Effects of the Hippopotamus on Explicit

and Implicit Memory

Um, we meant HIPPOCAMPUS.

(The real presentation begins now.)

Do Explicit and Implicit Memory Exist , if so, WHERE?

Derek M. Greene

Melissa M. Morris

Christine Rozhon

Rock the World!!

Explicit and Implicit Memory Systems are Functionally and

Spatially Distinct.

Past studies have tried to discern whether or not long term memory systems are subdivided into 2 types of memories, those being explicit and implicit.

These studies have primarily relied upon word recollection and fragment completion tasks, such as those conducted by Michael D. Rugg. Word recollection has depended upon the qualifying of the presented words as either old or new. Differences in event related potentials between the two have shown that there is evidence suggesting consciously and unconsciously recollected words. The old words can be further classified into remember vs. know. The difference between these two conditions are known as a subsequent memory effect The subsequent memory effect provides further evidence of the existence of two separate forms of memory. The benefits of these experiments has been diminished by the number of electrodes used during test.

Psychologist Neal Kroll and Andrew Yonelinas have further presented evidence for two separate memory systems based on studies done with patients with amnesia. Their research showed that during word completion tasks, amnesiacs could positively identify words shown at test while having no episodic memory of a prior presentation. This suggests that explicit and implicit systems are independent of each other.

Moving On!!

Do Palindromes Tap the Subject’s Implicit Memory System?

• Because palindromes all follow the same symmetrical physical structure, we believe that palindromes are likely to activate implicit memory systems.

• In palindromes, the structure, rather than the meanings of the letters, is remembered even with no specific memory of the word.

• Therefore during test the subject will be more likely to respond positively to distracter words, resulting in a greater observed effect on “know” response voltages.

• Because the meaning of words can be actively recalled and brought into conscious awareness, they fall into the area of explicit memory,

• The target words and the prime words were semantically similar; and further supports our belief that explicit memory is stimulated.

• During test, we expect that the subject will exhibit a greater “remember” response because of the related meaning.

Do Words Relating to War Reflect Explicit Memory Activation?

• One female subject

•First presented 400 words, 200 palindromes, 200 words related to war at study. At test, 200 distracter words were added, half related to war, half palindromes.

•Task: To identify at test which words were actively remembered, which were merely “known”, and which words were newly presented words, by entering choice on a keypad.

•EEGs were recorded from 16 electrodes

•EEGs were recorded from 99 ms before presentation of the word to 1200ms after presentation

Our ExperimentOur Experiment

Experiment Results

These ERP graphs clearly demonstrate a difference between the remember and know responses. Evidence of a subsequent memory effect exists on the T5 electrode. (This is what the arrow points to.)

T5 T6

As our data shows, at 300ms, the brain during the remember condition is more active while it is relatively inactive during the know condition. Spatially, at

500ms there is a clear difference in remember vs. know – the active areas of the brain during the know condition are centered more towards the left hemisphere of the brain, while the remember condition activates areas on both the left and

the right. This is also displayed at 600ms.

Discussion

• The remember and know conditions elicited different electrophysiological responses which provides support for the existence of two separate memory systems as shown by the subsequent memory effect.– The know condition activates the implicit memory system.– The remember condition activates the explicit system.

• Palindromes represent words that are structurally similar while war words were related semantically.– Words that are structurally similar tap implicit systems– Words that are semantically similar tap explicit memory.

• The spatial distribution of electrical charge over the brain shows that both memory systems rely heavily on the left side of the brain. The explicit memory system also extends into the right side of the brain. This extension suggest that there is a difference in the location of implicit and explicit memory systems.

Conclusions•The N170 is not specific to inverted faces of hippopotamuses .

•The N170 is larger than most West African Hippos.

•Whoops. Wrong Presentation Again.

I Love Tom Busey’s N170!!

Conclusions

• Our experiment provides strong evidence in support of our hypothesis that there are two functionally and spatially distinct memory systems.

• Through neuroimaging we can discern two distinct locations for explicit and implicit memory.– At 300, 500, 600 milliseconds, the areas of activation in

the explicit memory system extend from the left hemisphere into the right.

• The differences found spatially and in amplitude could be due to the semantic and structural differences in the stimuli.

Conclusions, continued

•Future experiments conducted in this same manner but using different sets of stimuli would contribute to a better understanding of the implicit and explicit memory systems. These experiments should take advantage of different testing techniques, such as PETs, to attempt to better define the spatial constraints of the two memory systems. It would also be to their advantage to pool together a larger sample of subjects to be tested.

THE END