findings reveal that:

  • High trait-anxious individuals did not differ from low trait-anxious individuals in their mean learning rate or in their behavioral or pupillary response to surprising adverse outcomes.
  • Nor did they show altered preferences for minimizing shock probability versus shock magnitude.
  • Instead, their pattern of decision-making was indicative of a selective difficulty with differentially updating action-outcome contingencies as a function of whether the current environment was stable or volatile.
  • Our pupilometry data also confirmed a specific insensitivity to environmental volatility and raised the possibility that this might reflect impoverished modulation by environmental volatility of activity in the locus coeruleus–norepinephrine system.

A deficit in this aspect of learning may have an important maintaining, or even etiological, role in the anxiety experienced by high trait-anxious individuals. We have taken a step toward elucidating this deficit, and hope to have illustrated how computational models can be integrated with behavioral and pupillometry analyses to begin to identify the mechanisms underlying disrupted decision making in high trait-anxious individuals.


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