Space-Time Receptive Fields of Visual Neurons

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Modern Views and Measurements of Visual Receptive Fields

Traditionally, the receptive field of a neuron is defined as the area of visual field within which visual stimulation influences neural responses. This classical notion no longer provides an adequate framework for understanding visual receptive fields. We must consider an additional dimension of time, and define receptive fields in the joint domain of space and time. For many cells in the visual cortex, there is no such thing as a unique spatial receptive field. Slides, animations here attempt to demonstrate this fact in an intuitively obvious manner.

For a written introductory material on this subject, please read our review paper (on-line version available): Receptive-field dynamics in the central visual pathways (TINS 1995) by DeAngelis, Ohzawa, and Freeman.

Methods

• Mapping receptive fields in space-time by reverse correlation
  
  Stimuli and analysis methods are described.

• Receptive fields of neurons in the early visual system
  
  Slide versions of figures in our Trends in Neurosciences 95 article.

• LGN cell (X, On-center, non-lagged)
  
  LGN (lateral geniculate nucleus) cells have a concentric RF with center-surround organization.

• Space-time separable receptive field of a simple cell
  
  These RFs are expressed as the product of two 1-D functions: a function of space and a function of time.
• Space-time inseparable receptive field of a simple cell
  
  These RFs are oriented and inseparable in the space-time domain. That is, the space-time RF cannot be expressed as the product of two 1-D functions, one of space and another of time. The space-time orientation is related to direction selectivity of these simple cells.
• Space-time RF of a simple cell in primate V1
  
  This RF animation on Dario Ringach's Web page at NYU shows a space-time RF obtained from a simple cell in V1. He uses a novel reverse correlation mapping techinque in the spatial frequency and orientation domain (using a bunch of sinusoidal gratings of different spatial frequencies and orientations). The spatial RF profile is reconstructed from these frequency domain data. In addition to allowing RF reconstructions, the dynamics of orientation tuning and spatial frequency tuning may be examined directly by this technique [animation of orientation tuning curves by Ringach]. Note that the reconstruction of RFs from the frequency domain data requires a linearity assumption.

• Complex cell
  
  There is no apparent elongated, oriented subfield structure for these cells. The RF of complex cells appear to be a broadly selective Gaussian in two dimensions of space (x, y) when mapped with a single bar-shaped stimulus.

• Binocular receptive fields and stereopsis
  
  Most neurons in the visual cortex are binocular. We consider receptive field properties with respect to binocular vision and stereopsis. Inhererently, a complete description of a binocular RF must be given in the 4-dimensional space (X, Y, Z, T), where (X, Y) defines the viewer's visual direction, Z is the distance from the viewer, and T is the time.

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