Moving through varied and complex environments every day is something that most people do with ease. However, if the input from the visual system is unavailable (e.g., damage to the optic nerves or smoke in a burning building), navigating and avoiding obstacles becomes much more demanding. It is therefore desirable to develop a navigation aide for use where visual input has become unavailable. There is a small body of research concerning such navigation aides and their efficacy. However, many issues that may have serious human factors repercussions for such a system are unexplored. This study was conducted in order to examine the effect of an attentionally demanding distractor task on wayfinding performance with an audio only navigation aide, in this case the System for Wearable Audio Navigation (SWAN). The distractor task was found to have a significant impact on wayfinding performance, which decreased when both tasks were performed simultaneously. However, performance on the distractor task improved during this time, in some cases reaching performance levels similar to when the distractor task was performed by itself. This result may be due to participants shifting attention to the task they perceive to be more difficult when asked to do both simultaneously, in this case the distractor task.

This thesis aimed to investigate the benefit of game-based dual-task recumbent bicycle (DT-RC) training among older adults. In addition, the thesis examined the change in cardiac fitness over an 8-week training program. Eleven healthy older adults (70-80 years old) were recruited and received an 8-week dual-task training program; combines a recumbent bicycle with interactive cognitive video games. Outcome measures were collected pre and post the intervention and included measures to assess COP for core balance, spatial-temporal gait variables, performance in visual tracking and cognitive games, neuropsychological tests and HR to workload ratio. Results showed a significant improvement in COP excursion, head tracking and success rate for cognitive games, trails making test and HR to workload ratio decreased by 44%. No significant effects were found for spatial-temporal gait variables. This study shows that the DT-RC program has beneficial effects on dual-task functions and cardiac fitness among healthy older adults.

The increase in the aging population has become one of the most important problems of our society in last few decades. As people grow older, they are at risk of falling and consequent injuries due to the effects of aging. A fall may be the first indication of an undetected illness related to the effects of aging. This study demonstrates the effects of aging on balance, spatio-temporal gait parameters, gaze stability, and cognitive skills under single task conditions and during dual-tasks conditions. In the present study, we included following three groups: Group 1: 30 young healthy adults (aged 20 ± 3 years); Group 2: 30 adults (aged 61.4 ± 4.4 years); Group 3: 30 older adults (aged 75 ± 4.5 years). A computer game based rehabilitation platform has been developed and was used for the single and dual task performance in standing and during treadmill walking. We observed that there was a significant age effect while dual tasking on standing balance, spatial and temporal gait parameters, gaze performance, and cognitive task performance. To conclude, this study shows a vast decline in walking and standing balance and ability to divide attention during dual tasking between the age groups 55-70 years and 71- 85 years and compares both these age groups with the more normative, healthy, young and athletic, 20-30 years old population.

Postural control is the skill developed allowing body equilibrium and orientation, allowing for an efficient interaction with the environment. This skill is developed from birth; the first major landmark is the maintenance of an upright stance of a child, followed by the skill to walk freely (Shumway-Cook & Woollacott, 1985). A second important development occurs between the ages of 7-10 years-old when children start to demonstrate adult-like postural control (Riach & Hayes, 1987). While adults and older adults have shown increased automaticity in postural control in a dual-task (DT) (Potvin-Desrochers, Richer, & Lajoie, 2017), children have not yet been studied. The purpose of this experiment was to determine if children aged 6-7, 8-9, and 10-11 years old would demonstrate better postural stability, and greater postural automaticity in a DT condition than in a postural task (PT). To verify this, children were asked to stand still on a force platform in a PT or in a DT condition (PT with concurrent cognitive task). Results showed that older children had better postural stability, as demonstrated by a smaller sway area (7.20 cm2), reduced sway variability (0.60 cm), and a slower MV of sway (4.70 cm/s) than younger children (12.37 cm2, 0.78 cm, 6.60 cm/s). Older children also had a higher MPF in the PT (0.24 Hz) than in the DT (0.16 Hz). A wavelet transformation revealed a greater contribution of the ultra-low frequency band in the PT (49.9%) than in the DT (46.8%) across all children. These results demonstrated that older children were more stable than younger children. The smaller contribution to the ultra-low band in the DT may be an indication that children rely less heavily on their visual system in the DT. This research shows that children do not demonstrate automaticity of postural control between the ages of 6-11 years.

Why are dual-task costs reduced with ideomotor (IM) compatible tasks (see e.g. Greenwald & Shulman, 1973)? In a series of experiments, I tested the way in which task structure affects dual-task performance (Halvorson et al., 2012). The results suggest that in some cases, typical dual-task costs arise from task structure rather than response limitations. Further examination of this question has shown that dual-task costs cannot be predicted solely on the basis of the relationship between the stimuli and the responses; the relationship between the tasks, or the task pairing, plays a critical role in whether the tasks overlap and performance is impaired. A series of experiments using novel task pairings showed that when one task uses a spatial central code and the other uses a verbal central code, dual-task costs are eliminated.

The present study validates the Treadmill Rehabilitation Platform (TRP) protocol that assessed standing balance performance; spatial and temporal gait variability; stability measures and visual spatial cognitive task performances. Healthy individuals (mean age = 61.4± 4.4 years; n = 30) performed tasks from the TRP protocol while standing and while walking on treadmill. Moderate to High test retest reliability was observed for the TRP tool measures with a few exceptions. Standing balance decreased significantly as visual task load increased. Spatial and temporal gait variability increased whereas walking stability decreased significantly as visual task load increased. Visual task performance decreased significantly as physical load increased. In conclusion, the TRP protocol allows us to assess the ability to prioritize the division of attention when visual spatial cognitive tasks are performed while standing and during walking. Also, it allows reliable assessment of the effects of compromised attention during the tasks performances.

It is generally agreed that language interpreting is cognitively demanding; how- ever, to date there is little evidence to indicate how working memory is involved in the task, perhaps due to methodological limitations. Based on a full considera- tion of key components of interpreting, two series of experiments were conducted to explore how working memory might play a role in discourse and sentence inter- preting. If working memory is implicated both in grammatical encoding into the target language, and in temporary storage of the discourse content, then higher demand in one function might compromise the other. Thus discourses that di er in word orders between languages could increase the processing load and leave less resource for memory maintenance, a ecting recall performance. In Experiment 1, Chinese-English bilingual participants' memory performance was compared when they translated passages from Chinese to English and from English to Chinese, where the expected word order was either congruent or incongruent between source and target. Recall was not sensitive to word order or direction of translation. Per- haps surprisingly, memory for incongruent discourses was numerically better than that for congruent sentences. Experiment 2 showed that interpreting trainees per- formed just like the participants in Experiment 1 did, suggesting that memory performance was not modulated by translation direction in pro cient translators. Experiment 3 explored the relationship between surface form transformation and recall. As discourse paraphrasing did not result in better recall than verbatim recall, it was concluded that the better memory performance for incongruent discourse in- terpreting suggested by Experiment 1 was not the result of active manipulation of word form or word order in interpreting. Finally, a free recall task among native English speakers showed that the incongruent discourses tested in earlier experi- ments were intrinsically more memorable than congruent discourses (Experiment 4). Despite this confound, this series of experiments highlighted the importance of comprehension in interpreting, but it did not rule out the role of working memory in the task. The role of working memory in interpreting was further explored using on-line measures in Experiments 5-8. Experiment 5 replicated a self-paced reading study by Ruiz, Paredes, Macizo, and Bajo (2008), comparing participants’ times to read sentences for translation to those to read them normally. The data showed that participants accessed lexical and syntactic properties of a target language in the reading-for-translation condition when resources were available to them. In order to explore the role of working memory in sentence interpreting, a dual-task paradigm was used in Experiment 6. When participants' working memory was occupied by a secondary task (digit preload), reading times were only different numerically between congruent and incongruent sentences. Crucially, reading times decreased as digit preload increased. Since there were no differences in the interpretations produced or in digit recall, it appears that participants were flexible in their resource allocation, suggesting that processing can be tuned up to optimise performance for concurrent tasks. Experiment 7 refined the procedure in the order of responses for the dual tasks but replicated the results of Experiment 6. A closer examination of participants’ interpretation responses showed that devices that could reduce processing load in target language production may have been strategically employed. Finally, another set of sentences were used in Experiment 8 in an attempt to replicate Experiment 5. A failure to replicate the earlier findings suggested that working memory demand might differ for different syntactic structures in sentence interpreting. All in all, this thesis shows that research in language interpreting benefits by taking a full account of the key components of interpreting. The use of on-line measures allowed us to take a ne-grained approach to the investigation of interpretation processes. It is proposed in this thesis that interpreting research may gain more insight from the data by incorporating some of the theories and methods typically used in research into language production.

Background Limitations in mobility resulting from balance impairments contribute substantially to falls in older adults. Aging also has a detrimental effect on cognition which influences mobility and balance. A low cost treadmill rehabilitation platform (TRP) and a custom computer game that provided single and dual task challenges while standing and walking were used to evaluate standing balance, gait variables, visual tracking and cognition game performances in active young and older adults. Objectives The study objectives were, 1) to determine the differences in performance-based measures of standing balance, treadmill walking, visual tracking and executive cognitive function between young and older adults and 2) to examine the effect of age and dual tasks on performance-based measures of balance, gait, visual tracking and cognition in both groups. Methods Thirty active young adults (Mean age: 26.7± 2 years) and thirty older adults (Mean age 61.4± 4.4 years) performed visual tracking and cognitive game tasks on three different physical and cognitive loads on the TRP. The treadmill was instrumented with a force sense array (FSA) pressure mat to record the centre of foot pressure excursions. A motion sense air mouse (Gyration Elite) mounted on a custom made helmet was used to interact with the on screen cursor of the computer screen to perform visual tracking and cognitive game tasks. Participants were also evaluated for balance using clinical tests. Results During single tasks, younger adults performed better than older adults in the AP direction while older adults demonstrated better balance in the ML direction. Single task walking did not demonstrate a difference between the two groups. During single task cognition, there was no difference during both cognitive games while young adults did better during the closed loop visual tracking task. During the dual tasks, both groups demonstrated a dual task effect in balance, walking and cognitive tasks. Younger adults performed better than older adults in all the physical and cognitive load conditions. Conclusion The study findings provided evidence for discussion on the effects of single and dual tasking conditions in young and older adults. Understanding the effects of dual tasks has important clinical implications because older adults engage themselves in a wide variety of activities that require cognitive, mobility and balance skills simultaneously. Identifying the age at which there is a compromise on the above and providing appropriate interventions would be very useful to prevent falls.

The present study validates the Treadmill Rehabilitation Platform (TRP) protocol that assessed standing balance performance; spatial and temporal gait variability; stability measures and visual spatial cognitive task performances. Healthy individuals (mean age = 61.4± 4.4 years; n = 30) performed tasks from the TRP protocol while standing and while walking on treadmill. Moderate to High test retest reliability was observed for the TRP tool measures with a few exceptions. Standing balance decreased significantly as visual task load increased. Spatial and temporal gait variability increased whereas walking stability decreased significantly as visual task load increased. Visual task performance decreased significantly as physical load increased. In conclusion, the TRP protocol allows us to assess the ability to prioritize the division of attention when visual spatial cognitive tasks are performed while standing and during walking. Also, it allows reliable assessment of the effects of compromised attention during the tasks performances.

Multitasking in background noise may involve greater cognitive processing demands than multitasking in quiet due to an increase in perceptual demands (Rabbitt, 1968; Pichora-Fuller & Schneider, 2000). This study investigated the effect of background noise in the listening environment on the ability of young adults with normal hearing and older adults with sensorineural hearing loss to perceive speech while performing a secondary task. A dual task paradigm, which included word recognition and visual serial recall, was used to examine ability to divide limited processing resources between two tasks. The number of digits to be recalled was varied in order to test the hypothesis that background noise would degrade multitasking abilities to a greater degree than in quiet for more difficult tasks. Participants included 37 native English speakers between 19-25 years of age with pure-tone thresholds better than or equal to 20 dB HL and 10 English speakers between 58-85 years of age with pure-tone thresholds greater than or equal to 25 dB HL in both ears. The results showed that background noise can have negative effects on the ability to multitask for both younger adults with normal hearing and older adults with hearing loss; however, this effect was greater for the older adults with hearing loss, especially when task demands were increased.