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The (mis)measure of emotion through psychophysiology

On New Year’s Eve 2016, Mariah Carey had a…notable performance in which she had difficulties rendering the songs “Emotions” and “We Belong Together”. She roared back on New Year’s Eve 2017, sparking the first meme of 2018.

Alas, it is unlikely that the field of psychophysiology will un-mangle its measurement of emotions with reflexes in such a short span of time.

My lab uses two reflexes to assess the experience of emotion, both of which can be elicited through short, loud noise probes. The startle blink reflex is measured underneath the eye, and it measures a defensive negative emotional state. The postauricular reflex is a tiny reflex behind the ear that measures a variety of positive emotional states. Unfortunately, neither reflex assesses emotion reliably.

When I say “reliably”, I mean an old-school meaning of reliability that addresses what percentage of variability in a measurement’s score is due to the construct it’s supposed to measure. The higher that percentage, the more reliable the measurement. In the case of these reflexes, in the best-case scenarios, about half of the variability in scores is due to the emotion they’re supposed to assess.

That’s pretty bad.

For comparison, the reliability of many personality traits is at least 80%, especially from modern scales with good attention to the internal consistency of what’s being measured. The reliability of height measurements is almost 95%.

Why is reflexive emotion’s reliability so bad?

Part of it likely stems from the fact that (at least in my lab), we measure emotion as a difference of reactivity during a specific emotion versus during neutral. For the postauricular reflex, we take the reflex magnitude during pleasant pictures and subtract from that the reflex magnitude during neutral pictures. For the startle blink, we take the reflex magnitude during aversive pictures and subtract from that the reflex magnitude during neutral pictures. Differences can have lower reliabilities than single measurements because the unreliability in both emotion and neutral measures compound when making the difference scores.

However, it’s even worse when we use reflex magnitudes just during pleasant or aversive pictures. In fact, it’s so bad that I’ve found both reflexes have negative reliabilities when measured just as the average magnitude during either pleasant or aversive pictures! That’s a recipe for a terrible, awful, no good, very bad day in the lab. That’s why I don’t look at reflexes during single emotions by themselves as good measures of emotion.

Now, some of these difficulties look like can be alleviated if you look at raw reflex magnitude during each emotion. If you do that, it looks like we could get reliabilities of 98% or more! So why don’t I do this?

Because from person to person, reflex magnitudes during any stimulus can differ over 100 times, which means that it’s a person’s overall reflex magnitude that raw reflex magnitudes are measuring – irrespective of any emotional state the person’s in at that moment.

Let’s take the example of height again. Let’s also suppose that feeling sad makes people’s shoulder’s stoop and head droop, so they should be shorter (that is, have a lower height measurement) whenever they’re feeling sad. I have people stand up while watching a neutral movie and a sad movie, and I measure their height four times during each movie to get a sense of how reliable the measurement of height is.

If all I do is measure the reliability of people’s mean height across the four sadness measurements, I’m likely to get a really high value. But what have I really measured there? Well, it’s just basically how tall people are – it doesn’t have anything to do with the effect of sadness on their height! To understand how sadness specifically affects people’s heights, I’d have to subtract their measured height in the neutral condition from that in the sad condition: a difference score.

Furthermore, if I wanted to take out entirely the variability associated with people’s heights from the effects of sadness I’m measuring (perhaps because I’m measuring participants whose heights vary from 1 inch to 100 inches), I can use a process called “within-subject z scoring”, which is what I use in my work. It doesn’t seem like the overall reflex magnitude people have predicts many interesting psychological states, so I feel confident in this procedure. Though my measurements aren’t great, at least they measure what I want to some degree.

What could I do to make reflexive measures of emotion better? Well, I’ve used four noise probes in each of four different picture contents to cover a broad range of positive emotions. One thing I could do is target a specific emotion within the positive or negative emotional domain and probe it sixteen times. Though it would reduce the generalizability of my findings, it would substantially improve reliability of the reflexes, as reliabilities tend to increase the more trials you include (because random variations have more opportunities to get cancelled out through averaging). For the postauricular reflex, I could also present lots of noise clicks instead of probes to increase the number of reflexes elicited during each picture. Unfortunately, click-elicited and probe-elicited reflexes only share about 16% of their variability, so it may be difficult to argue they’re measuring the same thing. That paper also shows you can’t do that for startle blinks, so that’s a dead end method for that reflex.

In short, there’s a lot of work to do before the psychophysiology of reflexive emotion can relax with its cup of tea after redeeming itself with a reliable, well-received performance (in the lab).

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