CORTICAL PROCESSING: NONLINEAR PROPERTIES OF CORTICAL

RESPONSES

Valentin Dragoi

Department of Neurobiology and Anatomy

Sinusoidal grating

Simple and complex V1 cells

Nonlinear response properties in V1: contrast invariance (Busse et al, 2009)

Recurrent model of orientation tuning explains contrast invariance (Somers et al., 1995)

End-stop inhibition results from interactions between neurons in different cortical layers (Bolz and Gilbert, 1986)

Temporal dynamics of receptive field size(Malone et al., 2007)

} ∆R1

} ∆R2

∆R1 < ∆R2Neuronal discrimination performance is higher on the flank of the tuning curve

} ∆R1

Sharper tuning curve is typically associated with improved discriminability

∆R1 < ∆R2

Measuring neuronal discrimination performance

∆R2}

∆θ

∆θ

Neuronal discriminability depends on the response difference at nearby stimuli (tuning curve slope) and response variability

Orientation-selective cells emerge by sparseness maximization (Olshausen and Field, Nature, 1996)

Neuronal responses are adapted to the statistics of natural stimuli

Orientation distribution of natural images

Orie

ntat

ion

mag

nitu

de (x

105)

Orie

ntat

ion

mag

nitu

de (x

105)

Dragoi et al, Neuron, 2001

Asymmetric representation of stimulus orientation in V1

Dragoi et al, Neuron, 2001

fMRI and behavioral measurements of an oblique effect in human striate cortex.(a) Stimuli were suprathreshold (75% contrast) 3 cpd gratings displayed as 2 patches (3°, centered 4.5° from fixation). Gratings of the same orientation and random phase were presented in 20-s blocks at 1 image per s. (b) Blue, red and green pixels shown in an occipital slice (perpendicular to calcarine sulcus) represent visual areas (V1, V2 and V3) defined using fMRI retinotopic-mapping techniques. An oblique effect is evident in the raw fMRI time courses averaged across all subjects. (c) Bars represent mean fMRI response amplitudes in V1 plotted as a function of orientation (averaged across all three subjects). For each block, fMRI amplitudes were estimated as the sinusoid best fits to the data. Estimated amplitudes were then averaged by orientation across subjects. The mean peak response was 2.09%. Here average amplitudes are shown relative to the maximum response for each subject; however, all statistics were calculated from raw amplitudes. Cardinal amplitudes were reliably larger than oblique amplitudes. Similar results were obtained in a second experiment. This effect was robust, as 6 of 7 subjects showed a within-subject effect and the seventh subject showed a strong trend. Differences were not artifacts of the display device, as absolute cardinal orientations still produced the largest responses in V1 when the display was tilted 45°. (d) Bars represent normalized sensitivity as a function of orientation. Measurements were made for both contrast detection and orientation discrimination using the same stimulus configuration and subjects described above. Thresholds were determined by fitting a Weibull function to the data from a spatial two-alternative, forced-choice task using a staircase procedure, and were then converted to sensitivity scores (1/threshold).

Oblique effect in human visual cortex (Furmanski and Engel, 2000)

Suggested readings

1. Malone BJ, Kumar VR, Ringach DL. Dynamics of receptive field size in primary visual cortex. J Neurophysiol. 2007 Jan;97(1):407-14. Epub 2006 Oct 4.

2. Vogels R, Orban GA. How well do response changes of striate neurons signal differences in orientation: a study in the discriminating monkey. J Neurosci. 1990 Nov;10(11):3543-58.

3. Olshausen BA, Field DJ. Emergence of simple-cell receptive field properties by learning a sparse code for natural images. Nature. 1996 Jun 13;381(6583):607-9.

CORTICAL PROCESSING: EXTRA-CLASSICAL RECEPTIVE FIELD

INFLUENCES

Valentin Dragoi

Department of Neurobiology and Anatomy

Center Response Surround Response Opponent Field Response

Surround effects in retina

Neuronal circuits in striate cortex

Cells with similar function are linked through horizontal connections

Filling-in effect in visual cortex (De Weerd et al, 1995)

Stimulus collinearity: psychophysical results (Kapadia et al, 1995)

Stimulus collinearity: psychophysical results (Kapadia et al, 1995)

Stimulus collinearity in monkey visual cortex (Kapadia et al, 1995)

A: spatial arrangement of the receptive field center and surround used to investigate contextual effects. The center grating stimulus is surrounded by a larger annulus field with the same mean luminance. B: responses to the high-contrast optimal center stimulus paired with high-contrast surround gratings of varying orientations. Cells 1 and 2 are adapted from Fig. 1, A and D, of Levitt and Lund (1997) . C: responses to the low-contrast optimal center stimulus paired with high-contrast surround gratings of varying orientations. Cells 3 and 4 are adapted from Fig. 1, D and E, of Levitt and Lund (1997) . Dashed lines in all panels indicate response to the optimal stimulus alone.

Center-surround interactions in primary visual cortex (adapted from Levitt and Lund, 1997)

Orientation- and contrast-dependent suppression and facilitation. A: responses to high-contrast optimal center stimulus (contrast 100%) paired with high-contrast surround of varying orientation ( ) and to surround stimulus alone ( ). Center contrast and surround orientation values are identical with those used by Levitt and Lund (1997) . B: responses to the low-contrast optimal center stimulus (contrast 15%) paired with a high-contrast surround of varying orientation ( ) and to the surround stimulus alone ( ). Center contrast and surround orientation values are identical with those used by Levitt and Lund (1997) . Dashed lines: response to the optimal stimulus alone (high center contrast value is 100% in A; low center contrast value is 15% in B).

Model of center-surround interactions in primary visual cortex (Dragoi and Sur, 2000)

Model of center-surround interactions in V1 (Dragoi and Sur, 2000)

Pop-out effect

What is the function of horizontal connections?

Geometrical illusions

Examples of geometrical illusions

Surround stimulation increases response sparseness in V1 (Vinje and Gallant, 2000)

Surround effects in rat somatosensorycortex (Moore et al, 1999)

Surround effects in rat somatosensorycortex (Moore et al, 1999)

Model of center-surround interactions in rat S1 (Moore et al, 1999)

Suggested readings

1. De Weerd P, Gattass R, Desimone R, Ungerleider LG. Responses of cells in monkey visual cortex during perceptual filling-in of an artificial scotoma. Nature. 1995 Oct 26;377(6551):731-4.

2. Levitt JB, Lund JS. Contrast dependence of contextual effects in primate visual cortex. Nature. 1997 May 1;387(6628):73-6.

3. Kapadia MK, Ito M, Gilbert CD, Westheimer G. Improvement in visual sensitivity by changes in local context: parallel studies in human observers and in V1 of alert monkeys. Neuron. 1995 Oct;15(4):843-56.

4. Vinje WE, Gallant JL. Sparse coding and decorrelation in primary visual cortex during natural vision. Science. 2000 Feb 18;287(5456):1273-6.

5. Moore CI, Nelson SB, Sur M. Dynamics of neuronal processing in rat somatosensorycortex. Trends Neurosci. 1999 Nov;22(11):513-20. Review.