6. Adaptation Flashcards
What is fMR-A?
fMR-A is used as a tool to Characterize neural selectivity
- Repetition of stimulus = reduction in haemodynamic response
How else is adaptation referred to in MRI literature?
Repetition suppression
What’s face Identity Adaptation?
Adapting to one face
- when viewing a mix of two faces (ambiguous face) after, the face is more likely to be seen as the face that we are not adapted to
Prolonged exposure to a visual stimulus (____) results in…
> 5 seconds
Aftereffects
Following adaptation, subsequent ambiguous stimuli look…
less like adaptor (repulsive)
… prolongs adaptation
shutting your eyes…
Troje et al (2006):
Adaptation to Biological motion
Adapted to either male or female biological motion figures (walking)
- Asked to determine the gender of an androgynous walker (neither male or female)
- Walker seen less like what the participant adapted to
!!We’ve got adaptation aftereffects to biological motion (which is a really complex stimulus)
Barraclough et al (2009):
- Do we adapt to hand actions?
- How does the perspective of an action affect our perception of it
- How selective are the neural representations for hand actions?
Participants rate the weight of objects on video on a 100-900g scale (can tell through whether it was lifted fast or slow):
- Pre-test experiment = just judging weight of stimuli
- Adaptation experiment:
- adapting to an action (heavy or light lift)
- inter-stimulus-interval (ISI; varied)
- then presented with a test action
Question: Is there a difference in how the action was seen in pre-test experiment compared to that same action following adaptation?
———–1—————–
!!!If adapted to light objects, subsequent objects were rated as heavier than when seen without adaptation
!!!!The opposite was found for adaptation to heavy objects
!!!Aftereffects are greater the more times the action is repeated during adaptation
!!!Adaptation decays over time (known from manipulating the ISI)
!!!effects of adaptation disappear around 8 seconds
————–2————-
Changing the degree from which the lifting is recorded:
!!We adapt to the specific perspective we saw the lifting from during adaptation
- the further the perspective from the adaptation one, the less of an aftereffect we see
- ————–3—————
- There are specific neurons sensitive to grasping actions and some to placing actions
- However, there are also neurons which activity overlaps across both placing and grasping actions
Adaptation & neural selectivity:
Half neurons respond to___, half respond to ____
humans,
other animals (monkey, dog)
Grossman et al (2010):
Tested repetition suppression in Biological Motion stimuli
- Is there common coding in neurons for multiple human actions (biological motion stimuli) or not
(are cells sensitive to specific actions or is there overlap)
- Actions presented in same and different positions of the visual field
(are cells sensitive to position in space?)
!!!Neurons are just as sensitive to the same action presented in a different part of the visual field
- Clips of actions presented at the same or different sizes
(are cells sensitive to size?)
!!!Neurons are just as sensitive to the same action presented in a different size
Issues with fMR-A:
would Repetition suppression (RS) with fMRI with sequential ~750ms stimuli induce adaptation?
No, need longer adaptation (~5s)
Issues with fMR-A:
How many neurons show repetition suppression? (Brown & Xiang, 1998)
~50%
Issues with fMR-A:
repetition suppression increases with repetition (up to ___ repeats) and…
~8
Will transfer across intervening stimuli
Issues with fMR-A:
Sawamura et al (2006)
Adaptation in monkeys using single cell recordings vs fMR-adaptation to see how they differ in the way they tell us about selectivity
- Recording from single cells show very high selectivity
- Using fMR-A greatly underestimated how selective the cells actually are
!!!fMR-A can infer selectivity of regions but it is not as accurate as we would like it to be in terms of how selective specific cells are
What are the three models explaining the effects of adaptation in neurons?
Fatigue model:
- The amplitude of neural response decreases following neural adaptation
Sharpening model:
- fewer neurons respond following neural adaptation
Facilitation model:
- Neurons respond quicker (shorter latency, quicker offset)
