PupilDiameterasaMeasureofEffortandSurpriseinWorkingMemoryandDecisionMaking

AditiJagannathan1,2,LeahBakst2,JosephT.McGuire2DublinHighSchool,Dublin,CA1; DepartmentofPsychologicalandBrainSciences,BostonUniversity,Boston,MA2

Introduction

Methods

Conclusions

References

Acknowledgements

Results

Participants predicted whether the face value of the next playing card would be higher or lower than the current one. If correct, the difference between cards was added to their total points. If incorrect, it was subtracted. Participants earned money proportional to their point total. Card values ranged from 2 to 9 and were drawn independently.

Participants were shown sequences of letters and asked to identify targets.

There were 3 conditions in which the targets were defined as follows:

• 0-Back: The letter was an ‘X’.• 1-Back: The letter matched the one

presented directly before it.• 2-Back: The letter matched the one

presented two letters before it.

Letters were presented for 0.5s with a 1.9s inter-letter interval. The conditions were interleaved in 10-trial blocks.

Face values with greater uncertainty show slower response times (RT).

RT and pupil size are positively correlated (R2 = 0.0758, p < 0.001).

This data is from one participant who completed two sessions of the experiment. The data includes:

• 12 runs of the Card Wager Task (each containing 35 trials).

•5 runs of the N-Back task (each containing 12 10-trial blocks, 4 per condition).

An EyeLink 1000+ eye tracker recorded pupil size at 500 Hz. Pupil size is expressed in percent deviation from the per-run average.

CardWagerTask

Methodology

N-BackTask

Trial Onset(0.5 s) Card 1

(2.8 s) Card 2(1.4 s) Feedback

(1.4 s)ITI

(1-7 s)

Eyes are often referred to as the window to the soul, but this phrase may hold more truth than previously thought. Recent research suggests that pupil diameter does in fact reflect internal factors like mental effort and arousal1,2.

In the context of decision-making and working memory, we hypothesized that:1. ↑ Uncertainty & Difficulty → ↑ Effort →

↑ Response Time & Pupil Diameter

2. ↑ Surprising outcomes → ↑ Arousal → ↑ Pupil Diameter

Pupil size increases with difficulty (↑ load on working memory).

RT and pupil size are positively correlated (R2 = 0.0581, p < 0.001).

o RISE Program

o Cognition and Decision Lab

o NSF 1755757

1. Lavín et al. (2014) Pupil dilation signals uncertainty and surprise in a learning gambling task. Front Behav Neurosci, 7:218.

2. Ekstein et al. (2016) Beyond eye gaze: What else can eyetracking reveal about cognition and cognitive development? Dev Cog Neurosci, 29:69-91.

Pupil size was greater when the participant responded incorrectly versus

correctly.

In both tasks, we found that:☑↑ Uncertainty & Difficulty → ↑ Effort → ↑ Response Time & Pupil Diameter

☑↑ Surprising outcomes → ↑ Arousal → ↑ Pupil Diameter

Additionally:• The effects of uncertainty in the Card

Wager Task continue past the moment of the decision, despite the fact that additional effort is not needed.

• In the N-Back task, the pupillary effect of target presence could be because targets are less common (and therefore surprising), or because it is more effortful to deviate from the normal response.

Future work will build on these results by investigating their associated brain processes.

Surprise

N-Back TaskEffort

Data shown from 2-Back blocks only. Participants did not receive feedback.

Trial Onset

Card 1 Card 2 Feedback

Average pupil diameter shows a

luminance response after each card is

shown.

Face values with greater uncertainty are associated with larger average pupil

size.

Both positive and negative surprise

increased pupil size compared to no

surprise.

Negative surprise may cause a stronger dilation than positive

surprise.

Letter Shown

Pupil size was greater when the participant reported that the target was

present versus absent.

Card Wager TaskEffort

Surprise