[Abstract Title]. - Society for Neuroscience

Title: Structural basis of IT responses to natural objects
Authors: *K. BOWMAN 1 , E. T. CARLSON 2 , C. E. CONNOR 1 ;
1 Dept. of Neurosci., 2 Dept. of Biomed. Engin., Johns Hopkins Univ., Baltimore, MD
Abstract: The fundamental question concerning higher-level ventral pathway cortex is how
neurons encode objects. This question is usually addressed by studying selective neural
responses to natural objects, but the neural coding scheme that explains this selectivity remains
unknown. We sought to understand responses to natural objects in terms of neural tuning for
geometric object structure. We studied responses of neurons in CIT/AIT (central and anterior
inferotemporal cortex) of awake macaque monkeys performing a fixation task. The same
neurons were tested both with natural object photographs and with abstract shapes that evolved
in response to neural feedback. The natural object set comprised 60 stimuli in 8 categories: faces,
hands, bodies, fruits, animals, manmade objects, plants, and predators. Abstract shapes were
constructed with piecewise Bezier spline functions that defined external boundary shape and
internal contrast. For each neuron, an initial generation of 40 abstract stimuli was created by
randomizing parameters controlling spline function shape. Subsequent stimulus generations
included partially morphed descendants of higher response stimuli from previous generations.
Descendants were probabilistically morphed at the local and global levels. Over the course of 6-8
generations, this method produced dense sampling in the tuning range of the cell. Convergence
of independent lineages confirmed that this evolutionary method discovered a global maximum
in most cases. Dense sampling with multiple lineages allowed us to fit linear/nonlinear geometric
models describing neural sensitivity to shape. Application of these models to the natural stimulus
responses showed that in many cases those responses can be understood in terms of metric
tuning for geometric object structure.
Disclosures: K. Bowman, None; E.T. Carlson, None; C.E. Connor, None.
Poster
261. Object and Faces: Neuronal Representation I
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 261.4/CC1
Topic: D.04.j. Processing of objects and faces
Support: Max Planck Society
RA1025-1/2
DFG SFB550