Browsing by Subject "Memory"

In the face of declines in memory related to specific events, people maintain intact general knowledge into very old age. Older adults often use this knowledge to support their remembering. Semantic illusions involve situations in which presented information contradicts correct knowledge; the illusion occurs when people fail to notice a contradiction with what they know. Compared to younger adults, older adults' later memories are surprisingly less affected by semantic illusions. That is, they use fewer errors seen in the semantic illusions as answers when later asked related general knowledge questions. Why do older adults show this reduced suggestibility, and what role does their intact knowledge play? In 5 experiments, I explored these questions. Older adults' reduced suggestibility was not due to an age difference in error detection: older adults were no better than younger adults at detecting the errors that contradicted their stored knowledge. In addition, episodic memory failures were not a major factor either; the evidence for their direct involvement was mixed. Instead, prior knowledge seems to have been particularly protective for older adults. They demonstrated more knowledge to begin with but also gained access to even more of their stored knowledge across the duration of experiments, leading them to be less suggestible following semantic illusions. There was also an indication that when knowledge was stably accessible, older adults had a tendency to rely on it more than did younger adults. Broadly, these findings indicate that older adults' intact prior knowledge provides important benefits to their remembering and can even protect them against acquiring erroneous information about the world.

Rapid data growth nowadays makes it more critical to reduce search time to improve the performance of search-intensive applications. However, huge data size makes it more difficult to efficiently perform search operations. Representative conventional approaches to reduce search time, such as CAM and in-memory databases, are no longer efficient because of the data explosion: CMOS-based CAM has low capacity which cannot be increased through CMOS scaling, and in-memory databases have performance degradation as data size increases. As a result, we have to exploit emerging nanotechnologies to accelerate search.

Among emerging nanotechnologies, memristors have become promising candidates to build storage structures because of high capacity, short switching time and low power consumption. However, the benefit we can obtain from these storage structures is limited by low endurance of memristors. In order to utilize the computation ability of memristors and deal with the endurance problem, we explore the design space of memristor-based storage structures.

We first propose MemCAM/MemTCAM, a configurable memristor-based CAM/TCAM design, in which we use memristors as both memory latches and logic gates. Computation ability of memristors makes it possible to perform range search and high density of memristors provides an opportunity to build MemCAM/MemTCAM with large capacity and small area. We use SPICE to model the memristor and analyze power and performance at different temperatures. The results show that it is feasible to build MemCAM and MemTCAM which have high capacity and can reduce total search time and energy consumption for search-intensive applications with huge data size.

We then propose four hybrid memristor-based storage structures, Hash-CAM, T-tree-CAM, TB+-tree, and TB+-tree-CAM, to solve the endurance problem. We use an analytical model to evaluate and compare the performance and lifetime of two software-implemented memory-based T-trees and these four hybrid storage structures. The results show that hybrid storage structures can utilize range search abilities, achieve better performance than memory-based T-trees, and improve lifetime from minutes to longer than 60 years. Furthermore, TB+-tree-CAM, a hybrid memristor-based storage structure combining T-tree, B+-tree and CAM, manages to balance between performance and lifetime and can outperform other storage structures when taking both performance and lifetime into consideration.