In the first Experiment, No-go signals appeared late during instruction presentation (see Fig. 1), allowing relatively much time for implementation, and relatively little time for cancelling implementation of the instructed mappings. Moreover, the ratio of Go to No-go trials was 2:1, so that participants presumably expected a given trial to be a Go trial.
We assumed that, under these conditions, participants would at least begin to implement the instructed S–R mappings on No-go trials. The impact of instruction implementation on size task performance on No-go trials should depend on how flexibly participants can interrupt and cancel the implementation process. On the one hand, it is possible that participants can interrupt preparation and delete the instructed mappings from working memory at any time during instruction implementation. This view seems consistent with findings suggesting that instruction-induced bindings are kept in some sort of working memory (Cohen-Kdoshay & Meiran, 2007) and may be rather weak compared to S–R associations consolidated by practice (Waszak et al., 2008; Brass et al., 2009; see “General discussion” for details). If participants can cancel instruction implementation at any point during preparation, we should not observe a cross-task compatibility effect in size task responses on No-go trials.
On the other hand, it is also conceivable that instruction implementation has proceeded too far to be successfully aborted when a late No-go signal finally appears. Accordingly, one might expect the instructed mappings to influence size task performance although the No-go signal rendered the instructed mappings useless.
Finally, we hypothesized that participants complete advance implementation of the mapping instructions on Go trials, and hence predicted a cross-task compatibility effect in size task responses on Go trials.
Thirty students from the city of Berlin (20 female, mean age = 24.4 years) received €12 or partial course credit for participation. All participants had normal or corrected to normal vision.
Design and procedure
Design and procedure were based on Wenke et al. (2007) with the only difference that the Go/No-go manipulation was added. New pairs of S–R mappings for the identity task were instructed at the beginning of each trial (e.g., N: left key, K: right key, on trial n; and D: left key, Z: right key, on trial n + 1; see Wenke et al., 2007, for details). No-go trials were signalled by colouring instructions after 2,700 ms. In between the instruction of the identity task and the presentation of its imperative stimulus, a logically unrelated size task had to be performed. The size task did not require spatially defined responses and letter identity was not a response relevant attribute. Instead, two letters were presented alongside each other in a grid (see Fig. 1) 800 ms after instruction offset, and the task was to judge the position of the physically larger letter by pressing the space key once or twice. There were three types of size task displays that differed with respect to letter overlap and compatibility between size and identity (see Fig. 1). Task-overlapping letters appeared on half of the size task trials and were either spatially compatible or spatially incompatible across tasks. Spatially compatible size task displays were those in which the letters appeared at grid positions that spatially corresponded to the (response) locations assigned to these letters by letter task instructions (e.g., a small N on the left and a K in bigger print on the right). In incompatible trials, letter position in the size task display and instructed response location did not correspond (e.g., a small K on the left and a big N on the right side). Finally, in non-overlapping trials, other letters than those instructed for the identity task were presented as size task targets. These trials served as a neutral baseline condition.
When participants committed an error in the size task, a 200 Hz tone was presented during the 300 ms interval between their size task response and the onset of the identity task target. After the 300 ms interval a single letter appeared at a central screen position, and remained on the screen until response, or for a maximum of 1,000 ms. This single letter served as a target for the letter identity task. On Go trials, participants responded according to the instructed mappings within the response window of 1,000 ms. On No-go trials they had to withhold responding to the letter and wait until the 1,000 ms had passed. When participants pressed the wrong key on Go trials, or when they failed to respond within the 1,000 ms response window, a 200 Hz tone was displayed during the 300 ms blank interval in the end of the trial. When they made a commission error on No-go trials they instead received written error feedback. The error message (mistake—responded though instruction had been coloured) remained on the screen for 2,000 ms. The next trial started after a blank inter-trial-interval of 800 ms.
For size task responses that required two successive key presses, we only considered the reaction time for the first key press because the inter-response intervals never reveal any effects with this paradigm (cf. Wenke et al., 2007).
Participants worked through two sessions of 400 trials with 16 blocks of 25 trials each. In all, 384 out of the 400 trials in each session were experimental (regular) trials. Assignment of specific letter pairs to the different overlap, compatibility, and size task response conditions were counterbalanced according to a Latin square (see Wenke et al., 2007, for details), with trial type (Go, No-go) as an additional factor in the counterbalancing scheme. Counterbalancing of letter pairs per condition across participants ensured (a) that one-third of the regular trials were No-go trials (128 total: 32 compatible, 64 neutral, 32 incompatible; equal frequencies for each combination of responses/to be avoided responses in the two tasks), and two-thirds of the trials were Go trials (256 total: 64 compatible, 128 neutral, 64 incompatible; equal frequencies for each combination of responses in the two tasks), and (b) that each participants saw the instructions for a specific letter pair only 4 times (twice in one session) during the entire experiment.
The remaining 16 trials in each session were catch trials (see Wenke et al., 2007). On catch trials, the letter task “target” was not amongst the instructed letters. Catch trials were added in order to ensure that participants encoded both S–R mappings in the instructions. As on No-go trials, participants were not supposed to respond to catch trial targets, and received the same written error message if they did.
Each session started with written instructions describing the procedure and the tasks, and three demo trials administered by the experimenter. Demonstration trials as well as practice trials featured digit instead of letter stimuli. The practice phase terminated when participants managed to complete a block of 24 practice trials with less than 11 errors (summed over both tasks), or after a maximum of three practice blocks. Experimental task instructions were then repeated with letter stimuli instead of digit stimuli, followed by four more practice trials containing letter stimuli, before the main part of the experiment started.
Six participants were excluded from the analyses because they committed more than 20% errors across all conditions in the size task, the letter identity task, or both, leaving 24 participants in the analyses. This exclusion criterion was applied to ensure robust reaction time estimates (also see Wenke et al., 2007). Note that it is independent of performance differences between conditions.
For the analyses of reaction times (RTs), we only considered trials in which both the size task and the identity task responses were correct. Correct RTs that were more than 2.5 standard deviations away from an individual’s mean per condition were discarded (3.32%). For the remaining data, mean RTs for correct trials were determined for each participant and task as a function of cross-task compatibility (compatible, neutral, incompatible) and identity task trial type (Go vs. No-go; only applies to size task). As mentioned before, non-overlapping letter stimuli in the size task served as a neutral baseline against which we compared spatially compatible overlapping letters in order to assess costs associated with encountering the same letters in the two tasks.Footnote 1
Individual error rates were calculated correspondingly, considering only responses with errors in one task. Trials in which errors were committed on both tasks were discarded (0.39%). Table 1 shows the RTs and error data for each task and condition. It becomes evident from Table 1 that Go trial responses in the letter identity task were much slower in the incompatible than in the compatible and neutral conditions. More importantly, there was a small compatibility effect in size task responses on both, letter task Go trials and No-go trials. In addition, size task responses were faster on letter No-go than letter-go trials. Separate ANOVAS for the two tasks showed that all effects were reliable.
Reaction times were submitted to a 2 × 3 ANOVA with trial type (letter task Go vs. No-go trials) and cross-task compatibility (incompatible, neutral, and compatible) as within-subjects factors. This analysis yielded a significant main effect of trial type, F(1,23) = 28.06, P < 0.01, MSE = 4103.48, indicating that size task responses were faster in letter identity task No-go trials than in Go trials. Importantly, the main effect of compatibility was also significant, F(2,46) = 5.37, P < 0.05, MSE = 268.06, whereas the interaction between compatibility and trial type was not, F(2,46) = 1.78, P > 0.18, MSE = 161.27. Planned comparisons that tested the compatibility effects (i.e., the difference between incompatible and compatible trials) separately for each trial type revealed that both, the 8 ms compatibility effect in Go trials and the 11 ms effect in No-go trials were reliable, F(1,23) = 5.01, P < 0.05, MSE = 333.06, and F(1,23) = 10.43, P < 0.01, MSE = 274.32, respectively. Moreover, comparisons between the compatible and the neutral conditions for each trial type indicated that RTs for neutral responses did not differ from compatible responses for Go trials, F(1,23) < 1, MSE = 629.42, nor for No-go trials, F(1,23) = 2.64, P > 0.11, MSE = 229.39, indicating that overlapping letter stimuli did not produce overlap costs (cf. Wenke et al., 2007).
Error rates in the size task were generally rather low, and neither differed between trial types, F(1,23) = 2.05, P > 0.16, MSE = 1.62, nor between compatibility conditions, F(2,46) = 2.79, P > 0.07, MSE = 1.62. The interaction between compatibility and trial type was not significant either, F(2,46) = 1.54, P > 0.22, MSE = 1.09.
Additional analyses Although none of the effects reached significance in the error analysis, there was an almost significant trend for participants to make fewer errors on incompatible trials than on neutral and compatible trials, especially on Go trials. Therefore, we wanted to ensure that the pattern of results revealed by the RT analyses was not compromised by speed-accuracy tradeoffs. To this end, we conducted a 2 × 3 MANOVA that simultaneously considered RTs and errors as dependent variables. The resulting centroids for each effect in Exp. 1 are shown in panels a–c in the left column of Fig. 2. Consistent with the RT ANOVA, the MANOVA revealed significant main effects of trial type, F(2,22) = 14.09, P < 0.01, and compatibility, F(4,90) = 4.54, P < 0.01 (all statistics based on Wilk’s Lambda). The interaction between trial type and compatibility was again not significant, F(4,90) = 1.68, P > 0.16.
Letter identity task
The one-way ANOVA of RTs for letter identity Go trials with compatibility (compatible, neutral, incompatible) as a within-subjects factor showed that compatibility conditions differed from each other, F(2,46) = 20.25, P < 0.01, MSE = 442.09. Planned comparisons revealed that responses on compatible trials significantly differed from incompatible trials, F(1,23) = 26.09, P < 0.01, MSE = 1117.59, whereas the difference between compatible and neutral trials was not significant, F(1,23) < 1, MSE = 573.26.
The corresponding one-way ANOVA of key errors in Go trials mirrored the RT results: the effect of compatibility was significant, F(2,46) = 24.4, P < 0.01, MSE = 4.29, indicating that participants committed more errors after incompatible size task displays than after neutral (non-overlapping) or compatible displays.
Finally, commission errors on No-go trials did not differ amongst compatibility conditions, F(2,46) < 1, MSE = 4.35.
The pattern of results was clear-cut with respect to both size task Go and No-go responses. Reactions were delayed when possible target letters of the succeeding identity task occupied spatial positions in the size task display that did not correspond to the instructed response locations. RTs of spatially corresponding responses were similar to RTs in neutral trials where the judged letters were different from the letters specified by instructions. That is, we obtained an interference-dominant pattern of results indicating RT costs for letters displayed at positions differing from the actually valid instructed S–R mappings.
The compatibility effect in Go trials generally replicates the findings by Wenke et al. (2007; Exp. 1) and can be explained by instruction-induced S–R binding. On this account (Wenke et al., 2007), representations of the instructed target features (i.e., letter identity) are linked to the instructed spatial features needed for later responding (e.g., N + LEFT, K + RIGHT) while reading the instructions, and the resulting links are implemented at a subverbal level for later use. When participants encounter the same letters in the interceding size task then letter identity, which is entirely irrelevant for the size task, automatically activates its associated spatial code. This in turn hampers stimulus identification (i.e., determining whether the bigger letter was on the left or the right) when the letters activate the “wrong” spatial codes, thereby slowing responses in the spatially incompatible condition. These instruction-induced S–R bindings are probably not of a verbal nature: first, the instructed mappings are completely irrelevant for performing the size task. Hence it is hard to see why participants would transform or translate a verbally represented rule during size task performance. Second, we found similar results as those observed here when the size task required judging the colour instead of the location of the bigger of two letters, and when participants held a tongue depressor in their mouths that supposedly blocked subvocal rehearsal (cf. Wenke et al., 2007, Exp. 2 and footnote 4). Hence we propose that quasi-perceptual or conceptual representations were integrated and bound at a subverbal level during some sort of cognitive simulation when situation models of the instructed situations were constructed (e.g., Barsalou, 1999; Glenberg & Robertson, 2000).
The important new finding of the current Exp. 1 concerns the compatibility effect in No-go trials. Responses in incompatible size task trials were reliably delayed even when the instructed mappings for the letter identity task were rendered irrelevant by a No-go signal. Moreover, the compatibility effect in No-go trials was similar to the effect in Go trials, suggesting that participants started to implement instructions at a subverbal level when the mappings for the identity task were presented. When a No-go signal finally appeared in No-go trials, rule implementation had proceeded too far for successful abortion. As a consequence, the established S–R links that were no longer valid influenced subsequent behaviour in a reflex-like manner.
Although the impact of letter task instructions on size task performance did not differ between Go- and No-go trials, the significant main effect of trial type showed that size task responses were generally faster on No-go trials than on Go trials. Assuming that the instructed mappings were already implemented on a subverbal level when the size task came on, it is unlikely that the Go-trial slowing reflects additional working memory demands associated with subvocal rehearsal of the instructed verbal rules. Instead, Go-trial slowing might primarily reflect general dual task or mixing costs (e.g., Kray & Lindenberger, 2000) related to keeping two tasks active and separate.
Finally, we also obtained an interference-dominant cross-task compatibility effect in the letter identity task. RTs were considerably delayed when the singular, centrally presented identity task target letter had occupied a position in the size task display that was spatially incompatible with the location of its instructed response.
The identity task effect can also be explained by binding-induced conflict between spatial codes if one assumes that re-binding of letter identity and spatial position information occurs when responding to spatially incompatible size task displays. Accordingly, responding to size task displays integrates the encountered situational features (including letter identity and spatial position information) into some sort of S–R episode (Logan, Taylor, & Etherton, 1999) or event file (Hommel, Müsseler, Aschersleben, & Prinz, 2001). When one of the letters encountered in the size task then re-appears as identity task target it activates the other features in the event file. Activation of the “wrong” spatial code on incompatible trials delays selecting the appropriate (instructed) spatial response.
Viewed this way, the identity task results seem to be (yet) another demonstration of response-based binding and re-binding similar to those already reported in the literature (e.g., Hommel, 1998, 2007; Hommel & Colzato, 2004; Waszak, Hommel, & Allport, 2003), and are therefore less interesting for the current research question. In contrast, the size task results directly speak to the question of instruction implementation. They suggest that a top-down mechanism integrates relevant stimulus and response features solely on the basis of instructions.
The compatibility effect in No-go trials of Exp. 1 seems to favour the view that advance implementation of instructions is the default mode. However, in Exp. 1, No-go signals were infrequent and appeared late. Therefore, it is possible that the effect observed in Exp. 1 reflects a strategic decision to always implement instructions. That is, Exp. 1 leaves open to what extent participants can strategically control whether or not to implement instructions. This question was addressed in Exp. 2.