Arash Yazdanbakhsh, MD, PhD
Neurobiology Department
Email: arash_yazdanbakhsh@hms.harvard.edu
In Margaret Livingstone Lab, I have been doing single cell recording to test:
1- Surface and contour perception and the role of contrast
2- Illusory contour and receptive field size
The modeling and psychophysical approach to the same problems at CNS Department (link to research there) and Psychology Department in Boston University naturally led to single cell recording.
The first and second order interactions within and around the cell receptive field helps to address part of the above topics.
(click the icons to see the time dynamics of first and second order interactions in gif format,
for avi click on here: First order.avi, second order (1).avi, Second order (2).avi )
First order.gif
Second order (1).gif
Second order
(2).gif 
The following is a summary of what so far has been going.
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Psychophysics |
Single cell stimulus |
Response |
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Though the edge geometry of the following panels are the same, squares, their ordinal depth, and grouping look different.
For single cell recording (a), (b), and (c) were transformed to the equivalent (a), (b), and (c).
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We singled out the bar stimulus and put it on the activation zone of the receptive field to check cell response. as well as doing sparse noise reverse correlation.
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For three sample cells: black curves for plain bar, colored curves for bars with opposite contrast wings.
End-stopped cell interaction maps are different for the same and opposite contrasts.
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Receptive fields can be put on the illusory contours of subjective square.
The size of activation zone of receptive filed is therefore important as to put the zone purely in the illusory part, otherwise, the inducers may fall into the receptive field. |
Therefore, one needs to determine receptive field size precisely: sparse noise reverse correlation is a good method. The right panels show the diagram of spike count profile and how to determine the activation zone border.
In particular, the cell response to neon versus no-neon condition can address if a V2 cell response is more related to the contrast value or subjective experience of neon-color spreading. |
Thresholding the activity can be done either by ear (green) or by spontaneous spike count (black). In V2, there is an offset between these two.
The finding on the white zone is consistent with the previous findings.
Notably, the cell response is related to the value of contrast rather than the percept of neon. |
Yazdanbakhsh A. and M Livingstone, (2006) Contrast-sign selectivity of End-stopping and Length-summation, Journal of Vision, 6(6): p.687
Livingstone M., A Yazdanbakhsh (2006) A fresh look at receptive-field size and illusory contour detection. Journal of vision 6(6): p.686
Yazdanbakhsh, A. and S. Grossberg, (2005) Laminar cortical dynamics of binocular rivalry. Journal of Vision, 5(8): p.1046
Yazdanbakhsh, A. and T. Watanabe, Horizontal and vertical illusory lines are different in determining the depth of their embedded surface. Journal of Vision, 2004. 4(8): p. 476
Grossberg and Yazdanbakhsh, Laminar cortical dynamics of 3-D surface stratification, transparency, and neon spreading. Journal of Vision, 2003. 3(9): p. 247
Yazdanbakhsh and Grossberg, How does perceptual grouping synchronize quickly under realistic neural constraints? Journal of Vision, 2003. 3(9): p. 757