Psychology, Cognitive

When adults attempt to learn new speech sounds, they do so in the context of the phonology of their native language. The purpose of the present work is to investigate the nature of the learning process; that is, to examine, in individuals, (1) the process of acquiring a new phonetic category, (2) the impact of learning a new phonetic category on a similar, existing category, and (3) transfer of learning to a novel phonetic context. Monolingual American English speakers were required to learn the Hindi voiced, unaspirated, dental stop consonant. Two synthetic speech continua (one voiced, the other voiceless) were created, spanning a range from Hindi dental to American English alveolar stop consonants. Subjects underwent a perceptual mapping procedure that included identification, judged goodness, and difference-rating tasks in order to establish how they perceived the stimuli initially. Then they participated in a two-alternative, forced-choice training program using only voiced, natural speech stimuli. Progress was monitored throughout training. Following training, the mapping procedure was repeated with both the voiced and voiceless continua. After at least a two-week delay with no further training, subjects participated in a follow-up test. Results indicate that the nature of change during the learning process depends on how the individual listener perceives the stimuli prior to training and on the order of presentation of stimuli.

Mismatch Negativity (MMN) is a component of the event-related potential (ERP) that is associated with the detection of novel stimuli in one's environment. Naatanen has suggested that a neural template theory provides the best explanation of the mechanism that underlies this psychophysiological phenomenon. The purpose of the present project was to propose that a Hebbian model of cell-assemblies (Hebb, 1949) provides a plausible competing theory of MMN. A Hebbian model is consistent with the evidence provided by imaging studies that demonstrate increased neural efficiency in learning cognitive (as opposed to skilled motor) tasks and with recent animal studies in an analogous model. This model suggests three hypotheses which were addressed by the present study. First, it is proposed that the method that is traditionally used to calculate MMN may not be the ideal. Specifically, it is proposed that the baseline measure used in the calculation does not yield optimal MMN data and the present experiment investigated a new method of gathering baseline data. Second, it was hypothesized that an investigation of sequence effects related to standard and deviant stimuli in an oddball paradigm would provide further support for a Hebbian reinterpretation of MMN. Finally, the argument is made that a Hebbian model of MMN garners additional support in terms of parsimony and ecological validity in addition to being consistent with our current understanding of the physiological underpinnings of learning phenomena. Results indicate that the new method of calculating MMN does, indeed, provide a more robust measure of MMN. Furthermore, sequence effects were demonstrated for both the standard and deviant stimuli, however the sequence effects observed in standard stimuli were not in the expected direction. Both practical and theoretical implications are discussed.

Source monitoring capabilities in children four, five, and six years of age classified along high and low inhibition abilities were investigated in three different conditions of source monitoring: reality monitoring, internal source monitoring, and external source monitoring. Specifically, children's misattribution errors in internal and reality source monitoring conditions with regard to their inhibition status was investigated. During one testing session, children were randomly assigned to the three source monitoring conditions and invited to participate in puzzle completion tasks. In the reality source monitoring condition, children and experimenters took turns placing the puzzle pieces on a puzzle board. In the internal source monitoring condition, children were requested to actually place half of the puzzle pieces of their choice and to pretend to place the other half on the board. In the external source monitoring condition, children were requested to watch two different experimenters taking turns placing puzzle pieces on the board. After a short retention interval, children were surprised with a puzzle piece recall test. Children's inhibition abilities were assessed with three different inhibition tasks during a subsequent testing session and consisted of a tapping test, Simon Says test, and response compatibility test. Median splits determined children's inhibition abilities as either high (efficient) or low (inefficient). Sets of analysis of variance tests compared participants' general recall performance abilities among the three conditions of source monitoring and evaluated participants' reality and internal performance abilities with regard to inhibition status. The first set of analyses indicated that children made the most recall errors in the external source monitoring condition and the fewest in the reality source monitoring condition. The second set of analyses revealed that 4-year-old boys, compared to 5- and 6-year-old boys, committed more errors toward the misattribution bias in the internal condition, while 4-year-old girls, compared to 5- and 6-year-old girls, committed more errors against the bias. The third set of analyses supported the hypothesis that inefficient inhibitors on the tapping task committed more errors toward the misattribution bias in the internal source monitoring condition than those in the reality condition.

Contextual impenetrability is the measurable consequence of informational encapsulation, which is a key feature of input systems hypothesized to be modular. The data from the current psycholinguistic literature do not clearly converge on support for or refutation of the modularity hypothesis with regard to the existence of contextual impenetrability for lexical access and gap-filling. Most previous research has focused on the influence of global context on lexical access. The experiments in this dissertation explore a more local context imposed by the argument structure and lexical conceptual structure of a verb on its direct object. The primary goal for this dissertation was to develop a set of test sentences appropriate for study with both cross-modal lexical priming and word-by-word reading to connect key experiments in the lexical access and gap-filling literature, then to determine if the outcomes supported or failed to support the existence of contextual impenetrability for lexical access and gap-filling. The outcomes of these experiments supported the hypothesis of contextual impenetrability for these linguistic operations. A secondary goal of this dissertation was to address recent criticisms of studies that have used cross-modal lexical priming to study the contextual impenetrability of gap-filling. The cross-modal lexical priming experiments in this dissertation demonstrated that it is unreasonable to attribute priming effects at hypothesized gap locations to artifacts such as hypothesized "continuation priming." The dissertation concludes with discussions of the implications of these results for two competing theories of mental structure (the modularity hypothesis and interactionist hypotheses) and recommendations for the appropriate interpretation of various experimental tasks and additional experiments.

The motion of an object may be perceived based on a change in location of either its surface or edges. By isolating the luminance changes produced by a moving object from the physical displacement of its surface and edges, it was found that a static object appears to move when the luminance changes are restricted to a narrow area adjacent to it. Therefore, changes in the luminance contrast of edges are sufficient for the perception of object motion. However, the existence of different motion signals based on luminance changes of edges and surfaces was confirmed by the occurrence of different motion percepts for the same stimulus configuration. As the width of the region which changed in luminance was increased, edge-based motion percepts were replaced by a surface-based motion percept. This study was primarily concerned with the interaction between the mechanisms that signal edge-based motion and surface-based motion. It was found that surface-based motion mechanisms inhibit edge-based motion mechanisms, even when the different motion patterns were in the same direction. Modulating the effects of this inhibition was facilitation between edge-based motion mechanisms when two sliding-edge motions were possible in the same direction. Less facilitation, and possibly inhibition, occurred when the sliding-edge motions were in the opposite compared with the same direction. Finally, there was even greater inhibition from surface-based motion mechanisms ado edge-based motion mechanisms when the different motion patterns were specified in the opposite compared with the same direction. It is concluded that much of the observed inhibition results from high-level perceptual processes that distinguish between whether particular luminance changes are caused by the disappearance and reappearance of one object or by the local movement of multiple objects. Assuming that jumping-object motion is perceived naturally when there is an interruption in the visual processing of a moving object, such as with blinking, the nature of the inhibition would serve to, reduce the inappropriate perception of motion for ether objects adjacent to the previously and newly occupied locations of the moving object.

Sensorimotor coordination is used in everyday behavior. This includes discrete reactive behaviors, such as maneuvers made to avoid a predator that was heard in the distance, or continuous rhythmic behaviors, such as riding a bicycle. Researchers have studied the behavioral aspects of sensorimotor coordination for over a century and various models have been proposed to account for these findings in terms of the nervous system. The purpose of this thesis was to use behavioral measures and electroencephalographic (EEG) recordings in humans to address several of the remaining issues regarding the spatiotemporal dynamics of cortical activity involved in continuous sensorimotor coordination. First, are the spatiotemporal patterns of cortical activity different for discrete and continuous coordination behaviors? To investigate discrete coordination, a simple reaction time (RT) task was used: upon each random presentation of the visual stimulus (2.5--3.5 sec ISI), subjects responded with a unimanual index finger flexion. Continuous coordination was studied via a synchronization-continuation paradigm, which used the same visual stimulus (1 sec ISI) and the same unimanual index finger flexion as in the reaction time task. By keeping the stimulus and motor properties constant for the two types of coordination it was hypothesized that differences in cortical activity would relate to an internal timekeeping system responsible for pacing the rhythmic movements made during continuous coordination. Several models postulate that oscillatory activity is used by the brain for maintaining task timing information (see Miall, 1989, and Church and Broadbent, 1991, for example). Frequency analysis revealed phase-locking of the alpha rhythm in the occipital lobe. This rhythm appears to play a role as a neural timekeeper mechanism: it was found that the degree of alpha phase-locking was predictable from the expected dependence on neural timekeeping, i.e. continuation was greater than synchronization, which is in turn was greater than reaction. These results also support the concept of modality specificity in neural timekeeping mechanisms (reviewed in Matell and Meck, 2004). Furthermore, the behavioral and EEG results support the theory that continuous sensorimotor coordination is largely influenced by timekeeping mechanisms, with sensory stimulation being employed occasionally to keep timing relatively accurate (Hary and Moore, 1987).

In this dissertation, we examined the neural correlates of motor coordination and music perception using a set of four fMRI experiments. The neural correlates of goal-directed action were examined in a group of healthy adults in experiment I using execution and imagery of a unimanual and a bimanual finger-sequencing task. Similar neural networks were engaged for execution and imagination of movement sequences. Interestingly, we also found that the sensorimotor cortical and cerebellar areas are functionally decoupled from the task network when people imagine but do not actually execute sequential actions. In experiment 2, we used the same finger-sequencing paradigm to study recovery of function during recovery from stroke. It was observed that the wide spread neural activity during the initial session became more localized during the last session. In addition, using imagery tasks, we showed that hemiplegic patients retained the ability to activate neural pathways that are normally involved in executing goal-directed action sequences, despite the loss of ability to actually execute movements. In experiment 3, we examined brain activity when musicians and non-musicians listened to expressive and mechanical versions of a musical piece. The expressive performance activated the limbic areas more than the mechanical version in both groups of subjects suggesting perception of affect. The pattern of neural activity was also dictated by their experience and familiarity with the piece of music. In addition, we found activation of language related areas when musicians listened to the expressive version suggesting shared neural resources for language and music. The neural basis of sensorimotor coordination and timing in Parkinson's disease was investigated in the last experiment, using a synchronization-syncopation task and the continuation paradigm. Different neural areas subserved timing during the two different modes of coordination. However, these differences persisted during their respective continuation phases. In order to compensate for the functional deficiency in Parkinson's disease, patients recruited functionally segregated circuits that connect the striatum and association areas of the parietal, premotor and prefrontal cortices.

A prominent deficit in Alzheimer's disease (AD) is a difficulty in recognizing and naming people. Unfamiliar and famous face recognition tasks are sparse in the neuropsychology literature. It was hypothesized that: a deficit in recognition of faces would be found for AD patients, the semantic mismatch condition would result in the longest response latency and least accurate naming, and semantic cues would not facilitate naming for the AD group. Accuracy and reaction time from ten mild AD patients diagnosed by NINCDS-ADRDA criteria and 10 normal controls (matched age, 66--82 years, education & ethnicity) were tested via unfamiliar and famous faces recognition memory tests and famous faces naming tasks with and without semantic interference. Both subject groups were more accurate on the famous face recognition rather than memory for unfamiliar faces, with significant group differences. The Stroop-like face naming task performance was characterized by an increased interference effect, semantic face-name mismatches produced the longest response delays, and less accurate face naming particularly in the AD group. The semantic cues resulted in a decrease in naming accuracy for the AD patients, which may be indicative of their name retrieval deficit. Consistent with existing face-name models, these findings suggest that the deficit in AD is related to semantic naming rather than the perceptual component of face recognition. Furthermore, the ability to correctly name faces even in the presence of interference may prove to be a diagnostic tool that is sensitive to face naming deficits characteristic in cases of brain damage.

Individuals with nonverbal learning disabilities (NLD) have an impaired ability to interpret facial expressions of emotion (FEE), the consequences of which can include progressively debilitating socioemotional disturbances. Thus, it is important to determine how the neuroanatomical structures underlying the perception of FEE in people with NLD differ from the normal population. To this end, functional magnetic resonance imaging was used to compare brain activation patterns in male and female adolescent subjects and male adult subjects with and without NLD. The subjects were presented with FEE at low and high intensities while they performed a gender decision task. Subjects with NLD displayed less activation in limbic areas responsible for processing emotion in the normal population. The NLD subjects exhibited more activity than controls in the orbital gyrus, inferior, middle and superior frontal gyri, fusiform and superior temporal gyri, insula, striatum and inferior and superior parietal lobules. Several of these structures participate in language function: as individuals with NLD have superior verbal abilities, it is probable that this population relies on their linguistic strengths to compensate for their nonverbal weaknesses whilst processing FEE. Additionally, because of an impaired capacity for attention to and discrimination of visual details, the NLD subjects showed more active responses for low intensity FEE in comparison to controls. This may have led to a failure of regions such as the middle and superior frontal and superior temporal gyri to habituate or sensitize appropriately to emotionally salient visual stimuli. In comparison with the normal population, people with NLD utilize different neural structures when processing FEE, in accordance with the strengths and deficits associated with the NLD syndrome.

The method of imitation provides an alternative approach to longstanding problems in speech research such as the organization of the vowel space and its relation to linguistic categories. Imitation of self-produced targets is particularly useful because (a) it allows a subject to report the quality of a multidimensional percept quickly and efficiently and (b) the subject is in principle capable of matching the target perfectly, so systematic deviations in the imitation can be ascribed to perceptuomotor biases. The self-imitation task was used to study perceptuomotor bias in the F1 x F2 vowel spaces of native speakers of American English, using two kinds of tasks. In "Serial Imitation", the imitations of a subject were played back to him for further imitation, thereby creating a set of trajectories in the vowel space. In "Multiple Imitation", each target was imitated several times, thereby allowing the perceptuomotor bias and variability to be calculated. Both tasks showed that subjects were consistently inaccurate in imitating themselves and that different subjects had different patterns of bias directions over the vowel space. The bias did not seem to be influenced by the temporal structure of the target nor by the subject's linguistic background and phonetic training. Articulatory modeling further showed that the bias was not due to low-level noise during production. The cause of the bias is posited to be the subject's psychological set, viz. his or her tacit notion of what aspects of the target are to be attended to and emphasized. An additional result was that while the bias directions differed across subjects, the distribution of bias magnitude and formant variability were remarkably consistent across subjects and sessions. In particular, F1 and F2 varied independently of each other and the formant standard deviations were similar to the formant discrimination limen. It is proposed that the psychological set is akin to a cognitive "policy" that can vary across subjects and sessions, while the underlying mechanism that carries out the policy is relatively unchanging.