Head position signal is crucial for preparing reaching movements because it contributes to specifying the position of body and target in space and relative to each other. However, it is unclear whether sensory information pertaining head position is used to control the movement after movement onset. In this study, nineteen participants performed discrete reaches towards a virtual target while neck vibration was randomly applied before and/or during the movement or not at all. The main dependent variable was the directional bias of the reaching finger. Neck vibration induced early leftward or late rightward trajectory biases. It appears that participants interpreted the sensed head shift as a target or an eye-in-head motion, which can be explained by individual differences in the use of reference frames. Nevertheless, body-centered and head-centered frames of reference appear to be important for the early and late stages of a goal-directed movement, respectively.

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.

Head position signal is crucial for preparing reaching movements because it contributes to specifying the position of body and target in space and relative to each other. However, it is unclear whether sensory information pertaining head position is used to control the movement after movement onset. In this study, nineteen participants performed discrete reaches towards a virtual target while neck vibration was randomly applied before and/or during the movement or not at all. The main dependent variable was the directional bias of the reaching finger. Neck vibration induced early leftward or late rightward trajectory biases. It appears that participants interpreted the sensed head shift as a target or an eye-in-head motion, which can be explained by individual differences in the use of reference frames. Nevertheless, body-centered and head-centered frames of reference appear to be important for the early and late stages of a goal-directed movement, respectively.

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.

Children with traumatic brain injury (TBI) often experience difficulties with inhibitory control (IC), manifest in both neurocognitive function (poor performance on the stop signal task, SST) and behavior (emergence of de novo attention-deficit/hyperactivity disorder, or secondary ADHD, S-ADHD). IC allows for the regulation of thought and action, and interacts with reward to modify behaviour adaptively as environments change. Children with developmental or primary ADHD (P-ADHD) exhibit poor IC and abnormalities when responding to rewards, yet the extent to which S-ADHD is similar to and different from P-ADHD in terms of these behaviours is not well-characterized. The cancellation and restraint versions of the SST were used to examine the effects of rewards on 2 distinct forms of IC in children and adolescents divided into 4 groups (control, TBI, S-ADHD, and P-ADHD). The SST requires participants to respond to a “go signal” and inhibit their responses when encountering a “stop signal”. Rewards improved performance similarly across groups, ages, and cancellation and restraint IC tasks. Adolescents exhibited better IC and faster and less variable response execution relative to children. Significant IC deficits were found in both tasks in the P-ADHD group, with participants with S-ADHD exhibiting intermediate cancellation performance relative to the other groups. Participants with TBI without S-ADHD were not impaired on either task. The relationship between neurocognitive and behavioral IC was examined by comparing multi-informant ratings of IC across groups, and examining the relationship between ratings and IC performance on the SST. Participants in the control and TBI groups were rated within the typical range, and exhibited fewer problems than either of the ADHD groups, who differed from each other (the P-ADHD group was rated as more inattentive than the S-ADHD group). Moderate to high concordance was found between parent and teacher reports, each of which was poorly concordant with self-reports. The P-ADHD and S-ADHD groups were unaware of their own deficits. Poorer IC predicted parent and teacher classification of participants into ADHD subtypes, although IC did not predict rating concordance. Despite similar clinical presentations, S-ADHD and P-ADHD differ in the phenotypic expression of behaviour and manifestation of IC across contexts.

Users of cochlear implants typically have difficulty differentiating talkers, identifying vocal expressions of emotion, and recognizing familiar melodies because of the degraded spectral cues provided by conventional implants. This thesis examined these abilities in a small, relatively privileged sample of young bilateral implant users. In Study 1 child implant users and a control sample of hearing children were required to judge whether various utterances were produced by a man, woman, or girl (Experiment 1) and to identify the voices of cartoon characters from familiar television programs (Experiment 2). Child implant users’ performance on talker classification was comparable to that of hearing children. Their identification of cartoon characters’ voices was less accurate than that of hearing children but well above chance levels. These findings challenge conventional wisdom about the talker identification difficulties of implant users. In Study 2 the children were required to indicate whether semantically neutral utterances (Experiment 1) or classical piano excerpts (Experiment 2) sounded “happy” or “sad”. In both cases, implant users performed less accurately than hearing children but well above chance levels. Although the findings on emotion recognition in music are in line with those of previous research, the findings on emotion in speech are at odds with claims that young implant users are insensitive to vocal affect. In Study 3 the children were required to identify the theme songs from familiar television programs on the basis of combined timing and pitch cues as well as timing or pitch cues alone. Implant users’ performance was comparable to that of hearing children except when the cues were restricted to pitch relations, which resulted in performance at chance levels. The findings suggest that the musical representations of young implanted listeners include precise information about timing and coarser information about pitch. They also demonstrate, for the first time, that children, both implant users and those with normal hearing, can identify familiar music on the basis of timing cues alone. Overall, the findings highlight the importance of timing cues for implant users, the range of individual differences, and habilitation possibilities for the recognition of talkers, emotion, and music.

Speaker identification is a challenge for cochlear implant users because their prosthesis restricts access to the cues that underlie natural voice quality. The present thesis examined speaker recognition in the context of spectrally degraded sentences. The listeners of interest were child implant users who were prelingually deaf as well as hearing children and adults who listened to speech via vocoder simulations of implant processing. Study 1 focused on child implant users' identification of a highly salient speaker—the mother (identified as mother)—and unfamiliar speakers varying in age and gender (identified as man, woman, or girl). In a further experiment, children were required to differentiate their mother's voice from the voices of unfamiliar women. Young hearing children were tested on the same tasks and stimuli. Although child implant users performed more poorly than hearing children overall, they successfully differentiated their mother's voice from other voices. In fact, their performance surpassed expectations based on previous studies of child and adult implant users. Even when natural variations in speaking style were reduced, child implant users successfully identified the speakers. The findings imply that person-specific differences in articulatory style contributed to implanted children's successful performance. Study 2 used vocoder simulations of cochlear implant processing to vary the spectral content of sentences produced by the man, woman, and girl from Study 1. The ability of children (5-7 years and 10-12 years) and adults with normal hearing to identify the speakers was affected by the level of spectral degradation and by the gender of the speaker. Female voices were more difficult to identify than was the man's voice, especially for the younger children. In some respects, hearing individuals' identification of degraded voices was poorer than that of child implant users in Study 1. In a further experiment, hearing children and adults were required to provide verbatim repetitions of spectrally degraded sentences. Their performance on this task greatly exceeded their performance on speaker identification at comparable levels of spectral degradation. The present findings underline the importance of ecologically valid materials and methods when assessing speaker identification, especially in children. Moreover, they raise questions about the efficacy of vocoder models for the study of speaker identification in cochlear implant users.