E XPERIMENT 2

We conducted Experiment 2 to test if we could replicate the absence of aftereffects during low-conflict trials from Experiment 1, and to allow a more fine-grained investigation (no conflict vs. low conflict vs. medium conflict vs. high conflict) of the potential

modulation of intention deactivation by transient cognitive-control demands during conflict trials. We reasoned that if intention deactivation was modulated by cognitive-control availability only during conflict trials, then aftereffects should be decreased in low-, compared to no-conflict trials, but should increase linearly with increasing conflict strength across medium- and high-conflict trials. Since cognitive-control-demand effects on

intention deactivation did not differ between younger and older adults in Experiment 1, we only investigated younger adults in Experiment 2.

3.5.1. Methods

Participants. Forty-eight participants (35 female, 19–29 years, Mage = 23.8, SDage = 2.9 years) took part in two sessions lasting approximately 1.5 h each, in exchange for partial course credit or 15 €.

Stimuli and Procedure. Stimuli and procedure for Experiment 2 were similar to Experiment 1, with the following changes: Ongoing-task trials comprised five or seven arrows that could appear at 12 possible locations on the screen. PM and test blocks consisted of 98 trials (90 standard, 4 PM/PMREPEATED, 4 oddball trials), with 80 trials in set size 7 (20 trials per arrow ratios 7:0, 6:1, 5:2 and 4:3) and 18 trials in set size 5 (6 trials per arrow ratios 5:0, 4:1 and 3:2). Deviant symbols for PM, PMREPEATED and oddball trials were drawn randomly from a pool of 32 symbols. Note that PM or PMREPEATED symbols were

presented pseudo-randomly throughout a block, with the restriction, that at least five trials were in between PM or PMREPEATED trial presentations.

3.5.2. Results

Analyses were conducted on trials of set-size 7 only, since only these contained PM and PMREPEATED stimuli. For RT analyses, errors (10.8% response failure or miss) and trials with RTs ± 2.5 SDs of a participant’s mean RT for a given arrow ratio and trial type within each block were excluded (2.5%). The relevant data is set forth in Figure 6 and Table 4

Manipulation checks. Similar to Experiment 1, we first examined the effects of cognitive-control demands on ongoing-task performance to assess whether increasing control demands decreased cognitive-control availability. To this aim, we conducted

repeated-measures ANOVAs on standard-trial RTs and error rates (excluding erroneous PM responses⁵) averaged across PM and test blocks as a function of arrow ratio (7:0, 6:1, 5:2, 4:3). Subsequently, we analyzed PM performance (RTs, error rates) in similar ANOVAS to determine whether potential cognitive-control-demand effects on aftereffects of completed intentions could be the result of PM-performance differences between cognitive-control demands.

Ongoing-task performance. Standard-trial RTs increased with increasing arrow ratio, F(3, 141) = 93.82, p < .001, ηp2 = .67, (7:0: 530 ms, 6:1: 670 ms, 5:2: 878 ms, 4:3: 1177 ms). This effect was mirrored by error data, F(3, 141) = 565.02, p < .001, ηp2 = .92, (7:0: 1.2%, 6:1: 3.1%, 5:2: 9.9%, 4:3: 28.1%).

PM performance. Arrow ratio did not affect RTs in PM trials (Table 4), F(3, 141) = 1.69, p = .173, ηp2 = .04. PM-error rates decreased with increasing arrow ratio, F(3, 141) = 16.11, p < .001, ηp2 = .26, in a linear fashion from 7:0 PM trials (22.3%) to 6:1 (14.7%) and 5:2 trials (10.8%), with a nominal increase to 4:3 PM trials (12.6%), F(1, 47) = 33.56, p < .001, ηp2

= .42 (linear contrast).

Aftereffects of completed intentions. To examine cognitive-control-demand effects on intention deactivation, we conducted repeated-measures ANOVAs involving the factor arrow ratio (7:0, 6:1, 5:2, 4:3) on aftereffects of completed intentions (i.e.,

performance differences between PMREPEATED and oddball trials) in RTs, commission errors and other error types (i.e., erroneous ongoing-task responses or response omissions). To determine statistical significance of the hypotheses-relevant effects of cognitive-control demands on intention deactivation, we used a Bonferroni-corrected alpha level of .0167 (.05/3). Note that p values for tests at Bonferroni-corrected alpha levels are denoted as p*.

RTs. Aftereffects of completed intentions did not differ statistically between arrow ratios, F(3, 141) = 0.62, p* = .549, ηp2 = .01 (69 ms, drm = 0.35; 73 ms, drm = 0.30; 98 ms, drm = 0.26; 49 ms, drm = 0.08 in arrow ratios 7:0, 6:1, 5:2, 4:3, respectively). Testing whether aftereffects differed between extreme poles of cognitive-control availability, as was suggested by visual inspection of the data, revealed no statistically significant difference between arrow ratio 7:0 and 4:3, t(47) = 0.52, p = .608, drm = 0.09.

Errors. Similar to RT data, we found no effect of arrow ratio on aftereffects of completed intentions in error rates, F(3, 141) = 0.14, p* = .839, ηp2 = .003.

Commission errors. Commission errors were rare and occurred almost exclusively in PMREPEATED trials (0.9% [27 trials]); only two commission errors occurred in standard trials (Table 5). Commission-error aftereffects were affected by arrow ratio, F(3, 141) = 4.50, p* = .010, ηp2 = .09 (1.8%, drm = 0.82; 0.9%, drm = 0.58; 0.3%, drm = 0.29; 0.5%, drm = 0.42 in arrow ratios 7:0, 6:1, 5:2, 4:3, respectively). Repeated contrasts revealed only nominally decreased commission-error aftereffects from 7:0 to 6:1 trials, F(1, 47) = 3.00, p = .090, ηp2 = .06, and from 6:1 to 5:2 trials, F(1, 47) = 3.78, p = .058, ηp2 = .07. Commission-error aftereffects also did not differ significantly between 5:2 and 4:3 trials, F(1, 47) = 0.66, p = .420, ηp2 = .01.

Additionally, testing the difference in commission-error aftereffects between the extreme poles of cognitive-control availability in this study (7:0 vs. 4:3), revealed larger aftereffects in 7:0 than in 4:3 trials, t(47) = 2.34, p = .024, drm = 0.52.

3.5.3. Discussion

In Experiment 2, we investigated effects of trial-by-trial cognitive-control demands on intention deactivation in younger adults. Results were straightforward: First, similar to Experiment 1, increasing the arrow ratio decreased speed and accuracy of ongoing-task performance; possibly reflecting a demand-dependent decrease in cognitive-control availability. Second, we again found decreasing PM-error rates with increasing cognitive-control demands, which may result from participants missing PM cues more often during trials in arrow ratios 7:0 and 6:1 due to their overall faster ongoing-task performance in these trials. Most importantly and in contrast to Experiment 1, we found no evidence for a modulation of aftereffects of completed intentions in terms of performance costs in

PMREPEATED compared to oddball trials by cognitive-control availability. That is, RT and error aftereffects were not modulated by transient cognitive-control demands in PMREPEATED trials.

Interestingly, however, we found that commission-error aftereffects decreased with increasing cognitive-control demands. We will discuss these effects in more detail in the general discussion.

Table 4

Mean (SD) Performance during PM- and Test Blocks in Experiment 2.

Arrow ratio (cognitive-control demand) Note. Error rates represent erroneous ongoing-task responses and response omissions.

aAftereffects represent performance differences between PMREPEATED and oddball trials.

Table 5

Mean (SD) Commission-error (CE) Rates during Test Blocks in Experiment 2.

Arrow ratio (cognitive-control demand)

aAftereffects represent performance differences between PMREPEATED and oddball trials.

Figure 6. Results from Experiment 2. (A) Mean response times (RT) and error rates (erroneous ongoing-task responses and response omissions) for performance in PM blocks and test blocks in Experiment 2 as a function of trial type (standard, PM, PMREPEATED, oddball) and arrow ratio (7:0, 6:1, 5:2, 4:3). (B) Mean commission-error (CE) rates during test blocks as a function of trial type and arrow ratio. Error bars represent standard errors of the mean.