Ashby和Maddox(1998)提出COVIS理論，來解釋人們是如何進行分類學習。而對COVIS理論所作的研究結果，有支持的結果(Ashby, Ell,& Waldron, 2003; Ashby,Maddox, & Bohil, 2002; Maddox, Ashby, Ing, & Pickering, 2003)，但也有不支持的結果(Nosofsky, Stanton, & Zaki, 2005; Stanton & Nosofsky, 2007)，因此分類學習系統是否如同COVIS理論所主張是由雙系統所構成，還應繼續加以探討。 在Maddox等人(2007)的「操弄按鍵轉換機率」實驗中，Maddox等人以COVIS理論的觀點來解釋此實驗所得的結果。然而，此實驗結果除了以COVIS理論的觀點來解釋之外，或許也可用認知資源消耗的觀點來加以解釋。因此本研究的主要目的是嘗試檢驗認知資源消耗觀點的解釋方法可行性。實驗一的主要目的是重製Maddox等人(2007)年研究所得結果，以確保本研究所使用的刺激材料、實驗流程和實驗設計都和Maddox等人相同，並可得到相同的結果。然而實驗一所得結果和Maddox等人(2007)結果不同，並且實驗一所得結果也不支持COVIS理論所提出的雙系統想法。基於實驗一無法得到和Maddox等人(2007)相同的結果，實驗二根據認知資源消耗觀點，繼續嘗試重製出和Maddox等人(2007)相同的實驗結果，藉由在轉換階段加入序列回憶作業的 操弄手法，實驗二中得到和Maddox等人(2007)相同的結果，並且可用認知資源消耗觀點對此結果進行解釋。而本研究認為如果「Maddox等人研究中受試者的認知資源量少於本研究中受試者的認知資源量」的假設可成立的話，Maddox等人(2007)實驗所得結果是有可能可用認知資源消耗觀點的說法加以解釋。因此對於Maddox等人(2007)年的「操弄按鍵轉換機率」實驗結果，除了以COVIS理論的觀點來解釋之外，也可用認知資源消耗觀點的解釋方法來進行解釋。

This thesis investigates the neurobiological pathways that underpin learning of visual categories, and the behaviour associated with these neural systems. The work contains two strands. The first assesses the neural and behavioural predictions of the COmpetition between Verbal and Implicit Systems (COVIS) account of category learning. The second aims to examine the brain regions implicated in the prototype effect after transcranial Direct Current Stimulation (tDCS) to the left dorsolateral prefrontal cortex (DLPFC). COVIS predicts there are separate explicit and implicit category learning systems. According to COVIS, the explicit system optimally learns rule-based (RB) categories and relies upon the frontal lobes for working memory (WM) and executive functioning processes, and the medial temporal lobes (MTL) to store decision boundaries. In contrast, the implicit system employs the basal ganglia to procedurally learn information-integration (II) categories through stimulus-response associations. Experiment 1 found little evidence of separable implicit or explicit systems in an fMRI study that investigated category decision making processes during RB and II category learning using conditions matched in difficulty, category separation and number of relevant stimulus dimensions. Contrary to the predictions of COVIS, the MTL was more active during the II condition compared to the RB condition, an area that should be more engaged by the explicit system. There was also extensive neural activation overlap found between RB and II learning. Experiments 2 and 3 aimed to generalise these neural findings to activation during feedback processing in RB and II conditions. Experiment 2 was a behavioural study which showed that adding a feedback delay necessary for fMRI data analysis did not differentially impact RB or II learning. Experiment 3, including this feedback delay, found the same neural pattern of results as Experiment 1 offering further support that the MTL is more engaged in II learning than RB learning. There was also again considerable overlap in the regions involved in the two tasks. Taken together, Experiments 1 to 3 found no evidence for the neurally dissociable category learning systems predicted by COVIS. Experiments 4, 5 and 6 investigated the behavioural dissociation reported by Smith et al. (2014) that deferring feedback to the end of a six trial block selectively impairs II learning compared to a unidimensional RB condition. Experiment 4 replicated this result. However, when equating the number of dimensions relevant for RB and II learning in Experiment 5, both conditions were hindered by deferring feedback, with Experiment 6 confirming that conjunctive RB learning was impaired by deferred feedback compared to immediate feedback. I concluded that the dissociation reported by Smith et al. is attributed to the use of a unidimensional category as a comparison for II performance, and that when the number of relevant stimulus dimensions between conditions are controlled there is little evidence for the separable systems of COVIS. Experiment 7 used tDCS to investigate if RB or II learning was differentially affected by anodal stimulation to the left DLPFC. Although there was no significant difference in learning between category conditions, during anodal stimulation participants improved less across blocks than those receiving sham stimulation. While the results suggest that the effect of tDCS on RB and II learning may be more tangible during stimulation, the numerical pattern of the data warrants further research into the possibility that RB participants are more affected by tDCS than II participants after stimulation to the left DLPFC. Strand 2 of this thesis aimed to further previous work that suggests anodal stimulation to the DLPFC during a prototype distortion task induced a prototype effect (better responding to unseen prototype trials than other category exemplars derived from this prototype) that was not present in sham participants. Contrary to this past work, Experiments 8 and 9 found that anodal stimulation to the left DLPFC inhibited a prototype effect that was present in sham participants. Experiment 10 implemented a combined tDCS and fMRI task and found that anodal participants engaged the stimulated DLPFC and the MTL more than sham participants in measures of the prototype effect. Based on these findings, this thesis argues that anodal tDCS to the left DLPFC inhibits perceptual learning by disrupting error prediction processes. Anodal participants are also considered to use generalization more than sham participants when perceiving category exemplars, a process attributed to the MTL.

Electrochemical sensing platforms including nanostructured materials have attracted increasing attention for diagnostic applications in recent decades. People in resource-limited places, particularly in low- and middle-income countries, continue to face problems finding high-quality medical treatment and technologies. This thesis aims to create affordable electrochemical-based point of care (PoC) diagnostic systems using laser-scribed graphene (LSG) material as the sensing platform. The use of LSG sensors for diagnostic purposes has been gaining attention. Compared to established methods for graphene synthesis, laser scribing provides many advantages, such as cost-effectiveness, fast electron mobility, mask-free production, green synthesis, good electrical conductivity, porosity, mechanical stability, and large surface area. Surface enhancement techniques hold great importance for sensitive and selective electrochemical performance. The first part of this dissertation includes the LSG fabrication and the possible nanoparticle deposition effect on LSG surfaces, particularly gold and silver nanoparticles. The electrodeposition technique was chosen to enhance the electrocatalytic activity with high surface coverage, higher sensitivity, and ease of surface modification. We also focused on possible surface activation techniques on LSG electrodes to achieve an enhancement in surface area through electrochemical strategies. In the second part of this dissertation, we focus on surface functionalization methods for the development of self-diagnostic devices. Namely, the LSG surface was engineered by recognition units such as antibodies, enzymes, and aptamers, as well as molecular imprinting as a non-biological approach. As a readout system, a custom-made potentiostat called KAUSTat was developed. The suggested devices have the potential to replace costly health care instrumentation with simple and practical miniaturized smart systems when combined with smartphone applications via Bluetooth connection.

In category learning, explicit processes function through the prefrontal cortex (PFC) and implicit processes function through the basal ganglia. Research suggested that these two systems compete with each other. The goal of this study was to shed light on this theory. 15 undergraduate subjects took part in an event-related experiment that required them to categorize computer-generated line-stimuli, which varied in length and/or angle depending on condition. Subjects participated in an explicit "rule-based" (RB) condition and an implicit "information-integration" (II) condition while connected to a functional near-infrared spectroscopy (fNIRS) apparatus, which measured the hemodynamic response (HR) in their PFC. Each condition contained 2 blocks. We hypothesized that the competition between explicit and implicit systems (COVIS) would be demonstrated if, by block 2, task-accuracy was approximately equal across conditions with PFC activity being comparatively higher in the II condition. This would indicate that subjects could learn the categorization task in both conditions but were only able to decipher an explicit rule in the RB condition; their PFC would struggle to do so in the II condition, resulting in perpetually high activation. In accordance with predictions, results revealed no difference in accuracy across conditions with significant difference in channel activation. There were channel trends (p < .1) which showed PFC activation decrease in the RB condition and increase in the II condition by block 2. While these results support our predictions, they are largely nonsignificant, which could be attributed to the event-related design. Future research should utilize a larger samples size for improved statistical power.