Modeling individual differences in free recall

Building off of, and incorporating, my previous work on individual differences in memory dynamics (as measured by a large-scale free-recall experiment known as PEERS), I am currently starting to work with the CML’s model of memory and temporal context known as CMR, the Context Maintenance and Retrieval model.

Generally, along with Dr. Karl Healey, I am working on fitting the model to each individual PEERS subject using a genetic algorithm. We will then examine the best-fit parameters for each subject for correlation with other behavioral measures and with the four factors discovered before. We will also see if any of the model parameters, or some combination thereof, are strongly predictive of general intelligence.


CA1 pyramidal cell tattoo

In August 2009 I got my first tattoo: an image of a reconstruction of a pyramidal neuron from area CA1 of the rat hippocampus. The reconstruction is taken from the paper:

Nace L Golding, Timothy J Mickus, Yael Katz, William L Kath, and Nelson Spruston. Factors mediating powerful voltage attenuation along CA1 pyramidal neuron dendrites. J Physiol October 1, 2005 568 (1) 69-82.

The paper can be found here. Dr Spruston provided more info about the model:

Scientifically, it’s one of three CA1 cells we reconstructed in detail after recording simultaneously from the soma and a dendrite. The recordings (performed by Nace Golding) were technically very diffcult and the reconstructions took several hours of tedious and careful work. The experiments provided data that constrained the model and provided more information about the basic properties of the neurons. Subsequently, the models have been really helpful in making predictions that led to new experimental discoveries.

I submitted my tattoo to Carl Zimmer’s excellent Science Tattoo Emporium, which was part of my inspiration for the venture.  It was published here on August 15th, 2009.

On November 1, 2011, a fleshed-out version of the blog post appeared in Zimmer’s book Science Ink: Tattoos of the Science Obsessed (Amazon link).  My page can be seen here:

Copyright 2011 Carl Zimmer. Click to enlarge.

TMS-ERP endophenotypes in schizophrenia

Using TMS-evoked potentials to probe neural response mechanisms in schizophrenia.

With Bruce Turetsky, MD and Mahendra Bhati, MD.

Presented at ICOSR 2009 by B. Turetsky.

More info coming soon.


Real-time MATLAB implementation of algorithm for DBS electrode placement

Senior design project at University of PennsylvaniaSchool of Engineering and Applied Science.

Real-time MATLAB implementation of functional localization and visualization of the STN from microelectrode recordings acquired during DBS surgery with unsupervised machine learning.

With Charles Li and John Paulett; advised by Stephen Wong, MD, Shabbar Danish, MD, and Leif Finkel, MD, Ph.D.

Patrick Crutchley, Charles Li and John Paulett, April 2007, Philadelphia, PA

Winner, Bioengineering Department Senior Design Award.

Published in Journal of Neural Engingeering: Wong et al., 2009.

More info coming soon.


PyEPL implementation of WMS/CVLT

Porting standardized tests of memory, mood, and personality into Python-based Experiment Programming Library (PyEPL: Geller et al. 2007; publicationproject page) in support of project Individual differences in free recall.

Tests included:

  1. Wechsler Memory Scale
  2. California Verbal Learning Test
  3. NEO-FFI
  4. PANAS-X
  5. SDFMS
  6. SWLS
  7. PSWQ

Personality/mood tests (3-7) used code written by Jonathan Miller.


Brain morphology endophenotypes in schizophrenia

This project involved constructing three-dimensional computer models of brains of individuals with schizophrenia and age-matched controls. From those models, we could determine sulcus volumes in areas implicated in developmental studies of schizophrenia.

Published in Turetsky et al., 2009. Abstract:

Embryonic insults during early gestation increase the risk of schizophrenia. Abnormal forebrain development during this period is often characterized by a shallow olfactory sulcus. The adjacent orbital sulcus does not develop until the third trimester and so is immune to early intrauterine insults. We measured olfactory and orbital sulcal depths in 36 patients and 28 control subjects. Patients had shallower olfactory sulci, but normal orbital sulci. Olfactory and orbital sulcal depths were correlated in controls, but not in patients. Olfactory sulcal depth may therefore be a biomarker denoting an early embryonic disruption in individuals at risk for schizophrenia.


Individual differences in free recall

I am leveraging a large dataset of free recall and recognition memory (known as PEERS) to investigate the correlational structure of several behavioral measures of free recall. In particular, I am interested in investigating the oft-found correlation between memory performance (recall probability) and fluid intelligence (IQ).

I presented preliminary findings at the Meeting for the Society for Mathematical Psychology in Summer 2012. (My poster can be found here.)

I later incorporated factor analysis into my investigation, and found four factors that underlie recall dynamics and can predict probability of recall to a high degree (accounted for 83% of variability), even though none of the features that went into factor analysis reflected recall success. Furthermore, the four recall dynamics factors can significantly predict IQ. This result has been written up with Karl Healey and Michael Kahana and is under review at JEP: General. (A PDF of its current state may be found here.)

I also presented this result (plus some extensions) in a poster at the 2013 Context and Episodic Memory Symposium. The poster can be seen here, or below.


Moved to “Completed” pending acceptance/minor revisions (fingers crossed).



If you’re seeing this in your RSS reader, it’s because you still have my old feed bookmarked there.

This particular feed will turn into a feed of projects I’ve been working on or have worked on in the past. I obviously haven’t updated the blog with new posts in a while, but if/when I do, they’ll show up in the feed

But you should totally stick around here if you want to hear about projects I’ve been working on. Super-exciting stuff. (Not really.)