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Memory Systems: Implicit and Explicit M. Jay Polsgrove and Shannon Walden Q 301, Fall 2000, Indiana University
Background Many studies have been done to find cognitive and neuropsychological information regarding memory. Previous research suggest s that memory is not a single entity but is composed of separate systems. This finding is due to quantifiable differences when comparing word types that imply the existence of two types of memory, known as implicit and explicit memory (Squire and Knowlton, 1990, p. 161, Rugg, 1995)). However, there is still a lack of conclusive evidence for the concrete existence of two separate types of memory. One component that is still not understood is the spatial activity of the brain as it correlates to ERP differences. Findings of two different areas of brain activity for different word types would gain support for two memory systems (Mc. Celland, et al. , 1995, and Rugg, 1995). This hypothesis is based on the research that says: 1. Explicit memory is recalled from memory (declarative and conscious). 2. Implicit memory is based on a sense of familiarity (non-declarative and unconscious). In this project we will distinguish between the memory systems, and whether or not there are two separate locations for each.
Methods • 1 male subject · 2 conditions (related low frequency words and non-related high frequency words) · EEG was recorded on 16 channels during testing · Each condition consisted of 300 words (200 hundred test and 100 distracter. ) · Phase one: conditions of test words from each condition were first randomized then presented to subject for 2 -second intervals. · Phase two: subject was presented a randomly developed list of all words (test and distracter). · Subject was asked to categorize each word as being either 1) know, 2) remember, or 3) new · A break was provided for the subject after every 50 -word block had been presented. ERP Analysis: -Data was collected every 100 ms -EEG data was analyzed by Mat Lab -Values for all 3 conditions was recorded for data for 16 channels -Differences between remember and new conditions were determined -ERP data used to represent brain activity -Differences between know and new conditions were determined by ERP data used to represent brain activity
Results Condition one: • There was greater brain activity for the know words than for the remembered words, especially in the initial and final stages ( see figure 1) • • Used low frequency words. Condition two: • There was greater activity for the remembered work than for the know words. Especially in the frontal and occipital lobes (see figure 2) • Used high frequency words.
Overall Analysis The know responses received a greater response in more areas of the brain than the remembered words. Most of the activity seems to be isolated in the frontal lobe for remembered words. For the know words brain activity is taking place over the entire brain. Also touching base with Broca’s and Weinekie’s areas. (See figures 3 and 4)
I. Two types of memory exist a. implicit (know), B. explicit (remembered) II. Condition One a. Related words i. House, roof, floor ii. Activate a larger response in known words iii. Low Frequency (Rugg, 1995) III. Condition Two a. Non-related words i. Only, simple, free ii. Activate a larger response for the remembered condition the frontal lobe iii. High frequency (Rugg, 1995)
IV. Overall Differences V. A. Significant quantitative difference VI. I. Know-new VII. Remembered-new VIII. B. Varied spatial representation in brain activity IX. I. Know-new X. 1. Frontal to occipital XI. A. Broca’s-Wernikies area XII. Remember-new XIII. 1. Frontal XIV. XV. A. Broca’s area to frontal
V. Information in this study supports evidence for two memory systems A. Graphic Representation I. Condition 1 1. Greater known 1. Greater remembered II. Condition 2 III. Overall 1. Greater activity in know vs. new
Conclusion Our experiment shows that two separate memory systems appear to be active (Squire and Knowlton, 1995). We discovered through process of analysis that each memory system (implicit / explicit) shows strong spatial differences for each condition. Two very prominent areas of the brain that were active during the experiment were Broca’s and Weirnikes area. This suggests words are first processed as language. The remembered words appear then be processed at the frontal lobe, where as the known word signal travels to toward the back of the brain. The differences in these to paths indicates that the remembered (remembered) word is processed and thought of through planning action. While the known (related) is visualized in Wernikies area. (Busey, 2000, p. 158). Graphically, the differences between known and remembered words suggest also suggest a differences in memory systems. In this analysis the remembered appears to have a greater brain activity than the known word. Depicting a greater thought for a remembered than known word. Due to the differences in both ERP and spatial values for the related and unrelated word groups used, this study supports the existence of two systems.
Further Study 1. Increased study number 2. More specific word groups (high vs. low) 3. Specifically target areas of the brain a. Broca’s / Wernikies
References Busey, T. (2000). COGS Q 301. Brain and Cognition. Bloomington: Indiana University. Mc. Clellan, J. , Mc. Naughton, B. , and O’Reilly, R. , (1995). Why there are complementary learning systems in the hippocampus and neocortex: insights from the successes of failures of connectionist models of learning and memory. Psychological Review 102 (3) 419 -457. Rugg, M. D. , (1995). Event-related potential studies of human memory. Ed. Gazzaniga, M. S. et-al. The Cognitive Neurosciences. (789 -801). Cambridge: The Mit Press. Squire, L. R. and Knowlton, B. J. (1995). Memory, hippocampus, and brain systems. Ed. Gazzaniga, M. S. et-al. The Cognitive Neurosciences. (825 -837. ). Cambridge: The Mit Press.