Drugs of abuse elicit dopamine release unconditionally, sensitizing the reward system to drugs and drug-associated stimuli resulting in compulsive drug-seeking and drug-taking behaviour. It has been discovered that these same dopamine neurons consistently respond to natural rewards when the reward delivery is at maximum uncertainty (50%). Reward uncertainty is a defining feature of gambling. Therefore, chronic increases in dopamine release from gambling-like stimuli could lead to sensitization of the reward pathways and contribute to gambling pathology. This study investigated the effects of repeated exposure to different probabilities of sucrose reward (0, 25%, 50%, 75%, 100%) on sensitivity to an amphetamine challenge (0.5 mg/kg) and development of sensitization after multiple amphetamine doses (5 x 1.0/kg) in Sprague–Dawley and Lewis rats. No significant group differences were found during the amphetamine challenge or amphetamine sensitization in either strain. Opportunities for improvement in the experimental paradigm and for future research are discussed.

Drugs of abuse elicit dopamine release unconditionally, sensitizing the reward system to drugs and drug-associated stimuli resulting in compulsive drug-seeking and drug-taking behaviour. It has been discovered that these same dopamine neurons consistently respond to natural rewards when the reward delivery is at maximum uncertainty (50%). Reward uncertainty is a defining feature of gambling. Therefore, chronic increases in dopamine release from gambling-like stimuli could lead to sensitization of the reward pathways and contribute to gambling pathology. This study investigated the effects of repeated exposure to different probabilities of sucrose reward (0, 25%, 50%, 75%, 100%) on sensitivity to an amphetamine challenge (0.5 mg/kg) and development of sensitization after multiple amphetamine doses (5 x 1.0/kg) in Sprague–Dawley and Lewis rats. No significant group differences were found during the amphetamine challenge or amphetamine sensitization in either strain. Opportunities for improvement in the experimental paradigm and for future research are discussed.

Humans need to rapidly select movements that achieve their goal while avoiding negative outcomes. The processes leading to these decisions have only recently been studied. In the typical paradigm used to gain insight into the decision process, participants aim to a target circle that is overlapped by a penalty circle. They receive 100 points for hitting the target, and lose points for hitting the penalty region. Previous research has shown that participants generally behave like a rational decision maker by adapting their endpoint when the distance between the target and penalty circle and the penalty value changes (although some suboptimal selection has been noted). The overall purpose of the research reported in the present thesis was to determine if there are contexts when participants’ behaviour is suboptimal in a rapid, motor decision making tasks. Taken together, the results from four studies showed that: 1) participants require experience and feedback to aim to optimal locations; 2) participants often aimed closer to target center than optimal; and, 3) probability (represented through spatial parameters) has more influence over participant’s motor decisions than does the value of the penalty. Therefore, participants’ actions do not necessarily conform to a rational model of decision making; rather, there are consistent biases arising in the selection, planning, and execution of actions in specific contexts. These findings and conclusions can lead to a more descriptive understanding of motor decision making to provide information that is in addition to prescriptive models of rational behaviour.

Humans need to rapidly select movements that achieve their goal while avoiding negative outcomes. The processes leading to these decisions have only recently been studied. In the typical paradigm used to gain insight into the decision process, participants aim to a target circle that is overlapped by a penalty circle. They receive 100 points for hitting the target, and lose points for hitting the penalty region. Previous research has shown that participants generally behave like a rational decision maker by adapting their endpoint when the distance between the target and penalty circle and the penalty value changes (although some suboptimal selection has been noted). The overall purpose of the research reported in the present thesis was to determine if there are contexts when participants’ behaviour is suboptimal in a rapid, motor decision making tasks. Taken together, the results from four studies showed that: 1) participants require experience and feedback to aim to optimal locations; 2) participants often aimed closer to target center than optimal; and, 3) probability (represented through spatial parameters) has more influence over participant’s motor decisions than does the value of the penalty. Therefore, participants’ actions do not necessarily conform to a rational model of decision making; rather, there are consistent biases arising in the selection, planning, and execution of actions in specific contexts. These findings and conclusions can lead to a more descriptive understanding of motor decision making to provide information that is in addition to prescriptive models of rational behaviour.

The present study examined whether infants aged 3 to 9 months displayed an adult-like left visual field bias when processing dynamic faces. In Experiment 1 infants aged 6 to 9 months viewed videos of dynamic face stimuli. Eye tracking data revealed that these infants showed a left visual field bias by attending significantly more to the right side of the faces. In Experiment 2 a younger group of infants, aged 3 to 6 months, failed to demonstrate a group left visual field bias. Instead, some infants displayed a consistent left visual field bias whereas others displayed a consistent right visual field bias. To our knowledge, these findings provide the first eye-tracking evidence to suggest the existence of a left visual field bias in infancy.

Previous work suggests that both concrete (e.g., hat, shoes) and abstract (e.g., god, devil) concepts with spatial associations engage attentional mechanisms, affecting subsequent target processing above or below fixation. Interestingly, both facilitatory and inhibitory effects have been reported to result from compatibility between target location and the meaning of the concept. To determine the conditions for obtaining these disparate effects, we varied the task (detection vs. discrimination), SOA, and concept type (abstract vs. concrete) across a series of experiments. Results suggest that the nature of the concepts underlies the different attentional effects. With abstract concepts, facilitation was observed across tasks and SOAs. With concrete concepts, inhibition was observed during the discrimination task and for short SOAs. Thus, the particular perceptual and metaphorical associations of a concept mediate their subsequent effects on visual target processing.

The present study examined whether infants aged 3 to 9 months displayed an adult-like left visual field bias when processing dynamic faces. In Experiment 1 infants aged 6 to 9 months viewed videos of dynamic face stimuli. Eye tracking data revealed that these infants showed a left visual field bias by attending significantly more to the right side of the faces. In Experiment 2 a younger group of infants, aged 3 to 6 months, failed to demonstrate a group left visual field bias. Instead, some infants displayed a consistent left visual field bias whereas others displayed a consistent right visual field bias. To our knowledge, these findings provide the first eye-tracking evidence to suggest the existence of a left visual field bias in infancy.

Previous work suggests that both concrete (e.g., hat, shoes) and abstract (e.g., god, devil) concepts with spatial associations engage attentional mechanisms, affecting subsequent target processing above or below fixation. Interestingly, both facilitatory and inhibitory effects have been reported to result from compatibility between target location and the meaning of the concept. To determine the conditions for obtaining these disparate effects, we varied the task (detection vs. discrimination), SOA, and concept type (abstract vs. concrete) across a series of experiments. Results suggest that the nature of the concepts underlies the different attentional effects. With abstract concepts, facilitation was observed across tasks and SOAs. With concrete concepts, inhibition was observed during the discrimination task and for short SOAs. Thus, the particular perceptual and metaphorical associations of a concept mediate their subsequent effects on visual target processing.

Lifespan theories of emotion suggest that the ability to regulate emotion improves with age. The supporting evidence, however, is indirect: older adults pay less attention to negative events, remember less negative information, and report fewer experiences of negative emotion. Few studies directly measure emotion regulation by explicitly instructing older adults to modulate their feelings while exposed to emotion-evoking stimuli. The purpose of this thesis was to directly compare younger and older adults in their ability to modulate feelings to investigate whether aging results in decline, stability, or improvement in emotion regulation and also to examine potential mechanisms underlying regulation skills. The study employed a startle modulation paradigm to measure both emotional reactivity and regulation. Two experimental tasks (Stroop colour-word interference, reversal learning) were also administered to explore the relationship between emotion regulation and two theoretically-relevant processes: (a) cognitive control and (b) modification of learned emotional associations. There were three main findings: (1) emotional reactivity was preserved in older adults. Both age groups showed emotion-modulated startle (negative > neutral) during the pre-regulation viewing period; (2) age-related decline in emotion regulation was evident on an objective measure of emotion regulation (startle eyeblink reflex) but not on a subjective measure (self-ratings). Specifically, for older adults, startle eyeblink was not enhanced or attenuated following increase and decrease instructions, respectively. In contrast, both groups showed similar modulation of valence and arousal ratings by regulation instruction (increase > look > decrease); (3) for older adults, reversal learning performance correlated positively with the degree of reappraisal-related startle attenuation in the decrease condition, suggesting a possible mechanism for impaired down-regulation. These findings suggest that even when emotional reactivity is similar, older adults are less effective at modulating their physiological responses.

Recent evidence suggests that the task of managing a bilingual individual’s two languages is carried out by general attentional mechanisms. Researchers have found evidence for bilingual advantages in attention, specifically on tasks that involve inhibiting irrelevant information, which are believed to stem from lifelong practice at inhibiting the language system not currently in use. In the present study we hypothesized that, since bilinguals are better at inhibiting irrelevant information, they should show memory disadvantages if previously irrelevant information becomes relevant. 12 bilingual and 12 monolingual participants (age range:19-27) were tested in an eye tracking paradigm where the relational manipulation effect (the tendency to direct more viewing to manipulated regions of previously viewed scenes) was used to access memory for scenes that had been presented as distractors during a study block. No differences in memory were observed. However, we observed a significant difference in general viewing patterns between the two language groups, such that bilinguals made significantly shorter fixations.