Midterm 2

Leonard M. Adleman A UTM can be built with DNA molecules

Given a network of nodes and directed connections between them, is there a path through the network that begins with the start node and concludes with the end node visiting each node only once. Binary (yes or no)

Step 1: Generate random paths on the network. Step 2: Keep only those paths that begin with the start city and conclude with the end city. Step 3: If there are N cities, keep only those paths of length N. Step 4: Keep only those that enter all cities at least once. Step 5. Any remaining paths are solutions (I.e., Hamiltonian paths).

leads to combinatorial explosion. brute-force serial search takes a very long, virtually forever (unintelligent computation)

performing the 5 steps in generation and test method in parallel search instead of serial

Watson & Crick

complementary single-stranded DNA or RNA sequences spontaneously bind together by hydrogen bonds to form a double-stranded molecule

copy information from one molecule into another

bind molecules together used to repair breaks in DNA

the “bio” nanomachines -slides along -reads each base -writes its complement onto new strand

• In a test tube, mix the prepared DNA pieces together (which will randomly link with each other, forming all different paths). • Perform PCR with ‘start’ and ‘end’ DNA pieces as primers (which creates millions’ copies of DNA strands with the right start and end). • Perform gel electrophoresis to identify only those pieces of right length (e.g., N=4). • Use DNA ‘probe’ molecules to check whether their paths pass through all intermediate cities. • All DNA pieces that are left in the tube should be precisely those representing Hamiltonian paths. • If the tube contains any DNA at all, then conclude that a Hamiltonian path exists, and otherwise not. When it does, the DNA sequence represents the specific path of the solution.

its enormous parallelism

over 4 million

Limited time capacity: contents of current awareness; storage mechanism that keeps a limited amount of information active fro a brief time such as a few seconds to minutes acoustic 18 seconds duration 7+-/2 items capacity

Retention memory curve participants count backwards by 3s during retention interval memory span drops steeply because of retroactive interference

classical information-processing view info -> sensory memory -> STM (maintenance via rehearsal which goes to LTM, or lost) -> LTM and retrieval back to STM • modern model replaces STM with WM

No WM is just referring to a concept or label for some sort of mental activities going on all over the brain, rather than a buffer place or loading dock

WM: temporary, fragile duration, limited capacity and size, relatively easy ease of entry, relatively easy ease of retrieval LTM: long-lasting, enduring duration, virtually unlimited capacity and size, effortful ease of entry (rehearsal), ease of retrieval difficult and slow and can be unsuccessful

report digit after probe

Primacy effect - LTM Recency effect - STM

better recognition for shorter-list items

SIMPLE model - Bayesian model CMR model - connectionist model Both model the same pattern

error patterns ion memory tasks double dissociations after brain lesions

remembers old explicit memories formed before surgery but cannot form new explicit memories (severe anterograde)