Object recognition memory (ORM) refers to both recognition of an object and the memory of having seen it before. In humans, ORM has been investigated using functional neuroimaging and electrophysiological techniques with tests of episodic memory retrieval involving recollection of previously studied items. Processes involved in the maintenance of a mental state adopted for the performance of a retrieval task (retrieval mode) appear to involve right frontal neural regions. More transient processes occurring at the time of item recollection (retrieval success) have shown scalp activity over parietal and right frontal regions. This activity is thought to originate in the medial temporal lobes and the underlying right frontal cortex respectively. The aforementioned findings have been derived mainly from studies using verbal stimuli. It is uncertain whether the same neural regions are involved in object recollection. It is also uncertain whether sustained modal and transient item-related activity involve the same or different right frontal regions. In this study, steady-state probe topography (SSPT) was used to investigate both sustained and transient processes involved in the retrieval of abstract pictorial objects from memory. The ability to vary the evaluation period of the steady-state visually evoked potential (SSVEP) allows investigation of cognitive processes occurring over different time scales. Neural regions involved in sustained modal processes were identified by examining the SSVEP values averaged over the duration of a memory retrieval task. Sustained SSVEP effects were observed over right fronto-temporal regions. Neural regions involved in transient retrieval success processes were identified by comparing the transient SSVEP responses to tasks with different memory loads. Comparison of a higher with a lower memory load condition showed SSVEP effects over parieto-temporal and right inferior frontal regions. Larger differences between memory loads gave effects that were larger and more right lateralized. Retrieval mode and retrieval success processes showed SSVEP effects over different right frontal regions. It was also found that, in contrast to the left lateralized parietal ERP response to recollected verbal stimuli, the SSVEP effects produced with abstract pictorial shapes showed a more bilateral pattern. This was considered to reflect the relatively non-verbalizable pictorial nature of the stimuli.

Novices and experts show distinct differences in the performance of many tasks. Experts may perform a task quickly and accurately with seemingly little attention or effort, whilst novices will perform the same task more slowly and with great effort. The transition from novice to expert performance occurs only after extended practice and has been conceptualized as a transition from controlled to automatic processing, and has been modeled as a reduction in attention or cognitive resources. Alternatively, based on findings relating to learning in the domain of number arithmetic, it has also been modeled as a transition from an algorithmic, or computationally-based process, to the use of memory retrieval. However, relatively few studies have investigated the changes in brain activity associated with such a transition. In this study, the Steady-State Probe Topography technique was used to investigate differences in the topography of the Steady-State Visual Evoked Potential (SSVEP) between an unpracticed and a well-practiced analogue of number arithmetic, Alphabet arithmetic. Subjects showed decreases in response time with practice that followed a power law and were suggestive of automatization. During initial, unpracticed performance of the task, processing of the Alphabet Arithmetic equations was characterised by increased SSVEP amplitude and decreased latency in frontal regions, whilst after extended practice, performance was characterised by reduced SSVEP amplitude and increased latency. It is suggested that the frontal activity during the initial, unpracticed stage of the task implicates a role for working memory, whilst the amplitude decrease and latency increase observed in the well-practiced task may reflect a reduction in excitation, consistent with ideas of an improvement in brain efficiency, and possibly an increase in inhibitory processes.

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2006. / Title from first page of PDF file (viewed December 13, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Thesis (M.A.)--York University, 2002. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 63-66). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71617.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Background: The event related potential (ERP) is an important electrophysiological response to an internal or external stimulus on human body. In some studies, the ERP-based brain computer interface (BCI) systems were created in visual or auditory modality. However, in these type of BCIs, either the eyes or ears of the users are occupied when they are making a choice. It is not convenient to communicate with others. Thus, a somatosensory ERP based BCI can be developed to overcome this issue. According to this, the analysis of somatosensory ERP features is necessary to evaluate if somatosensory ERP is eligible for BCIs as an input. Objective: 1. To study ERP features and design of P300 experiment. 2. To compare three types of P300 features elicited by three modalities. 3. To produce ERP response by electrical stimuli delivered to different position, and analyze ERP features. Methods: Two experiments were conducted. In experiment 1, three modalities, including visual, auditory and electrical modality, were used to produce P300 response. Experiment 2 only presented electrical stimuli. In experiment 1 two electrical stimuli were presented with different intensities at one location, whereas four electrical stimuli were showed at different location with the same intensity. The amplitude and latency were compared among three modalities, and the ERP topography of experiment 2 was also analyzed. Result and conclusion: Fourteen subjects’ data were analyzed in our study. The amplitude and latency of electrical P300 were similar to auditory ERP. But the ERP of visual modality had the largest amplitude and shortest latency. This result shows that electrical P300 can work as well as auditory P300 in BCIs, but not as good as visual P300. In experiment 2, the latency of electrical ERP occurred around 280 ms, and the amplitude and the topography showed that the largest amplitude was located around Cz electrode. This type of ERP in experiment 2 was considered as P3a, which also can be used in BCI systems. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Medical Sciences

A new method for the estimation of the EEG evoked potential (EP) is presented in this thesis. This method is based on a new model of the EEG response which is assumed to be the sum of the EP and independent correlated Gaussian noise representing the spontaneous EEG activity. The EP is assumed to vary in both shape and latency, with the shape variation represented by correlated Gaussian noise which is modulated by the EP. The latency of the EP is also assumed to vary over the ensemble of responses in a random manner governed by some unspecified probability density. No assumption on stationarity is needed for the noise. / With the model described in state-space form, a Kalman filter is constructed, and the variance of the innovation process of the response measurements is derived. A maximum likelihood solution to the EP estimation problem is then obtained via this innovation process. / Tests using simulated responses show that the method is effective in estimating the EP signal at signal-to-noise ratio as low as -6db. Other tests using real normal visual response data yield reasonably consistent EP estimates whose main components are narrower and larger than the ensemble average. In addition, the likelihood function obtained by our method can be used as a discriminant between normal and abnormal responses, and it requires smaller ensembles than other methods.

Thesis (M. Med. Sc.)--University of Hong Kong, 2007.