Caltech Library System

About | Browse | Search | Caltech Student Instructions

Type of Document	Dissertation
Author	Carter, Ronald McKell
URN	etd-06022006-124040
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-06022006-124040
Title	Explicit and implicit processes in human aversive conditioning
Degree	PhD
Option	Biology
Advisory Committee	Advisor Name Title Christof Koch Committee Chair John Morgan Allman Committee Member John O'Doherty Committee Member Ralph Adolphs Committee Member Shinsuke Shimojo Committee Member
Keywords	pavlovian association working memory learning declarative Non-conscious Conscious perceptual learning extinction
Date of Defense	2006-05-24
Availability	mixed
Abstract The ability to adapt to a changing environment is central to an organism’s success. The process of associating two stimuli (as in associative conditioning) requires very little in the way of neural machinery. In fact, organisms with only a few hundred neurons show conditioning that is specific to an associated cue. This type of learning is commonly referred to as implicit learning. The learning can be performed in the absence of the subject’s ability to describe it. One example of learning that is thought to be implicit is delay conditioning. Delay conditioning consists of a single cue (a tone, for example) that starts before, and then overlaps with, an outcome (like a pain stimulus). In addition to associating sensory cues, humans routinely link abstract concepts with an outcome. This more complex learning is often described as explicit since subjects are able to describe the link between the stimulus and outcome. An example of conditioning that requires this type of knowledge is trace conditioning. Trace conditioning includes a separation of a few seconds between the cue and outcome. Explicit learning is often proposed to involve a separate system, but the degree of separation between implicit associations and explicit learning is still debated. We describe aversive conditioning experiments in human subjects used to study the degree of interaction that takes place between explicit and implicit systems. We do this in three ways. First, if a higher order task (in this case a working memory task) is performed during conditioning, it reduces not only explicit learning but also implicit learning. Second, we describe the area of the brain involved in explicit learning during conditioning and confirm that it is active during both trace and delay conditioning. Third, using functional magnetic resonance imaging (fMRI), we describe hemodynamic activity changes in perceptual areas of the brain that occur during delay conditioning and persist after the learned association has faded. From these studies, we conclude that there is a strong interaction between explicit and implicit learning systems, with one often directly changing the function of the other.
Files	Filename       Size       Approximate Download Time (Hours:Minutes:Seconds)     28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access    1_RMC_Contents.pdf 152.55 Kb 00:00:42 00:00:21 00:00:19 00:00:09 < 00:00:01   2_RMC_CH1_Introduction.pdf 142.49 Kb 00:00:39 00:00:20 00:00:17 00:00:08 < 00:00:01   3_RMC_CH2.pdf 593.26 Kb 00:02:44 00:01:24 00:01:14 00:00:37 00:00:03   4_RMC_CH3.pdf 312.70 Kb 00:01:26 00:00:44 00:00:39 00:00:19 00:00:01   6_RMC_CH5_Discussion.pdf 144.60 Kb 00:00:40 00:00:20 00:00:18 00:00:09 < 00:00:01   7_RMC_Appendix.pdf 533.52 Kb 00:02:28 00:01:16 00:01:06 00:00:33 00:00:02   8_RMC_References.pdf 160.75 Kb 00:00:44 00:00:22 00:00:20 00:00:10 < 00:00:01 There are 2 files which have been withheld at the author's request. indicates that a file or directory is accessible from the campus network only and must not be distributed to non-campus persons.