What is it about?

Daily smokers and matched, non-smokers controls were presented with either nicotine-related images (i.e., people smoking) or neutral images, matched for several key features (e.g., luminance). Meanwhile, their eyes were continuously monitored by an eye-tracker, and we took particular interest in the pattern of dilation and constriction shown by the pupils. Pupil dilation is an important index of autonomic activity: it accurately reflects motivational, affective, and attentional reactions to salient stimuli. We found that, differently from controls, smokers presented pupil constriction when viewing images related to nicotine. This effect was robust enough to accurately predict the smoking status of new individuals (in a cross-validation setup) and was far better than traditional proxy measures of attentional bias such as response times and eye movements. Pupil constriction was more pronounced for light smokers, suggesting either a role for craving or a stage of dependence in which visual stimuli are still considered appetitive reinforcers.

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Why is it important?

Pupil dilation is an established physiological measure that indexes attraction, both appetitive and aversive learning, motivation, and classic conditioning. The finding of pupil constriction is indeed very surprising and counterintuitive. However, pupil size has typically been measured in a cumbersome, coarse way and along a protracted time window. Although pupil dilation for salient stimuli may still be expected after a sufficiently long fixation time, the fast event-related design of our study, which allows enhanced resolution, sheds new light on the early stages of visual exploration and suggests that a brief dip (i.e., pupil constriction) can take place and that this dip has the potential to become a relevant biomarker of nicotine addiction. We discuss this finding in terms of the deployment of attentional resources caused by nicotine-related stimuli in smokers, e.g., an early capture of visual attention; we also discuss the intriguing possibility that constriction may reflect the unfolding of predictive sensory tuning processes, concurring to bias perception toward salient stimuli by transiently increasing visual acuity for selected stimuli.


Measuring attentional bias may provide a useful, objective measure for either craving or dependence stage, i.e. a robust biomarker of addiction to nicotine, which could be leveraged upon as informative proxy to acquire in interventional studies. Pupil size appears to be in a more than ideal position for this aim, in that it is capable to jointly reflect affective, perceptual/attentional, and cognitive processes, thus returning an appropriately multifaceted picture. The potential to provide an integrated readout of several networks and processes (e.g., perceptual, cognitive) also puts forward firmly pupil size as a powerful and informative index for future basic research on vision and cognition. Particularly intriguing are accounts that postulate an active role of perceptual systems in constantly generating predictions about the incoming sensory information, which may be probed precisely through the careful assessment of changes in pupil size.

Elvio Blini
INSERM U1028, ImpAct, and Lyon Neuroscience Center

Read the Original

This page is a summary of: Pupil size as a robust marker of attentional bias toward nicotine-related stimuli in smokers, Psychonomic Bulletin & Review, October 2022, Springer Science + Business Media,
DOI: 10.3758/s13423-022-02192-z.
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