1. The Components of the Phenomenon of Repetition Suppression
Good afternoon.
Today I am going to talk about my proposal.
The topic I am interested in and will introduce today is about behavioral priming and its neural basis.

2. Priming Effect A behavioral phenomenon
changes in the performance in a task when a stimuli is presented repeatedly
So, what is priming?
Priming is a behavioral phenomenon that, During a task, when the same stimulus is presented repeatedly, there will be a change in how well the subject perform the task.
Let me take the experiment of Buckner at 1998 as example.
In this experiment, subjects saw a list of items and decided whether those items could move on their own in the first session.
Then, they took in part in another session of the same experiment, that was almost identical to the first session.
But the only difference was that, some of the items shown here had already been used in the first session, for example, an owl. (click)
And they found that, the response to the repeated-shown stimulus became faster, but those was shown the first time in this session didn’t, for example, a butterfly. (click)
Buckner et al (1998)

3. Repetition Suppression
A phenomenon found when using brain imaging technique to investigate priming.
Decrease of neuronal activation when stimuli occur more than once
People have been curious about what the neural basis of priming is.
And, with the develop of brain imaging techniques, like PET and fMRI, one robust finding is that when a priming paradigm is used, the repeated stimulus usually shows less activation compared to novel items.
Just like the picture shown.
The slice of brain imaging shows more activation for the new stimuli, (click) than those repeated. (click)
And in a time course, you can also see the BOLD signal of repetition stimuli is decreased. (click)
This phenomenon is sometimes called repetition suppression.
And because behavioral priming and repetition suppression often occur together, repetition suppression has been proposed to be the neural basis of behavioral priming. --

4. Further Research Perceptual RS is suggested to be an automatic process
Bottom-up
If it is the truth, why there are situations stimuli presented repeatedly but no RS found?
Further research suggests that, repetition suppression at the perceptual level is an automatic process.
That is, as long as a stimulus is presented, you will see repetition suppression at the fusiform gyrus, or regions about object recognition.
But there exists some experiment results that seem to contradict this suggestion, like the one directed by Henson and his colleagues at 2002.

5. Study with condition which RS can not be found
Face Repetition Effects in Implicit and Explicit Memory Tests as Measured by fMRI (Henson et al., 2002)
So, let's talk some detail about Henson and his colleagues' experiment at 2002.
Because what we want to investigate further is based on it.
Because my proposal is based on this experiment done by Henson and his colleagues at 2002 that is mentioned above, let me describe this experiment in more detail.

6. In Henson's experiment, they uses a continuous-design paradigm.
Famous and unfamiliar faces are used as stimuli in the experiment and sequentially presented.
Subjects need to do two kind of tasks, implicit task and explicit task, in two separate sessions.
The implicit task is to tell if the face is famous or not.
The explicit task is to tell if the face have presented before in the experiment.
And they use two button to make a yes/no decision

8. One Account for the Result
This account is based on neurophysiological study (Miller and Desimone, 1994)
Cells show decreased firing rate to repetition stimuli
Cells show increased firing rate to stimuli of attention
( maybe some kind of thought like Hey, This is it! )
attended
unattended
One of their account to explain this result is based on a neurophysiological study by Miller and Desimone at 1994.
According to their research, there are two different kind of cells in the brain.
One kind of cells show decreased firing rate when stimulus is presented repeatedly.
The other kind of cells show a intrinsically different property, that the firing rate increases when the stimulus is attended, but shows no or little change when the stimulus is unattended.

9. So, in the experiment directed by Henson and his colleagues at 2002, the decreased firing rate to repeated stimuli always exists, because both of the tasks involve repeatedly presented stimuli, just like the blue bar shown in the two picture.
However, the activation of cells which show selective property to attention differs.
These cells show increased firing rate in the explicit task only when a stimulus is presented repeatedly, because subjects must pay attention to do a recognition task about whether a face is seen before, that means subjects tend to pay attention to repeated stimuli in this conventional recognition task with yes/no decision.
But in the implicit task, they always need to pay attention to the famous-judgment task at every presence of stimuli , so the same or similar level of increased firing rate is ALWAYS shown.
And the result is that the implicit task still shows repetition suppression, the explicit task, however, doesn’t show significant change in the activation because it is balanced, as the picture shown.

10. Hypothesis
When the explicit task is to attend to the stimulus presented the first time, the brain region engaged in the face processing will show repetition suppression, and that RS will be even stronger than the repetition suppression in the implicit task
But, to examine the suggestion mentioned above, we need to conduct a further experiment more specific to see if our suggestion is correct.
So, we now give our experiment a more definite hypothesis, that is, when forcing the subject to use perceptual representation, There will be RS in perceptual regions even in recognition tasks, as the picture illustrated here.
So, to investigate this result further, we suggest a hypothesis.
That is, when we change the focus to the new stimuli in the recognition task, the region that didn’t show repetition suppression in the original task, will show significant repetition suppression.
If we use pictures to show this idea, it just seems that we exchange the positions of the two red bars.
And that repetition suppression will be even stronger than that in the implicit task.

11. Method
25 participants
Independent factor  Attend the new/repeated faces
Dependant factor  the existence of Repetition suppression
Using 3T fMRI scanner
Stimuli : Familiar Faces
Two different tasks
When new faces presented, press Y button. If not, press N.
When repeated faces presented, press Y button. If not, press N.
An additional priming task as the original Henson’s study used

12. Procedure

13. Expected Result
RS should be observed in FFA at the “attend new faces” condition (Additionally, RS in this condition should be greater than the condition of priming task)
No RS is observed in FFA at the “attend repeated faces” condition (As the study of Henson showed)
Over all, the results should be consistent with the finding of Desimone et al

14. If Alternative Result If no RS are found in the both conditions,
Maybe attention is not so important in this kind of recognition task
The paradigm is still not well designed to investigate this issue
The finding of Desimone et al can not be applied to the FFA, or even not for the human