Indiana University-Purdue University Indianapolis (IUPUI) / Several pathological disorders are characterized by maladaptive decision-making (Dalley & Robbins, 2017). Decision-making tasks, such as Delay Discounting (DD), are used to assess the behavioral manifestations of maladaptive decision-making in both clinical and preclinical settings (de Wit, Flory, Acheson, Mccloskey, & Manuck, 2007). DD measures cognitive impulsivity and broadly refers to the inability to delay gratification (Hamilton et al., 2015). How decisions are made in tasks that measure DD can be understood by assessing patterns of behavior that are observable in the sequences of choices or the statistics that accompany each choice (e.g. response latency). These measures have led to insights that suggest strategies that are used by the agent to facilitate the decision (Linsenbardt, Smoker, Janetsian-Fritz, & Lapish, 2016). The current set of analyses aims to use individual trial data to identify the neural underpinnings associated with strategy transition during DD. A greater understanding of how strategy change occurs at a neural level will be useful for developing cognitive and behavioral strategies aimed at reducing impulsive choice. The rat dorso-medial prefrontal cortex (dmPFC) has been implicated as an important brain region for recognizing the need to change strategy during DD (Powell & Redish, 2016). Using advanced statistical techniques, such as demixed principal component analysis (dPCA), we can then begin to understand how decision representations evolve over the decision- making process to impact behaviors such as strategy change. This study was the first known attempt at using dPCA applied to individual sessions to accurately model how decision representations evolve across individual trials. Evidence exists that representations follow a breakdown and remapping at the individual trial level (Karlsson, Tervo, & Karpova, 2012; Powell & Redish, 2016). Furthermore, these representational changes across individual trials have previously been proposed to act as a signal to change strategies (Powell & Redish, 2016). This study aimed to test the hypothesis that a ‘breakdown’ followed by a ‘remapping’ of the decision representation would act as a signal to change strategy that is observable in the behavior of the animal. To investigate the relationship between trials surrounding the breakdown and/or subsequent remapping of the decision representation and trials surrounding strategy changes, sequences of trials surrounding the breakdown and/or remapping were compared to sequences of 9 trials surrounding the strategy-change trial. Strategy types consisted of either exploiting the immediate lever (IM-Exploit), delay lever (DEL-Exploit), or exploring between the two lever options (Explore). Contrary to the hypothesis, an overall relationship between breakdown and remapping trial sequences were not associated with change-trial sequences. In partial support of the hypothesis however, at the 4-sec delay when the subjective value of the immediate reward was high, a relationship between breakdown sequence and strategy change sequence was detected for when the animal was exploiting the delay lever (e.g. DEL-Exploit strategy). This result suggests that a breakdown in decision representation may act as a signal to prompt strategy change under certain contexts. One notable finding of this study was that the decision representation was much more robust at the 4-sec delay compared to the 8-sec delay, suggesting that decisions at the 4-sec delay contain more context that differentiate the two choice options (immediate or delay). In other words, the encoding of the two choice options was more dissociable at the 4-sec delay compared to the 8-sec delay, which was quantified by measuring the average distance between the two representations (immediate and delay) on a given trial. Given that Wistar rats are equally likely to choose between the immediate and delay choice alternatives at the 8-sec delay (Linsenbardt et al., 2016), this finding provides further support for current prevalent theories of how animals use a cognitive search process to mentally imagine choice alternatives during deliberation. If context which differentiates choice options at the 8-sec delay is less dissociable, it is likely that the cognitive search process would be equally likely to find either choice option. If the choice options are equally likely to be found, it would be assumed that the choice alternatives would also be equally likely to be chosen, which is what has been observed in Wistar rats at the 8-sec delay.

With the developing radar technology, radars have been started to be used in the airborne platforms due to the need of fast, accurate and reliable information about the enemies. The most important and tactically needed information is the movements in an observation area. The detection of a ground moving target buried in a dense clutter environment from a moving air platform is a very challenging problem even today. The geometry of the operation, the course of the flight and structure of the clutter are the most effective parameters of this problem. There are some &ldquo / Ground Moving Target Indication&rdquo / (GMTI) techniques that have been studied for the last twenty years to overcome this problem. In this thesis, the simulation of some of these techniques in a realistic environment and the comparison of their performances are discussed. In this work, a GMTI simulator is developed to generate the environment containing the clutter and the noise signals, to locate and simulate the targets in this environment and to apply the GMTI techniques on the raw data generated by the simulator. The generation of the clutter signals including the internal clutter motion (ICM) for different types of clutter distributions is one of the most important parts of this thesis. The GMTI techniques being investigated throughout this thesis are &ldquo / Displaced Phase Center Antenna&rdquo / (DPCA), &ldquo / Along-Track Interferometry&rdquo / (ATI), &ldquo / Adaptive DPCA&rdquo / , &ldquo / Pre-Doppler Sigma-Delta STAP&rdquo / and &ldquo / Post-Doppler Sigma-Delta STAP&rdquo / techniques. These techniques are compared according to their clutter suppression and target detection performances under different environmental conditions.

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