Arash Yazdanbakhsh, MD, PhD

Harvard Medical School

Neurobiology Department

 

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 Current webpage, Boston University

 

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 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    Description: K:Users:Arash:Desktop:Screen Shot 2013-07-01 at 5.53.08 PM.png    Second order (1).gif     Description: K:Users:Arash:Desktop:Screen Shot 2013-07-01 at 5.53.16 PM.png  Second order (2).gif   Description: K:Users:Arash:Desktop:Screen Shot 2013-07-01 at 5.53.27 PM.png

                              

 

Publication list

 

 

The following is a summary of what so far has been going.

 

Psychophysics

Single cell stimulus

Response

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).

 

 

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.

 

 

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.

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.

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