James Enns

This dissertation explores the hypothesis that cognitive engagement is an important predictor of the relationship between exercise and executive functioning. Chapter 1 introduces the background claim that exercise benefits executive functioning. This includes reviewing the relationship between exercise and improvements in executive functioning via changes in cerebral blood flow and neuroplasticity. The exercise-executive function relationship is also reviewed via literature on exercise history, duration, intensity, and type. This review concludes by introducing the primary hypothesis of this dissertation, namely, that cognitively-engaging exercise should predict better executive functioning. Chapter 2 tested this hypothesis through an empirical study (N = 145) of undergraduates who self-reported their executive function use during exercise, and then completed executive function tasks (i.e., flanker and backward span). Students reporting engagement in exercise that relied on inhibitory control were found to perform better on a flanker task, and students reporting engagement in exercise that relied on cognitive flexibility performed better on a backward span task. Chapter 3 recruited an independent sample of undergraduates (N = 228) and had them complete different executive function tasks (i.e., stop-signal and trail making B). The main finding was that when students reported engaging in exercise that relied on inhibitory control they had faster stop-signal reaction time and made fewer trail making errors, and when they reported engaging in exercise that relied on cognitive flexibility they had slower stop-signal reaction time and trail making completion time. Chapter 4 recruited a more diverse sample of participants (e.g., older, more males; N = 225) and had them complete the same executive function tasks as chapter 2. The main finding was that correlations now ran in opposite directions. When individuals engaged in exercise that relied on inhibitory control, they performed worse on a flanker task, and when they engaged in exercise that relied on cognitive flexibility, they performed worse on a backward span task. Chapter 5 summarizes these findings and speculates that cognitively-engaging exercise may predict better or worse executive functioning depending on the underlying motivation and context driving one to exercise, as well as discussing the potential role of leisure activity.

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Observing others is predicting others. Humans have a natural tendency to make predictions about other people’s future behavior. This predisposition sits at the basis of social cognition: others become accessible to us because we are able to simulate their internal states, and in this way make predictions about their future behavior (Blakemore & Decety, 2001). In this thesis, I examine prediction in the social realm through three main contributions. The first contribution is of a theoretical nature, the second is methodological, and the third contribution is empirical. On the theoretical plane, I present a new framework for cooperative social interactions – the predictive joint-action model, which extends previous models of social interaction (Wolpert, Doya, & Kawato, 2003) to include the higher level goals of joint action and planning (Vesper, Butterfill, Knoblich, & Sebanz, 2010). Action prediction is central to joint-action. A recent theory proposes that social awareness to someone else’s attentional states underlies our ability to predict their future actions (Graziano, 2013). In the methodological realm, I developed a procedure for investigating the role of sensitivity to other’s attention control states in action prediction. This method offers a way to test the hypothesis that humans are sensitive to whether someone’s spatial attention was endogenously controlled (as in the case of choosing to attend towards a particular event) or exogenously controlled (as in the case of attention being prompted by an external event), independent of their sensitivity to the spatial location of that person’s attentional focus. On the empirical front, I present new evidence supporting the hypothesis that social cognition involves the predictive modeling of other’s attentional states. In particular, a series of experiments showed that observers are sensitive to someone else’s attention control and that this sensitivity occurs through an implicit kinematic process linked to social aptitude. In conclusion, I bring these contributions together. I do this by offering an interpretation of the empirical findings through the lens of the theoretical framework, by discussing several limitations of the present work, and by pointing to several questions that emerge from the new findings, thereby outlining avenues for future research on social cognition.

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Previous research has shown that two heads working together can outperform one working alone, but whether such benefits result from social interaction or the statistical facilitation of independent performance is not clear. Here I apply Miller’s (1982; Ulrich, Miller & Schröter, 2007) race model inequality (RMI) model to distinguish between these two possibilities. This model was developed to test whether response times to two signals compared to one were especially fast because the observer could detect a signal in either of two ways (i.e., separate activation models) or because both signals contributed to a common pool of activation (i.e., coactivation models). I explored the independent versus interactive benefits of social collaboration in four experiments. In a first experiment I replicated Miller’s classic finding that coactivation underlies the faster responses to two targets than one during simple visual search by a single individual. However I found that two-person team performance was no faster than the performance of two independent individuals. Reasoning that the division of the cognitive load between collaborators was important to achieving collaborative performance gains, I employed a more complex enumeration visual search task in three subsequent experiments. With this task I found that performance by two-person teams exceeded the fastest possible performance of two independent individuals. This violated Miller’s RMI and indicated that interpersonal interaction produced the collaborative cognition performance gains. I then linked the magnitude of these collaborative gains to features of the interpersonal interaction between team members, including verbal communication, affiliation, and non-verbal communication such as posture, gesture, and body movement. Together these experiments serve as an important proof of concept that Miller’s RMI can be applied to differentiate between the independent and interactive benefits of collaborative cognition. In addition they demonstrate that the interactive benefits of collaborative cognition are influenced by features of the social interaction between collaborators.

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I present new evidence about the relationships between learning and synaesthesia, particularly grapheme-colour synaesthesia, in which individuals experience letters and numbers as coloured. As part of the largest survey of synaesthetic tendencies ever performed, I show that second language acquisition can act as a trigger for the development of synaesthesia, such that children who learn a second language in grade school are three times more likely to develop synaesthesia as native bilinguals. I also demonstrate that previous reports of a sex bias in synaesthesia are almost certainly due to response and compliance biases, rather than any real differences in the prevalence of synaesthesia between men and women. In a detailed examination of the influences of learning on synaesthetic experiences, I show that synaesthetic colours are influenced by knowledge about letters’ shapes, frequencies, alphabetical order, phonology, and categorical qualities. Finally, I demonstrate that synaesthesia can itself be exploited in learning. All these results are presented as supporting a developmental learning hypothesis of synaesthesia, in which synaesthesia develops, at least in part, because it is useful.

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While searching for objects in a cluttered environment, observers confront two tasks: selecting where to search, and identifying the targets. Chapter 1 reviews major theories of visual search, and highlights their approaches to these two functions. While anatomical, neurological, and behavioural evidence suggests dissociation between spatial selection and identity extraction, there is a vast controversy about this issue among visual-search accounts. This review demonstrates that none of these theories has adopted the right tool to independently manipulate the two functions. A new methodology is suggested in which the two functions are manipulated independently using spatial cueing to manipulate localization, and the attentional blink – AB - to manipulate identification (AB: impaired identification of the second of two briefly-displayed sequential targets). In examining the separability of spatial selection and identity extraction, additive-factors logic is adopted: if two factors (here: spatial cueing and AB) influence independent stages of processing, they will have additive effects on the dependent measure. Conversely, whenever additivity occurs, the underlying mechanisms can be assumed to be independent. Experiments in Chapter 2 show that cueing and the AB have additive effects, confirming the hypothesis that the two functions are separable. The results are accounted for by relating them to two major parallel pathways in the visual system: the dorsal and ventral pathways. Based on the characteristics of each pathway, it is plausible to assume that spatial cues (indexing spatial selection) are processed along the dorsal pathway while identification is processed along the ventral pathway. The two functions are therefore separable because they are mediated by mechanisms that are anatomically and functionally distinct.The experiment in Chapter 3 was designed to address contrary evidence regarding the separability of location and identity processing. It shows that those results were due to a procedural, artefactual ceiling. In Chapter 4, a prediction is tested based on the interpretation of results in the first study: if cueing involves both the dorsal and ventral pathways it should interfere with the AB; the results support this prediction. Chapter 5 discusses how these results collectively support the separability of spatial and identity processing, and also discusses future directions.

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Attention is essential to everyday life: without some selective function to guide and limit the processing of incoming information, our visual system would be overwhelmed. A description of the spatiotemporal dynamics of attention is critical to our understanding of this basic human cognitive function and is the primary goal of this dissertation. In particular, the research reported here is aimed at examining two aspects of the spatiotemporal dynamics of attention: a) the rate at which the focus of attention is shrunk and expanded along with the factors that influence this rate, and b) the factorsgoverning whether attention is deployed as either a unitary or a divided focus. The present research examines the spatiotemporal dynamics of focal attention by monitoring the pattern of accuracy that occurs when participants attempt to identify two targets embedded in simultaneously presented streams of items. By asking participants to monitor these streams simultaneously, with the spatial and temporal positions of the two targets in the streams being varied incrementally, it is possible to index the extent of focal attention in both space and time. Chapter 2 develops this behavioural procedure and assesses the rate at which the focus of attention is contracted. A qualitative model is put forward and tested. Chapter 3 examines factors that modulate the temporal course of attentional narrowing in young adults who presumably can exercise efficient control of attentional processes. In contrast, Chapter 4 examines the effect of reduced attentional control by examining the same process in older adults. The second goal of this thesis was to examine whether focal attention is deployed as a unitary or a divided focus. These two perspectives are generally viewed as mutually exclusive. The alternative hypothesis pursued in Chapter 5 is that focal attention can be deployed as either a single, unitary focus or divided into multiple foci, depending on the observers mental set and on the task demands. The final chapter then combines and compares the findings across all experiments and evaluates how they fit in with current theories of visual attention.

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