Mechanisms of impulsivity in humans and other animals

Jeffrey R. Stevens

University of Nebraska-Lincoln

jeffreyrstevens.quarto.pub/az2022

What is impulsivity?

Impulsivity defined

inability to wait
preference for risky outcomes
tendency to act without forethought
insensitivity to consequences
inability to inhibit inappropriate behaviors

Golden retriever sitting with treat on its nose waiting for command to release it. — Photo by McDobbie Hu

Impulsivity applied

Woman taking bite of green apple.

Three people running on treadmills in exercise clothes.

Man in suit looking at stock tickers.

Water with plastics, trash, and an oily sheen.

Impulsivity refined

Intertemporal choice

“decisions in which the benefits associated with different outcomes occur at different times”

Pinyon jay in pine tree with a pine nut in its mouth. — Photo by Marie Read

Impulsivity measured

In humans

Which would you prefer?

$100 today

$110 in 30 days

Impulsivity measured

In other animals

Pinyon jay in front of a computer monitor displaying a red circle and blue circle.

Chimpanzee behind plexiglas enclosure sticking its finger in a plastic hole to signal choice of six grapes on a yellow tray. Two grapes are displayed on a yellow tray on the other side of the apparatus.

Is impulsivity a trait?

At the species level

Do different species show similar levels of consistency?

Ring-tailed lemur sitting on top of stump. Photo by Julie Ricard: https://unsplash.com/photos/bBmPedpthvw

Chimpanzee looking up toward the left. Photo by Zdeněk Macháček: https://unsplash.com/photos/83gB_koMuvA

Primate impulsivity in intertemporal choice task

Chimpanzee behind plexiglas enclosure sticking its finger in a plastic hole to signal choice of six grapes on a yellow tray. Two grapes are displayed on a yellow tray on the other side of the apparatus.

Blank graph of maximium waiting time on the x-axis and 13 primate species on the y-axis.

Graph of maximum waiting time (in seconds) on the x-axis and 13 primate species on the y-axis. Each species shows the individual subject data as circles, species means as filled triangles, and a boxplot.

At the individual level

Are individuals consistent in impulsivity across contexts?

Two brown dogs running through grass, one with a ball in its mouth. Photo by Mia Anderson: https://unsplash.com/photos/2k6v10Y2dIg.

Intertemporal choice and caching in pinyon jays

Pinyon jay in front of a computer monitor displaying a red circle and blue circle. Pinyon jay behind an ice cube tray filled with sand and with a pine nut laying on top.

Intertemporal choice and caching in pinyon jays

Blank graph of mean number of caches on the x-axis and mean delay to large reward (in seconds) on the y-axis.

Graph of mean number of caches on the x-axis and mean delay to large reward (in seconds) on the y-axis. Pattern show a correlation coefficient (r) of 0.41 with dots showing individual points and a regression line tilted up and to the right.

Blank graph of photoperiod categories of long day and short day on the x-axis and mean number of caches on the y-axis.

Graph of photoperiod categories of long day and short day on the x-axis and mean number of caches on the y-axis. Dots are individual data points, with means as diamonds and 95% confidence intervals as error bars. The mean of the short delay data is significantly higher than the long delay data.

Blank graph of photoperiod categories of long day and short day on the x-axis and mean percent choice for larger option on the y-axis.

Blank graph of photoperiod categories of long day and short day on the x-axis and mean percent choice for larger option on the y-axis. Dots are individual data points, with means as diamonds and 95% confidence intervals as error bars. The mean of the short delay data similar to the long delay data.

Spatial impulsivity in dogs

Two small black dogs are chasing a squirrel in the grass. One dog and the squirrel are caught in mid-air.

Spatial impulsivity in dogs

Do owner perceptions of dog impulsivity match behavior?

Brown dog looking at plate of three treats on a white plate. A second yellow plate with one treat sits on the other side of a white barrier.

Two blank graphs with owner perceptions of dog impulsivity on the x-axis and distance traveled (in meters) on the y-axis.

Two graphs with owner perceptions of dog impulsivity on the x-axis and distance traveled (in meters) on the y-axis. Dots represent individual subject data, with regression lines and 95% confidence interval bands. The lines are flat indicating no relationship between the variables.

A forest plot from a meta-analysis showing significant effects for two studys, non-significant effects for four studies, and a non-significant model-averaged effect.

Meta-analysis of dog impulsivity

Does the literature show evidence for correlations across impulsivity tasks?

Screened > 10,000 articles to uncover 12 articles with multiple measures of impulsivity
Gathered info on 12 behavioral measures
Included owner perceptions of dog impulsivity (DIAS)

Meta-analysis of dog impulsivity

3 of 33 pairs of tasks report significant correlations

7 data sets correlating A not B with cylinder task

Meta-analysis of dog impulsivity

A forest plot from a meta-analysis showing non-significant effects for seven studies and a non-significant model-averaged effect.

Impulsivity as a trait

Evidence for species differences
Not much evidence for impulsivity as a trait in indivdual animals
Impulsivity appears to be more context-specific

What mechanisms underlie impulsivity?

Temporal discounting

Reward amount $A$ discounted by time delay $t$

Temporal discounting

Which would you prefer?

$100 in 1 day

$110 in 30 days

Similarity model

Which would you prefer?

$100 in 1 day

$110 in 30 days

Similarity model

Decision tree of similiarity model with first note as 'Amount similar?' with branches 'Yes' and 'No'. The next level of nodes are both 'Delay similar?' with branches 'Yes' and 'No'. If Amount is similar and Delay is not, the terminal node is 'Smaller, sooner'. If Amount is not similar and Delay is similar, the terminal node is 'Larger, later'. If Amount and Delay are both either similar or not similar, the terminal node is a question mark.

Similarity effects on choice

Can similarity judgments account for intertemporal choice?

Intertemporal choices

Would you rather receive $7 in 15 days or $10 in 22 days?

Similarity judgments

Do you consider $7 and $10 to be similar or dissimilar?
Do you consider 15 and 22 days to be similar or dissimilar?

Similarity effects on choice

The models

Discounting models

Hyperbolic, exponential, arithmetic

Similarity model

Similarity effects on choice

Graph with six Discounting models and one Similarity model on the x-axis and predictive accuracy on the y-axis. For each model, there is boxplot overlaid with a diamond representing the mean and error bars representing the 95% confidence intervals. The mean for the similarity model is about the same as one discounting model, and the other discounting model means are lower.

Graph with six Discounting models and seven Similarity models on the x-axis and predictive accuracy on the y-axis. For each model, there is boxplot overlaid with a diamond representing the mean and error bars representing the 95% confidence intervals. The six new similarity models all have higher means than any of the previously revealed discounting and similarity models.

Similarity judgment process

What features predict similarity judgments?

A table of eleven predictors and their formulas: small value, large value, difference, ratio, mean ratio, log ratio, relative difference, disparity ratio, salience, discriminability, logistic.

Similarity judgment process

What features predict similarity judgments?

Percent of participants as top feature

	Difference	Ratio	Large	Relative difference	Logistic
Amount	71%	27%	0%	1%	1%
Delay	62%	33%	1%	3%	2%

Similarity judgment process

What features predict similarity judgments?

Blank faceted graph with ten panels. The top five panels are for amount judgments; the bottom five panels are delay judgments. Each column is a different ratio: 0.5, 0.667, 0.75, 0.8, 0.9. The x-axis is difference and the y-axis is proportion judged similar.

Similarity as a mechanism

Similarity judgments can predict intertemporal choices
Numerical differences and ratios predict these judgments
Numerical differences and ratios contribute independently

Can we alter impulsivity?

The Logic

Flowchart showing Similarity judgments point towards Choice.

Flowchart showing Difference and Ratio both point to Similarity judgments.

Flowchart showing Difference and Ratio both point to Similarity judgments which points towards Choice.

Framing effects

Does framing amounts and delays in different units influence similarity and choice?

$5 vs. $10 or 500¢ vs. 1000¢

7 days vs. 14 days or 1 week vs. 2 weeks

Same ratio
Different difference

Larger differences $\rightarrow$ more dissimilar

Framing amounts

Framing of amounts influences similarity

Blank graph of condition on the x-axis (with dollars and cents as categories) and percent similar on the y-axis.

Graph of condition on the x-axis (with dollars and cents as categories) and percent similar on the y-axis. A raincloud plot show the individual data points at each level of percent similar along with a density plot. Overlaid is a boxplot with error bards for the 95% confidence intervals around the median. The dollars median is higher than the cents median.

Framing amounts

Framing of amounts influences choice

Blank graph of condition on the x-axis (with dollars and cents as categories) and percent larger, later on the y-axis.

Graph of condition on the x-axis (with dollars and cents as categories) and percent larger, later on the y-axis. A raincloud plot show the individual data points at each level of percent larger later along with a density plot. Overlaid is a boxplot with error bards for the 95% confidence intervals around the median. The dollars median is lower than the cents median.

Framing delays

Framing of delays influences similarity

Framing delays

Can’t tell if framing of delays influences choice

Altering impulsivity

Framing units can leverage ratio and difference features
Amount frames influence similarity and choice
Delay frames are not as clear

Conclusion

Take home message

Impulsivity is context-specific in other animals
Similarity is viable alternative mechanism for impulsive choice
We may be able to leverage similarity to nudge choice

jstevens5@unl.edu

Adaptive Decision Making Lab

decisionslab.unl.edu

@JeffStevensADML

Canine Cognition and Human Interaction Lab

dogcog.unl.edu

@UNL_CCHIL

jeffreyrstevens.quarto.pub/az2022