Participants practiced either an easy or difficult motion-direction discrimination for 3584 trials across 4 sessions. Both accuracy and response time improved in both groups, with stronger effects in the Difficult training group. The pupil diameter was analyzed at two timescales: slow tonic averages across experimental blocks and rapid phasic changes from the pre-stimulus baseline.
Difficult training group phasic pupillary response by training session
Easy training group phasic pupillary response by training session.
The group averaged phasic pupil waveforms revealed two distinct peaks on each trial. The latency of the first peak decreased with practice in both groups and the peak amplitude decreased in the Difficult group. The tonic pupillary data revealed a strong within-session decrease and a non-monotonic, inverted-U pattern across sessions that peaked earlier in the Difficult group.