Comparison of contrast-normalization and threshold models of the responses of simple cells in cat striate cortex

D. J. Tolhurst, D. J. Heeger

Research output: Contribution to journalArticle

Abstract

In almost every study of the linearity of spatiotemporal summation in simple cells of the cat's visual cortex, there have been systematic mismatches between the experimental observations and the predictions of the linear theory. These mismatches have generally been explained by supposing that the initial spatiotemporal summation stage is strictly linear, but that the following output stage of the simple cell is subject to some contrast-dependent nonlinearity. Two main models of the output nonlinearity have been proposed: the threshold model (e.g. Tolhurst and Dean, 1987) and the contrast-normalization model (e.g. Heeger, 1992a, b). In this paper, the two models are fitted rigorously to a variety of previously published neurophysiological data, in order to determine whether one model is a better explanation of the data. We reexamine data on the interaction between two bar stimuli presented in different parts of the receptive field; on the relationship between the receptive-field map and the inverse Fourier transform of the spatial-frequency tuning curve; on the dependence of response amplitude and phase on the spatial phase of stationary gratings; on the relationships between the responses to moving and modulated gratings; and on the suppressive action of gratings moving in a neuron's nonpreferred direction. In many situations, the predictions of the two models are similar, but the contrast-normalization model usually fits the data slightly better than the threshold model, and it is easier to apply the equations of the normalization model. More importantly, the normalization model is naturally able to account very well for the details and subtlety of the results in experiments where the total contrast energy of the stimuli changes; some of these phenomena are completely beyond the scope of the threshold model. Rigorous application of the models' equations has revealed some situations where neither model fits quite well enough, and we must suppose, therefore, that there are some subtle nonlinearities still to be characterized.

Original languageEnglish (US)
Pages (from-to)293-309
Number of pages17
JournalVisual Neuroscience
Volume14
Issue number2
StatePublished - Mar 1997

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Visual Cortex
Cats
Fourier Analysis
Neurons
Direction compound

Keywords

  • Contrast normalization
  • Directional selectivity
  • Linear summation
  • Nonlinear responses
  • Response suppression
  • Simple cells
  • Thresholds
  • Visual cortex

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Comparison of contrast-normalization and threshold models of the responses of simple cells in cat striate cortex. / Tolhurst, D. J.; Heeger, D. J.

In: Visual Neuroscience, Vol. 14, No. 2, 03.1997, p. 293-309.

Research output: Contribution to journalArticle

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