Figures and data
Pupil size differs during saccade planning across directions.
a Twenty participants planned saccades in a cued direction. Saccades were executed as fast as possible upon cue offset. b All 36 possible saccade targets around the visual field. Only eight equally spaced locations were shown per trial. c Pupil size over time, split and averaged during saccade planning in oblique/cardinal, upward/downward, and left/rightward directions, locked to cue offset. Shaded areas indicate ± 1 s.e.m. d Averaged z-transformed pupil size during planning (−150 ms– 170 ms post cue, gray area in e) across directions. e Linear mixed-effects model using obliqueness, verticalness, horizontalness of directions, and saccade properties to predict pupil size during saccade planning. f Standardized partial coefficients per predictor with 95% confidence intervals. *p < .05, **p < .01, ***p < .001.
Saccade preferences differ across directions and are predicted by sac-cade costs.
a The same twenty participants freely selected one of two saccade targets. b The average saccade preferences across directions (sum selected/sum offered). Shaded bands indicate ± 1 s.e.m.. c Saccade costs correlated negatively with saccade preferences across directions: costly directions were avoided and affordable directions preferred. Black datapoints represent directions (averaged across participants). d Pupil size was larger for avoided compared with preferred directions. e Saccade costs predicted saccade selection on a trial-by-trial basis (56.64%). Together, the saccade costs in the first task predicted saccade preferences in the subsequent task. c-e Error bars reflect bootstrapped 95% confidence intervals. d-e Black datapoints represent participants. **p < .01, ***p < .001.
Saccade curvature and latency reveal active weighing of cost during sac-cade selection.
a Schematic layout of saccade trajectories curving away (magenta) or toward (cyan) non-selected options. Curvature was calculated as the peak deviation from a straight line between gaze positions at saccade onset and offset. The top-right histogram shows that more saccades curved away than toward the nonselected option. b Difference in pupil size during the saccade planning task is linked to the peak curvature deviation in the saccade preference task. c Same as b, but now linked to saccade latency in the saccade preference task. Larger differences in pupil size are related to more oculomotor conflict between the two options, as reflected in more curvature away from the non-selected option and slower saccade latencies. b, c Black line depicts the relationship across all trials, gray lines denote regression fits per participant. d Saccade-cost based prediction of saccade selection split for toward and away curving trials. On a trial-by-trial basis, saccade costs predicted saccade selection above chance (59.72%) when saccades curved away from the non-selected option. In contrast, saccade costs did not predict saccade selection for ‘toward’ saccades. Black datapoints represent participants. All error bars reflect bootstrapped 95% confidence intervals. ***p < .001
Saccade costs underlie saccade preferences in natural viewing.
a Fourty-one participants searched for small letters (’Z’ or ‘H’) in natural scenes (Exp. 1; n = 16), and either ignored (single task) or additionally attended (dual task) to an auditory number stream (Exp. 2; n = 25). b Saccade preferences during search without auditory stimulation. c Preferred directions were associated with a smaller pupil size prior to the saccade (Exp. 1). d, e Same as b, c but now for Exp. 2 without attending the auditory number stream (single task). Preferred directions were again associated with a smaller pupil size preceding the saccade (Exp. 2). f Same as d but now under the increased cognitive demand of the (primary) auditory digit counting (dual) task. g Adjustment in saccade preferences between single- and dual-task conditions in percentage points. h Less saccades were executed in the more demanding dual-task condition. Black datapoints represent participants. i Pupil size during the single task predicted direction adjustments under additional cognitive demand. Costly saccades as assessed during the single-task condition were especially cut in the dual-task condition. b, d, f, g Shaded bands represent ±1 s.e.m.. Other error bars reflect bootstrapped 95% confidence intervals. c, e, i Black lines depict the relationship across all trials, gray lines denote regression fits per participant. ***p < .001.
Saccade-locked pupil traces as index of saccade costs in different directions. Using the average pupil size in the 350 ms before saccade onset (saccade-locked), results remained qualitatively identical. Planning oblique saccades was associated with a larger pupil size than cardinal ones (β = 9.897, SE = 2.223, t = 4.451, p < .001), and downward saccades were associated with a larger pupil size than upward saccades (β = .471, SE = .112, t = 4.189, p < .001). A slightly increased pupil size for leftward compared with rightward saccades was observed as well (β = .260, SE = .107, t = 2.436, p = .015).
Full outcomes of the linear mixed-effects model analyzing pupil size assessed saccade costs across directions.
Full outcomes of the linear mixed-effects model predicting pupil size using saccade preferences and control variables in Experiment 1.
Full outcomes of the linear mixed-effects model predicting pupil size using saccade preferences and control variables in Experiment 2.
