Age-Related Differences in Decision-Making: Evidence Accumulation is More Gradual in Older Age

Figures & data

Figure 1. Sample paths for the diffusion model and the Lévy flight model.

Note: Panel (a): Sample paths of the diffusion model with normally distributed noise, i.e., α = 2.Panel (b): Sample paths of a Lévy flight model with more heavy-tailed Cauchy-distributed noise, i.e., α = 1.

Table 1. Mean parameter values, response times, and accuracy rates in the letter-number-discrimination task and participant characteristics for the two age groups.

	Younger adults		Older adults				95% CI
	M	SD	M	SD	t(df = 78)	p*	LL	UL	Cohen´s d
$\alpha$	1.59	0.19	1.78	0.17	4.87	<.001	0.11	0.27	1.09
$a$	1.41	0.51	2.13	0.57	5.92	<.001	0.47	0.95	1.32
$v_n$	−3.62	1.16	−4.24	1.08	−2.47	.22	−1.12	−0.12	−0.55
$v_l$	3.49	1.04	4.23	1.07	3.14	<.05	0.27	1.21	0.70
$t_0$	0.31	0.03	0.37	0.05	6.82	<.001	0.04	0.08	1.53
$z_r$	0.52	0.08	0.51	0.05	−0.57	1.00	−0.04	0.02	−0.13
Mean RTcorrect	0.51	0.06	0.63	0.08	8.24	<.001	0.10	0.16	1.80
Mean RTerror	0.48	0.09	0.57	0.10	4.56	<.001	0.05	0.14	1.02
Accuracy	0.96	0.03	0.98	0.02	5.78	<.001	0.02	0.03	1.17
Education	15.76	1.86	16.08	2.15	0.70	1.00	−0.58	1.21	0.16
MoCA	–	–	27.73	1.34	–	–	–	–	–
Vocabulary	17.55	3.27	22.90	4.47	6.11	<.001	3.61	7.09	1.37
Speed	91.05	14.53	71.48	14.58	−6.02	<.001	−26.05	−13.10	−1.34
Pos. mood	32.00	6.09	33.21	7.46	0.80	1.00	−1.82	4.24	0.18
Neg. mood	12.58	2.91	10.43	0.87	−4.48	<.001	−3.11	−1.19	−1.00

Note: N = 40 in each group. In the older group, error response times are based on 34 participants and df = 72 for the comparison of error response times as six participants did not commit any errors. *obtained p-values are Bonferroni-corrected to account for the 14 tests presented in this table. CI = confidence interval for the mean difference; LL = lower limit; UL = upper limit; $\alpha$ = stability parameter; $a$ = boundary separation; $v_n$ = drift rate for number stimuli; $v_l$= drift rate for letter stimuli; $t_0$ = non-decisional time; $z_r$ = relative starting point; RT_correct = response times for correct responses, in seconds; RT_error = response times for error responses, in seconds. For the t-test, response times were log-transformed and accuracy was arcsin transformed. Education = years of education; MoCA = scores (maximum of 30) in the Montreal Cognitive Assessment assessed for older adults only (Nasreddine et al., 2005); Vocabulary = raw score (maximum of 33) on the Mill-Hill Vocabulary Scale (Raven, 1982); Speed = perceptual-motor speed, assessed by the number of correct responses on the Digit Symbol Task (Wechsler, 1997); Positive and Negative mood = scores (possible values 10–50) on the Positive and Negative Affect Scale (Watson, 1988).

Figure 2. Kernel density of mean alpha-values for the two age groups in the letter-number-discrimination task.

N = 40 in each group. Circles at the bottom represent individual α-values of the participants.

Table 2. Goodness of fit for the diffusion model vs. Lévy flight model.

	Younger adults		Older adults
	M	SD	M	SD
$p_{DM}$	0.04	0.12	0.19	0.32
$B{F}_{DM}$	0.07	0.23	4.65	21.29
$N_{DM}$	1		6
$N_{LFM}$	39		34

Note: $p_{DM}=p(diffusionmodel|data)$ is the mean posterior model probability for the diffusion model given the data (i.e., the empirical response time distribution). The probability for the Lévy flight model results as $p_{LFM}=1-p_{DM}$. $B{F}_{DM}$ is the mean Bayes factor in favor of the diffusion model. $N_{DM}$ and $N_{LFM}$ give the numbers of participants for whom the diffusion model or the Lévy flight model, respectively, shows the better fit.

Nasreddine, Z. S., Phillips, N. A., Bédirian, V., Charbonneau, S., Whitehead, V. … Chertkow, H. (2005). The Montreal Cognitive Assessment, MoCA: A brief screening tool for mild cognitive impairment. Journal of the American Geriatrics Society, 53(4), 695–699. doi:10.1111/j.1532-5415.2005.53221.x

 PubMed Web of Science ®Google Scholar

Raven, J. C. (1982). Revised manual for Raven’s progressive matrices and vocabulary scale. Windsor, UK: NFER Nelson.

 Google Scholar

Wechsler, D. (1997). Administration and scoring manual for the WAIS–III. San Antonio, TX: Psychological Corporation.

 Google Scholar

Watson, D. (1988). The vicissitudes of mood measurement: Effects of varying descriptors, time frames, and response formats on measures of positive and negative affect. Journal of Personality and Social Psychology, 55(1), 128–141. doi:10.1037/0022-3514.55.1.128

 PubMed Web of Science ®Google Scholar