Abstract
The notion of “mind-reading” by carefully observing another individual's physiological responses has recently become commonplace in popular culture, particularly in the context of brain imaging. The question remains, however, whether outwardly accessible physiological signals indeed betray a decision before a person voluntarily reports it. In one experiment we asked observers to push a button at any time during a 10-s period (“immediate overt response”). In a series of three additional experiments observers were asked to select one number from five sequentially presented digits but concealed their decision until the trial's end (“covert choice”). In these experiments observers either had to choose the digit themselves under conditions of reward and no reward, or were instructed which digit to select via an external cue provided at the time of the digit presentation. In all cases pupil dilation alone predicted the choice (timing of button response or chosen digit, respectively). Consideration of the average pupil-dilation responses, across all experiments, showed that this prediction of timing was distinct from a general arousal or reward-anticipation response. Furthermore, the pupil dilation appeared to reflect the post-decisional consolidation of the selected outcome rather than the pre-decisional cognitive appraisal component of the decision. Given the tight link between pupil dilation and norepinephrine levels during constant illumination, our results have implications beyond the tantalizing mind-reading speculations. These findings suggest that similar noradrenergic mechanisms may underlie the consolidation of both overt and covert decisions.
Highlights
In social and financial interactions,timing can be everything.Whether flirting at the bar or playing a game of poker, it is often considered strategic to conceal your choices with periods of apparent deliberation
Here we show that pupil dilation can betray an individual’s decision before it is openly revealed
Pupil diameter was found to increase at the time of a decision irrespective of whether the choice related to the voluntary execution of a motor act or the selection of a digit from a series of five numbers
Summary
In social and financial interactions,timing can be everything.Whether flirting at the bar or playing a game of poker, it is often considered strategic to conceal your choices with periods of apparent deliberation The privacy of such mental events is generally taken for granted, it may be violated by measuring the brain’s electrical or metabolic activity (Libet, et al, 1983; Soon et al, 2008). Pupillary responses were the focus of numerous psychophysiological studies throughout the 1960’s, 70’s and 80’s (for review see Loewenfeld, 1993; Andrews and Purves, 1997; Beatty and LuceroWagoner, 2000) In these studies, the pupil response was considered to be an index of vaguely defined mental states grouped under general labels such as “arousal” (Bradshaw, 1967; Yoss et al, 1970) or “mental activity” (Hess and Polt, 1964; Kahneman and Beatty, 1966) that were routinely observed during a variety of cognitive tasks. Our aim was to show, for the first time, that similar processes may be important for the consolidation of cognitive decisions, using pupil dilation as a measure of NE release
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