Comparación de resultados con los dos escenarios, actividades ambientales del contratista y programas ambiental propuestos. Vía a cielo abierto

The goal of this project was to investigate attention in aphasia from a domain-general perspective, with a particular focus on intra-individual variability (IIV) in attention over time. We began by offering a schema for understanding attention and language in aphasia, followed by two experiments that examined the effect of task demands on IIV in attention in both PWA and healthy controls.

In Chapter 2 we presented a theoretical framework for understanding the relationship between attention, language processing, and IIV in aphasia, taking into account the impact of brain injury on these constructs and the possible impact of IIV on language assessment and treatment in PWA. The schema (See Figure 6.1) suggests that when considering attention in aphasia, it is important to take into account the existence of multiple types of attention, some of which are more complex – or more demanding – than others. It also suggests that

attention, as a domain-general, gateway process, helps to support speech- language processing. However, the schema also suggests that brain damage can impact attention and language differentially – in other words, even though attention has an impact on language, brain damage can impact these two processes in different ways. Finally, it proposes that task demands – both attentional demands and language processing demands – can impact IIV in performance, and, finally, proposes a possible causal link between IIV and performance on language assessments, as well as on language treatment

this schema in mind.

Figure 6.1. Schema described in Chapter 2 of this manuscript

The results of the first experiment, described in Chapter 4, showed that PWA exhibited higher levels of BS-IIV than did healthy controls. This provided evidence that BS-IIV in attention is increased in PWA even in situations where no language processing is required. This suggests that between-session fluctuations in attention are pervasive in PWA across a wide variety of tasks, which in turn suggests that BS-IIV in attention is an important metric to further examine in PWA. Additionally, results from the first experiment showed a task effect on BS- IIV for the PWA group, such that increased task demands elicited higher degrees

of BS-IIV, whereas this pattern was not observed for controls. This suggests that in more complex environments with more attentional demands, PWA may

experience additional breakdowns in attention that are not experienced by healthy individuals. Finally, the fact that this experiment did not uncover any significant associations between IIV in attention and scores on language measures suggests that while attention, as a domain-general process, may provide support for language processing, one cannot necessarily predict an individual’s language ability based on the degree of between-session fluctuations in their attention over time. The results of this experiment help to validate the theoretical schema, providing evidence that not only do PWA exhibit impaired attention, they also exhibit IIV in performance on attention tasks, and,

furthermore, that IIV is dependent on task demands.

The results of the second experiment, described in Chapter 5, did not reveal group differences in BS-IIV in attention. As discussed previously, there are several factors that may have influenced this result. For one thing, the first and second experiments were fundamentally different from each other due to the use of different tasks: the first experiment consisted of a fine-grained analysis of BS- IIV in both visual and auditory non-linguistic attention, while the second

experiment had a broader scope, as well as a particular focus on language elements and multimodal integration. The difference in results may also have been due in part to differences in the order of task administration. Another factor may have been the BS-COV adjustments that were necessary in the second

experiment – a phenomenon which was also likely a function of task demands. The implication of these collective results is that IIV is fundamentally task-

dependent in nature: the particular demands involved in a task or situation have a major impact on the levels of BS-IIV and WS-IIV that are observed.

Independent of the differences between the two experiments, task effects were a major theme throughout the course of this project. Both experiments showed that adding task demands/complexity elicited higher degrees of intra- individual variability in PWA, and that this was true for both BS-IIV and WS-IIV. In the second experiment, this pattern was in fact observed to some degree for controls as well as for PWA. However, one important difference between the two groups was that when true language processing demands were added to a task, levels of BS-IIV and WS-IIV appeared to increase more for PWA than for

controls. This is an important finding because it indicates that even very simple language processing demands can cause increased attentional fluctuations in PWA.

While the second experiment did not uncover group differences in BS-IIV in attention, it did uncover group differences in WS-IIV in attention, providing evidence that PWA exhibit increased variability in performance from moment to moment, relative to healthy age-matched controls. These findings may have important implications for understanding attention deficits in PWA. The fact that a significant group effect was found, such that PWA exhibited higher degrees of WS-IIV than controls, aligns with findings from other neurologically impaired

populations. It seems that brain damage – even brain damage of which language impairments are the most salient consequence – increases the degree of

moment-to-moment fluctuations in attention on both domain-general and

language-specific tasks. Additionally, not only was WS-IIV found to be higher in PWA than in controls, it was also found to correlate well with scores on several standardized tests measuring both linguistic and non-linguistic tasks. This suggests that PWA exhibit increased WS-IIV on a very fundamental, domain- general level, and that this in turn pervades many different types of tasks.

These results are not surprising – as discussed throughout this

manuscript, attention is by nature a time-based construct, so fluctuations over time would be expected to impact it in a meaningful way. However, little research had previously been directed at this dimension of attention in PWA. The one study that had previously investigated WS-IIV in attention in aphasia looked only at standard deviations of reaction times and did not examine the impact of task demands (King, 1995). Our results are therefore unique in the field of aphasia research thus far and provide an important foundation for other work specifically looking at WS-IIV in aphasia.

Interestingly, little evidence was found of associations between BS-IIV and WS-IIV in attention, suggesting that these two indices of variability may represent two separate constructs, perhaps differentially impacting treatment. This lack of association was underscored by the two cluster analyses examining inter-

each of the two types of IIV, the specifics of cluster membership were different across the two types: for instance, a PWA who exhibited a high BS-COV.adj on a given task would not necessarily exhibit a high WS-COV on the same task, and vice versa. These findings necessitate one final update of the schema, as shown in Figure 6.2.

Figure 6.2. Revised Schema Allowing for Differential Impact of

Task Demands on the Two Types of IIV

This lack of association between BS-IIV and WS-IIV is not unexpected, as previous research on BS-IIV and WS-IIV suggests that these two types of

variability may stem from different sources. Relatively little is known about the causes of BS-IIV, but it has been theorized that it may be a function of

or other factors that might cause an individual to feel that she is having a “good day” or a “bad day” (Sliwinski, Smyth, Hofer, & Stawski, 2006), and that it is therefore somewhat of a behavioral construct. WS-IIV, on the other hand, is thought to be related to endogenous factors, i.e., it may be somewhat more physiologically based. In a 2009 review, MacDonald and colleagues discuss a variety of possible causes of WS-IIV, including aspects of brain structure and function, as well as alterations in the activity of neurotransmitters such as

dopamine (MacDonald, Li, & Bäckman, 2009). A more recent fMRI study on the neural correlates of WS-IIV also revealed an apparently complex interplay between the default mode network and active attentional networks in the brain (Esterman, Noonan, Rosenberg, & DeGutis, 2012).

Collectively, the results of these experiments suggest that both WS-IIV and BS-IIV are important dimensions of performance to consider in aphasia and may turn out to have important long-term implications for understanding attention in PWA, particularly as it may relate to treatment outcomes. Despite the fact that PWA have, as a group, been shown to have deficits in attention processing, relatively little consideration has been given to the possible impact of these attentional deficits on language therapy situations. It is important to remember that a language therapy session is a complex environment that likely places high demands on the attentional system. An individual therapy session includes both language processing demands and high attentional demands, as well as

two hours. A lack of consistent attention within a single session may have a substantial negative impact on the benefits that the patient is able to reap from that session. Our finding that IIV increases even more when even simple language demands are added becomes particularly important here, as it suggests that the challenging linguistic aspects of a language therapy session could drive BS-IIV and/or WS-IIV up even further. Again, our finding of

decrements in attention performance when language demands are added is consistent with earlier work suggesting that language and attention demands interact with each other, resulting in decreased performance in PWA (Murray, Holland, & Beeson, 1998, Hula, McNeil, & Sung, 2007).

The findings of this project – specifically, that PWA experience higher degrees of fluctuations in their ability to attend than their healthy, age-matched counterparts, and that PWA experience increased fluctuations in attention when task demands are increased and language demands are added – suggest that fluctuations in attention are important to examine more closely in aphasia. Our finding of inter-individual differences in BS-IIV and WS-IIV among PWA points to IIV as a possible explanation for why some PWA show greater improvement in therapy than others. Future research should look directly at the relationship between IIV in attention and improvement in a therapy program over time.

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