Category: Selected articles

• Non-negative matrix factorization for receptive field analysis

  Using Non-negative matrix factorization instead of SVD Sujay, a labmate of mine came to me with an interesting analysis problem. He’s looking at perisaccadic changes in receptive fields in V4. The saccade-triggered receptive fields shows two activations: an initial one at the pre-saccadic location, and a later one at the remapped location. Basically, the activation…

  April 1, 2014

• Why second-order methods can be futile in non-convex problems

  I’ve been working on fitting a convolutional model of neurons in primary and intermediate visual cortex. A non-convex optimization problem must be solved to estimate the parameters of the model. It has a form similar to: There are some shared weights to further complicate things, but the most salient features is that it’s a 3-layer…

  April 4, 2013

• Category representation in the brain

  Jack Gallant has been focusing a lot of recent lab efforts in the analysis of large-scale fMRI recordings. They published an interesting paper in Neuron last month about the representation of categories in cortex.

  January 24, 2013

• Topography conquers all

  The eye faithfully maps visual space to different positions on the retina. This retinotopy is preserved as the signal is forwarded from retinal ganglion cells to the LGN, then to V1, and onwards. Cells which are physically adjacent on a retinotopic map have receptive fields corresponding to similar positions in space. More generally, properties like…

  April 5, 2012

• Using an iterated extended Kalman filter to decode place cells

  Decoding neuronal activity is a powerful technique to study how information is encoded in a population and how it might be extracted by other brains areas. Hippocampal place cells are a prime example of a system that can be studied fruitfully from a decoding persepective. In a typical place cell decoding experiment, a population of…

  February 6, 2012

• Hierarchical processing of complex motion

  I’m thrilled to announce that our paper, Hierarchical processing of complex motion along the dorsal visual pathway, has been published in PNAS. In this work, we looked at the response properties of neurons in area MST (the medial superior temporal area). MST neurons are part of the dorsal visual pathway; they are strongly selective for…

  January 31, 2012