I agree that most measures (including the ones that I mentioned being pessimistic about) could be used to update one’s estimated probability that an actor is malevolent, but like you, I’d be most interested in which measures give the highest value of information (relative to the costs and invasiveness of the measure).
I could have done a better job of explaining why I think that pupillometry, and particularly the measurement of pupillary responses to specific stimuli, would be much more difficult to game (if it was possible at all) relative to body language analysis and eye tracking. It’s because the muscles that control pupil size are not innervated by skeletal muscle but by smooth muscle, which is widely accepted as being not under conscious control. (The muscles involved are called the dilator pupillae, activated by the sympathetic nervous system, and the sphincter pupillae, activated by the parasympathetic nervous system). Having said this, there are some arguments (and some case studies) suggesting that one could indirectly train oneself to change one’s pupil size (e.g., via mental arithmetic or other forms of mental effort) or that some people may be able to find other methods of (training themselves to) change their pupillary size at will (here’s a video of someone doing it). But to me the main question is whether the initial response to specific stimuli (e.g., negative emotional stimuli, for which pupil responses are observed [in non-psychopathic people] within 2,000 ms of the stimulus) would be under voluntary control, and this seems very unlikely to me.
Early pupillary responses to certain stimuli are under the influence of subcortical structures, including the amygdala, and I think this point is particularly relevant to psychopathy. When we view faces, there’s a subcortical route to the amygdala which carries that information faster than it can be consciously processed and which allows the amygdala to be one of the first brain areas to trigger a fear response in reaction to someone seeing a fearful face. Why is this relevant? Well, there’s evidence that psychopaths demonstrate hypoactivity in their amygdala (relative to controls) in response to viewing human faces. And it seems that psychopaths’ pupillary responses to negative facial expressions differ[1] from those of controls (in that their pupils don’t dilate in response to negative stimuli [relative to neutral stimuli] like non-psychopaths’ pupils do) within the first 2000 ms of the stimulus being presented, not after.
If someone’s pupillary responses to negative facial expressions differ from non-psychopathic people, even if they somehow became aware of that and tried to alter it, I suspect it would be incredibly difficult (if it was possible at all) for them to voluntarily change their pupil size (in response to emotional stimuli) quickly enough to mimic normality. For these reasons, I think that assessing pupillary responses to viewing fearful faces is worth investigating as a cheap, noninvasive measure of psychopathy that would be much harder to manipulate relative to other cheap, noninvasive measures (if it was possible to manipulate at all, which I don’t think it would be).
Below, I briefly describe two little studies that are too small to be useful on their own but which make me think it’s worth at least exploring pupillometry a little more (as just one potential measure among a set of possible measures).
This little study included 82 males recruited from low and medium secure psychiatric hospitals in the United Kingdom, grouped according to whether they had low or high Factor 1 (interpersonal) factor scores based on the Psychopathy Checklist—Revised. The high Factor 1 group (n = 25) had a score of ≥10 on Factor 1 psychopathy and the low Factor 1 group (n = 27) had a score of ≤ 4. The chart below shows the difference in pupil diameter in response to negatively-valenced emotional images (compared to neutral images) for participants with high Factor 1 psychopathy scores (who had less pupil dilation in the first 2000 ms after the stimulus) compared to those with low Factor 1 psychopathy scores.
This little study included 73 adult male prisoners with histories of serious sexual or violent offenses, and it assessed psychopathy via The Triarchic Psychopathy Measure (TriPM; Drislane et al., 2014), which is a 58-item self-report measure with three subscales: Boldness, Meanness, and Disinhibition. They averaged participants’ pupil size measurements across each individual stimulus fixation for the duration of the stimulus display, then calculated an overall mean pupil size for each participant, across all trials, and calculated the percentage difference in pupil diameter for each stimulus category compared to the overall mean. They found weak but significant negative correlations between TriPM meanness scores and pupil dilation in response to a range of emotional stimuli (listed below).
I agree that most measures (including the ones that I mentioned being pessimistic about) could be used to update one’s estimated probability that an actor is malevolent, but like you, I’d be most interested in which measures give the highest value of information (relative to the costs and invasiveness of the measure).
I could have done a better job of explaining why I think that pupillometry, and particularly the measurement of pupillary responses to specific stimuli, would be much more difficult to game (if it was possible at all) relative to body language analysis and eye tracking. It’s because the muscles that control pupil size are not innervated by skeletal muscle but by smooth muscle, which is widely accepted as being not under conscious control. (The muscles involved are called the dilator pupillae, activated by the sympathetic nervous system, and the sphincter pupillae, activated by the parasympathetic nervous system). Having said this, there are some arguments (and some case studies) suggesting that one could indirectly train oneself to change one’s pupil size (e.g., via mental arithmetic or other forms of mental effort) or that some people may be able to find other methods of (training themselves to) change their pupillary size at will (here’s a video of someone doing it). But to me the main question is whether the initial response to specific stimuli (e.g., negative emotional stimuli, for which pupil responses are observed [in non-psychopathic people] within 2,000 ms of the stimulus) would be under voluntary control, and this seems very unlikely to me.
Early pupillary responses to certain stimuli are under the influence of subcortical structures, including the amygdala, and I think this point is particularly relevant to psychopathy. When we view faces, there’s a subcortical route to the amygdala which carries that information faster than it can be consciously processed and which allows the amygdala to be one of the first brain areas to trigger a fear response in reaction to someone seeing a fearful face. Why is this relevant? Well, there’s evidence that psychopaths demonstrate hypoactivity in their amygdala (relative to controls) in response to viewing human faces. And it seems that psychopaths’ pupillary responses to negative facial expressions differ[1] from those of controls (in that their pupils don’t dilate in response to negative stimuli [relative to neutral stimuli] like non-psychopaths’ pupils do) within the first 2000 ms of the stimulus being presented, not after.
If someone’s pupillary responses to negative facial expressions differ from non-psychopathic people, even if they somehow became aware of that and tried to alter it, I suspect it would be incredibly difficult (if it was possible at all) for them to voluntarily change their pupil size (in response to emotional stimuli) quickly enough to mimic normality. For these reasons, I think that assessing pupillary responses to viewing fearful faces is worth investigating as a cheap, noninvasive measure of psychopathy that would be much harder to manipulate relative to other cheap, noninvasive measures (if it was possible to manipulate at all, which I don’t think it would be).
Below, I briefly describe two little studies that are too small to be useful on their own but which make me think it’s worth at least exploring pupillometry a little more (as just one potential measure among a set of possible measures).
This little study included 82 males recruited from low and medium secure psychiatric hospitals in the United Kingdom, grouped according to whether they had low or high Factor 1 (interpersonal) factor scores based on the Psychopathy Checklist—Revised. The high Factor 1 group (n = 25) had a score of ≥10 on Factor 1 psychopathy and the low Factor 1 group (n = 27) had a score of ≤ 4. The chart below shows the difference in pupil diameter in response to negatively-valenced emotional images (compared to neutral images) for participants with high Factor 1 psychopathy scores (who had less pupil dilation in the first 2000 ms after the stimulus) compared to those with low Factor 1 psychopathy scores.
This little study included 73 adult male prisoners with histories of serious sexual or violent offenses, and it assessed psychopathy via The Triarchic Psychopathy Measure (TriPM; Drislane et al., 2014), which is a 58-item self-report measure with three subscales: Boldness, Meanness, and Disinhibition. They averaged participants’ pupil size measurements across each individual stimulus fixation for the duration of the stimulus display, then calculated an overall mean pupil size for each participant, across all trials, and calculated the percentage difference in pupil diameter for each stimulus category compared to the overall mean. They found weak but significant negative correlations between TriPM meanness scores and pupil dilation in response to a range of emotional stimuli (listed below).