Strengths and Limitations

This study was designed to provide a more detailed understanding of how various concurrent tasks would affect speech intensity levels in individuals with Parkinson’s disease. In doing so, novel tasks were created with varying levels of difficulty. The experimental design of the study is one of its strengths, as previous research had not taken into account how task novelty and task difficulty would affect concurrent task performance and instead utilized familiar tasks that were relatively easy to perform, such as counting (Ho et al., 2002). In using novel tasks, this study was able to examine how an individual’s speech intensity may change as they adjust to the demands of the task at hand.

Although this study did reveal a substantial amount of new information about the relationship between concurrent task performance and speech intensity, there are certain methodological limitations that need to be considered. The main limitations of this study can be grouped into two categories; sample and participant characteristics, and task – related limitations.

4.4.1

Sample and Participant Characteristics

The first limitation of this study is related to sample size. Data were collected from twenty-two healthy older adults and thirteen individuals with idiopathic Parkinson’s disease. Subtle differences between tasks may have been too small to be detected with the current sample size for the experimental group, which may explain why certain main effects and interactions did not reach significance. Another possible limitation related to participant characteristics is the participants’ cognitive ability. Each participant with Parkinson’s disease was given the MoCA. The control participants did not complete a cognitive screening tool such as the MoCA. This is a limitation of the study because some of the normal participants may have had an undetected mild cognitive impairment that influenced the results.

4.4.2

Task-Related

Additional limitations of the study may be related to the type of tasks that were used. First and foremost, it was difficult to design tasks that did not require the use of multiple modalities at once. For example, in the case of the cognitive task, the participant was required to solve the math question, and then verbally report it. This does require the engagement of various mental processes that would be likely to overlap with processes that would be used in the linguistic task and the motor task. The overlapping of activated processes across tasks prevents direct conclusions about which processes may be more inhibitory or affected during concurrent task performance. In addition to this, it cannot be explicitly stated as to whether the participants were performing the tasks concurrently or serially. The tasks were created in order to promote concurrent processing but it is not possible to be absolutely certain that concurrent processing of the tasks occurred. Due to the methodology of this study, the subjects’ performance on the concurrent tasks could have been influenced by practice effects. No difference was found between the

concurrent and non-concurrent (isolated) tasks. But the study design required the isolation task to always be performed before the corresponding concurrent task.

Therefore, each time the isolation task was completed, the participant was learning how to perform the task, whereas when they performed the concurrent task, they already knew what to expect and how to complete the task.

An additional concern is that performance on the concurrent tasks could have been confounded by fatigue, as they were always performed second to the isolation tasks, therefore later in the testing session. Depending on the subject’s performance, this could have ranged in time from 15 minutes into the session to an hour after the session began. Ideally, to solve these issues, practice trials for each task would have been performed, and then the isolation and concurrent task conditions counterbalanced across participants to eliminate the potential for practice and fatigue effects. Another limitation of this study relates to the creation of the verb generation task. The initial noun list used in the pilot study was taken from Del Missiers and Crescentini (2011) study of Italian noun-verb associations and was translated into English. The generated list of nouns was then given to 50 undergraduate students to complete. The association and selection strength for each

noun-verb pair was based on the responses provided by the undergraduate students. It was assumed that the noun-verb association results obtained from this preliminary study of young individuals would predict the performance of the older participants but there may have been age-related factors that influenced the results related to the differences across difficulty levels in the linguistic (noun-verb generation) task. The verb generation task was developed via the preliminary study of younger adults primarily because of time constraints and the availability of young volunteers; however, for future studies involving older Parkinson participants, a verb generation task should be piloted and designed on a healthy older adult population.

A concern for the linguistic task and cognitive task is the possible effect of the syllable length of the target response on the intensity values. For example, as the difficulty level of math task increased the syllable length of the target responses by the participants also increased (i.e. the number six was an answer for the low difficulty level whereas twenty-three was an answer for a higher difficulty level).