Cognitive and Linguistic Task Performance

Performance scores for the cognitive and linguistic tasks were scored out of 15, with 0 being the lowest score possible, and a score of 15 being the highest score

obtainable. Performance scores for these two tasks were collected and compared across groups, task condition, task type and difficulty level.

The cognitive and linguistic task performance was associated with a significant difference between the participant groups. The control participants had significantly higher cognitive and linguistic performance scores than the participants with Parkinson’s disease. The difference in task performance between these groups could be attributed to cognitive decline in executive functioning for those with Parkinson’s disease. Individuals with Parkinson’s disease have displayed working memory impairments and language problems (Bastiaanse & Leenders, 2009; Pagonabarraga & Kuliesevsky, 2012). Deficits in these areas would inhibit an individual’s ability to manipulate the presented stimuli to accurately answer the question (Theodoros & Ramig, 2011), which could explain the difference in scores between the control group and the participants with Parkinson’s disease. In this study, scores for the cognitive task were comparable between both

groups, with each group scoring 4.80 (control) and 4.78 (Parkinson’s disease) out of 5 for each difficulty level. A greater difference in task score was observed for the linguistic task, with the controls scoring 4.08 out of a possible 5, and the participants with Parkinson’s disease scoring 2.62 out of 5. Greater impairment was found for the linguistic task, a result that has been observed in previous studies. Bastiaanse and

Leenders (2009), Crescentini et al. (2008) and Péran et al. (2003) found significant differences in verb production between healthy older adults and individuals with

Parkinson’s disease. The poor performance given by the Parkinson’s disease participants was explained through deficits in non-linguistic cognitive functions, namely verbal working memory.

Interestingly, task condition was not found to be significant for task performance for the cognitive and linguistic tasks. It could be suggested, from this data set, that performance was not enhanced or degraded by concurrent task performance but that instead, the participants in both groups were able to meet the demands on concurrent task performance and performed equally as well under these conditions. This result was surprising given that previous research by McKinlay, Grace, Dalrymple-Alford and Roger (2010) and Pagonabarraga & Kuliesevsky (2012) found that individuals with Parkinson’s disease often struggle to perform tasks concurrently. A trade-off theory of cognitive resources across tasks may be responsible for the result found in this study. Participants may have tried to focus more efforts on maximizing their performance on the secondary task, drawing attentional resources away from the speech task. This trade-off of cognitive resources had been previously observed by Holmes, Jenkins, Johnson, Adams and Spaulding (2010) in their study of postural stability and speech for those with Parkinson’s disease. In this study, individuals with Parkinson’s disease were found to over-constrain their posture prior to performing the speech task and postural task concurrently. By doing this, it is proposed that an individual would be able to allocate more attention and effort to performing the second task. However, this “posture-first” principle diminished the individual’s ability to adapt and maintain stability as the tasks progressed. Similar results were found by Li, Abbud, Fraser and DeMont (2012) in a study assessing the effect of a concurrent cognitive task on gait. The participants were able to maintain their performance on a secondary task by prioritizing performance for the cognitive task over gait. The cognitive task did not experience any dual-task costs, however, stride length and duration increased to compensate. This same principle of task prioritization may have been at work in this study, as individuals focused more attention on trying to complete the cognitive and linguistic task, and in turn, reduced their ability to regulate their speech production.

Scores for both groups were found to be significantly higher for the cognitive task than for the linguistic task. It can be interpreted that both the healthy older adults and the participants with Parkinson’s disease found the linguistic task to be more challenging than the cognitive task. Dromey and Benson (2003) found a similar result. In looking at lip kinematics, Dromey and Benson (2003) discovered that greater kinematic errors were made, as well as an increase in the spatiotemporal index, suggesting that the verb

generation linguistic task affected the speech production process more than the cognitive or motor task. Dromey and Bates (2005) also found higher scores for their cognitive task (two-digit math subtraction problems) in both the isolation and concurrent speech

conditions, than the linguistic task (sentence generation) in either condition. These results indicate that participants may find the linguistic task more difficult than the cognitive task due to overlapping processes with speech production (Dromey & Benson, 2003).

Performance for both groups decreased within each difficulty level as the task increased in difficulty. This result is contrary to the hypothesis based on the energizing effect. Increasing the difficulty for the task did not result in improved performance based on the energizing effect theory, but instead showed a decrease in performance. Fraser, Li and Penhune (2010) found that task performance for a semantic judgment task decreased as difficulty level increased in both young adults and healthy older adults. This decrease in performance could be attributed to the increased cognitive demands placed on the individual and his/her inability to meet the demands of the task as required. As the task difficulty increased, more cognitive resources were required for accurate performance. In using a limited capacity system, such as the episodic buffer in working memory, the system may become overloaded by the increase in cognitive effort, resulting in an increase in performance errors (Baddeley, 2000). The increase in task demands as difficulty level increased may have challenged the participants’ working memory capacity, which in turn presented itself as a difficulty level effect.

The control participants and participants with Parkinson’s disease performed similarly on the cognitive task, however, the individuals with Parkinson’s disease performed significantly poorer on the linguistic task. Conclusions about task difficulty

can be derived from this result. Both groups performed similarly for the cognitive task. From this, it is suggested that the processes required for mathematical addition may be less affected in Parkinson’s disease than the verb-related language processes required for the linguistic task. Verb production deficits have been found to be associated with Parkinson’s disease (Bastiaanse & Leenders, 2009; Crescentini et al., 2008). This could account for the degraded performance by the group with Parkinson’s disease for the linguistic task when compared to the healthy controls.

It should be noted that the healthy controls also had lower performance on the linguistic task relative to the cognitive task and there was a significant task type by difficulty level interaction. This interaction was related to the finding that both groups performed significantly worse on the linguistic task as the difficulty level of the task increased, whereas performance remained fairly stable for the cognitive task as difficulty increased. Evidence from this analysis suggests that the participants in both groups found the linguistic task more difficult than the cognitive task.