Outcome tasks

Before identifying and describing the selected outcome tasks, some issues as-sociated with task selection need to be addressed. Firstly, while all the tasks are se-lected to measure some aspect of executive functioning, there is an issue with task-impurity (Miyake et al., 2000), that is, any cognitive tasks involves multiple pro-cesses. For example, one executive function task may not just utilise the considered ability, but employ multiple latent cognitive processes, which are not openly identifi-able by the task. This means that two executive function tasks may be correlated be-cause they both use verbal materials, for example, rather that both relying on the ex-ecutive function. It is for this reason that exex-ecutive functions and WMC have relied on procedures where latent variables are extracted from a range of related executive functioning tasks to infer these cognitive markers. Thus, while the current research aims to investigate a number of executive abilities, using single tasks to measure dif-ferent aspects of executive function limits my concluding remarks. For instance, this thesis may not be able to claim that inhibition is exclusively affected by self-regula-tion if performance is found to decline on the Stroop task. One of the benefits of adopting De Houwer’s (2011) distinction between functional and cognitive markers is that although identifying cognitive markers of a common resource might be diffi-cult, functional markers are silent as to what the common resources or processes might be.

The second issue in choosing outcome tasks is that while there is evidence for depletion effects in commonly used executive outcome tasks, there are many in-stances where depletion effects have been difficult to replicate, such as operation span, Stroop, and other working memory tasks (Dang, 2017; Healey et al., 2011; Xu et al., 2014). In addition, in the Carter et al. (2015) meta-analysis, although there were significant depletion effects found on Stroop and working memory tasks, when uncorrected for publication bias, there were high levels of heterogeneity among the studies. It is important to note that some of the outcome tasks employed in the cur-rent experiment (Stroop and OSPAN tasks) deviate from more common versions of the task. The meta-analyses of the depletion literature, refer to section 1.6.3, point out that many of the executive tasks have been employed as both depleting and out-come tasks. If these tasks are in fact depleting, then it is possible that taking a pre-test measure would lead to depletion effects. As such, the choice of outcome tasks was based on finding the version of each task that could be completed in the shortest

amount of time without sacrificing reliability. In short, while the outcome tasks have been selected because they have been used in previous ego-depletion research, it re-mains possible that depletion effects will not be evident in one or more of the current experiments.

3.2.2.1. Stroop colour word task (Stroop; Golden & Freshwater, 1978). In-hibition is often incorporated into depletion research on the assumption that partici-pants must regulate their behaviour by inhibiting or suppressing a prepotent response (Wallace & Baumeister, 2002), such as the conflict described above. The Stroop task has been one of the most frequently used outcome measures in depletion research.

The adapted Stroop task (Golden & Freshwater, 1978) requires participants to name as quickly and accurately the colour of the ink that words representing colour names are printed in.

From the executive functioning perspective, the Stroop task has been used as a measure of inhibition. Errors, or delayed responses, under the task have been ex-plained as issues in conflict-resolution processing. The conflict arises from the desire to name the word rather than identifying the colour. However, Dang et al. (2017) also suggested that the Stroop task also involved goal-maintenance, for instance, identify the ink colour, and attempted to distinguish between goal-maintenance and response conflict-resolution under the Stroop task. Their meta-analysis indicated that depletion effects on the Stroop task were a function of whether reaction time or errors were the dependent measure and on the percentage of congruent and incongruent trials within the task (Dang et al., 2017), as outlined in section 2.5. Dang and colleagues (2017) concluded that there was more evidence for the goal-maintenance explanation than for the response conflict-resolution account.

In the current set of studies, the Stroop colour word test (Golden & Freshwa-ter, 1978) has been adopted. The Stroop colour word task (Golden & FreshwaFreshwa-ter, 1978) is a standardised neuropsychological test that is widely used in examining cog-nitive impairment. This version of the Stroop task consists of three subtasks, namely word-reading, colour-naming, and colour-word naming. The word-reading subtask measures reading speed and acts as a control condition for the later incongruent sub-task. The colour-naming subtask is another control condition that requires partici-pants to accurately name colours. Lastly, the colour-word naming subtask consists of all incongruent stimuli, where participants must name the ink colour rather than read

the incongruent colour names. This subtask is assumed to reflect the inhibition fac-tor. Neither of the word reading and colour-naming subtasks should involve execu-tive function processes, as these subtasks do not require execuexecu-tive abilities. As such, there would be no expectation that performance on these subtasks should be related to performance on the letter-crossing task. In contrast, there should be a relationship between letter-crossing ability and performance on the colour-word naming subtask, if executive resources, such as inhibition or goal-maintenance, underpin both.

3.2.2.2. Operation Span task (OSPAN; Turner & Engle, 1989). Working memory tasks have also been widely used in the self-regulation research. Complex span tasks have been the standard for measures of WMC research and feature promi-nently in experiments linking WMC to executive function and executive attention.

The operation span (OSPAN) task has been adopted in the current set of experi-ments. This task consists of two components: a memory component as measured by serial recall and a processing component as measured by responses to mathematical equations. The dual-tasking elements of concurrent storing in memory and mathe-matical processing are why it is broadly accepted as a working memory measure.

However, it is also clear that executive updating is also involved in the task, in that participants have to continually update and maintain multiple items in memory. They have to shift their attention continually between processing and memory components.

They also must form new temporary associations between words and serial position cues, implicating the importance of binding operations. In short, the OSPAN task measures many of the executive attributes that form the basis of the current research.

Furthermore, the OSPAN task has been a successful measure in reliably measuring depletion effects (Schmeichel, 2007). Processes in working memory are also respon-sible in goal representation and attention, suppression of irrelevant material, and the regulation of relevant items; all of which are thought to be critical to self-regulation processing (Hofmann et al., 2012).

Much of the literature that has been cited where the OSPAN task is involved, concentrates only on the memory measure (i.e., the serial recall of word items), as it is this component of the task that is geared to measure memory capacity. In the cur-rent experiments performance on the processing components of the task are also measured (i.e., the responding to mathematical equations). While, binding, updating, and memory components are not required in this aspect of the task, a common execu-tive functioning component may be involved in the task. It is plausible that those

who are efficient executive functioning processors may also be efficient mathematic problem solvers. Thereby, there may be some similarity shown in correlations be-tween letter-crossing task performance and the processing and memory measures, but there may also be unique correlations involving the memory component only.

3.2.2.3. Immediate Serial Recall task (ISR). While complex span tasks have frequently been used in the depletion literature, simple span tasks have been less frequently used. One of the basic assumptions of the working memory literature is that complex span tasks such as digit span, or letter span, or immediate serial recall do not rely upon executive function. Instead, it has been assumed that these tasks re-flect memory rehearsal mechanisms. Much of the evidence supporting this distinc-tion comes from the demonstradistinc-tion that complex span tasks are better predictors of higher order cognitive abilities than simple span tasks (Unsworth & Engle, 2006, 2007). However, this general observation does not account for when the difficulty of the simple span task is increased. Thus, Unsworth and Engle (2006) showed that with short lists in the simple span task, complex span measures were better predictors of higher cognitive abilities than simple span measures. However, with list lengths of five, six or seven items simple span tasks were just as good predictors of higher cog-nitive abilities as complex span tasks. This suggests that as simple span tasks become more difficult, they tend to rely on those same cognitive processes that underpin complex span tasks.

While the individual differences in memory capacity literature argue for sim-ple rehearsal processes underpinning simsim-ple span tasks, formal and computational models of immediate serial recall tasks suggest that more complex processes occur.

Most models argue that memory for serial order is established by the temporary bind-ing of items to position cues (Burgess & Hitch, 1999, 2006; Henson, 1998; Lewan-dowsky & Farrell, 2008). At retrieval, the position cues are used to generate potential candidates for recall with multiple candidates being generated for consideration (Burgess & Hitch, 1999, 2006; Henson, 1998; Lewandowsky & Farrell, 2008). A second step, where response competition is resolved to generate a single item for re-call, is also an essential component of the recall process. Thereby, while common ex-ecutive functioning abilities (i.e., inhibition, switching and updating) do not feature highly in the discussion of immediate serial recall, binding and conflict-resolution are heavily involved in explanations of this task.

In the following experiments an immediate serial recall (ISR) task is em-ployed. On each trial participants recall five words in the order in which they were presented. Task difficulty is manipulated by varying the length of the words that have to be remembered. A robust finding in the serial recall research is that short words are better remembered than long words. Therefore, recall memory for two-syl-lable words are compared to three-syltwo-syl-lable words and four syltwo-syl-lable words in the cur-rent research. The working assumption is that executive function markers will not be observed on the trials containing shorter words. However, it might be the case that such markers will be present on the trials involving the four syllable words.

3.2.2.4. Proactive Interference Immediate Serial Recall task (PI-ISR).

While the ISR task is not typically associated with executive functioning, the task can be adapted to test some of those functions. The fourth outcome task involves the ISR task where proactive interference is manipulated (Tolan & Tehan, 2002). Proac-tive interference is the intrusion of prior memories of items or information with cur-rent memories. In this task, each trial consists of either one block, or list, of four words or two blocks of four words. The one-block trials correspond to the simple ISR task where participants are presented with four words and have to recall those items in their serial order of presentation. In the two-block trials the first block is pre-sented and this is followed by a !, which is a cue for the participant to forget the first block and concentrate on remembering the second block for recall. On these two-block trials, two items from the same semantic category are presented in the lists, one in the first block (i.e., a foil) and one in the second block (i.e., a target). The foil item in the first block is introduced to proactively interfere with the recall of target item in the second block. Thereby two sources of proactive interference may occur: the four to-be-forgotten items in the first block can interfere with the items in the second block, and the to-be-forgotten member of a category in the first block can interfere with the related item in the second block.

All trials involve the temporary bindings of items with their block and serial position within the block. The two-block trials also require updating the to-be-re-membered items, the suppression or inhibition of the items in the first block, and some means of resolving response conflict between targets and foils. Goal-mainte-nance is clearly required to identify and maintain relevant items. Goal-neglect would then result in the intrusion of an irrelevant item or the breaking down of bindings of the relevant to-be-remembered stream of items to their serial positions.

Given the logic involved in the predictions involved in the ISR task, execu-tive function markers should not be involved in the one-block trials but rather, should be evident in the two-block trials. That is, there is no expectation that performance on the letter-crossing task should be related to performance on the one-block trials.

There should be relationships between the letter-crossing task and the two-block tri-als to the extent that both tasks share executive resources.