Fig 1.
Starlings were trained in a multialternative environment.
a. European starling (S. vulgaris, [photo credit: Dick Daniels, http://carolinabirds.org/]/CC BY-SA https://creativecommons.org/licenses/by-sa/3.0]). b. Alternatives present in the experimental environment. Each symbol depicts a profitability ratio (a specific combination of amount and delay) and each shading, a profitability (a given ratio of amount to delay in rewards/second). Lines join stimuli with equal profitability. Within each profitability pair, the larger symbol indicates the Larger–Later profitability ratio and the smaller symbol the Smaller–Sooner one. c. Rate of responding in probe trials (mean ± SEM, n = 9 birds). All data included in this figure can be found in the S1 Data file.
Fig 2.
Profitability impacts response times and choices.
a. Preference in choice trials (mean proportion picked when presented paired with any of the other 5 profitability ratios) versus response time in single-option trials (means ± SEM, n = 9 birds). Inset shows individual data. Symbols match panel in Fig 1b. The dashed line shows a Deming regression (Estimated model: y = −0.0072x + 0.8259, [slope = 95% CI −0.004 to −0.0104]). b. Mean proportion of choices in every binary-choice combination (n = 9 birds). All data included in this figure can be found in the S1 Data file.
Fig 3.
a. ΔRT toward each profitability ratio between single-option and choice trials, averaged against the other 5 combinations; bottom row shows means across subjects. White cells are tied cases in which differences were lower than 1s in either direction. b. Number of nontied cases (out of 54) as a function of increasing minimal absolute response time difference (black) and corresponding binomial p-value (gray). c. Mean differences of individual mean response times in single-option trials minus individual mean response times in choice trials (n = 9, mean ± SEM). Inset shows individual animal means, with symbols laterally displaced for visualization purposes. (same data as bottom row in a.) d. Same as in c. for bootstrapped differences. A repeated-measures ANOVA, with option (6 levels) and difference as factors (2 levels), and mean ΔRTs as dependent variable, showed a significant effect of difference, only (Greenhouse–Geisser adjusted F(1,8) = 7.307, p = 0.027, η2p = 0.660). All data included in this figure can be found in the S1 Data file. RT, response time; ΔRT, difference in response time.
Fig 4.
When profitability is equated, starlings prefer larger–later alternatives.
a. Proportion larger–later alternative chosen against the equal profitability smaller–sooner combination (mean ± SEM, n = 9 birds). Dots show individual animals, laterally displaced for visualization purposes. Two-tailed t-tests against 50%, smallest t(8) = 2.912, *p < 0.05, **p < 0.01, smallest Cohen’s d = 2.05, effect size = [0.71, 0.96]. b. Long-term rate of returns R in which the time in the ITI is given the same decision weight as the delay between response and outcome (R = amount/(ITI + delay); equivalent to the slope of the dashed lines) and profitability as in Fig 1b (slope of solid lines). Inset shows R2 of linear regressions between observed preference ranking (mean across animals, n = 9) and long-term estimated rate of returns when the common ITI is given a discounted weight (R = amount / (w*ITI + delay), computed with increasing w); note that the strongest predictive power is for a long-term rate computation that includes an 8% weight of the ITI. All data included in this figure can be found in the S1 Data file. ITI, intertrial-interval.