Competing models of eye movement control during reading disagree over the extent to which eye movements reflect ongoing linguistic and lexical processing, as opposed to visual/oculomotor factors (for reviews, see Rayner, 1998, 2009a). To address this controversy, participants’ eye movements were monitored in four experiments that manipulated a wide range of lexical variables. Specifically, Experiment 1 manipulated contextual predictability by presenting target words (e.g., teeth) in a high-predictability prior context (e.g. “The dentist told me to brush my teeth to prevent cavities.”) versus a low-predictability prior context (e.g., “I'm planning to take better care of my teeth to prevent cavities.”), Experiment 2 manipulated lexical ambiguity by presenting biased homographs (e.g., bank, crown, dough) in a subordinate-instantiating versus a dominant-instantiating prior context, and Experiments 3A and 3B manipulated word frequency by contrasting high frequency target words (e.g., table) and low frequency target words (e.g., banjo). In all four experiments, I used distributional analyses to examine the time-course of lexical influences on fixation times. Ex-Gaussian fitting (Staub, White, Drieghe, Hollway, & Rayner, 2010) revealed that all three lexical variables (i.e., predictability, lexical ambiguity, word frequency) were fast-acting enough to shift the entire distribution of fixation times, and a survival analysis technique (Reingold, Reichle, Glaholt, & Sheridan, 2012) revealed rapid lexical effects that emerged as early as 112 ms from the start of the fixation. Building on these findings, Experiments 3A and 3B provided evidence that lexical processing is delayed in an unsegmented text condition that contained numbers instead of spaces (e.g., “John4decided8to5sell9the7table2in3the9garage6sale”), relative to a normal text condition (e.g., “John decided to sell the table in the garage sale”). These findings have implications for ongoing theoretical debates concerning eye movement control, lexical ambiguity resolution, and the role of interword spaces during reading. In particular, the present findings provide strong support for models of eye movement control that assume that lexical influences can have a rapid influence on the majority of fixation durations, and are inconsistent with models that assume that fixation times are primarily determined by visual/oculomotor constraints.

The current study evaluated whether robotic guidance can influence movement planning and/or the use of online proprioceptive feedback. Participants were divided into three groups wherein they practiced an aiming task unassisted or via a robotic device that led them through a trajectory with an asymmetric or symmetric velocity profile. Baseline performance was measured prior to training and a post-test included control and tendon vibration trials. Temporal, spatial, and kinematic variables were used to assess planning and online control mechanisms. Results indicated that tendon vibration altered the way individuals planned their movements and used online sensory feedback. Robotic-guided groups appeared to use online feedback to a lesser extent than the unassisted group during tendon vibration trials, based on kinematic data. Individuals may become less inclined to use erroneous proprioceptive feedback following robotic guidance, supporting the potential benefit of robotics in neuro-motor rehabilitation for those with proprioceptive deficits.

In four experiments on insight problem solving, we investigated the time course of the development of solution knowledge prior to response, as well as the impact of stimulus familiarity on task performance and eye movement measures. In each experiment, participants solved anagram problems while their eye movements were monitored. In Experiments 1a and 1b, each anagram problem consisted of a circular array of letters: a scrambled four-letter solution word containing three consonants and one vowel, and an additional randomly-placed distractor consonant. Viewing times on the distractor consonant compared to the solution consonants provided an online measure of knowledge of the solution. Viewing times on the distractor consonant and the solution consonants were indistinguishable early in the trial. In contrast, several seconds prior to the response, viewing times on the distractor consonant decreased in a gradual manner compared to viewing times on the solution consonants. Importantly, this pattern was obtained across both trials in which participants reported the subjective experience of insight and trials in which they did not. These findings are consistent with the availability of partial knowledge of the solution prior to such information being accessible to subjective phenomenal awareness. In Experiments 2 and 3, each anagram problem consisted of a centrally located three-letter string plus three additional individual letters located above and to the side of the central letter string. All the letters in the central letter string were members of the five-letter solution word, while one of the individual letters was a randomly placed distractor. In Experiment 2, we replicated our findings of the gradual development of solution knowledge using this more complex stimulus display. In Experiment 3, we manipulated the familiarity of the central letter string by presenting it either in the form of a three-letter word, or as a meaningless string of letters. Behavioural measures showed an overall negative impact of familiarity on task performance, while eye movement measures revealed a more complex pattern of effects, including both interference and facilitation. Critically, the effects of familiarity on problem solving did not interact with the development of solution knowledge prior to response.

Master of Science / Department of Psychological Sciences / Kimberly Kirkpatrick / The present experiments examined the effect of different uncertain-reward magnitudes (i.e., gains and losses) on global and local probabilistic choice behavior in rats. In two experiments, rats were given a choice between a variable-amount certain outcome that delivered 2 or 4 pellets and a variable-amount uncertain outcome that probabilistically delivered a larger reward. In Experiment 1, the larger uncertain outcome was always 11 pellets and different groups received 1, 2, or 4 pellets for the uncertain small reward. In Experiment 2, the uncertain small reward was always 4 pellets and different groups received 6, 9, or 11 pellets for the uncertain large reward. In both experiments, the rats increased their uncertain choice behavior with the probability of uncertain food. In Experiment 1, the magnitude of the uncertain small outcome affected choice behavior; there was no such effect of the uncertain large reward magnitude in Experiment 2. The group differences in choice behavior suggest that the expected value of the certain choice served as a reference point distinguishing uncertain gains and losses, and that the rats exhibited differential sensitivities to such outcomes. As some extant theoretical frameworks of choice behavior seem unable to account for all of the present data, a possible mechanism for the present results is proposed. These results emphasize the importance of identifying the choice outcomes that constitute gains and losses in animals such that the effects of prior uncertain gains and losses on subsequent choice behavior can be adequately and comprehensively understood.

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When seen through a stereoscope, a Gabor pattern (a Gaussian enveloped sinusoid) that is masked by visual noise is more readily detectable when it appears in front of or behind the noise than when it is embedded in the noise itself. The enhanced visibility brought about by stereo cues is referred to as binocular unmasking. In this work, we investigated whether binocular unmasking may also occur with visual objects more complex than simple Gabor patterns, and with tasks more demanding than detection. Specifically, we examined the effects of binocular unmasking in the detection, categorization, and identification of noise masked images of natural objects. We observed the occurrence of binocular unmasking in all three tasks. However, the size of this effect was greater for detection performance than for categorization or identification performance; the latter two benefited to the same extent by the availability of stereoscopic cues. We argue that these results suggest that low level stereoscopic depth cues may play a helpful role, not only in simple detection tasks with psychophysical stimuli, but also in the perception of complex stimuli depicting natural objects.

Feature binding refers to the fundamental challenge of the brain to integrate sensory information registered by distinct brain regions to form a unified neural representation of a stimulus. While the human cognitive literature has established that attentional processes in a frontoparietal cortical network support feature binding, the neurochemical contributions to this attentional process remain unknown. Using systemic administration of the cholinergic muscarinic receptor antagonist scopolamine and a digging-based rat feature binding task that used both odor and texture stimuli, it was demonstrated that blockade of acetylcholine (ACh) at the muscarinic receptors impaired rats’ ability to feature bind at encoding, and it was proposed that ACh may support the attentional processes necessary for feature binding (Botly & De Rosa, 2007). This series of experiments further investigated a role for ACh and the cholinergic basal forebrain (BF) in feature binding. In Experiment 1, a cross-species experimental design was employed in which rats under the systemic influence of scopolamine and human participants under divided-attention performed comparable feature binding tasks using odor stimuli for rats and coloured-shape visual stimuli for humans. Given the comparable performance impairments demonstrated by both species, Experiment 1 suggested that ACh acting at muscarinic receptors supports the attentional processes necessary for feature binding at encoding. Experiments 2-4 investigated the functional neuroanatomy of feature binding using bilateral quisqualic acid excitotoxic (Experiment 2) and 192 IgG-saporin cholinergic immunotoxic (Experiments 3 and 4) brain lesions that were assessed for completeness using histological and immunohistological analyses. Using the crossmodal digging-based rat feature binding task, Experiment 2 revealed that the nucleus basalis magnocellularis (NBM) of the BF is critically involved in feature binding, and Experiment 3 revealed that cholinergic neurons in the NBM are necessary for feature binding at encoding. Lastly, in Experiment 4, rats performed visual search, the standard test of feature binding in humans, with touchscreen-equipped operant chambers. Here it was also revealed that cholinergic neurons in the NBM of the BF are critical for efficient visual search. Taken together, these behavioural, pharmacological, and brain-lesion findings have provided insights into the neurochemical contributions to the fundamental attentional process of feature binding.

Previous research suggests that the amount of food that women eat may fluctuate depending on their impression-management motivation; however, the results do not provide direct evidence supporting such an explanation. That is, no studies conducted to date have actually manipulated impression-management motivation and measured its effects on eating behavior. The present program of research aimed to confirm that eating behavior in women does, in fact, change as a result of impression-management motivation. Experiments 1, 2, and 3 tested this by manipulating impression-management motivation via direct and explicit instructions. Experiment 3 was also designed to investigate how impression-management motivation might affect eating in situations in which females are eating with a friend (as opposed to a stranger). The results demonstrate that women motivated to make a good impression on a male stranger (Experiments 1 & 2) and a female stranger (Experiments 2 & 3) eat less than do those for whom the desire to make a positive impression has been disrupted. The results also confirm previous findings showing that women eat less when eating with a male stranger than when eating with a female stranger (Experiments 1 & 2). The findings from Experiment 3 suggest that there may be a different pattern of eating associated with impression-management motivation when women eat with female friends; it was found that participants ate more with a friend when they were motivated to make a good impression compared to when this motive was not present. These results may be explained by impression-management theory, in combination with notions about the complexity of female friendships and female-female competition surrounding eating, dieting, weight, and appearance.

Two studies were devised to determine why the difference in manual aiming performance, between full vision and no vision, is decreased for a randomized visual feedback schedule. In study one, aiming accuracy and precision was assessed for up to four trials in the same vision condition, following a switch in visual feedback availability. In experiment one, visual feedback availability was uncertain; while in experiment two, certainty was provided. Results of both experiments revealed that the precision of the first trial immediately following the switch in visual condition was reminiscent of the trial that preceded it, even when performed under different visual conditions. For study two, the inter-trial interval was evaluated by extending the interval to five seconds. Results indicated no reminiscence effect. Overall, we suggest that when the inter-trial trial is brief, individuals rely on offline visual information from the preceding trial to plan the subsequent movement, regardless of certainty.

This study investigated the neuroplastic changes that accompany speech identification training using magnetoencephalography (MEG). Participants completed three practice sessions over two consecutive days. In the morning group, practice occurred in the morning and evening of the first day, and in the morning of the next day; whereas, in the evening group, practice occured in the evening of the first day, and in the morning and evening of the second day. In both groups, behavioural improvement between the first session and last session was comparable. Neuromagnetic data showed practice-related changes in N1m amplitude between the first and last sessions. A time-of-day (TOD) of practice effect was found for P2m mean amplitude. In both groups, P2m-related changes with practice were greater when consecutive sessions occurred between days than within a day. The results are consistent with the proposal that task-related changes in the P2m wave are an index of perceptual learning.